C# HTTP Request Parser (no longer maintained)
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HttpMachine is a C# HTTP request parser. It implements a state machine with Adrian Thurston's excellent state machine compiler, Ragel. Because Ragel supports C, D, Java, Ruby, it wouldn't be hard to port this library to those languages.

HttpMachine is Copyright (c) 2011 Benjamin van der Veen. HttpMachine is licensed under the MIT License. See LICENSE.txt.


  • HTTP/1.1 and 1.0
  • Supports pipelined requests
  • Tells your server if it should keep-alive
  • Extracts the length of the entity body
  • Support for parsing responses.

Eminently-possible future features

  • Support for decoding chunked transfers.
  • Support for protocol upgrade.


HttpMachine provides HTTP data through callbacks. To receive these callbacks, implement either the IHttpRequestParserDelegate or the IHttpResponseParserDelegate interface.

// common interface for both requests and responses
public interface IHttpParserDelegate
    void OnMessageBegin(HttpParser parser);
    void OnHeaderName(HttpParser parser, string name);
    void OnHeaderValue(HttpParser parser, string value);
    void OnHeadersEnd(HttpParser parser);
    void OnBody(HttpParser parser, ArraySegment<byte> data);
    void OnMessageEnd(HttpParser parser);

public interface IHttpRequestParserDelegate : IHttpParserDelegate
    void OnMethod(HttpParser parser, string method);
    void OnRequestUri(HttpParser parser, string requestUri);
    void OnPath(HttpParser parser, string path);
    void OnFragment(HttpParser parser, string fragment);
    void OnQueryString(HttpParser parser, string queryString);

public interface IHttpResponseParserDelegate : IHttpParserDelegate
    void OnResponseCode(HttpParser parser, int statusCode, string statusReason); 

Then, create an instance of HttpParser. Whenever you read data, execute the parser on the data. The Execute method returns the number of bytes successfully parsed. If the returned value is not the same as the length of the buffer you provided, an error occurred while parsing. Make sure you provide a zero-length buffer at the end of the stream, as some callbacks may still be pending.

var handler = new MyHttpParserDelegate();
var parser = new HttpParser(handler);

var buffer = new byte[1024 /* or whatever you like */]

int bytesRead;

while ((bytesRead = inputStream.Read(buffer, 0, buffer.Length)) > 0)
    if (bytesRead != parser.Execute(new ArraySegment<byte>(buffer, 0, bytesRead))
        goto error; /* or whatever you like */

// ensure you get the last callbacks.

The parser has three public properties:

// HTTP version provided in the request
public int MajorVersion { get; }
public int MinorVersion { get; }

// inspects "Connection" header and HTTP version (if any) to recommend a connection behavior
public bool ShouldKeepAlive { get; }

These properties are only guaranteed to be accurate in the OnBody and OnMessageEnd callbacks.