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HTTP Tunneling

, 14 Jun 2000 373K 15.5K 124
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This article describes how to open arbitrary TCP connections through proxy servers
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    The application discussed in this article provides the ability to make TCP connections through a proxy server. Often computers are behind firewalls that deny many connections. But HTTP connection is usually allowed and is made through a proxy server. This article will show how arbitrary TCP connections can be made using HTTP protocol and the proxy server.


    When an HTTP connection is made through a proxy server the client (usually the browser) sends the request to the proxy. The proxy opens the connection to the destination, sends the request, receives the response and sends it back to the client. The HTTP protocol specifies a request method called CONNECT. The CONNECT method can be used by the client to inform the proxy server that a connection to some host on some port is required. The proxy server, if allows such connections, tries to connect to the destination address specified in the request header. If it the operation fails it sends back to the client a negative HTTP response and close the connection. If the operation succeeded then send back an HTTP positive response and the connection is consider established. After that, the proxy does not care what data is transferred between client requesting the connection and the destination. It just forwards data in both ways acting as a tunnel.

    About the protocol

    We are interested in CONNECT method from the HTTP protocol. After the applications opens a connection with the proxy server it must send the connect request in the form of an HTTP request:

    CONNECT <destination_address>:<destination_port> <http_version><CR><LF>

    The proxy server process the request and try to make a connection to <destionation_address>:<destination_port>.

    The proxy server sends back an HTTP response in the form:

    <http_version> <code> <message><CR><LF>

    If it is a positive response (code=200) then after the empty line the proxy begins to acts as a tunnel and forwards data. If it is a negative response (code!=200) then connection is closed after the empty line.

    The HTTPTunneling application

    The application act as specified in a configuration file. An entry in the configuration file locks like this:

    <Source port> <Destination address> <Destination port> <Proxy address> <Proxy port>

    If the application is running and an entry in the configuration files changes, the application automatically updates itself.

    For every entry in the configuration file the application creates a port listener. This is a thread that opens a socket on <Source port> and waits for connection. When a request arrives on that port it tries to open a tunnel to the <Destination address>:< port>. If the <Proxy address> and <Proxy port> are missing, a direct connection is made. If the field are present it opens a connection to the proxy and sends a CONNECT request using the method specified above. The tunnel construction is made in a separate thread to let the port listener to accept immediatelly new connections. After the connection is established a tunnel object is constructed based on the opened sockets, sockets are marked as non-blocking and the object is passed to manager object. The thread that has created the tunnel is destroyed. Data transfer is made on a single thread. When one of the ends closes the connection the tunnel closes the other and the tunnel is marked as inactive. The manager finds the tunnel inactive and removes it from the list of active tunnels.

    By default the application generates log information in HTTPTunneling.log file. This file can be consulted to find wrong application behaviour.

    Known problems

    • If no data transfer is made the proxy could close the connection, event neither the initiator neither the destination has closed the connection.
    • Proxy authorization may be required. This can be easily solved including in the HTTP request the Proxy-Authorization field.


    June 15, 2000

    • Posted.


    This article has no explicit license attached to it but may contain usage terms in the article text or the download files themselves. If in doubt please contact the author via the discussion board below.

    A list of licenses authors might use can be found here


    About the Author

    Alex Turc
    United States United States
    No Biography provided

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    Comments and Discussions

    Questionwhat does it mean? Pin
    Anonymous22-Oct-02 17:49
    sussAnonymous22-Oct-02 17:49 
    Questioncan i know how long i spend at connecting to internet through a proxy? Pin
    leon.li22-Oct-02 17:14
    memberleon.li22-Oct-02 17:14 
    Generalchat2 Pin
    evgeni11-Oct-02 2:37
    sussevgeni11-Oct-02 2:37 
    Generalfree my port !!! Pin
    _Vince_30-Sep-02 13:31
    suss_Vince_30-Sep-02 13:31 
    Generalchat over proxy Pin
    mohamad22-Sep-02 6:52
    membermohamad22-Sep-02 6:52 
    GeneralTunnel failed Pin
    meta19-Jun-02 21:15
    membermeta19-Jun-02 21:15 
    GeneralRe: Tunnel failed Pin
    teste28-Sep-02 11:18
    sussteste28-Sep-02 11:18 
    Questionhow to write firewall? Pin
    rama surendra babu19-Jun-02 4:40
    memberrama surendra babu19-Jun-02 4:40 
    AnswerRe: how to write firewall? Pin
    Anonymous12-Aug-02 8:18
    sussAnonymous12-Aug-02 8:18 
    GeneralGo and test this great proxy/tunel Pin
    Anonymous17-Jun-02 5:16
    memberAnonymous17-Jun-02 5:16 
    GeneralWinVNC Pin
    Anonymous28-May-02 1:14
    memberAnonymous28-May-02 1:14 
    GeneralRe: WinVNC Pin
    concise28-Jan-03 7:18
    sussconcise28-Jan-03 7:18 
    GeneralProblem in Source Safe Window Pin
    koorosh13-Apr-02 19:39
    memberkoorosh13-Apr-02 19:39 
    GeneralRe: Problem in Source Safe Window Pin
    Anonymous14-Jun-02 19:20
    memberAnonymous14-Jun-02 19:20 
    GeneralAnonymity Pin
    Rubikz11-Dec-01 11:23
    memberRubikz11-Dec-01 11:23 
    GeneralSomeone! Pin
    Boggan11-Oct-01 8:32
    memberBoggan11-Oct-01 8:32 
    Generalasdf Pin
    Anonymous8-Jun-01 4:59
    memberAnonymous8-Jun-01 4:59 
    Generaltunnel Pin
    tkt3-Jun-01 1:14
    membertkt3-Jun-01 1:14 
    GeneralRe: tunnel Pin
    shekhar5-Jun-01 15:49
    membershekhar5-Jun-01 15:49 
    GeneralRe: tunnel Pin
    CyberCying4-Jun-02 9:20
    memberCyberCying4-Jun-02 9:20 
    GeneralRealAudio Pin
    Anonymous16-May-01 5:09
    memberAnonymous16-May-01 5:09 
    GeneralProblems with MS Proxy Pin
    Fil Mackay19-Mar-01 13:27
    memberFil Mackay19-Mar-01 13:27 
    GeneralNTLM authentication with http-tunneling Pin
    Anonymous13-Dec-00 19:28
    memberAnonymous13-Dec-00 19:28 
    GeneralRe: NTLM authentication with http-tunneling Pin
    hendy6-Sep-01 20:15
    memberhendy6-Sep-01 20:15 
    QuestionHow to use Satellite Pin
    shomeet24-Nov-00 2:08
    membershomeet24-Nov-00 2:08 
    QuestionCan i any data send/receve by this demo program? Pin
    artram9-Nov-00 17:55
    memberartram9-Nov-00 17:55 
    GeneralIntegration into the NDK Pin
    MichaelD16-Oct-00 0:42
    sussMichaelD16-Oct-00 0:42 
    GeneralAlot of Proxies don't support CONNECT Pin
    Dave21-Sep-00 9:38
    sussDave21-Sep-00 9:38 
    GeneralRe: Alot of Proxies don't support CONNECT Pin
    livni13-Nov-00 1:46
    memberlivni13-Nov-00 1:46 
    Questionwhen and when not to tunnel? Pin
    Shaun Wilde13-Sep-00 5:17
    sussShaun Wilde13-Sep-00 5:17 
    AnswerRe: when and when not to tunnel? Pin
    Alex Turc13-Sep-00 6:11
    sussAlex Turc13-Sep-00 6:11 
    GeneralRe: when and when not to tunnel? Pin
    Shaun Wilde13-Sep-00 6:15
    sussShaun Wilde13-Sep-00 6:15 
    GeneralRe: when and when not to tunnel? Pin
    Peter Weyzen3-Jan-01 10:23
    memberPeter Weyzen3-Jan-01 10:23 
    GeneralGood Job!!! Pin
    Krakhead29-Aug-00 16:34
    sussKrakhead29-Aug-00 16:34 
    QuestionDemo??? Pin
    Nozy29-Jul-00 0:57
    sussNozy29-Jul-00 0:57 
    AnswerRe: Demo??? Pin
    Alex Turc30-Jul-00 20:39
    sussAlex Turc30-Jul-00 20:39 
    GeneralTips for Win98 users Pin
    Poul Dahl26-Jun-00 2:14
    sussPoul Dahl26-Jun-00 2:14 
    QuestionCan u provide a simple example Pin
    Visual20-Jun-00 14:51
    sussVisual20-Jun-00 14:51 
    AnswerRe: Can u provide a simple example Pin
    Alex Turc20-Jun-00 21:54
    sussAlex Turc20-Jun-00 21:54 
    QuestionHow about Sock ver 4 & 5 Pin
    Netcoder20-Jun-00 14:42
    sussNetcoder20-Jun-00 14:42 
    AnswerRe: How about Sock ver 4 & 5 Pin
    Krakhead29-Aug-00 16:30
    sussKrakhead29-Aug-00 16:30 

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