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temporary commit to fix lint in async-web-server
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@Alex-deVis
Alex-deVis committed Dec 28, 2024
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Showing 1 changed file with 85 additions and 85 deletions.
170 changes: 85 additions & 85 deletions content/assignments/async-web-server/src/http-parser/README.md
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Original file line number Diff line number Diff line change
Expand Up @@ -10,23 +10,22 @@ 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.
- 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 path, query string, fragment
* Message body

- Header fields and values
- Content-Length
- Request method
- Response status code
- Transfer-Encoding
- HTTP version
- Request path, query string, fragment
- Message body

Usage
-----
Expand All @@ -35,37 +34,41 @@ 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:

http_parser_settings settings;
settings.on_path = my_path_callback;
settings.on_header_field = my_header_field_callback;
/* ... */
```c
http_parser_settings settings;
settings.on_path = my_path_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;
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.
size_t len = 80*1024, nparsed;
char buf[len];
ssize_t recved;
```c
size_t len = 80*1024, nparsed;
char buf[len];
ssize_t recved;
recved = recv(fd, buf, len, 0);
recved = recv(fd, buf, len, 0);
if (recved < 0) {
/* Handle error. */
}
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);
/* 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. */
}
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
Expand All @@ -84,50 +87,48 @@ 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 Web Socket 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
```plain
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 http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-75 for more
(See <http://tools.ietf.org/html/draft-hixie-thewebsocketprotocol-75> for more
information the Web Socket 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()`.
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.
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_path, on_query_string, on_uri, on_fragment,
(common) on_header_field, on_header_value, on_body;
- 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_path, on_query_string, on_uri, on_fragment,
(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.
Expand All @@ -142,30 +143,29 @@ 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 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 |
------------------------ ------------ --------------------------------------------

(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 |
------------------------ ------------ --------------------------------------------

See examples of reading in headers:

* [partial example](http://gist.github.com/155877) in C
* [from http-parser tests](http://github.com/ry/http-parser/blob/37a0ff8928fb0d83cec0d0d8909c5a4abcd221af/test.c#L403) in C
* [from Node library](http://github.com/ry/node/blob/842eaf446d2fdcb33b296c67c911c32a0dabc747/src/http.js#L284) in Javascript
- [partial example](http://gist.github.com/155877) in C
- [from http-parser tests](http://github.com/ry/http-parser/blob/37a0ff8928fb0d83cec0d0d8909c5a4abcd221af/test.c#L403) in C
- [from Node library](http://github.com/ry/node/blob/842eaf446d2fdcb33b296c67c911c32a0dabc747/src/http.js#L284) in Javascript

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