tahoe-lafs/docs/webapi.txt

This document has six sections:

1.  the basic API for how to programmatically control your tahoe node
2.  convenience methods
3.  safety and security issues
4.  features for controlling your tahoe node from a standard web browser
5.  debugging and testing features
6.  XML-RPC (coming soon)


1. the basic API for how to programmatically control your tahoe node

a. connecting to the tahoe node

Writing "8123" into $NODEDIR/webport causes the node to run a webserver on port
8123. Writing "tcp:8123:interface=127.0.0.1" into $NODEDIR/webport does the same
but binds to the loopback interface, ensuring that only the programs on the
local host can connect.  This is the value that gets written into
$NODEDIR/webport when a Tahoe node is created.

Using "ssl:8123:privateKey=mykey.pem:certKey=cert.pem" would run an SSL
server. See twisted.application.strports for more details.

This webport can be set when the node is created by passing a --webport
option to the 'tahoe create-client' command. By default, the node listens on
port 8123, on the loopback (127.0.0.1) interface.

b. file names

The node provides some small number of "virtual drives". In the 0.5 release,
this number is two: the first is the global shared vdrive, the second is the
private non-shared vdrive. We will call the global one "global", and we will
refer to the second one by "$PRIVATE_VDRIVE_URI", to show that to use it you
have to insert the specific URI for that private vdrive.

For the purpose of this document, let us assume that the vdrives currently
contain the following directories and files:

global/
global/Documents/
global/Documents/notes.txt

$PRIVATE_VDRIVE_URI/
$PRIVATE_VDRIVE_URI/Pictures/
$PRIVATE_VDRIVE_URI/Pictures/tractors.jpg
$PRIVATE_VDRIVE_URI/Pictures/family/
$PRIVATE_VDRIVE_URI/Pictures/family/bobby.jpg

Within the webserver, there is a tree of resources. The top-level "vdrive"
resource gives access to files and directories in all of the user's virtual
drives. For example, the URL that corresponds to notes.txt would be:

http://localhost:8123/vdrive/global/Documents/notes.txt

and the URL for tractors.jpg would be:

http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/Pictures/tractors.jpg

In addition, each directory has a corresponding URL. The Pictures URL is:

http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/Pictures

Note that all filenames in URLs are required to be UTF-8 encoded, so
"resume.doc" (with an acute accent on both E's) would be accessed with:

 http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/r%C3%A9sum%C3%A9.doc

The filenames inside upload POST forms are interpreted using whatever
character set was provided in the conventional '_charset' field, and defaults
to UTF-8 if not otherwise specified. The JSON representation of each
directory contains native unicode strings. Tahoe directories are specified to
contain unicode filenames, and cannot contain binary strings that are not
representable as such.

c. URIs

From the "URIs" chapter in architecture.txt, recall that each file and
directory has a unique "URI". This is a string which provides a secure
reference to the file or directory: if you know the URI, you can retrieve
(and possibly modify) the object. If you don't know the URI, you cannot
access the object.

A separate top-level namespace ("uri/" instead of "vdrive/") is used to
access to files and directories directly by URI, rather than by going through
the pathnames in the vdrive.

For example, this identifies a file or directory:

http://localhost:8123/uri/$URI

And this identifies a file or directory named "tractors.jpg" in a
subdirectory "Pictures" of the identified directory:

http://localhost:8123/uri/$URI/Pictures/tractors.jpg

In the following examples, "$URL" is a shorthand for a URL like the ones
above, either with "vdrive/" and a vdrive name as the top level and a
sequence of slash-separated pathnames following, or with "uri/" as the top
level, followed by a URI, optionally followed by a sequence of
slash-separated pathnames.


Now, what can we do with these URLs? By varying the HTTP method
(GET/PUT/POST/DELETE) and by appending a type-indicating query argument, we
control what we want to do with the data and how it should be presented.

d. examining files or directories

  GET $URL?t=json

  out: json description of $URL

  This returns machine-parseable information about the indicated file or
  directory in the HTTP response body. The JSON always contains a list, and
  the first element of the list is always a flag that indicates whether the
  referenced object is a file or a directory.

  If it is a file, then the information includes file size and URI, like
  this:

   GET $FILEURL?t=json :

    [ "filenode", { "ro_uri": file_uri,
                    "size": bytes,
                    "metadata": {"ctime": 1202777696.7564139,
                                 "mtime": 1202777696.7564139
                                 }
                    } ]

  If it is a directory, then it includes information about the children of
  this directory, as a mapping from child name to a set of data about the
  child (the same data that would appear in a corresponding GET?t=json of the
  child itself). The child entries also include metadata about each child,
  including creation- and modification- timestamps. The output looks like
  this:

   GET $DIRURL?t=json :

    [ "dirnode", { "rw_uri": read_write_uri,
                   "ro_uri": read_only_uri,
                   "children": {
                     "foo.txt": [ "filenode", { "ro_uri": uri,
                                                "size": bytes,
                                                "metadata": {
                                                  "ctime": 1202777696.7564139,
                                                  "mtime": 1202777696.7564139
                                                 }
                                               } ],
                     "subdir":  [ "dirnode", { "rw_uri": rwuri,
                                               "ro_uri": rouri,
                                                "metadata": {
                                                  "ctime": 1202778102.7589991,
                                                  "mtime": 1202778111.2160511,
                                                 }
                                              } ]
                    } } ]

  In the above example, note how 'children' is a dictionary in which the keys
  are child names and the values depend upon whether the child is a file or a
  directory. The value is mostly the same as the JSON representation of the
  child object (except that directories do not recurse -- the "children"
  entry of the child is omitted, and the directory view includes the metadata
  that is stored on the directory edge).

  Then the rw_uri field will be present in the information about a directory
  if and only if you have read-write access to that directory,

e. downloading a file

  GET $URL

  out: file contents or dir metadata
  options:
        save=<boolean> - If true add header "Content-Disposition: attachment"

  If the indicated object is a file, then this simply retrieves the contents
  of the file. The file's contents are provided in the body of the HTTP
  response.

  If the indicated object a directory, then this returns an HTML page,
  intended to be displayed to a human by a web browser, which contains HREF
  links to all files and directories reachable from this directory. These
  HREF links do not have a t= argument, meaning that a human who follows them
  will get pages also meant for a human. It also contains forms to upload new
  files, and to delete files and directories. These forms use POST methods to
  do their job.

  You can add the "save=true" argument, which adds a 'Content-Disposition:
  attachment' header to prompt most web browsers to save the file to disk
  rather than attempting to display it.

  A filename (from which a MIME type can be derived, for use in the
  Content-Type header) can be specified using a 'filename=' query argument.
  This is especially useful if the $URL does not end with the name of the
  file (e.g. if it ends with the URI of the file instead). This filename is
  also the one used if the 'save=true' argument is set. For example:

   GET http://localhost:8123/uri/$TRACTORS_URI?filename=tractors.jpg

f. uploading a file

  PUT http://localhost:8123/uri

   in: file contents
   out: file write cap

   Upload a file, using the data from the HTTP request body, and returning
   the resulting URI as the HTTP response body. This does not make the file
   visible from the virtual drive -- to do that, see section 1.h. below, or
   the convenience method in section 2.a..

  POST http://localhost:8123/uri?t=upload

   This action also uploads a file without attaching it to a virtual drive
   directory, but can be used from an HTML form. The response is an HTML page
   that describes the results of the upload, including the resulting URI (but
   also including information about which peers were used, etc). If a
   when_done=URL argument is provided, the reponse is a redirect to the given
   URL instead of the upload-results page.

  POST http://localhost:8123/uri?t=upload&mutable=true

   This action also uploads a file without attaching it to a virtual drive
   directory, but creates a mutable file (SSK) instead of an immutable one.
   The response contains the new URI that was created.

  PUT http://localhost:8123/uri?mutable=true

   This second form also accepts data from the HTTP request body, but creates
   a mutable file (SSK) instead of an immutable one (CHK). The response
   contains the new URI that was created.


g. creating a new directory

  PUT http://localhost:8123/uri?t=mkdir

   in: (nothing)
   out: directory write cap

   Create a new empty directory and return its URI as the HTTP response body.
   This does not make the newly created directory visible from the virtual
   drive, but you can use section 1.h. to attach it, or the convenience method
   in section 2.XXX.

 POST http://localhost:8123/uri?t=mkdir

   in: (nothing)
   out: directory write cap

   Just like the equivalent PUT form, but this can be called from an HTML
   form.

 POST http://localhost:8123/uri?t=mkdir&redirect_to_result=true

   in: (nothing)
   out: redirects to the /uri/$NEWDIRURI page

   This also creates an unlinked directory, but instead of returning the URI
   as a string, this form will return an HTTP Redirect that takes you to the
   new directory's HTML page, just as if you had directed your browser to
   /uri/$NEWDIRURI . If you bookmark this page, you'll be able to get back to
   the directory again in the future.

   This method is the recommended way to create a new root directory. There
   is a "Create Directory" button on the Welcome page to invoke this action.


h. attaching a file or directory as the child of an extant directory

  PUT $URL?t=uri

  in: child cap
  out: the same child cap
  options:
        replace=<boolean> - If true, overwrite existing contents.

  This attaches a child (either a file or a directory) to the given directory
  $URL is required to indicate a directory as the second-to-last element and
  the desired filename as the last element, for example:

   PUT http://localhost:8123/uri/$URI_OF_SOME_DIR/Pictures/tractors.jpg
   PUT http://localhost:8123/uri/$URI_OF_SOME_DIR/tractors.jpg
   PUT http://localhost:8123/uri/$PRIVATE_VDRIVE_URI/Pictures/tractors.jpg

  (Note that a URI_OF_SOME_DIR and a PRIVATE_VDRIVE_URI are each just
  separate URIs, and there is nothing special about the latter except that it
  is useful to put all of the user's top-level files and directories into one
  place, so we choose to use that particular directory to be the user's main
  directory.)

  The URI of the child is provided in the body of the HTTP request,
  and this same URI is returned in the response body.

  There is an optional "?replace=" param whose value can be "true", "t", "1",
  "false", "f", or "0" (case-insensitive), and which defaults to "true". If
  the indicated directory already contains the given child name, then if
  replace is true then the value of that name is changed to be the new URI.
  If replace is false then an HTTP 409 "Conflict" error is returned.

  This can be used to attach a shared directory (a directory that other
  people can read or write) to the vdrive. Intermediate directories, if any,
  are created on-demand.

i. removing a name from a directory

  DELETE $URL

  This removes the given name from the given directory. $URL is required to
  indicate a directory as the second-to-last element and the name to remove
  from that directory as the last element, just as in section 1.g..

  Note that this does not actually delete the resource that the name points
  to from the tahoe grid -- it only removes this name in this directory. If
  there are other names in this directory or in other directories that point
  to the resource, then it will remain accessible through those paths. Even
  if all names pointing to this resource are removed from their parent
  directories, then if someone is in possession of the URI of this resource
  they can continue to access the resource through the URI. Only if a person
  is not in possession of the URI, and they do not have access to any
  directories which contain names pointing to this resource, are they
  prevented from accessing the resource. (This behavior is very similar to
  the way hardlinks and anonymous files work in traditional unix
  filesystems).

2. convenience methods

a. uploading a file and attaching it to the vdrive

  PUT $URI

  in: file contents
  out: file write cap

  statuses:
  200 - File updated.  [FIXME: Is this true yet?]
  201 - File created.  [FIXME: Is this true yet?]

  Upload a file and link it into the the vdrive at the location specified by
  $URI. The last item in the $URI must be a filename, and the second-to-last
  item must identify a directory.

  It will create intermediate directories as necessary. The file's contents
  are taken from the body of the HTTP request. For convenience, the HTTP
  response contains the URI that results from uploading the file, although
  the client is not obligated to do anything with the URI. According to the
  HTTP/1.1 specification (rfc2616), this should return a 200 (OK) code when
  modifying an existing file, and a 201 (Created) code when creating a new
  file. (TODO: as of 0.5, the web server only returns 200, never 201).

  To use this, run 'curl -T localfile http://localhost:8123/vdrive/global/newfile'

3. safety and security issues -- names vs. URIs

The vdrive provides a mutable filesystem, but the ways that the filesystem
can change are limited. The only thing that can change is that the mapping
from child names to child objects that each directory contains can be changed
by adding a new child name pointing to an object, removing an existing child
name, or changing an existing child name to point to a different object.

Obviously if you query tahoe for information about the filesystem and then
act upon the filesystem (such as by getting a listing of the contents of a
directory and then adding a file to the directory), then the filesystem might
have been changed after you queried it and before you acted upon it.
However, if you use the URI instead of the pathname of an object when you act
upon the object, then the only change that can happen is when the object is a
directory then the set of child names it has might be different. If, on the
other hand, you act upon the object using its pathname, then a different
object might be in that place, which can result in more kinds of surprises.

For example, suppose you are writing code which recursively downloads the
contents of a directory. The first thing your code does is fetch the listing
of the contents of the directory. For each child that it fetched, if that
child is a file then it downloads the file, and if that child is a directory
then it recurses into that directory. Now, if the download and the recurse
actions are performed using the child's name, then the results might be
wrong, because for example a child name that pointed to a sub-directory when
you listed the directory might have been changed to point to a file (in which
case your attempt to recurse into it would result in an error and the file
would be skipped), or a child name that pointed to a file when you listed the
directory might now point to a sub-directory (in which case your attempt to
download the child would result in a file containing HTML text describing the
sub-directory!).

If your recursive algorithm uses the uri of the child instead of the name of
the child, then those kinds of mistakes just can't happen. Note that both the
child's name and the child's URI are included in the results of listing the
parent directory, so it isn't any harder to use the URI for this purpose.

In general, use names if you want "whatever object (whether file or
directory) is found by following this name (or sequence of names) when my
request reaches the server". Use URIs if you want "this particular object".

4. features for controlling your tahoe node from a standard web browser

a. uri redirect

  GET http://localhost:8123/uri?uri=$URI

  This causes a redirect to /uri/$URI, and retains any additional query
  arguments (like filename= or save=). This is for the convenience of web
  forms which allow the user to paste in a URI (obtained through some
  out-of-band channel, like IM or email).

  Note that this form merely redirects to the specific file or directory
  indicated by the URI: unlike the GET /uri/$URI form, you cannot traverse to
  children by appending additional path segments to the URL.

b. web page offering rename

  GET $URL?t=rename-form&name=$CHILDNAME

  This provides a useful facility to browser-based user interfaces. It
  returns a page containing a form targetting the "POST $URL t=rename"
  functionality described below, with the provided $CHILDNAME present in the
  'from_name' field of that form. I.e. this presents a form offering to
  rename $CHILDNAME, requesting the new name, and submitting POST rename.

c. POST forms

  POST $URL
  t=upload
  name=childname  (optional)
  file=newfile

  This instructs the node to upload a file into the given directory. We need
  this because forms are the only way for a web browser to upload a file
  (browsers do not know how to do PUT or DELETE). The file's contents and the
  new child name will be included in the form's arguments. This can only be
  used to upload a single file at a time. To avoid confusion, name= is not
  allowed to contain a slash (a 400 Bad Request error will result). The
  response is the file read-cap (URI) of the resulting file.


  POST $URL
  t=upload
  name=childname  (optional)
  mutable="true"
  file=newfile

  This instructs the node to upload a file into the given directory, using a
  mutable file (SSK) rather than the usual immutable file (CHK). As a result,
  further operations to the same $URL will not cause the identity of the file
  to change. The response is the file write-cap (URI) of the resulting
  mutable file.


  POST $URL
  t=overwrite
  file=newfile

  This is used to replace the existing (mutable) file's contents with new
  ones. It may only be used when $URL refers to a mutable file, as created by
  POST $URL?t=upload&mutable=true, or PUT /uri?t=mutable . The name
  associated with the uploaded file is ignored. TODO: rethink this, it's kind
  of weird.


  POST $URL
  t=mkdir
  name=childname

  This instructs the node to create a new empty directory. The name of the
  new child directory will be included in the form's arguments.


  POST $URL
  t=uri
  name=childname
  uri=newuri

  This instructs the node to attach a child that is referenced by URI (just
  like the PUT $URL?t=uri method). The name and URI of the new child
  will be included in the form's arguments.


  POST $URL
  t=delete
  name=childname

  This instructs the node to delete a file from the given directory. The name
  of the child to be deleted will be included in the form's arguments.


  POST $URL
  t=rename
  from_name=oldchildname
  to_name=newchildname

  This instructs the node to rename a child within the given directory. The
  child specified by 'from_name' is removed, and reattached as a child named
  for 'to_name'. This is unconditional and will replace any child already
  present under 'to_name', akin to 'mv -f' in unix parlance.


  POST $URL
  t=check

  This triggers the FileChecker to determine the current "health" of the
  given file, by counting how many shares are available. The results will be
  displayed on the directory page containing this file.


5. debugging and testing features

GET $URL?t=download&localfile=$LOCALPATH
GET $URL?t=download&localdir=$LOCALPATH

  The localfile= form instructs the node to download the given file and write
  it into the local filesystem at $LOCALPATH. The localdir= form instructs
  the node to recursively download everything from the given directory and
  below into the local filesystem. To avoid surprises, the localfile= form
  will signal an error if $URL actually refers to a directory, likewise if
  localdir= is used with a $URL that refers to a file.

  This request will only be accepted from an HTTP client connection
  originating at 127.0.0.1 . This request is most useful when the client node
  and the HTTP client are operated by the same user. $LOCALPATH should be an
  absolute pathname.

  This form is only implemented for testing purposes, because of a trivially
  easy attack: any web server that the local browser visits could serve an
  IMG tag that causes the local node to modify the local filesystem.
  Therefore this form is only enabled if you create a file named
  'webport_allow_localfile' in the node's base directory.

PUT $NEWURL?t=upload&localfile=$LOCALPATH
PUT $NEWURL?t=upload&localdir=$LOCALPATH

  This uploads a file or directory from the node's local filesystem to the
  vdrive. As with "GET $URL?t=download&localfile=$LOCALPATH", this request
  will only be accepted from an HTTP connection originating from 127.0.0.1 .

  The localfile= form expects that $LOCALPATH will point to a file on the
  node's local filesystem, and causes the node to upload that one file into
  the vdrive at the given location. Any parent directories will be created in
  the vdrive as necessary.

  The localdir= form expects that $LOCALPATH will point to a directory on the
  node's local filesystem, and it causes the node to perform a recursive
  upload of the directory into the vdrive at the given location, creating
  parent directories as necessary. When the operation is complete, the
  directory referenced by $NEWURL will contain all of the files and
  directories that were present in $LOCALPATH, so this is equivalent to the
  unix commands:

   mkdir -p $NEWURL; cp -r $LOCALPATH/* $NEWURL/

  Note that the "curl" utility can be used to provoke this sort of recursive
  upload, since the -T option will make it use an HTTP 'PUT':

   curl -T /dev/null 'http://localhost:8123/vdrive/global/newdir?t=upload&localdir=/home/user/directory-to-upload'

  This form is only implemented for testing purposes, because any attacker's
  web server that a local browser visits could serve an IMG tag that causes
  the local node to modify the local filesystem. Therefore this form is only
  enabled if you create a file named 'webport_allow_localfile' in the node's
  base directory.

GET $URL?t=manifest

  Return an HTML-formatted manifest of the given directory, for debugging.

GET $URL?t=deep-size

  Return a number (in bytes) containing the sum of the filesize of all
  immutable files reachable from the given directory. This is a rough lower
  bound of the total space consumed by this subtree. It does not include
  space consumed by directories or immutable files, nor does it take
  expansion or encoding overhead into account. Later versions of the code may
  improve this estimate upwards.

6. XMLRPC (coming soon)

  http://localhost:8123/xmlrpc

  This resource provides an XMLRPC server on which all of the previous
  operations can be expressed as function calls taking a "pathname" argument.
  This is provided for applications that want to think of everything in terms
  of XMLRPC.

   listdir(vdrivename, path) -> dict of (childname -> (stuff))
   put(vdrivename, path, contents) -> URI
   get(vdrivename, path) -> contents
   mkdir(vdrivename, path) -> URI
   put_localfile(vdrivename, path, localfilename) -> URI
   get_localfile(vdrivename, path, localfilename)
   put_localdir(vdrivename, path, localdirname)   # recursive
   get_localdir(vdrivename, path, localdirname)   # recursive
   put_uri(vdrivename, path, URI)

   etc..