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docs/frontends/CLI.txt
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@ -1,56 +1,63 @@
= The Tahoe CLI commands =
======================
The Tahoe CLI commands
======================
1. Overview
2. CLI Command Overview
3. Node Management
4. Virtual Drive Manipulation
4.1. Starting Directories
4.1.1. SECURITY NOTE: For users of shared systems
4.2. Command Syntax Summary
4.3. Command Examples
5. Virtual Drive Maintenance
6. Debugging
1. `Overview`_
2. `CLI Command Overview`_
3. `Node Management`_
4. `Filesystem Manipulation`_
== Overview ==
1. `Starting Directories`_
2. `Command Syntax Summary`_
3. `Command Examples`_
Tahoe provides a single executable named "tahoe", which can be used to create
and manage client/server nodes, manipulate the filesystem, and perform
5. `Storage Grid Maintenance`_
6. `Debugging`_
Overview
========
Tahoe provides a single executable named "``tahoe``", which can be used to
create and manage client/server nodes, manipulate the filesystem, and perform
several debugging/maintenance tasks.
This executable lives in the source tree at "bin/tahoe". Once you've done a
build (by running "make"), bin/tahoe can be run in-place: if it discovers
This executable lives in the source tree at "``bin/tahoe``". Once you've done a
build (by running "make"), ``bin/tahoe`` can be run in-place: if it discovers
that it is being run from within a Tahoe source tree, it will modify sys.path
as necessary to use all the source code and dependent libraries contained in
that tree.
If you've installed Tahoe (using "make install", or by installing a binary
If you've installed Tahoe (using "``make install``", or by installing a binary
package), then the tahoe executable will be available somewhere else, perhaps
in /usr/bin/tahoe . In this case, it will use your platform's normal
in ``/usr/bin/tahoe``. In this case, it will use your platform's normal
PYTHONPATH search paths to find the tahoe code and other libraries.
== CLI Command Overview ==
CLI Command Overview
====================
The "tahoe" tool provides access to three categories of commands.
The "``tahoe``" tool provides access to three categories of commands.
* node management: create a client/server node, start/stop/restart it
* filesystem manipulation: list files, upload, download, delete, rename
* debugging: unpack cap-strings, examine share files
* node management: create a client/server node, start/stop/restart it
* filesystem manipulation: list files, upload, download, delete, rename
* debugging: unpack cap-strings, examine share files
To get a list of all commands, just run "tahoe" with no additional arguments.
"tahoe --help" might also provide something useful.
To get a list of all commands, just run "``tahoe``" with no additional
arguments. "``tahoe --help``" might also provide something useful.
Running "tahoe --version" will display a list of version strings, starting
Running "``tahoe --version``" will display a list of version strings, starting
with the "allmydata" module (which contains the majority of the Tahoe
functionality) and including versions for a number of dependent libraries,
like Twisted, Foolscap, pycryptopp, and zfec.
== Node Management ==
Node Management
===============
"tahoe create-node [NODEDIR]" is the basic make-a-new-node command. It
"``tahoe create-node [NODEDIR]``" is the basic make-a-new-node command. It
creates a new directory and populates it with files that will allow the
"tahoe start" command to use it later on. This command creates nodes that
"``tahoe start``" command to use it later on. This command creates nodes that
have client functionality (upload/download files), web API services
(controlled by the 'webport' file), and storage services (unless
"--no-storage" is specified).
@ -58,18 +65,18 @@ have client functionality (upload/download files), web API services
NODEDIR defaults to ~/.tahoe/ , and newly-created nodes default to
publishing a web server on port 3456 (limited to the loopback interface, at
127.0.0.1, to restrict access to other programs on the same host). All of the
other "tahoe" subcommands use corresponding defaults.
other "``tahoe``" subcommands use corresponding defaults.
"tahoe create-client [NODEDIR]" creates a node with no storage service.
That is, it behaves like "tahoe create-node --no-storage [NODEDIR]".
"``tahoe create-client [NODEDIR]``" creates a node with no storage service.
That is, it behaves like "``tahoe create-node --no-storage [NODEDIR]``".
(This is a change from versions prior to 1.6.0.)
"tahoe create-introducer [NODEDIR]" is used to create the Introducer node.
"``tahoe create-introducer [NODEDIR]``" is used to create the Introducer node.
This node provides introduction services and nothing else. When started, this
node will produce an introducer.furl, which should be published to all
clients.
"tahoe create-key-generator [NODEDIR]" is used to create a special
"``tahoe create-key-generator [NODEDIR]``" is used to create a special
"key-generation" service, which allows a client to offload their RSA key
generation to a separate process. Since RSA key generation takes several
seconds, and must be done each time a directory is created, moving it to a
@ -77,22 +84,23 @@ separate process allows the first process (perhaps a busy wapi server) to
continue servicing other requests. The key generator exports a FURL that can
be copied into a node to enable this functionality.
"tahoe run [NODEDIR]" will start a previously-created node in the foreground.
"``tahoe run [NODEDIR]``" will start a previously-created node in the foreground.
"tahoe start [NODEDIR]" will launch a previously-created node. It will launch
"``tahoe start [NODEDIR]``" will launch a previously-created node. It will launch
the node into the background, using the standard Twisted "twistd"
daemon-launching tool. On some platforms (including Windows) this command is
unable to run a daemon in the background; in that case it behaves in the
same way as "tahoe run".
same way as "``tahoe run``".
"tahoe stop [NODEDIR]" will shut down a running node.
"``tahoe stop [NODEDIR]``" will shut down a running node.
"tahoe restart [NODEDIR]" will stop and then restart a running node. This is
"``tahoe restart [NODEDIR]``" will stop and then restart a running node. This is
most often used by developers who have just modified the code and want to
start using their changes.
== Filesystem Manipulation ==
Filesystem Manipulation
=======================
These commands let you exmaine a Tahoe filesystem, providing basic
list/upload/download/delete/rename/mkdir functionality. They can be used as
@ -114,7 +122,8 @@ As of Tahoe v1.7, passing non-ASCII characters to the CLI should work,
except on Windows. The command-line arguments are assumed to use the
character encoding specified by the current locale.
=== Starting Directories ===
Starting Directories
--------------------
As described in architecture.txt, the Tahoe distributed filesystem consists
of a collection of directories and files, each of which has a "read-cap" or a
@ -125,11 +134,11 @@ connected together into a directed graph.
To use this collection of files and directories, you need to choose a
starting point: some specific directory that we will refer to as a
"starting directory". For a given starting directory, the "ls
[STARTING_DIR]:" command would list the contents of this directory,
the "ls [STARTING_DIR]:dir1" command would look inside this directory
for a child named "dir1" and list its contents, "ls
[STARTING_DIR]:dir1/subdir2" would look two levels deep, etc.
"starting directory". For a given starting directory, the "``ls
[STARTING_DIR]:``" command would list the contents of this directory,
the "``ls [STARTING_DIR]:dir1``" command would look inside this directory
for a child named "dir1" and list its contents, "``ls
[STARTING_DIR]:dir1/subdir2``" would look two levels deep, etc.
Note that there is no real global "root" directory, but instead each
starting directory provides a different, possibly overlapping
@ -138,9 +147,9 @@ perspective on the graph of files and directories.
Each tahoe node remembers a list of starting points, named "aliases",
in a file named ~/.tahoe/private/aliases . These aliases are short UTF-8
encoded strings that stand in for a directory read- or write- cap. If
you use the command line "ls" without any "[STARTING_DIR]:" argument,
then it will use the default alias, which is "tahoe", therefore "tahoe
ls" has the same effect as "tahoe ls tahoe:". The same goes for the
you use the command line "``ls``" without any "[STARTING_DIR]:" argument,
then it will use the default alias, which is "tahoe", therefore "``tahoe
ls``" has the same effect as "``tahoe ls tahoe:``". The same goes for the
other commands which can reasonably use a default alias: get, put,
mkdir, mv, and rm.
@ -148,7 +157,7 @@ For backwards compatibility with Tahoe-1.0, if the "tahoe": alias is not
found in ~/.tahoe/private/aliases, the CLI will use the contents of
~/.tahoe/private/root_dir.cap instead. Tahoe-1.0 had only a single starting
point, and stored it in this root_dir.cap file, so Tahoe-1.1 will use it if
necessary. However, once you've set a "tahoe:" alias with "tahoe set-alias",
necessary. However, once you've set a "tahoe:" alias with "``tahoe set-alias``",
that will override anything in the old root_dir.cap file.
The Tahoe CLI commands use the same filename syntax as scp and rsync
@ -168,30 +177,32 @@ alias, you can use that alias as an argument to commands.
The best way to get started with Tahoe is to create a node, start it, then
use the following command to create a new directory and set it as your
"tahoe:" alias:
"tahoe:" alias::
tahoe create-alias tahoe
After that you can use "tahoe ls tahoe:" and "tahoe cp local.txt tahoe:",
and both will refer to the directory that you've just created.
After that you can use "``tahoe ls tahoe:``" and
"``tahoe cp local.txt tahoe:``", and both will refer to the directory that
you've just created.
==== SECURITY NOTE: For users of shared systems ====
SECURITY NOTE: For users of shared systems
``````````````````````````````````````````
Another way to achieve the same effect as the above "tahoe create-alias"
command is:
command is::
tahoe add-alias tahoe `tahoe mkdir`
However, command-line arguments are visible to other users (through the
'ps' command, or the Windows Process Explorer tool), so if you are using a
tahoe node on a shared host, your login neighbors will be able to see (and
capture) any directory caps that you set up with the "tahoe add-alias"
capture) any directory caps that you set up with the "``tahoe add-alias``"
command.
The "tahoe create-alias" command avoids this problem by creating a new
The "``tahoe create-alias``" command avoids this problem by creating a new
directory and putting the cap into your aliases file for you. Alternatively,
you can edit the NODEDIR/private/aliases file directly, by adding a line like
this:
this::
fun: URI:DIR2:ovjy4yhylqlfoqg2vcze36dhde:4d4f47qko2xm5g7osgo2yyidi5m4muyo2vjjy53q4vjju2u55mfa
@ -203,38 +214,58 @@ other arguments you type there, but not the caps that Tahoe uses to permit
access to your files and directories.
=== Command Syntax Summary ===
Command Syntax Summary
----------------------
tahoe add-alias alias cap
tahoe create-alias alias
tahoe list-aliases
tahoe mkdir
tahoe mkdir [alias:]path
tahoe ls [alias:][path]
tahoe webopen [alias:][path]
tahoe put [--mutable] [localfrom:-]
tahoe put [--mutable] [localfrom:-] [alias:]to
tahoe put [--mutable] [localfrom:-] [alias:]subdir/to
tahoe put [--mutable] [localfrom:-] dircap:to
tahoe put [--mutable] [localfrom:-] dircap:./subdir/to
tahoe put [localfrom:-] mutable-file-writecap
tahoe get [alias:]from [localto:-]
tahoe cp [-r] [alias:]frompath [alias:]topath
tahoe rm [alias:]what
tahoe mv [alias:]from [alias:]to
tahoe ln [alias:]from [alias:]to
tahoe backup localfrom [alias:]to
=== Command Examples ===
Command Examples
----------------
tahoe mkdir
``tahoe mkdir``
This creates a new empty unlinked directory, and prints its write-cap to
stdout. The new directory is not attached to anything else.
tahoe add-alias fun DIRCAP
``tahoe add-alias fun DIRCAP``
An example would be:
An example would be::
tahoe add-alias fun URI:DIR2:ovjy4yhylqlfoqg2vcze36dhde:4d4f47qko2xm5g7osgo2yyidi5m4muyo2vjjy53q4vjju2u55mfa
@ -243,67 +274,83 @@ tahoe add-alias fun DIRCAP
directory. Use "tahoe add-alias tahoe DIRCAP" to set the contents of the
default "tahoe:" alias.
tahoe create-alias fun
``tahoe create-alias fun``
This combines 'tahoe mkdir' and 'tahoe add-alias' into a single step.
This combines "``tahoe mkdir``" and "``tahoe add-alias``" into a single step.
tahoe list-aliases
``tahoe list-aliases``
This displays a table of all configured aliases.
tahoe mkdir subdir
tahoe mkdir /subdir
``tahoe mkdir subdir``
``tahoe mkdir /subdir``
This both create a new empty directory and attaches it to your root with the
name "subdir".
tahoe ls
tahoe ls /
tahoe ls tahoe:
tahoe ls tahoe:/
``tahoe ls``
``tahoe ls /``
``tahoe ls tahoe:``
``tahoe ls tahoe:/``
All four list the root directory of your personal virtual filesystem.
tahoe ls subdir
``tahoe ls subdir``
This lists a subdirectory of your filesystem.
tahoe webopen
tahoe webopen tahoe:
tahoe webopen tahoe:subdir/
tahoe webopen subdir/
``tahoe webopen``
``tahoe webopen tahoe:``
``tahoe webopen tahoe:subdir/``
``tahoe webopen subdir/``
This uses the python 'webbrowser' module to cause a local web browser to
open to the web page for the given directory. This page offers interfaces to
add, dowlonad, rename, and delete files in the directory. If not given an
alias or path, opens "tahoe:", the root dir of the default alias.
tahoe put file.txt
tahoe put ./file.txt
tahoe put /tmp/file.txt
tahoe put ~/file.txt
``tahoe put file.txt``
``tahoe put ./file.txt``
``tahoe put /tmp/file.txt``
``tahoe put ~/file.txt``
These upload the local file into the grid, and prints the new read-cap to
stdout. The uploaded file is not attached to any directory. All one-argument
forms of "tahoe put" perform an unlinked upload.
forms of "``tahoe put``" perform an unlinked upload.
tahoe put -
tahoe put
``tahoe put -``
``tahoe put``
These also perform an unlinked upload, but the data to be uploaded is taken
from stdin.
tahoe put file.txt uploaded.txt
tahoe put file.txt tahoe:uploaded.txt
``tahoe put file.txt uploaded.txt``
``tahoe put file.txt tahoe:uploaded.txt``
These upload the local file and add it to your root with the name
"uploaded.txt"
tahoe put file.txt subdir/foo.txt
tahoe put - subdir/foo.txt
tahoe put file.txt tahoe:subdir/foo.txt
tahoe put file.txt DIRCAP:./foo.txt
tahoe put file.txt DIRCAP:./subdir/foo.txt
``tahoe put file.txt subdir/foo.txt``
``tahoe put - subdir/foo.txt``
``tahoe put file.txt tahoe:subdir/foo.txt``
``tahoe put file.txt DIRCAP:./foo.txt``
``tahoe put file.txt DIRCAP:./subdir/foo.txt``
These upload the named file and attach them to a subdirectory of the given
root directory, under the name "foo.txt". Note that to use a directory
@ -311,55 +358,65 @@ tahoe put file.txt DIRCAP:./subdir/foo.txt
than ":", to help the CLI parser figure out where the dircap ends. When the
source file is named "-", the contents are taken from stdin.
tahoe put file.txt --mutable
``tahoe put file.txt --mutable``
Create a new mutable file, fill it with the contents of file.txt, and print
the new write-cap to stdout.
tahoe put file.txt MUTABLE-FILE-WRITECAP
``tahoe put file.txt MUTABLE-FILE-WRITECAP``
Replace the contents of the given mutable file with the contents of file.txt
and prints the same write-cap to stdout.
tahoe cp file.txt tahoe:uploaded.txt
tahoe cp file.txt tahoe:
tahoe cp file.txt tahoe:/
tahoe cp ./file.txt tahoe:
``tahoe cp file.txt tahoe:uploaded.txt``
``tahoe cp file.txt tahoe:``
``tahoe cp file.txt tahoe:/``
``tahoe cp ./file.txt tahoe:``
These upload the local file and add it to your root with the name
"uploaded.txt".
tahoe cp tahoe:uploaded.txt downloaded.txt
tahoe cp tahoe:uploaded.txt ./downloaded.txt
tahoe cp tahoe:uploaded.txt /tmp/downloaded.txt
tahoe cp tahoe:uploaded.txt ~/downloaded.txt
``tahoe cp tahoe:uploaded.txt downloaded.txt``
``tahoe cp tahoe:uploaded.txt ./downloaded.txt``
``tahoe cp tahoe:uploaded.txt /tmp/downloaded.txt``
``tahoe cp tahoe:uploaded.txt ~/downloaded.txt``
This downloads the named file from your tahoe root, and puts the result on
your local filesystem.
tahoe cp tahoe:uploaded.txt fun:stuff.txt
``tahoe cp tahoe:uploaded.txt fun:stuff.txt``
This copies a file from your tahoe root to a different virtual directory,
set up earlier with "tahoe add-alias fun DIRCAP".
tahoe rm uploaded.txt
tahoe rm tahoe:uploaded.txt
``tahoe rm uploaded.txt``
``tahoe rm tahoe:uploaded.txt``
This deletes a file from your tahoe root.
tahoe mv uploaded.txt renamed.txt
tahoe mv tahoe:uploaded.txt tahoe:renamed.txt
``tahoe mv uploaded.txt renamed.txt``
``tahoe mv tahoe:uploaded.txt tahoe:renamed.txt``
These rename a file within your tahoe root directory.
tahoe mv uploaded.txt fun:
tahoe mv tahoe:uploaded.txt fun:
tahoe mv tahoe:uploaded.txt fun:uploaded.txt
``tahoe mv uploaded.txt fun:``
``tahoe mv tahoe:uploaded.txt fun:``
``tahoe mv tahoe:uploaded.txt fun:uploaded.txt``
These move a file from your tahoe root directory to the virtual directory
set up earlier with "tahoe add-alias fun DIRCAP"
tahoe backup ~ work:backups
``tahoe backup ~ work:backups``
This command performs a full versioned backup of every file and directory
underneath your "~" home directory, placing an immutable timestamped
@ -377,7 +434,7 @@ tahoe backup ~ work:backups
should delete the stale backupdb.sqlite file, to force "tahoe backup" to
upload all files to the new grid.
tahoe backup --exclude=*~ ~ work:backups
``tahoe backup --exclude=*~ ~ work:backups``
Same as above, but this time the backup process will ignore any
filename that will end with '~'. '--exclude' will accept any standard
@ -387,16 +444,15 @@ tahoe backup --exclude=*~ ~ work:backups
attention that the pattern will be matched against any level of the
directory tree, it's still impossible to specify absolute path exclusions.
tahoe backup --exclude-from=/path/to/filename ~ work:backups
``tahoe backup --exclude-from=/path/to/filename ~ work:backups``
'--exclude-from' is similar to '--exclude', but reads exclusion
patterns from '/path/to/filename', one per line.
tahoe backup --exclude-vcs ~ work:backups
``tahoe backup --exclude-vcs ~ work:backups``
This command will ignore any known file or directory that's used by
version control systems to store metadata. The list of the exluded
names is:
version control systems to store metadata. The excluded names are:
* CVS
* RCS
@ -417,13 +473,18 @@ tahoe backup --exclude-vcs ~ work:backups
* .hgignore
* _darcs
== Storage Grid Maintenance ==
Storage Grid Maintenance
========================
tahoe manifest tahoe:
tahoe manifest --storage-index tahoe:
tahoe manifest --verify-cap tahoe:
tahoe manifest --repair-cap tahoe:
tahoe manifest --raw tahoe:
``tahoe manifest tahoe:``
``tahoe manifest --storage-index tahoe:``
``tahoe manifest --verify-cap tahoe:``
``tahoe manifest --repair-cap tahoe:``
``tahoe manifest --raw tahoe:``
This performs a recursive walk of the given directory, visiting every file
and directory that can be reached from that point. It then emits one line to
@ -441,46 +502,47 @@ tahoe manifest --raw tahoe:
strings, and cap strings. The last line of the --raw output will be a JSON
encoded deep-stats dictionary.
tahoe stats tahoe:
``tahoe stats tahoe:``
This performs a recursive walk of the given directory, visiting every file
and directory that can be reached from that point. It gathers statistics on
the sizes of the objects it encounters, and prints a summary to stdout.
== Debugging ==
Debugging
=========
For a list of all debugging commands, use "tahoe debug".
"tahoe debug find-shares STORAGEINDEX NODEDIRS.." will look through one or
"``tahoe debug find-shares STORAGEINDEX NODEDIRS..``" will look through one or
more storage nodes for the share files that are providing storage for the
given storage index.
"tahoe debug catalog-shares NODEDIRS.." will look through one or more storage
nodes and locate every single share they contain. It produces a report on
stdout with one line per share, describing what kind of share it is, the
"``tahoe debug catalog-shares NODEDIRS..``" will look through one or more
storage nodes and locate every single share they contain. It produces a report
on stdout with one line per share, describing what kind of share it is, the
storage index, the size of the file is used for, etc. It may be useful to
concatenate these reports from all storage hosts and use it to look for
anomalies.
"tahoe debug dump-share SHAREFILE" will take the name of a single share file
"``tahoe debug dump-share SHAREFILE``" will take the name of a single share file
(as found by "tahoe find-shares") and print a summary of its contents to
stdout. This includes a list of leases, summaries of the hash tree, and
information from the UEB (URI Extension Block). For mutable file shares, it
will describe which version (seqnum and root-hash) is being stored in this
share.
"tahoe debug dump-cap CAP" will take a URI (a file read-cap, or a directory
"``tahoe debug dump-cap CAP``" will take a URI (a file read-cap, or a directory
read- or write- cap) and unpack it into separate pieces. The most useful
aspect of this command is to reveal the storage index for any given URI. This
can be used to locate the share files that are holding the encoded+encrypted
data for this file.
"tahoe debug repl" will launch an interactive python interpreter in which the
Tahoe packages and modules are available on sys.path (e.g. by using 'import
"``tahoe debug repl``" will launch an interactive python interpreter in which
the Tahoe packages and modules are available on sys.path (e.g. by using 'import
allmydata'). This is most useful from a source tree: it simply sets the
PYTHONPATH correctly and runs the 'python' executable.
"tahoe debug corrupt-share SHAREFILE" will flip a bit in the given sharefile.
This can be used to test the client-side verification/repair code. Obviously
this command should not be used during normal operation.
"``tahoe debug corrupt-share SHAREFILE``" will flip a bit in the given
sharefile. This can be used to test the client-side verification/repair code.
Obviously, this command should not be used during normal operation.

94
docs/frontends/FTP-and-SFTP.txt
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@ -1,15 +1,19 @@
= Tahoe-LAFS FTP and SFTP Frontends =
=================================
Tahoe-LAFS FTP and SFTP Frontends
=================================
1. FTP/SFTP Background
2. Tahoe-LAFS Support
3. Creating an Account File
4. Configuring FTP Access
5. Configuring SFTP Access
6. Dependencies
7. Immutable and mutable files
1. `FTP/SFTP Background`_
2. `Tahoe-LAFS Support`_
3. `Creating an Account File`_
4. `Configuring FTP Access`_
5. `Configuring SFTP Access`_
6. `Dependencies`_
7. `Immutable and mutable files`_
8. `Known Issues`_
== FTP/SFTP Background ==
FTP/SFTP Background
===================
FTP is the venerable internet file-transfer protocol, first developed in
1971. The FTP server usually listens on port 21. A separate connection is
@ -26,8 +30,8 @@ Both FTP and SFTP were developed assuming a UNIX-like server, with accounts
and passwords, octal file modes (user/group/other, read/write/execute), and
ctime/mtime timestamps.
== Tahoe-LAFS Support ==
Tahoe-LAFS Support
==================
All Tahoe-LAFS client nodes can run a frontend FTP server, allowing regular FTP
clients (like /usr/bin/ftp, ncftp, and countless others) to access the
@ -49,12 +53,12 @@ HTTP-based login mechanism, backed by simple PHP script and a database. The
latter form is used by allmydata.com to provide secure access to customer
rootcaps.
== Creating an Account File ==
Creating an Account File
========================
To use the first form, create a file (probably in
BASEDIR/private/ftp.accounts) in which each non-comment/non-blank line is a
space-separated line of (USERNAME, PASSWORD, ROOTCAP), like so:
space-separated line of (USERNAME, PASSWORD, ROOTCAP), like so::
% cat BASEDIR/private/ftp.accounts
# This is a password line, (username, password, rootcap)
@ -69,11 +73,11 @@ these strings.
Now add an 'accounts.file' directive to your tahoe.cfg file, as described
in the next sections.
== Configuring FTP Access ==
Configuring FTP Access
======================
To enable the FTP server with an accounts file, add the following lines to
the BASEDIR/tahoe.cfg file:
the BASEDIR/tahoe.cfg file::
[ftpd]
enabled = true
@ -85,7 +89,7 @@ interface only. The "accounts.file" pathname will be interpreted
relative to the node's BASEDIR.
To enable the FTP server with an account server instead, provide the URL of
that server in an "accounts.url" directive:
that server in an "accounts.url" directive::
[ftpd]
enabled = true
@ -100,8 +104,8 @@ if you connect to the FTP server remotely. The examples above include
":interface=127.0.0.1" in the "port" option, which causes the server to only
accept connections from localhost.
== Configuring SFTP Access ==
Configuring SFTP Access
=======================
The Tahoe-LAFS SFTP server requires a host keypair, just like the regular SSH
server. It is important to give each server a distinct keypair, to prevent
@ -122,16 +126,16 @@ policy by including ":interface=127.0.0.1" in the "port" option, which
causes the server to only accept connections from localhost.
You will use directives in the tahoe.cfg file to tell the SFTP code where to
find these keys. To create one, use the ssh-keygen tool (which comes with the
standard openssh client distribution):
find these keys. To create one, use the ``ssh-keygen`` tool (which comes with
the standard openssh client distribution)::
% cd BASEDIR
% ssh-keygen -f private/ssh_host_rsa_key
% cd BASEDIR
% ssh-keygen -f private/ssh_host_rsa_key
The server private key file must not have a passphrase.
Then, to enable the SFTP server with an accounts file, add the following
lines to the BASEDIR/tahoe.cfg file:
lines to the BASEDIR/tahoe.cfg file::
[sftpd]
enabled = true
@ -144,7 +148,7 @@ The SFTP server will listen on the given port number and on the loopback
interface only. The "accounts.file" pathname will be interpreted
relative to the node's BASEDIR.
Or, to use an account server instead, do this:
Or, to use an account server instead, do this::
[sftpd]
enabled = true
@ -158,13 +162,13 @@ isn't very useful except for testing.
For further information on SFTP compatibility and known issues with various
clients and with the sshfs filesystem, see
<http://tahoe-lafs.org/trac/tahoe-lafs/wiki/SftpFrontend>.
http://tahoe-lafs.org/trac/tahoe-lafs/wiki/SftpFrontend .
Dependencies
============
== Dependencies ==
The Tahoe-LAFS SFTP server requires the Twisted "Conch" component (a "conch" is a
twisted shell, get it?). Many Linux distributions package the Conch code
The Tahoe-LAFS SFTP server requires the Twisted "Conch" component (a "conch" is
a twisted shell, get it?). Many Linux distributions package the Conch code
separately: debian puts it in the "python-twisted-conch" package. Conch
requires the "pycrypto" package, which is a Python+C implementation of many
cryptographic functions (the debian package is named "python-crypto").
@ -183,8 +187,8 @@ http://twistedmatrix.com/trac/ticket/3462 . The Tahoe-LAFS node will refuse to
start the FTP server unless it detects the necessary support code in Twisted.
This patch is not needed for SFTP.
== Immutable and Mutable Files ==
Immutable and Mutable Files
===========================
All files created via SFTP (and FTP) are immutable files. However, files
can only be created in writeable directories, which allows the directory
@ -211,22 +215,26 @@ read-only.
If SFTP is used to write to an existing mutable file, it will publish a
new version when the file handle is closed.
Known Issues
============
== Known Issues ==
Mutable files are not supported by the FTP frontend (ticket #680). Currently,
a directory containing mutable files cannot even be listed over FTP.
Mutable files are not supported by the FTP frontend (`ticket #680
<http://tahoe-lafs.org/trac/tahoe-lafs/ticket/680>`_). Currently, a directory
containing mutable files cannot even be listed over FTP.
The FTP frontend sometimes fails to report errors, for example if an upload
fails because it does meet the "servers of happiness" threshold (ticket #1081).
Upload errors also may not be reported when writing files using SFTP via sshfs
(ticket #1059).
fails because it does meet the "servers of happiness" threshold (`ticket #1081
<http://tahoe-lafs.org/trac/tahoe-lafs/ticket/1081>`_). Upload errors also may not
be reported when writing files using SFTP via sshfs (`ticket #1059
<http://tahoe-lafs.org/trac/tahoe-lafs/ticket/1059>`_).
Non-ASCII filenames are not supported by FTP (ticket #682). They can be used
with SFTP only if the client encodes filenames as UTF-8 (ticket #1089).
Non-ASCII filenames are not supported by FTP (`ticket #682
<http://tahoe-lafs.org/trac/tahoe-lafs/ticket/682>`_). They can be used
with SFTP only if the client encodes filenames as UTF-8 (`ticket #1089
<http://tahoe-lafs.org/trac/tahoe-lafs/ticket/1089>`_).
The gateway node may incur a memory leak when accessing many files via SFTP
(ticket #1045).
(`ticket #1045 <http://tahoe-lafs.org/trac/tahoe-lafs/ticket/1045>`_).
For other known issues in SFTP, see
<http://tahoe-lafs.org/trac/tahoe-lafs/wiki/SftpFrontend>.

149
docs/frontends/download-status.txt
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@ -1,3 +1,11 @@
===============
Download status
===============
Introduction
============
The WUI will display the "status" of uploads and downloads.
The Welcome Page has a link entitled "Recent Uploads and Downloads"
@ -18,53 +26,110 @@ http://tahoe-lafs.org/trac/tahoe-lafs/ticket/1169#comment:1
Then Zooko lightly edited it while copying it into the docs/
directory.
-------
What's involved in a download?
==============================
First, what's involved in a download?:
Downloads are triggered by read() calls, each with a starting offset (defaults
to 0) and a length (defaults to the whole file). A regular webapi GET request
will result in a whole-file read() call.
downloads are triggered by read() calls, each with a starting offset (defaults to 0) and a length (defaults to the whole file). A regular webapi GET request will result in a whole-file read() call
each read() call turns into an ordered sequence of get_segment() calls. A whole-file read will fetch all segments, in order, but partial reads or multiple simultaneous reads will result in random-access of segments. Segment reads always return ciphertext: the layer above that (in read()) is responsible for decryption.
before we can satisfy any segment reads, we need to find some shares. ("DYHB" is an abbreviation for "Do You Have Block", and is the message we send to storage servers to ask them if they have any shares for us. The name is historical, from Mojo Nation/Mnet/Mountain View, but nicely distinctive. Tahoe-LAFS's actual message name is remote_get_buckets().). Responses come back eventually, or don't.
Once we get enough positive DYHB responses, we have enough shares to start downloading. We send "block requests" for various pieces of the share. Responses come back eventually, or don't.
When we get enough block-request responses for a given segment, we can decode the data and satisfy the segment read.
When the segment read completes, some or all of the segment data is used to satisfy the read() call (if the read call started or ended in the middle of a segment, we'll only use part of the data, otherwise we'll use all of it).
Each read() call turns into an ordered sequence of get_segment() calls. A
whole-file read will fetch all segments, in order, but partial reads or
multiple simultaneous reads will result in random-access of segments. Segment
reads always return ciphertext: the layer above that (in read()) is responsible
for decryption.
With that background, here is the data currently on the download-status page:
Before we can satisfy any segment reads, we need to find some shares. ("DYHB"
is an abbreviation for "Do You Have Block", and is the message we send to
storage servers to ask them if they have any shares for us. The name is
historical, from Mojo Nation/Mnet/Mountain View, but nicely distinctive.
Tahoe-LAFS's actual message name is remote_get_buckets().). Responses come
back eventually, or don't.
"DYHB Requests": this shows every Do-You-Have-Block query sent to storage servers and their results. Each line shows the following:
the serverid to which the request was sent
the time at which the request was sent. Note that all timestamps are relative to the start of the first read() call and indicated with a "+" sign
the time at which the response was received (if ever)
the share numbers that the server has, if any
the elapsed time taken by the request
also, each line is colored according to the serverid. This color is also used in the "Requests" section below.
Once we get enough positive DYHB responses, we have enough shares to start
downloading. We send "block requests" for various pieces of the share.
Responses come back eventually, or don't.
"Read Events": this shows all the FileNode read() calls and their overall results. Each line shows:
the range of the file that was requested (as [OFFSET:+LENGTH]). A whole-file GET will start at 0 and read the entire file.
the time at which the read() was made
the time at which the request finished, either because the last byte of data was returned to the read() caller, or because they cancelled the read by calling stopProducing (i.e. closing the HTTP connection)
the number of bytes returned to the caller so far
the time spent on the read, so far
the total time spent in AES decryption
total time spend paused by the client (pauseProducing), generally because the HTTP connection filled up, which most streaming media players will do to limit how much data they have to buffer
effective speed of the read(), not including paused time
When we get enough block-request responses for a given segment, we can decode
the data and satisfy the segment read.
"Segment Events": this shows each get_segment() call and its resolution. This table is not well organized, and my post-1.8.0 work will clean it up a lot. In its present form, it records "request" and "delivery" events separately, indicated by the "type" column.
Each request shows the segment number being requested and the time at which the get_segment() call was made
Each delivery shows:
segment number
range of file data (as [OFFSET:+SIZE]) delivered
elapsed time spent doing ZFEC decoding
overall elapsed time fetching the segment
effective speed of the segment fetch
When the segment read completes, some or all of the segment data is used to
satisfy the read() call (if the read call started or ended in the middle of a
segment, we'll only use part of the data, otherwise we'll use all of it).
"Requests": this shows every block-request sent to the storage servers. Each line shows:
the server to which the request was sent
which share number it is referencing
the portion of the share data being requested (as [OFFSET:+SIZE])
the time the request was sent
the time the response was received (if ever)
the amount of data that was received (which might be less than SIZE if we tried to read off the end of the share)
the elapsed time for the request (RTT=Round-Trip-Time)
Data on the download-status page
================================
Also note that each Request line is colored according to the serverid it was sent to. And all timestamps are shown relative to the start of the first read() call: for example the first DYHB message was sent at +0.001393s about 1.4 milliseconds after the read() call started everything off.
DYHB Requests
-------------
This shows every Do-You-Have-Block query sent to storage servers and their
results. Each line shows the following:
* the serverid to which the request was sent
* the time at which the request was sent. Note that all timestamps are
relative to the start of the first read() call and indicated with a "+" sign
* the time at which the response was received (if ever)
* the share numbers that the server has, if any
* the elapsed time taken by the request
Also, each line is colored according to the serverid. This color is also used
in the "Requests" section below.
Read Events
-----------
This shows all the FileNode read() calls and their overall results. Each line
shows:
* the range of the file that was requested (as [OFFSET:+LENGTH]). A whole-file
GET will start at 0 and read the entire file.
* the time at which the read() was made
* the time at which the request finished, either because the last byte of data
was returned to the read() caller, or because they cancelled the read by
calling stopProducing (i.e. closing the HTTP connection)
* the number of bytes returned to the caller so far
* the time spent on the read, so far
* the total time spent in AES decryption
* total time spend paused by the client (pauseProducing), generally because the
HTTP connection filled up, which most streaming media players will do to
limit how much data they have to buffer
* effective speed of the read(), not including paused time
Segment Events
--------------
This shows each get_segment() call and its resolution. This table is not well
organized, and my post-1.8.0 work will clean it up a lot. In its present form,
it records "request" and "delivery" events separately, indicated by the "type"
column.
Each request shows the segment number being requested and the time at which the
get_segment() call was made.
Each delivery shows:
* segment number
* range of file data (as [OFFSET:+SIZE]) delivered
* elapsed time spent doing ZFEC decoding
* overall elapsed time fetching the segment
* effective speed of the segment fetch
Requests
--------
This shows every block-request sent to the storage servers. Each line shows:
* the server to which the request was sent
* which share number it is referencing
* the portion of the share data being requested (as [OFFSET:+SIZE])
* the time the request was sent
* the time the response was received (if ever)
* the amount of data that was received (which might be less than SIZE if we
tried to read off the end of the share)
* the elapsed time for the request (RTT=Round-Trip-Time)
Also note that each Request line is colored according to the serverid it was
sent to. And all timestamps are shown relative to the start of the first
read() call: for example the first DYHB message was sent at +0.001393s about
1.4 milliseconds after the read() call started everything off.

1420
docs/frontends/webapi.txt
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11
docs/specifications/URI-extension.txt
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@ -1,5 +1,6 @@
"URI Extension Block"
===================
URI Extension Block
===================
This block is a serialized dictionary with string keys and string values
(some of which represent numbers, some of which are SHA-256 hashes). All
@ -13,7 +14,7 @@ clients who do not wish to do incremental validation) can be performed solely
with the data from this block.
At the moment, this data block contains the following keys (and an estimate
on their sizes):
on their sizes)::
size 5
segment_size 7
@ -42,7 +43,7 @@ files, regardless of file size. Therefore hash trees (which have a size that
depends linearly upon the number of segments) are stored elsewhere in the
bucket, with only the hash tree root stored in this data block.
This block will be serialized as follows:
This block will be serialized as follows::
assert that all keys match ^[a-zA-z_\-]+$
sort all the keys lexicographically
@ -51,7 +52,7 @@ This block will be serialized as follows:
write(netstring(data[k]))
Serialized size:
Serialized size::
dense binary (but decimal) packing: 160+46=206
including 'key:' (185) and netstring (6*3+7*4=46) on values: 231

157
docs/specifications/dirnodes.txt
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@ -1,5 +1,6 @@
= Tahoe-LAFS Directory Nodes =
==========================
Tahoe-LAFS Directory Nodes
==========================
As explained in the architecture docs, Tahoe-LAFS can be roughly viewed as
a collection of three layers. The lowest layer is the key-value store: it
@ -13,12 +14,30 @@ friends.
This document examines the middle layer, the "filesystem".
== Key-value Store Primitives ==
1. `Key-value Store Primitives`_
2. `Filesystem goals`_
3. `Dirnode goals`_
4. `Dirnode secret values`_
5. `Dirnode storage format`_
6. `Dirnode sizes, mutable-file initial read sizes`_
7. `Design Goals, redux`_
1. `Confidentiality leaks in the storage servers`_
2. `Integrity failures in the storage servers`_
3. `Improving the efficiency of dirnodes`_
4. `Dirnode expiration and leases`_
8. `Starting Points: root dirnodes`_
9. `Mounting and Sharing Directories`_
10. `Revocation`_
Key-value Store Primitives
==========================
In the lowest layer (key-value store), there are two operations that reference
immutable data (which we refer to as "CHK URIs" or "CHK read-capabilities" or
"CHK read-caps"). One puts data into the grid (but only if it doesn't exist
already), the other retrieves it:
already), the other retrieves it::
chk_uri = put(data)
data = get(chk_uri)
@ -26,13 +45,14 @@ already), the other retrieves it:
We also have three operations which reference mutable data (which we refer to
as "mutable slots", or "mutable write-caps and read-caps", or sometimes "SSK
slots"). One creates a slot with some initial contents, a second replaces the
contents of a pre-existing slot, and the third retrieves the contents:
contents of a pre-existing slot, and the third retrieves the contents::
mutable_uri = create(initial_data)
replace(mutable_uri, new_data)
data = get(mutable_uri)
== Filesystem Goals ==
Filesystem Goals
================
The main goal for the middle (filesystem) layer is to give users a way to
organize the data that they have uploaded into the grid. The traditional way
@ -48,23 +68,24 @@ The directory structure is therefore a directed graph of nodes, in which each
node might be a directory node or a file node. All file nodes are terminal
nodes.
== Dirnode Goals ==
Dirnode Goals
=============
What properties might be desirable for these directory nodes? In no
particular order:
1: functional. Code which does not work doesn't count.
2: easy to document, explain, and understand
3: confidential: it should not be possible for others to see the contents of
a directory
4: integrity: it should not be possible for others to modify the contents
of a directory
5: available: directories should survive host failure, just like files do
6: efficient: in storage, communication bandwidth, number of round-trips
7: easy to delegate individual directories in a flexible way
8: updateness: everybody looking at a directory should see the same contents
9: monotonicity: everybody looking at a directory should see the same
sequence of updates
1. functional. Code which does not work doesn't count.
2. easy to document, explain, and understand
3. confidential: it should not be possible for others to see the contents of
a directory
4. integrity: it should not be possible for others to modify the contents
of a directory
5. available: directories should survive host failure, just like files do
6. efficient: in storage, communication bandwidth, number of round-trips
7. easy to delegate individual directories in a flexible way
8. updateness: everybody looking at a directory should see the same contents
9. monotonicity: everybody looking at a directory should see the same
sequence of updates
Some of these goals are mutually exclusive. For example, availability and
consistency are opposing, so it is not possible to achieve #5 and #8 at the
@ -102,7 +123,8 @@ version 1 and other shares of version 2). In extreme cases of simultaneous
update, mutable files might suffer from non-monotonicity.
== Dirnode secret values ==
Dirnode secret values
=====================
As mentioned before, dirnodes are simply a special way to interpret the
contents of a mutable file, so the secret keys and capability strings
@ -126,7 +148,8 @@ URI:DIR2-RO:buxjqykt637u61nnmjg7s8zkny:ar8r5j99a4mezdojejmsfp4fj1zeky9gjigyrid4u
is a read-capability URI, both for the same dirnode.
== Dirnode storage format ==
Dirnode storage format
======================
Each dirnode is stored in a single mutable file, distributed in the Tahoe-LAFS
grid. The contents of this file are a serialized list of netstrings, one per
@ -159,7 +182,8 @@ other users who have read-only access to 'foo' will be unable to decrypt its
rwcap slot, this limits those users to read-only access to 'bar' as well,
thus providing the transitive readonlyness that we desire.
=== Dirnode sizes, mutable-file initial read sizes ===
Dirnode sizes, mutable-file initial read sizes
==============================================
How big are dirnodes? When reading dirnode data out of mutable files, how
large should our initial read be? If we guess exactly, we can read a dirnode
@ -171,6 +195,8 @@ will cost us at least another RTT.
Assuming child names are between 10 and 99 characters long, how long are the
various pieces of a dirnode?
::
netstring(name) ~= 4+len(name)
chk-cap = 97 (for 4-char filesizes)
dir-rw-cap = 88
@ -181,8 +207,10 @@ various pieces of a dirnode?
JSON({ctime=float,mtime=float,'tahoe':{linkcrtime=float,linkmotime=float}}): 137
netstring(metadata) = 4+137 = 141
so a CHK entry is:
so a CHK entry is::
5+ 4+len(name) + 4+97 + 5+16+97+32 + 4+137
And a 15-byte filename gives a 416-byte entry. When the entry points at a
subdirectory instead of a file, the entry is a little bit smaller. So an
empty directory uses 0 bytes, a directory with one child uses about 416
@ -193,7 +221,7 @@ get 139ish bytes of data in each share per child.
The pubkey, signature, and hashes form the first 935ish bytes of the
container, then comes our data, then about 1216 bytes of encprivkey. So if we
read the first:
read the first::
1kB: we get 65bytes of dirnode data : only empty directories
2kB: 1065bytes: about 8
@ -205,42 +233,44 @@ we read the mutable file, which should give good performance (one RTT) for
small directories.
== Design Goals, redux ==
Design Goals, redux
===================
How well does this design meet the goals?
#1 functional: YES: the code works and has extensive unit tests
#2 documentable: YES: this document is the existence proof
#3 confidential: YES: see below
#4 integrity: MOSTLY: a coalition of storage servers can rollback individual
mutable files, but not a single one. No server can
substitute fake data as genuine.
#5 availability: YES: as long as 'k' storage servers are present and have
the same version of the mutable file, the dirnode will
be available.
#6 efficient: MOSTLY:
network: single dirnode lookup is very efficient, since clients can
fetch specific keys rather than being required to get or set
the entire dirnode each time. Traversing many directories
takes a lot of roundtrips, and these can't be collapsed with
promise-pipelining because the intermediate values must only
be visible to the client. Modifying many dirnodes at once
(e.g. importing a large pre-existing directory tree) is pretty
slow, since each graph edge must be created independently.
storage: each child has a separate IV, which makes them larger than
if all children were aggregated into a single encrypted string
#7 delegation: VERY: each dirnode is a completely independent object,
to which clients can be granted separate read-write or
read-only access
#8 updateness: VERY: with only a single point of access, and no caching,
each client operation starts by fetching the current
value, so there are no opportunities for staleness
#9 monotonicity: VERY: the single point of access also protects against
retrograde motion
1. functional: YES: the code works and has extensive unit tests
2. documentable: YES: this document is the existence proof
3. confidential: YES: see below
4. integrity: MOSTLY: a coalition of storage servers can rollback individual
mutable files, but not a single one. No server can
substitute fake data as genuine.
5. availability: YES: as long as 'k' storage servers are present and have
the same version of the mutable file, the dirnode will
be available.
6. efficient: MOSTLY:
network: single dirnode lookup is very efficient, since clients can
fetch specific keys rather than being required to get or set
the entire dirnode each time. Traversing many directories
takes a lot of roundtrips, and these can't be collapsed with
promise-pipelining because the intermediate values must only
be visible to the client. Modifying many dirnodes at once
(e.g. importing a large pre-existing directory tree) is pretty
slow, since each graph edge must be created independently.
storage: each child has a separate IV, which makes them larger than
if all children were aggregated into a single encrypted string
7. delegation: VERY: each dirnode is a completely independent object,
to which clients can be granted separate read-write or
read-only access
8. updateness: VERY: with only a single point of access, and no caching,
each client operation starts by fetching the current
value, so there are no opportunities for staleness
9. monotonicity: VERY: the single point of access also protects against
retrograde motion
=== Confidentiality leaks in the storage servers ===
Confidentiality leaks in the storage servers
--------------------------------------------
Dirnode (and the mutable files upon which they are based) are very private
against other clients: traffic between the client and the storage servers is
@ -261,7 +291,8 @@ attacker may be able to build up a graph with the same shape as the plaintext
filesystem, but with unlabeled edges and unknown file contents.
=== Integrity failures in the storage servers ===
Integrity failures in the storage servers
-----------------------------------------
The mutable file's integrity mechanism (RSA signature on the hash of the file
contents) prevents the storage server from modifying the dirnode's contents
@ -276,7 +307,8 @@ version number. This insures that one or two misbehaving storage servers
cannot cause this rollback on their own.
=== Improving the efficiency of dirnodes ===
Improving the efficiency of dirnodes
------------------------------------
The current mutable-file -based dirnode scheme suffers from certain
inefficiencies. A very large directory (with thousands or millions of
@ -305,7 +337,6 @@ mutable file scheme which will use shared parameters to reduce the
directory-creation effort to a bare minimum (picking a random number instead
of generating two random primes).
When a backup program is run for the first time, it needs to copy a large
amount of data from a pre-existing filesystem into reliable storage. This
means that a large and complex directory structure needs to be duplicated in
@ -345,7 +376,8 @@ encryption keys for each component directory, to get the benefits of both
schemes at once.
=== Dirnode expiration and leases ===
Dirnode expiration and leases
-----------------------------
Dirnodes are created any time a client wishes to add a new directory. How
long do they live? What's to keep them from sticking around forever, taking
@ -377,14 +409,16 @@ prompts the client to send out lease-cancellation messages, allowing the data
to be deleted.
== Starting Points: root dirnodes ==
Starting Points: root dirnodes
==============================
Any client can record the URI of a directory node in some external form (say,
in a local file) and use it as the starting point of later traversal. Each
Tahoe-LAFS user is expected to create a new (unattached) dirnode when they first
start using the grid, and record its URI for later use.
== Mounting and Sharing Directories ==
Mounting and Sharing Directories
================================
The biggest benefit of this dirnode approach is that sharing individual
directories is almost trivial. Alice creates a subdirectory that she wants to
@ -409,7 +443,8 @@ indicate whether they want to grant read-write or read-only access to the
recipient. The recipient then needs an interface to drag the new folder into
their vdrive and give it a home.
== Revocation ==
Revocation
==========
When Alice decides that she no longer wants Bob to be able to access the
shared directory, what should she do? Suppose she's shared this folder with

30
docs/specifications/file-encoding.txt
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@ -1,5 +1,6 @@
== FileEncoding ==
=============
File Encoding
=============
When the client wishes to upload an immutable file, the first step is to
decide upon an encryption key. There are two methods: convergent or random.
@ -43,8 +44,7 @@ table that maps SI to shares.
Anybody who knows a Storage Index can retrieve the associated ciphertext:
ciphertexts are not secret.
[[Image(file-encoding1.png)]]
.. image:: file-encoding1.svg
The ciphertext file is then broken up into segments. The last segment is
likely to be shorter than the rest. Each segment is erasure-coded into a
@ -60,7 +60,7 @@ aka landlord, aka storage node, aka peer). The "share" held by each remote
shareholder is nominally just a collection of these blocks. The file will
be recoverable when a certain number of shares have been retrieved.
[[Image(file-encoding2.png)]]
.. image:: file-encoding2.svg
The blocks are hashed as they are generated and transmitted. These
block hashes are put into a Merkle hash tree. When the last share has been
@ -71,7 +71,7 @@ nodes ahead of time, so we can validate each block independently.
The root of this block hash tree is called the "block root hash" and
used in the next step.
[[Image(file-encoding3.png)]]
.. image:: file-encoding3.svg
There is a higher-level Merkle tree called the "share hash tree". Its leaves
are the block root hashes from each share. The root of this tree is called
@ -89,11 +89,11 @@ time, sufficient download queries can be generated in parallel).
The URI (also known as the immutable-file read-cap, since possessing it
grants the holder the capability to read the file's plaintext) is then
represented as a (relatively) short printable string like so:
represented as a (relatively) short printable string like so::
URI:CHK:auxet66ynq55naiy2ay7cgrshm:6rudoctmbxsmbg7gwtjlimd6umtwrrsxkjzthuldsmo4nnfoc6fa:3:10:1000000
[[Image(file-encoding4.png)]]
.. image:: file-encoding4.svg
During download, when a peer begins to transmit a share, it first transmits
all of the parts of the share hash tree that are necessary to validate its
@ -102,7 +102,7 @@ that are necessary to validate the first block. Then it transmits the
first block. It then continues this loop: transmitting any portions of the
block hash tree to validate block#N, then sending block#N.
[[Image(file-encoding5.png)]]
.. image:: file-encoding5.svg
So the "share" that is sent to the remote peer actually consists of three
pieces, sent in a specific order as they become available, and retrieved
@ -125,13 +125,14 @@ peers) into decoding, to produce the first segment of crypttext, which is
then decrypted to produce the first segment of plaintext, which is finally
delivered to the user.
[[Image(file-encoding6.png)]]
.. image:: file-encoding6.svg
== Hashes ==
Hashes
======
All hashes use SHA-256d, as defined in Practical Cryptography (by Ferguson
and Schneier). All hashes use a single-purpose tag, e.g. the hash that
converts an encryption key into a storage index is defined as follows:
converts an encryption key into a storage index is defined as follows::
SI = SHA256d(netstring("allmydata_immutable_key_to_storage_index_v1") + key)
@ -142,7 +143,8 @@ Using SHA-256d (instead of plain SHA-256) guards against length-extension
attacks. Using the tag protects our Merkle trees against attacks in which the
hash of a leaf is confused with a hash of two children (allowing an attacker
to generate corrupted data that nevertheless appears to be valid), and is
simply good "cryptograhic hygiene". The "Chosen Protocol Attack" by Kelsey,
Schneier, and Wagner (http://www.schneier.com/paper-chosen-protocol.html) is
simply good "cryptograhic hygiene". The `"Chosen Protocol Attack" by Kelsey,
Schneier, and Wagner <http://www.schneier.com/paper-chosen-protocol.html>`_ is
relevant. Putting the tag in a netstring guards against attacks that seek to
confuse the end of the tag with the beginning of the subsequent value.

470
docs/specifications/mutable.txt
View File

@ -1,7 +1,22 @@
=============
Mutable Files
=============
This describes the "RSA-based mutable files" which were shipped in Tahoe v0.8.0.
= Mutable Files =
1. `Consistency vs. Availability`_
2. `The Prime Coordination Directive: "Don't Do That"`_
3. `Small Distributed Mutable Files`_
1. `SDMF slots overview`_
2. `Server Storage Protocol`_
3. `Code Details`_
4. `SMDF Slot Format`_
5. `Recovery`_
4. `Medium Distributed Mutable Files`_
5. `Large Distributed Mutable Files`_
6. `TODO`_
Mutable File Slots are places with a stable identifier that can hold data
that changes over time. In contrast to CHK slots, for which the
@ -27,7 +42,8 @@ shares cannot read or modify them: the worst they can do is deny service (by
deleting or corrupting the shares), or attempt a rollback attack (which can
only succeed with the cooperation of at least k servers).
== Consistency vs Availability ==
Consistency vs. Availability
============================
There is an age-old battle between consistency and availability. Epic papers
have been written, elaborate proofs have been established, and generations of
@ -45,25 +61,26 @@ effective ways to merge multiple versions, so inconsistency is not
necessarily a problem (i.e. directory nodes can usually merge multiple "add
child" operations).
== The Prime Coordination Directive: "Don't Do That" ==
The Prime Coordination Directive: "Don't Do That"
=================================================
The current rule for applications which run on top of Tahoe is "do not
perform simultaneous uncoordinated writes". That means you need non-tahoe
means to make sure that two parties are not trying to modify the same mutable
slot at the same time. For example:
* don't give the read-write URI to anyone else. Dirnodes in a private
directory generally satisfy this case, as long as you don't use two
clients on the same account at the same time
* if you give a read-write URI to someone else, stop using it yourself. An
inbox would be a good example of this.
* if you give a read-write URI to someone else, call them on the phone
before you write into it
* build an automated mechanism to have your agents coordinate writes.
For example, we expect a future release to include a FURL for a
"coordination server" in the dirnodes. The rule can be that you must
contact the coordination server and obtain a lock/lease on the file
before you're allowed to modify it.
* don't give the read-write URI to anyone else. Dirnodes in a private
directory generally satisfy this case, as long as you don't use two
clients on the same account at the same time
* if you give a read-write URI to someone else, stop using it yourself. An
inbox would be a good example of this.
* if you give a read-write URI to someone else, call them on the phone
before you write into it
* build an automated mechanism to have your agents coordinate writes.
For example, we expect a future release to include a FURL for a
"coordination server" in the dirnodes. The rule can be that you must
contact the coordination server and obtain a lock/lease on the file
before you're allowed to modify it.
If you do not follow this rule, Bad Things will happen. The worst-case Bad
Thing is that the entire file will be lost. A less-bad Bad Thing is that one
@ -91,7 +108,8 @@ run. The Prime Coordination Directive therefore applies to inter-node
conflicts, not intra-node ones.
== Small Distributed Mutable Files ==
Small Distributed Mutable Files
===============================
SDMF slots are suitable for small (<1MB) files that are editing by rewriting
the entire file. The three operations are:
@ -103,7 +121,8 @@ the entire file. The three operations are:
The first use of SDMF slots will be to hold directories (dirnodes), which map
encrypted child names to rw-URI/ro-URI pairs.
=== SDMF slots overview ===
SDMF slots overview
-------------------
Each SDMF slot is created with a public/private key pair. The public key is
known as the "verification key", while the private key is called the
@ -138,6 +157,8 @@ The read-write URI consists of the write key and the verification key hash.
The read-only URI contains the read key and the verification key hash. The
verify-only URI contains the storage index and the verification key hash.
::
URI:SSK-RW:b2a(writekey):b2a(verification_key_hash)
URI:SSK-RO:b2a(readkey):b2a(verification_key_hash)
URI:SSK-Verify:b2a(storage_index):b2a(verification_key_hash)
@ -158,64 +179,75 @@ write enabler with anyone else.
The SDMF slot structure will be described in more detail below. The important
pieces are:
* a sequence number
* a root hash "R"
* the encoding parameters (including k, N, file size, segment size)
* a signed copy of [seqnum,R,encoding_params], using the signature key
* the verification key (not encrypted)
* the share hash chain (part of a Merkle tree over the share hashes)
* the block hash tree (Merkle tree over blocks of share data)
* the share data itself (erasure-coding of read-key-encrypted file data)
* the signature key, encrypted with the write key
* a sequence number
* a root hash "R"
* the encoding parameters (including k, N, file size, segment size)
* a signed copy of [seqnum,R,encoding_params], using the signature key
* the verification key (not encrypted)
* the share hash chain (part of a Merkle tree over the share hashes)
* the block hash tree (Merkle tree over blocks of share data)
* the share data itself (erasure-coding of read-key-encrypted file data)
* the signature key, encrypted with the write key
The access pattern for read is:
* hash read-key to get storage index
* use storage index to locate 'k' shares with identical 'R' values
* either get one share, read 'k' from it, then read k-1 shares
* or read, say, 5 shares, discover k, either get more or be finished
* or copy k into the URIs
* read verification key
* hash verification key, compare against verification key hash
* read seqnum, R, encoding parameters, signature
* verify signature against verification key
* read share data, compute block-hash Merkle tree and root "r"
* read share hash chain (leading from "r" to "R")
* validate share hash chain up to the root "R"
* submit share data to erasure decoding
* decrypt decoded data with read-key
* submit plaintext to application
* hash read-key to get storage index
* use storage index to locate 'k' shares with identical 'R' values
* either get one share, read 'k' from it, then read k-1 shares
* or read, say, 5 shares, discover k, either get more or be finished
* or copy k into the URIs
* read verification key
* hash verification key, compare against verification key hash
* read seqnum, R, encoding parameters, signature
* verify signature against verification key
* read share data, compute block-hash Merkle tree and root "r"
* read share hash chain (leading from "r" to "R")
* validate share hash chain up to the root "R"
* submit share data to erasure decoding
* decrypt decoded data with read-key
* submit plaintext to application
The access pattern for write is:
* hash write-key to get read-key, hash read-key to get storage index
* use the storage index to locate at least one share
* read verification key and encrypted signature key
* decrypt signature key using write-key
* hash signature key, compare against write-key
* hash verification key, compare against verification key hash
* encrypt plaintext from application with read-key
* application can encrypt some data with the write-key to make it only
available to writers (use this for transitive read-onlyness of dirnodes)
* erasure-code crypttext to form shares
* split shares into blocks
* compute Merkle tree of blocks, giving root "r" for each share
* compute Merkle tree of shares, find root "R" for the file as a whole
* create share data structures, one per server:
* use seqnum which is one higher than the old version
* share hash chain has log(N) hashes, different for each server
* signed data is the same for each server
* now we have N shares and need homes for them
* walk through peers
* if share is not already present, allocate-and-set
* otherwise, try to modify existing share:
* send testv_and_writev operation to each one
* testv says to accept share if their(seqnum+R) <= our(seqnum+R)
* count how many servers wind up with which versions (histogram over R)
* keep going until N servers have the same version, or we run out of servers
* if any servers wound up with a different version, report error to
application
* if we ran out of servers, initiate recovery process (described below)
=== Server Storage Protocol ===
* hash write-key to get read-key, hash read-key to get storage index
* use the storage index to locate at least one share
* read verification key and encrypted signature key
* decrypt signature key using write-key
* hash signature key, compare against write-key
* hash verification key, compare against verification key hash
* encrypt plaintext from application with read-key
* application can encrypt some data with the write-key to make it only
available to writers (use this for transitive read-onlyness of dirnodes)
* erasure-code crypttext to form shares
* split shares into blocks
* compute Merkle tree of blocks, giving root "r" for each share
* compute Merkle tree of shares, find root "R" for the file as a whole
* create share data structures, one per server:
* use seqnum which is one higher than the old version
* share hash chain has log(N) hashes, different for each server
* signed data is the same for each server
* now we have N shares and need homes for them
* walk through peers
* if share is not already present, allocate-and-set
* otherwise, try to modify existing share:
* send testv_and_writev operation to each one
* testv says to accept share if their(seqnum+R) <= our(seqnum+R)
* count how many servers wind up with which versions (histogram over R)
* keep going until N servers have the same version, or we run out of servers
* if any servers wound up with a different version, report error to
application
* if we ran out of servers, initiate recovery process (described below)
Server Storage Protocol
-----------------------
The storage servers will provide a mutable slot container which is oblivious
to the details of the data being contained inside it. Each storage index
@ -228,7 +260,7 @@ as the filename.
The container holds space for a container magic number (for versioning), the
write enabler, the nodeid which accepted the write enabler (used for share
migration, described below), a small number of lease structures, the embedded
data itself, and expansion space for additional lease structures.
data itself, and expansion space for additional lease structures::
# offset size name
1 0 32 magic verstr "tahoe mutable container v1" plus binary
@ -270,53 +302,63 @@ portions of the container are inaccessible to the clients.
The two methods provided by the storage server on these "MutableSlot" share
objects are:
* readv(ListOf(offset=int, length=int))
* returns a list of bytestrings, of the various requested lengths
* offset < 0 is interpreted relative to the end of the data
* spans which hit the end of the data will return truncated data
* readv(ListOf(offset=int, length=int))
* testv_and_writev(write_enabler, test_vector, write_vector)
* this is a test-and-set operation which performs the given tests and only
applies the desired writes if all tests succeed. This is used to detect
simultaneous writers, and to reduce the chance that an update will lose
data recently written by some other party (written after the last time
this slot was read).
* test_vector=ListOf(TupleOf(offset, length, opcode, specimen))
* the opcode is a string, from the set [gt, ge, eq, le, lt, ne]
* each element of the test vector is read from the slot's data and
compared against the specimen using the desired (in)equality. If all
tests evaluate True, the write is performed
* write_vector=ListOf(TupleOf(offset, newdata))
* offset < 0 is not yet defined, it probably means relative to the
end of the data, which probably means append, but we haven't nailed
it down quite yet
* write vectors are executed in order, which specifies the results of
overlapping writes
* return value:
* error: OutOfSpace
* error: something else (io error, out of memory, whatever)
* (True, old_test_data): the write was accepted (test_vector passed)
* (False, old_test_data): the write was rejected (test_vector failed)
* both 'accepted' and 'rejected' return the old data that was used
for the test_vector comparison. This can be used by the client
to detect write collisions, including collisions for which the
desired behavior was to overwrite the old version.
* returns a list of bytestrings, of the various requested lengths
* offset < 0 is interpreted relative to the end of the data
* spans which hit the end of the data will return truncated data
* testv_and_writev(write_enabler, test_vector, write_vector)
* this is a test-and-set operation which performs the given tests and only
applies the desired writes if all tests succeed. This is used to detect
simultaneous writers, and to reduce the chance that an update will lose
data recently written by some other party (written after the last time
this slot was read).
* test_vector=ListOf(TupleOf(offset, length, opcode, specimen))
* the opcode is a string, from the set [gt, ge, eq, le, lt, ne]
* each element of the test vector is read from the slot's data and
compared against the specimen using the desired (in)equality. If all
tests evaluate True, the write is performed
* write_vector=ListOf(TupleOf(offset, newdata))
* offset < 0 is not yet defined, it probably means relative to the
end of the data, which probably means append, but we haven't nailed
it down quite yet
* write vectors are executed in order, which specifies the results of
overlapping writes
* return value:
* error: OutOfSpace
* error: something else (io error, out of memory, whatever)
* (True, old_test_data): the write was accepted (test_vector passed)
* (False, old_test_data): the write was rejected (test_vector failed)
* both 'accepted' and 'rejected' return the old data that was used
for the test_vector comparison. This can be used by the client
to detect write collisions, including collisions for which the
desired behavior was to overwrite the old version.
In addition, the storage server provides several methods to access these
share objects:
* allocate_mutable_slot(storage_index, sharenums=SetOf(int))
* returns DictOf(int, MutableSlot)
* get_mutable_slot(storage_index)
* returns DictOf(int, MutableSlot)
* or raises KeyError
* allocate_mutable_slot(storage_index, sharenums=SetOf(int))
* returns DictOf(int, MutableSlot)
* get_mutable_slot(storage_index)
* returns DictOf(int, MutableSlot)
* or raises KeyError
We intend to add an interface which allows small slots to allocate-and-write
in a single call, as well as do update or read in a single call. The goal is
to allow a reasonably-sized dirnode to be created (or updated, or read) in
just one round trip (to all N shareholders in parallel).
==== migrating shares ====
migrating shares
````````````````
If a share must be migrated from one server to another, two values become
invalid: the write enabler (since it was computed for the old server), and
@ -357,7 +399,8 @@ operations on either client or server.
Migrating the leases will require a similar protocol. This protocol will be
defined concretely at a later date.
=== Code Details ===
Code Details
------------
The MutableFileNode class is used to manipulate mutable files (as opposed to
ImmutableFileNodes). These are initially generated with
@ -370,13 +413,15 @@ NOTE: this section is out of date. Please see src/allmydata/interfaces.py
The methods of MutableFileNode are:
* download_to_data() -> [deferred] newdata, NotEnoughSharesError
* if there are multiple retrieveable versions in the grid, get() returns
the first version it can reconstruct, and silently ignores the others.
In the future, a more advanced API will signal and provide access to
the multiple heads.
* update(newdata) -> OK, UncoordinatedWriteError, NotEnoughSharesError
* overwrite(newdata) -> OK, UncoordinatedWriteError, NotEnoughSharesError
* download_to_data() -> [deferred] newdata, NotEnoughSharesError
* if there are multiple retrieveable versions in the grid, get() returns
the first version it can reconstruct, and silently ignores the others.
In the future, a more advanced API will signal and provide access to
the multiple heads.
* update(newdata) -> OK, UncoordinatedWriteError, NotEnoughSharesError
* overwrite(newdata) -> OK, UncoordinatedWriteError, NotEnoughSharesError
download_to_data() causes a new retrieval to occur, pulling the current
contents from the grid and returning them to the caller. At the same time,
@ -386,7 +431,7 @@ change has occured between the two, this information will be out of date,
triggering the UncoordinatedWriteError.
update() is therefore intended to be used just after a download_to_data(), in
the following pattern:
the following pattern::
d = mfn.download_to_data()
d.addCallback(apply_delta)
@ -399,7 +444,7 @@ its own. To accomplish this, the app needs to pause, download the new
(post-collision and post-recovery) form of the file, reapply their delta,
then submit the update request again. A randomized pause is necessary to
reduce the chances of colliding a second time with another client that is
doing exactly the same thing:
doing exactly the same thing::
d = mfn.download_to_data()
d.addCallback(apply_delta)
@ -419,7 +464,7 @@ retry forever, but such apps are encouraged to provide a means to the user of
giving up after a while.
UCW does not mean that the update was not applied, so it is also a good idea
to skip the retry-update step if the delta was already applied:
to skip the retry-update step if the delta was already applied::
d = mfn.download_to_data()
d.addCallback(apply_delta)
@ -456,12 +501,11 @@ you want to replace the file's contents with completely unrelated ones. When
raw files are uploaded into a mutable slot through the tahoe webapi (using
POST and the ?mutable=true argument), they are put in place with overwrite().
The peer-selection and data-structure manipulation (and signing/verification)
steps will be implemented in a separate class in allmydata/mutable.py .
=== SMDF Slot Format ===
SMDF Slot Format
----------------
This SMDF data lives inside a server-side MutableSlot container. The server
is oblivious to this format.
@ -470,44 +514,47 @@ This data is tightly packed. In particular, the share data is defined to run
all the way to the beginning of the encrypted private key (the encprivkey
offset is used both to terminate the share data and to begin the encprivkey).
# offset size name
1 0 1 version byte, \x00 for this format
2 1 8 sequence number. 2^64-1 must be handled specially, TBD
3 9 32 "R" (root of share hash Merkle tree)
4 41 16 IV (share data is AES(H(readkey+IV)) )
5 57 18 encoding parameters:
57 1 k
58 1 N
59 8 segment size
67 8 data length (of original plaintext)
6 75 32 offset table:
75 4 (8) signature
79 4 (9) share hash chain
83 4 (10) block hash tree
87 4 (11) share data
91 8 (12) encrypted private key
99 8 (13) EOF
7 107 436ish verification key (2048 RSA key)
8 543ish 256ish signature=RSAenc(sigkey, H(version+seqnum+r+IV+encparm))
9 799ish (a) share hash chain, encoded as:
"".join([pack(">H32s", shnum, hash)
for (shnum,hash) in needed_hashes])
10 (927ish) (b) block hash tree, encoded as:
"".join([pack(">32s",hash) for hash in block_hash_tree])
11 (935ish) LEN share data (no gap between this and encprivkey)
12 ?? 1216ish encrypted private key= AESenc(write-key, RSA-key)
13 ?? -- EOF
::
(a) The share hash chain contains ceil(log(N)) hashes, each 32 bytes long.
# offset size name
1 0 1 version byte, \x00 for this format
2 1 8 sequence number. 2^64-1 must be handled specially, TBD
3 9 32 "R" (root of share hash Merkle tree)
4 41 16 IV (share data is AES(H(readkey+IV)) )
5 57 18 encoding parameters:
57 1 k
58 1 N
59 8 segment size
67 8 data length (of original plaintext)
6 75 32 offset table:
75 4 (8) signature
79 4 (9) share hash chain
83 4 (10) block hash tree
87 4 (11) share data
91 8 (12) encrypted private key
99 8 (13) EOF
7 107 436ish verification key (2048 RSA key)
8 543ish 256ish signature=RSAenc(sigkey, H(version+seqnum+r+IV+encparm))
9 799ish (a) share hash chain, encoded as:
"".join([pack(">H32s", shnum, hash)
for (shnum,hash) in needed_hashes])
10 (927ish) (b) block hash tree, encoded as:
"".join([pack(">32s",hash) for hash in block_hash_tree])
11 (935ish) LEN share data (no gap between this and encprivkey)
12 ?? 1216ish encrypted private key= AESenc(write-key, RSA-key)
13 ?? -- EOF
(a) The share hash chain contains ceil(log(N)) hashes, each 32 bytes long.
This is the set of hashes necessary to validate this share's leaf in the
share Merkle tree. For N=10, this is 4 hashes, i.e. 128 bytes.
(b) The block hash tree contains ceil(length/segsize) hashes, each 32 bytes
(b) The block hash tree contains ceil(length/segsize) hashes, each 32 bytes
long. This is the set of hashes necessary to validate any given block of
share data up to the per-share root "r". Each "r" is a leaf of the share
has tree (with root "R"), from which a minimal subset of hashes is put in
the share hash chain in (8).
=== Recovery ===
Recovery
--------
The first line of defense against damage caused by colliding writes is the
Prime Coordination Directive: "Don't Do That".
@ -540,63 +587,70 @@ somebody else's.
The write-shares-to-peers algorithm is as follows:
* permute peers according to storage index
* walk through peers, trying to assign one share per peer
* for each peer:
* send testv_and_writev, using "old(seqnum+R) <= our(seqnum+R)" as the test
* this means that we will overwrite any old versions, and we will
overwrite simultaenous writers of the same version if our R is higher.
We will not overwrite writers using a higher seqnum.
* record the version that each share winds up with. If the write was
accepted, this is our own version. If it was rejected, read the
old_test_data to find out what version was retained.
* if old_test_data indicates the seqnum was equal or greater than our
own, mark the "Simultanous Writes Detected" flag, which will eventually
result in an error being reported to the writer (in their close() call).
* build a histogram of "R" values
* repeat until the histogram indicate that some version (possibly ours)
has N shares. Use new servers if necessary.
* If we run out of servers:
* if there are at least shares-of-happiness of any one version, we're
happy, so return. (the close() might still get an error)
* not happy, need to reinforce something, goto RECOVERY
* permute peers according to storage index
* walk through peers, trying to assign one share per peer
* for each peer:
RECOVERY:
* read all shares, count the versions, identify the recoverable ones,
discard the unrecoverable ones.
* sort versions: locate max(seqnums), put all versions with that seqnum
in the list, sort by number of outstanding shares. Then put our own
version. (TODO: put versions with seqnum <max but >us ahead of us?).
* for each version:
* attempt to recover that version
* if not possible, remove it from the list, go to next one
* if recovered, start at beginning of peer list, push that version,
continue until N shares are placed
* if pushing our own version, bump up the seqnum to one higher than
the max seqnum we saw
* if we run out of servers:
* schedule retry and exponential backoff to repeat RECOVERY
* admit defeat after some period? presumeably the client will be shut down
eventually, maybe keep trying (once per hour?) until then.
* send testv_and_writev, using "old(seqnum+R) <= our(seqnum+R)" as the test
* this means that we will overwrite any old versions, and we will
overwrite simultaenous writers of the same version if our R is higher.
We will not overwrite writers using a higher seqnum.
* record the version that each share winds up with. If the write was
accepted, this is our own version. If it was rejected, read the
old_test_data to find out what version was retained.
* if old_test_data indicates the seqnum was equal or greater than our
own, mark the "Simultanous Writes Detected" flag, which will eventually
result in an error being reported to the writer (in their close() call).
* build a histogram of "R" values
* repeat until the histogram indicate that some version (possibly ours)
has N shares. Use new servers if necessary.
* If we run out of servers:
* if there are at least shares-of-happiness of any one version, we're
happy, so return. (the close() might still get an error)
* not happy, need to reinforce something, goto RECOVERY
Recovery:
* read all shares, count the versions, identify the recoverable ones,
discard the unrecoverable ones.
* sort versions: locate max(seqnums), put all versions with that seqnum
in the list, sort by number of outstanding shares. Then put our own
version. (TODO: put versions with seqnum <max but >us ahead of us?).
* for each version:
* attempt to recover that version
* if not possible, remove it from the list, go to next one
* if recovered, start at beginning of peer list, push that version,
continue until N shares are placed
* if pushing our own version, bump up the seqnum to one higher than
the max seqnum we saw
* if we run out of servers:
* schedule retry and exponential backoff to repeat RECOVERY
* admit defeat after some period? presumeably the client will be shut down
eventually, maybe keep trying (once per hour?) until then.
== Medium Distributed Mutable Files ==
Medium Distributed Mutable Files
================================
These are just like the SDMF case, but:
* we actually take advantage of the Merkle hash tree over the blocks, by
reading a single segment of data at a time (and its necessary hashes), to
reduce the read-time alacrity
* we allow arbitrary writes to the file (i.e. seek() is provided, and
O_TRUNC is no longer required)
* we write more code on the client side (in the MutableFileNode class), to
first read each segment that a write must modify. This looks exactly like
the way a normal filesystem uses a block device, or how a CPU must perform
a cache-line fill before modifying a single word.
* we might implement some sort of copy-based atomic update server call,
to allow multiple writev() calls to appear atomic to any readers.
* we actually take advantage of the Merkle hash tree over the blocks, by
reading a single segment of data at a time (and its necessary hashes), to
reduce the read-time alacrity
* we allow arbitrary writes to the file (i.e. seek() is provided, and
O_TRUNC is no longer required)
* we write more code on the client side (in the MutableFileNode class), to
first read each segment that a write must modify. This looks exactly like
the way a normal filesystem uses a block device, or how a CPU must perform
a cache-line fill before modifying a single word.
* we might implement some sort of copy-based atomic update server call,
to allow multiple writev() calls to appear atomic to any readers.
MDMF slots provide fairly efficient in-place edits of very large files (a few
GB). Appending data is also fairly efficient, although each time a power of 2
@ -608,7 +662,8 @@ the block hash tree and the actual data).
MDMF1 uses the Merkle tree to enable low-alacrity random-access reads. MDMF2
adds cache-line reads to allow random-access writes.
== Large Distributed Mutable Files ==
Large Distributed Mutable Files
===============================
LDMF slots use a fundamentally different way to store the file, inspired by
Mercurial's "revlog" format. They enable very efficient insert/remove/replace
@ -624,7 +679,8 @@ back an entire tree to a specific point in history.
LDMF1 provides deltas but tries to avoid dealing with multiple heads. LDMF2
provides explicit support for revision identifiers and branching.
== TODO ==
TODO
====
improve allocate-and-write or get-writer-buckets API to allow one-call (or
maybe two-call) updates. The challenge is in figuring out which shares are on
@ -639,9 +695,9 @@ do for updating the write enabler. However we need to know which lease to
update.. maybe send back a list of all old nodeids that we find, then try all
of them when we accept the update?
We now do this in a specially-formatted IndexError exception:
"UNABLE to renew non-existent lease. I have leases accepted by " +
"nodeids: '12345','abcde','44221' ."
We now do this in a specially-formatted IndexError exception:
"UNABLE to renew non-existent lease. I have leases accepted by " +
"nodeids: '12345','abcde','44221' ."
confirm that a repairer can regenerate shares without the private key. Hmm,
without the write-enabler they won't be able to write those shares to the

57
docs/specifications/outline.txt
View File

@ -1,4 +1,6 @@
= Specification Document Outline =
==============================
Specification Document Outline
==============================
While we do not yet have a clear set of specification documents for Tahoe
(explaining the file formats, so that others can write interoperable
@ -8,7 +10,13 @@ Tahoe.
We currently imagine 4 documents.
== #1: Share Format, Encoding Algorithm ==
1. `#1: Share Format, Encoding Algorithm`_
2. `#2: Share Exchange Protocol`_
3. `#3: Server Selection Algorithm, filecap format`_
4. `#4: Directory Format`_
#1: Share Format, Encoding Algorithm
====================================
This document will describe the way that files are encrypted and encoded into
shares. It will include a specification of the share format, and explain both
@ -43,7 +51,8 @@ from destroying shares). We don't yet have a document dedicated to explaining
these, but let's call it "Access Control" for now.
== #2: Share Exchange Protocol ==
#2: Share Exchange Protocol
===========================
This document explains the wire-protocol used to upload, download, and modify
shares on the various storage servers.
@ -75,7 +84,8 @@ each protocol. The first one to be written will describe the Foolscap-based
protocol that tahoe currently uses, but we anticipate a subsequent one to
describe a more HTTP-based protocol.
== #3: Server Selection Algorithm, filecap format ==
#3: Server Selection Algorithm, filecap format
==============================================
This document has two interrelated purposes. With a deeper understanding of
the issues, we may be able to separate these more cleanly in the future.
@ -90,27 +100,27 @@ of work?
This question implies many things, all of which should be explained in this
document:
* the notion of a "grid", nominally a set of servers who could potentially
hold shares, which might change over time
* a way to configure which grid should be used
* a way to discover which servers are a part of that grid
* a way to decide which servers are reliable enough to be worth sending
shares
* an algorithm to handle servers which refuse shares
* a way for a downloader to locate which servers have shares
* a way to choose which shares should be used for download
* the notion of a "grid", nominally a set of servers who could potentially
hold shares, which might change over time
* a way to configure which grid should be used
* a way to discover which servers are a part of that grid
* a way to decide which servers are reliable enough to be worth sending
shares
* an algorithm to handle servers which refuse shares
* a way for a downloader to locate which servers have shares
* a way to choose which shares should be used for download
The server-selection algorithm has several obviously competing goals:
* minimize the amount of work that must be done during upload
* minimize the total storage resources used
* avoid "hot spots", balance load among multiple servers
* maximize the chance that enough shares will be downloadable later, by
uploading lots of shares, and by placing them on reliable servers
* minimize the work that the future downloader must do
* tolerate temporary server failures, permanent server departure, and new
server insertions
* minimize the amount of information that must be added to the filecap
* minimize the amount of work that must be done during upload
* minimize the total storage resources used
* avoid "hot spots", balance load among multiple servers
* maximize the chance that enough shares will be downloadable later, by
uploading lots of shares, and by placing them on reliable servers
* minimize the work that the future downloader must do
* tolerate temporary server failures, permanent server departure, and new
server insertions
* minimize the amount of information that must be added to the filecap
The server-selection algorithm is defined in some context: some set of
expectations about the servers or grid with which it is expected to operate.
@ -185,7 +195,8 @@ Tahoe-1.3.0 filecaps do not contain hostnames, because the failure of DNS or
an individual host might then impact file availability (however the
Introducer contains DNS names or IP addresses).
== #4: Directory Format ==
#4: Directory Format
====================
Tahoe directories are a special way of interpreting and managing the contents
of a file (either mutable or immutable). These "dirnode" files are basically

10
docs/specifications/servers-of-happiness.txt
View File

@ -1,4 +1,6 @@
= Servers of Happiness =
====================
Servers of Happiness
====================
When you upload a file to a Tahoe-LAFS grid, you expect that it will
stay there for a while, and that it will do so even if a few of the
@ -34,7 +36,8 @@ health provides a stronger assurance of file availability over time;
with 3-of-10 encoding, and happy=7, a healthy file is still guaranteed
to be available even if 4 peers fail.
== Measuring Servers of Happiness ==
Measuring Servers of Happiness
==============================
We calculate servers-of-happiness by computing a matching on a
bipartite graph that is related to the layout of shares on the grid.
@ -71,7 +74,8 @@ of shares later without having to re-encode the file. Also, it is
computationally reasonable to compute a maximum matching in a bipartite
graph, and there are well-studied algorithms to do that.
== Issues ==
Issues
======
The uploader is good at detecting unhealthy upload layouts, but it
doesn't always know how to make an unhealthy upload into a healthy

70
docs/specifications/uri.txt
View File

@ -1,5 +1,15 @@
==========
Tahoe URIs
==========
= Tahoe URIs =
1. `File URIs`_
1. `CHK URIs`_
2. `LIT URIs`_
3. `Mutable File URIs`_
2. `Directory URIs`_
3. `Internal Usage of URIs`_
Each file and directory in a Tahoe filesystem is described by a "URI". There
are different kinds of URIs for different kinds of objects, and there are
@ -7,11 +17,11 @@ different kinds of URIs to provide different kinds of access to those
objects. Each URI is a string representation of a "capability" or "cap", and
there are read-caps, write-caps, verify-caps, and others.
Each URI provides both '''location''' and '''identification''' properties.
'''location''' means that holding the URI is sufficient to locate the data it
Each URI provides both ``location`` and ``identification`` properties.
``location`` means that holding the URI is sufficient to locate the data it
represents (this means it contains a storage index or a lookup key, whatever
is necessary to find the place or places where the data is being kept).
'''identification''' means that the URI also serves to validate the data: an
``identification`` means that the URI also serves to validate the data: an
attacker who wants to trick you into into using the wrong data will be
limited in their abilities by the identification properties of the URI.
@ -22,11 +32,12 @@ modify it. Directories, for example, have a read-cap which is derived from
the write-cap: anyone with read/write access to the directory can produce a
limited URI that grants read-only access, but not the other way around.
source:src/allmydata/uri.py is the main place where URIs are processed. It is
src/allmydata/uri.py is the main place where URIs are processed. It is
the authoritative definition point for all the the URI types described
herein.
== File URIs ==
File URIs
=========
The lowest layer of the Tahoe architecture (the "grid") is reponsible for
mapping URIs to data. This is basically a distributed hash table, in which
@ -41,11 +52,12 @@ For mutable entries, the URI identifies a "slot" or "container", which can be
filled with different pieces of data at different times.
It is important to note that the "files" described by these URIs are just a
bunch of bytes, and that __no__ filenames or other metadata is retained at
bunch of bytes, and that **no** filenames or other metadata is retained at
this layer. The vdrive layer (which sits above the grid layer) is entirely
responsible for directories and filenames and the like.
=== CHI URIs ===
CHK URIs
--------
CHK (Content Hash Keyed) files are immutable sequences of bytes. They are
uploaded in a distributed fashion using a "storage index" (for the "location"
@ -58,7 +70,7 @@ tagged SHA-256d hash, then truncated to 128 bits), so it does not need to be
physically present in the URI.
The current format for CHK URIs is the concatenation of the following
strings:
strings::
URI:CHK:(key):(hash):(needed-shares):(total-shares):(size)
@ -71,9 +83,9 @@ representation of the size of the data represented by this URI. All base32
encodings are expressed in lower-case, with the trailing '=' signs removed.
For example, the following is a CHK URI, generated from the contents of the
architecture.txt document that lives next to this one in the source tree:
architecture.txt document that lives next to this one in the source tree::
URI:CHK:ihrbeov7lbvoduupd4qblysj7a:bg5agsdt62jb34hxvxmdsbza6do64f4fg5anxxod2buttbo6udzq:3:10:28733
URI:CHK:ihrbeov7lbvoduupd4qblysj7a:bg5agsdt62jb34hxvxmdsbza6do64f4fg5anxxod2buttbo6udzq:3:10:28733
Historical note: The name "CHK" is somewhat inaccurate and continues to be
used for historical reasons. "Content Hash Key" means that the encryption key
@ -86,7 +98,8 @@ about the file's contents (except filesize), which improves privacy. The
URI:CHK: prefix really indicates that an immutable file is in use, without
saying anything about how the key was derived.
=== LIT URIs ===
LIT URIs
--------
LITeral files are also an immutable sequence of bytes, but they are so short
that the data is stored inside the URI itself. These are used for files of 55
@ -97,14 +110,15 @@ LIT URIs do not require an upload or download phase, as their data is stored
directly in the URI.
The format of a LIT URI is simply a fixed prefix concatenated with the base32
encoding of the file's data:
encoding of the file's data::
URI:LIT:bjuw4y3movsgkidbnrwg26lemf2gcl3xmvrc6kropbuhi3lmbi
The LIT URI for an empty file is "URI:LIT:", and the LIT URI for a 5-byte
file that contains the string "hello" is "URI:LIT:nbswy3dp".
=== Mutable File URIs ===
Mutable File URIs
-----------------
The other kind of DHT entry is the "mutable slot", in which the URI names a
container to which data can be placed and retrieved without changing the
@ -117,10 +131,10 @@ contents).
Mutable slots use public key technology to provide data integrity, and put a
hash of the public key in the URI. As a result, the data validation is
limited to confirming that the data retrieved matches _some_ data that was
limited to confirming that the data retrieved matches *some* data that was
uploaded in the past, but not _which_ version of that data.
The format of the write-cap for mutable files is:
The format of the write-cap for mutable files is::
URI:SSK:(writekey):(fingerprint)
@ -129,7 +143,7 @@ that is used to encrypt the RSA private key, and (fingerprint) is the base32
encoded 32-byte SHA-256 hash of the RSA public key. For more details about
the way these keys are used, please see docs/mutable.txt .
The format for mutable read-caps is:
The format for mutable read-caps is::
URI:SSK-RO:(readkey):(fingerprint)
@ -143,45 +157,45 @@ Historical note: the "SSK" prefix is a perhaps-inaccurate reference to
"Sub-Space Keys" from the Freenet project, which uses a vaguely similar
structure to provide mutable file access.
== Directory URIs ==
Directory URIs
==============
The grid layer provides a mapping from URI to data. To turn this into a graph
of directories and files, the "vdrive" layer (which sits on top of the grid
layer) needs to keep track of "directory nodes", or "dirnodes" for short.
source:docs/dirnodes.txt describes how these work.
docs/dirnodes.txt describes how these work.
Dirnodes are contained inside mutable files, and are thus simply a particular
way to interpret the contents of these files. As a result, a directory
write-cap looks a lot like a mutable-file write-cap:
write-cap looks a lot like a mutable-file write-cap::
URI:DIR2:(writekey):(fingerprint)
Likewise directory read-caps (which provide read-only access to the
directory) look much like mutable-file read-caps:
directory) look much like mutable-file read-caps::
URI:DIR2-RO:(readkey):(fingerprint)
Historical note: the "DIR2" prefix is used because the non-distributed
dirnodes in earlier Tahoe releases had already claimed the "DIR" prefix.
== Internal Usage of URIs ==
Internal Usage of URIs
======================
The classes in source:src/allmydata/uri.py are used to pack and unpack these
various kinds of URIs. Three Interfaces are defined (IURI, IFileURI, and
IDirnodeURI) which are implemented by these classes, and string-to-URI-class
conversion routines have been registered as adapters, so that code which
wants to extract e.g. the size of a CHK or LIT uri can do:
wants to extract e.g. the size of a CHK or LIT uri can do::
{{{
print IFileURI(uri).get_size()
}}}
print IFileURI(uri).get_size()
If the URI does not represent a CHK or LIT uri (for example, if it was for a
directory instead), the adaptation will fail, raising a TypeError inside the
IFileURI() call.
Several utility methods are provided on these objects. The most important is
{{{ to_string() }}}, which returns the string form of the URI. Therefore {{{
IURI(uri).to_string == uri }}} is true for any valid URI. See the IURI class
``to_string()``, which returns the string form of the URI. Therefore
``IURI(uri).to_string == uri`` is true for any valid URI. See the IURI class
in source:src/allmydata/interfaces.py for more details.