mirror of
https://github.com/zerotier/ZeroTierOne.git
synced 2024-12-27 16:28:52 +00:00
247 lines
9.1 KiB
Markdown
247 lines
9.1 KiB
Markdown
HTTP Parser
|
|
===========
|
|
|
|
[](https://travis-ci.org/nodejs/http-parser)
|
|
|
|
This is a parser for HTTP messages written in C. It parses both requests and
|
|
responses. The parser is designed to be used in performance HTTP
|
|
applications. It does not make any syscalls nor allocations, it does not
|
|
buffer data, it can be interrupted at anytime. Depending on your
|
|
architecture, it only requires about 40 bytes of data per message
|
|
stream (in a web server that is per connection).
|
|
|
|
Features:
|
|
|
|
* No dependencies
|
|
* Handles persistent streams (keep-alive).
|
|
* Decodes chunked encoding.
|
|
* Upgrade support
|
|
* Defends against buffer overflow attacks.
|
|
|
|
The parser extracts the following information from HTTP messages:
|
|
|
|
* Header fields and values
|
|
* Content-Length
|
|
* Request method
|
|
* Response status code
|
|
* Transfer-Encoding
|
|
* HTTP version
|
|
* Request URL
|
|
* Message body
|
|
|
|
|
|
Usage
|
|
-----
|
|
|
|
One `http_parser` object is used per TCP connection. Initialize the struct
|
|
using `http_parser_init()` and set the callbacks. That might look something
|
|
like this for a request parser:
|
|
```c
|
|
http_parser_settings settings;
|
|
settings.on_url = my_url_callback;
|
|
settings.on_header_field = my_header_field_callback;
|
|
/* ... */
|
|
|
|
http_parser *parser = malloc(sizeof(http_parser));
|
|
http_parser_init(parser, HTTP_REQUEST);
|
|
parser->data = my_socket;
|
|
```
|
|
|
|
When data is received on the socket execute the parser and check for errors.
|
|
|
|
```c
|
|
size_t len = 80*1024, nparsed;
|
|
char buf[len];
|
|
ssize_t recved;
|
|
|
|
recved = recv(fd, buf, len, 0);
|
|
|
|
if (recved < 0) {
|
|
/* Handle error. */
|
|
}
|
|
|
|
/* Start up / continue the parser.
|
|
* Note we pass recved==0 to signal that EOF has been received.
|
|
*/
|
|
nparsed = http_parser_execute(parser, &settings, buf, recved);
|
|
|
|
if (parser->upgrade) {
|
|
/* handle new protocol */
|
|
} else if (nparsed != recved) {
|
|
/* Handle error. Usually just close the connection. */
|
|
}
|
|
```
|
|
|
|
HTTP needs to know where the end of the stream is. For example, sometimes
|
|
servers send responses without Content-Length and expect the client to
|
|
consume input (for the body) until EOF. To tell http_parser about EOF, give
|
|
`0` as the fourth parameter to `http_parser_execute()`. Callbacks and errors
|
|
can still be encountered during an EOF, so one must still be prepared
|
|
to receive them.
|
|
|
|
Scalar valued message information such as `status_code`, `method`, and the
|
|
HTTP version are stored in the parser structure. This data is only
|
|
temporally stored in `http_parser` and gets reset on each new message. If
|
|
this information is needed later, copy it out of the structure during the
|
|
`headers_complete` callback.
|
|
|
|
The parser decodes the transfer-encoding for both requests and responses
|
|
transparently. That is, a chunked encoding is decoded before being sent to
|
|
the on_body callback.
|
|
|
|
|
|
The Special Problem of Upgrade
|
|
------------------------------
|
|
|
|
HTTP supports upgrading the connection to a different protocol. An
|
|
increasingly common example of this is the WebSocket protocol which sends
|
|
a request like
|
|
|
|
GET /demo HTTP/1.1
|
|
Upgrade: WebSocket
|
|
Connection: Upgrade
|
|
Host: example.com
|
|
Origin: http://example.com
|
|
WebSocket-Protocol: sample
|
|
|
|
followed by non-HTTP data.
|
|
|
|
(See [RFC6455](https://tools.ietf.org/html/rfc6455) for more information the
|
|
WebSocket protocol.)
|
|
|
|
To support this, the parser will treat this as a normal HTTP message without a
|
|
body, issuing both on_headers_complete and on_message_complete callbacks. However
|
|
http_parser_execute() will stop parsing at the end of the headers and return.
|
|
|
|
The user is expected to check if `parser->upgrade` has been set to 1 after
|
|
`http_parser_execute()` returns. Non-HTTP data begins at the buffer supplied
|
|
offset by the return value of `http_parser_execute()`.
|
|
|
|
|
|
Callbacks
|
|
---------
|
|
|
|
During the `http_parser_execute()` call, the callbacks set in
|
|
`http_parser_settings` will be executed. The parser maintains state and
|
|
never looks behind, so buffering the data is not necessary. If you need to
|
|
save certain data for later usage, you can do that from the callbacks.
|
|
|
|
There are two types of callbacks:
|
|
|
|
* notification `typedef int (*http_cb) (http_parser*);`
|
|
Callbacks: on_message_begin, on_headers_complete, on_message_complete.
|
|
* data `typedef int (*http_data_cb) (http_parser*, const char *at, size_t length);`
|
|
Callbacks: (requests only) on_url,
|
|
(common) on_header_field, on_header_value, on_body;
|
|
|
|
Callbacks must return 0 on success. Returning a non-zero value indicates
|
|
error to the parser, making it exit immediately.
|
|
|
|
For cases where it is necessary to pass local information to/from a callback,
|
|
the `http_parser` object's `data` field can be used.
|
|
An example of such a case is when using threads to handle a socket connection,
|
|
parse a request, and then give a response over that socket. By instantiation
|
|
of a thread-local struct containing relevant data (e.g. accepted socket,
|
|
allocated memory for callbacks to write into, etc), a parser's callbacks are
|
|
able to communicate data between the scope of the thread and the scope of the
|
|
callback in a threadsafe manner. This allows http-parser to be used in
|
|
multi-threaded contexts.
|
|
|
|
Example:
|
|
```c
|
|
typedef struct {
|
|
socket_t sock;
|
|
void* buffer;
|
|
int buf_len;
|
|
} custom_data_t;
|
|
|
|
|
|
int my_url_callback(http_parser* parser, const char *at, size_t length) {
|
|
/* access to thread local custom_data_t struct.
|
|
Use this access save parsed data for later use into thread local
|
|
buffer, or communicate over socket
|
|
*/
|
|
parser->data;
|
|
...
|
|
return 0;
|
|
}
|
|
|
|
...
|
|
|
|
void http_parser_thread(socket_t sock) {
|
|
int nparsed = 0;
|
|
/* allocate memory for user data */
|
|
custom_data_t *my_data = malloc(sizeof(custom_data_t));
|
|
|
|
/* some information for use by callbacks.
|
|
* achieves thread -> callback information flow */
|
|
my_data->sock = sock;
|
|
|
|
/* instantiate a thread-local parser */
|
|
http_parser *parser = malloc(sizeof(http_parser));
|
|
http_parser_init(parser, HTTP_REQUEST); /* initialise parser */
|
|
/* this custom data reference is accessible through the reference to the
|
|
parser supplied to callback functions */
|
|
parser->data = my_data;
|
|
|
|
http_parser_settings settings; /* set up callbacks */
|
|
settings.on_url = my_url_callback;
|
|
|
|
/* execute parser */
|
|
nparsed = http_parser_execute(parser, &settings, buf, recved);
|
|
|
|
...
|
|
/* parsed information copied from callback.
|
|
can now perform action on data copied into thread-local memory from callbacks.
|
|
achieves callback -> thread information flow */
|
|
my_data->buffer;
|
|
...
|
|
}
|
|
|
|
```
|
|
|
|
In case you parse HTTP message in chunks (i.e. `read()` request line
|
|
from socket, parse, read half headers, parse, etc) your data callbacks
|
|
may be called more than once. Http-parser guarantees that data pointer is only
|
|
valid for the lifetime of callback. You can also `read()` into a heap allocated
|
|
buffer to avoid copying memory around if this fits your application.
|
|
|
|
Reading headers may be a tricky task if you read/parse headers partially.
|
|
Basically, you need to remember whether last header callback was field or value
|
|
and apply the following logic:
|
|
|
|
(on_header_field and on_header_value shortened to on_h_*)
|
|
------------------------ ------------ --------------------------------------------
|
|
| State (prev. callback) | Callback | Description/action |
|
|
------------------------ ------------ --------------------------------------------
|
|
| nothing (first call) | on_h_field | Allocate new buffer and copy callback data |
|
|
| | | into it |
|
|
------------------------ ------------ --------------------------------------------
|
|
| value | on_h_field | New header started. |
|
|
| | | Copy current name,value buffers to headers |
|
|
| | | list and allocate new buffer for new name |
|
|
------------------------ ------------ --------------------------------------------
|
|
| field | on_h_field | Previous name continues. Reallocate name |
|
|
| | | buffer and append callback data to it |
|
|
------------------------ ------------ --------------------------------------------
|
|
| field | on_h_value | Value for current header started. Allocate |
|
|
| | | new buffer and copy callback data to it |
|
|
------------------------ ------------ --------------------------------------------
|
|
| value | on_h_value | Value continues. Reallocate value buffer |
|
|
| | | and append callback data to it |
|
|
------------------------ ------------ --------------------------------------------
|
|
|
|
|
|
Parsing URLs
|
|
------------
|
|
|
|
A simplistic zero-copy URL parser is provided as `http_parser_parse_url()`.
|
|
Users of this library may wish to use it to parse URLs constructed from
|
|
consecutive `on_url` callbacks.
|
|
|
|
See examples of reading in headers:
|
|
|
|
* [partial example](http://gist.github.com/155877) in C
|
|
* [from http-parser tests](http://github.com/joyent/http-parser/blob/37a0ff8/test.c#L403) in C
|
|
* [from Node library](http://github.com/joyent/node/blob/842eaf4/src/http.js#L284) in Javascript
|