llhttp

Port of [http_parser][0] to [llparse][1].

Why?

Let's face it, [http_parser][0] is practically unmaintainable. Even introduction of a single new method results in a significant code churn.

This project aims to:

• Make it maintainable
• Verifiable
• Improving benchmarks where possible

More details in Fedor Indutny's talk at JSConf EU 2019

How?

Over time, different approaches for improving [http_parser][0]'s code base were tried. However, all of them failed due to resulting significant performance degradation.

This project is a port of [http_parser][0] to TypeScript. [llparse][1] is used to generate the output C source file, which could be compiled and linked with the embedder's program (like [Node.js][7]).

Performance

So far llhttp outperforms http_parser:

	input size	bandwidth	reqs/sec	time
llhttp	8192.00 mb	1777.24 mb/s	3583799.39 req/sec	4.61 s
http_parser	8192.00 mb	694.66 mb/s	1406180.33 req/sec	11.79 s

llhttp is faster by approximately 156%.

Maintenance

llhttp project has about 1400 lines of TypeScript code describing the parser itself and around 450 lines of C code and headers providing the helper methods. The whole [http_parser][0] is implemented in approximately 2500 lines of C, and 436 lines of headers.

All optimizations and multi-character matching in llhttp are generated automatically, and thus doesn't add any extra maintenance cost. On the contrary, most of http_parser's code is hand-optimized and unrolled. Instead describing "how" it should parse the HTTP requests/responses, a maintainer should implement the new features in [http_parser][0] cautiously, considering possible performance degradation and manually optimizing the new code.

Verification

The state machine graph is encoded explicitly in llhttp. The [llparse][1] automatically checks the graph for absence of loops and correct reporting of the input ranges (spans) like header names and values. In the future, additional checks could be performed to get even stricter verification of the llhttp.

Usage

#include "stdio.h"
#include "llhttp.h"
#include "string.h"

int handle_on_message_complete(llhttp_t* parser) {
    fprintf(stdout, "Message completed!\n");
    return 0;
}

int main() {
    llhttp_t parser;
    llhttp_settings_t settings;

    /*Initialize user callbacks and settings */
    llhttp_settings_init(&settings);

    /*Set user callback */
    settings.on_message_complete = handle_on_message_complete;

    /*Initialize the parser in HTTP_BOTH mode, meaning that it will select between
    *HTTP_REQUEST and HTTP_RESPONSE parsing automatically while reading the first
    *input.
    */
    llhttp_init(&parser, HTTP_BOTH, &settings);

    /*Parse request! */
    const char* request = "GET / HTTP/1.1\r\n\r\n";
    int request_len = strlen(request);

    enum llhttp_errno err = llhttp_execute(&parser, request, request_len);
    if (err == HPE_OK) {
        fprintf(stdout, "Successfully parsed!\n");
    } else {
        fprintf(stderr, "Parse error: %s %s\n", llhttp_errno_name(err), llhttp_get_error_reason(&parser));
    }
}

For more information on API usage, please refer to src/native/api.h.

API

llhttp_settings_t

The settings object contains a list of callbacks that the parser will invoke.

The following callbacks can return 0 (proceed normally), -1 (error) or HPE_PAUSED (pause the parser):

• on_message_begin: Invoked when a new request/response starts.
• on_message_complete: Invoked when a request/response has been completedly parsed.
• on_url_complete: Invoked after the URL has been parsed.
• on_method_complete: Invoked after the HTTP method has been parsed.
• on_protocol_complete: Invoked after the protocol has been parsed.
• on_version_complete: Invoked after the HTTP version has been parsed.
• on_status_complete: Invoked after the status code has been parsed.
• on_header_field_complete: Invoked after a header name has been parsed.
• on_header_value_complete: Invoked after a header value has been parsed.
• on_chunk_header: Invoked after a new chunk is started. The current chunk length is stored in parser->content_length.
• on_chunk_extension_name_complete: Invoked after a chunk extension name is started.
• on_chunk_extension_value_complete: Invoked after a chunk extension value is started.
• on_chunk_complete: Invoked after a new chunk is received.
• on_reset: Invoked after on_message_complete and before on_message_begin when a new message is received on the same parser. This is not invoked for the first message of the parser.

The following callbacks can return 0 (proceed normally), -1 (error) or HPE_USER (error from the callback):

• on_url: Invoked when another character of the URL is received.
• on_status: Invoked when another character of the status is received.
• on_method: Invoked when another character of the method is received. When parser is created with HTTP_BOTH and the input is a response, this also invoked for the sequence HTTP/ of the first message.
• on_protocol: Invoked when another character of the protocol is received.
• on_version: Invoked when another character of the version is received.
• on_header_field: Invoked when another character of a header name is received.
• on_header_value: Invoked when another character of a header value is received.
• on_chunk_extension_name: Invoked when another character of a chunk extension name is received.
• on_chunk_extension_value: Invoked when another character of a extension value is received.

The callback on_headers_complete, invoked when headers are completed, can return:

• 0: Proceed normally.
• 1: Assume that request/response has no body, and proceed to parsing the next message.
• 2: Assume absence of body (as above) and make llhttp_execute() return HPE_PAUSED_UPGRADE.
• -1: Error
• HPE_PAUSED: Pause the parser.

void llhttp_init(llhttp_t* parser, llhttp_type_t type, const llhttp_settings_t* settings)

Initialize the parser with specific type and user settings.

uint8_t llhttp_get_type(llhttp_t* parser)

Returns the type of the parser.

uint8_t llhttp_get_http_major(llhttp_t* parser)

Returns the major version of the HTTP protocol of the current request/response.

uint8_t llhttp_get_http_minor(llhttp_t* parser)

Returns the minor version of the HTTP protocol of the current request/response.

uint8_t llhttp_get_method(llhttp_t* parser)

Returns the method of the current request.

int llhttp_get_status_code(llhttp_t* parser)

Returns the method of the current response.

uint8_t llhttp_get_upgrade(llhttp_t* parser)

Returns 1 if request includes the Connection: upgrade header.

void llhttp_reset(llhttp_t* parser)

Reset an already initialized parser back to the start state, preserving the existing parser type, callback settings, user data, and lenient flags.

void llhttp_settings_init(llhttp_settings_t* settings)

Initialize the settings object.

llhttp_errno_t llhttp_execute(llhttp_t* parser, const char* data, size_t len)

Parse full or partial request/response, invoking user callbacks along the way.

If any of llhttp_data_cb returns errno not equal to HPE_OK - the parsing interrupts, and such errno is returned from llhttp_execute(). If HPE_PAUSED was used as a errno, the execution can be resumed with llhttp_resume() call. In that case the input should be advanced to the last processed byte from the parser, which can be obtained via llhttp_get_error_pos().

In a special case of CONNECT/Upgrade request/response HPE_PAUSED_UPGRADE is returned after fully parsing the request/response. If the user wishes to continue parsing, they need to invoke llhttp_resume_after_upgrade().

if this function ever returns a non-pause type error, it will continue to return the same error upon each successive call up until llhttp_init() is called.

If this function returns HPE_OK, it means all the input has been consumed and parsed.

llhttp_errno_t llhttp_finish(llhttp_t* parser)

This method should be called when the other side has no further bytes to send (e.g. shutdown of readable side of the TCP connection.)

Requests without Content-Length and other messages might require treating all incoming bytes as the part of the body, up to the last byte of the connection.

This method will invoke on_message_complete() callback if the request was terminated safely. Otherwise a error code would be returned.

int llhttp_message_needs_eof(const llhttp_t* parser)

Returns 1 if the incoming message is parsed until the last byte, and has to be completed by calling llhttp_finish() on EOF.

int llhttp_should_keep_alive(const llhttp_t* parser)

Returns 1 if there might be any other messages following the last that was successfully parsed.

void llhttp_pause(llhttp_t* parser)

Make further calls of llhttp_execute() return HPE_PAUSED and set appropriate error reason.

Do not call this from user callbacks! User callbacks must return HPE_PAUSED if pausing is required.

void llhttp_resume(llhttp_t* parser)

Might be called to resume the execution after the pause in user's callback.

See llhttp_execute() above for details.

Call this only if llhttp_execute() returns HPE_PAUSED.

void llhttp_resume_after_upgrade(llhttp_t* parser)

Might be called to resume the execution after the pause in user's callback. See llhttp_execute() above for details.

Call this only if llhttp_execute() returns HPE_PAUSED_UPGRADE

llhttp_errno_t llhttp_get_errno(const llhttp_t* parser)

Returns the latest error.

const char* llhttp_get_error_reason(const llhttp_t* parser)

Returns the verbal explanation of the latest returned error.

User callback should set error reason when returning the error. See llhttp_set_error_reason() for details.

void llhttp_set_error_reason(llhttp_t* parser, const char* reason)

Assign verbal description to the returned error. Must be called in user callbacks right before returning the errno.

HPE_USER error code might be useful in user callbacks.

const char* llhttp_get_error_pos(const llhttp_t* parser)

Returns the pointer to the last parsed byte before the returned error. The pointer is relative to the data argument of llhttp_execute().

This method might be useful for counting the number of parsed bytes.

const char* llhttp_errno_name(llhttp_errno_t err)

Returns textual name of error code.

const char* llhttp_method_name(llhttp_method_t method)

Returns textual name of HTTP method.

const char* llhttp_status_name(llhttp_status_t status)

Returns textual name of HTTP status.

void llhttp_set_lenient_headers(llhttp_t* parser, int enabled)

Enables/disables lenient header value parsing (disabled by default). Lenient parsing disables header value token checks, extending llhttp's protocol support to highly non-compliant clients/server.

No HPE_INVALID_HEADER_TOKEN will be raised for incorrect header values when lenient parsing is "on".

Enabling this flag can pose a security issue since you will be exposed to request smuggling attacks. USE WITH CAUTION!

void llhttp_set_lenient_chunked_length(llhttp_t* parser, int enabled)

Enables/disables lenient handling of conflicting Transfer-Encoding and Content-Length headers (disabled by default).

Normally llhttp would error when Transfer-Encoding is present in conjunction with Content-Length.

This error is important to prevent HTTP request smuggling, but may be less desirable for small number of cases involving legacy servers.

Enabling this flag can pose a security issue since you will be exposed to request smuggling attacks. USE WITH CAUTION!

void llhttp_set_lenient_keep_alive(llhttp_t* parser, int enabled)

Enables/disables lenient handling of Connection: close and HTTP/1.0 requests responses.

Normally llhttp would error the HTTP request/response after the request/response with Connection: close and Content-Length.

This is important to prevent cache poisoning attacks, but might interact badly with outdated and insecure clients.

With this flag the extra request/response will be parsed normally.

Enabling this flag can pose a security issue since you will be exposed to poisoning attacks. USE WITH CAUTION!

void llhttp_set_lenient_transfer_encoding(llhttp_t* parser, int enabled)

Enables/disables lenient handling of Transfer-Encoding header.

Normally llhttp would error when a Transfer-Encoding has chunked value and another value after it (either in a single header or in multiple headers whose value are internally joined using ,).

This is mandated by the spec to reliably determine request body size and thus avoid request smuggling.

With this flag the extra value will be parsed normally.

Enabling this flag can pose a security issue since you will be exposed to request smuggling attacks. USE WITH CAUTION!

void llhttp_set_lenient_version(llhttp_t* parser, int enabled)

Enables/disables lenient handling of HTTP version.

Normally llhttp would error when the HTTP version in the request or status line is not 0.9, 1.0, 1.1 or 2.0. With this flag the extra value will be parsed normally.

Enabling this flag can pose a security issue since you will allow unsupported HTTP versions. USE WITH CAUTION!

void llhttp_set_lenient_data_after_close(llhttp_t* parser, int enabled)

Enables/disables lenient handling of additional data received after a message ends and keep-alive is disabled.

Normally llhttp would error w