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diff --git a/http-parser/README.md b/http-parser/README.md new file mode 100644 index 0000000..b265d71 --- /dev/null +++ b/http-parser/README.md @@ -0,0 +1,246 @@ +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_parser` 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_parser` 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 |