HTTP Tunneling in Go

HTTP Tunneling can be used in situations similar to the requirements of using VPN, for example, to be able to access a localhost server from outside. This talk will introduce the specific implementation of HTTP tunneling and give audiences a deep knowledge of TCP and HTTP level implementation in Go.

Specifically, this talk discusses the idea of HTTP Tunneling in Go.

Transcript

1. HTTP Tunneling in Go
   Kazuki Higashiguchi
   April 23, 2022 @ Go Conference 2022 Spring
   

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2. Agenda
   HTTP(S)
   Client
   WebSocket
   server
   WebSocket
   client
   HTTP(S)
   Server
   1. HTTP Tunneling
   2. Establish bidirectional connection using WebSocket
   3. HTTP Tunneling over WebSocket
   

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3. About Me
   Kazuki Higashiguchi
   Backend Engineer at Autify.
   ID: @hgsgtk
   

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4. Autify Solution
   No-code AI-powered software testing automation
   services for Web/Mobile applications
   AI automatically maintenance test
   scripts
   No code unlocks automation at
   scale
   

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5. Agenda
   HTTP(S)
   Client
   WebSocket
   server
   WebSocket
   client
   HTTP(S)
   Server
   1. HTTP Tunneling
   2. Establish bidirectional connection using WebSocket
   3. HTTP Tunneling over WebSocket
   

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6. HTTP tunneling
   ● Create a network link between two computers in
   conditions of restricted network connectivity.
   e.g. firewalls, NATs, ACLs
   ● Use a protocol of higher level (HTTP) to transport a
   lower level protocol (TCP)
   

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7. HTTP CONNECT method
   ● Start bidirectional communications with the requested
   resource
   e.g. access HTTPS websites, HTTP proxy server
   HTTP(S)
   Client
   HTTP(S)
   Server
   Proxy
   (Gateway)
   

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8. HTTP tunneling with CONNECT
   Quoted from HTTP: The Definitive Guide / 8.5 Tunnels
   1. Client sends CONNECT request
   2. Gateway opens TCP connection
   to the server
   3. Gateway returns HTTP ready
   message to the client
   4. Start bidirectional
   communication of raw packets
   of data
   

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9. A case study: elazarl/goproxy
   elazarl/goproxy: An HTTP proxy library for Go
   $ curl -I -x http://localhost:8080 https://example.com
   HTTP/1.0 200 OK
   A basic sample code:
   

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10. Tunneling implementation in elazarl/goproxy
    https://github.com/elazarl/goproxy/blob/0bfa7c564b
    5ffbece2f0832eb4e714fb971f70f3/https.go#L95
    

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11. Tunneling implementation in elazarl/goproxy
    1
    2
    3
    

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12. Step 1: Take over the proxy connection
    http.Hijacker interface allows an HTTP handler to take over
    the connection.
    

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13. Step 2: Open TCP connections
    Opens TCP connection using net.Dial
    Returns HTTP ready message: 200 Connection established
    

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14. Step 3: Streaming with io.Copy
    

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15. Streaming: TLS handshake over TCP connection
    ● TLS handshake is done
    using the streaming
    ● Application data is sent and
    receive after TLS
    handshake
    

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16. Key takeaways
    ● HTTP Tunneling uses a protocol of higher level (HTTP)
    to transport a lower level protocol (TCP)
    ● The basic flow of HTTP tunneling using the HTTP
    Connect method
    ● http.Hijack and io.Copy are key functions to implement
    HTTP tunneling in Go
    

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17. Agenda
    HTTP(S)
    Client
    WebSocket
    server
    WebSocket
    client
    HTTP(S)
    Server
    1. HTTP Tunneling
    2. Establish bidirectional connection using WebSocket
    3. HTTP Tunneling over WebSocket
    

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18. Establish bidirectional connections
    WebSocket
    server
    WebSocket
    client
    Handshake
    WebSocket
    Conn
    WebSocket
    Conn
    HTTP(S)
    Client
    WebSocket
    server
    WebSocket
    client
    HTTP(S)
    Server
    

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19. Bidirectional connections
    ● Long/short polling
    ● WebSockets
    ● Server-Sent Events
    ● HTTP/2 Push
    ● etc
    

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20. WebSockets
    ● A mechanism for low-cost,
    full-duplex communication on Web
    ● Designed to work over HTTP
    (compatible with the HTTP
    protocol)
    ● Handshake -> Messages -> Close
    

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21. WebSocket client and server using gorilla/websocket
    Client:
    gorilla/websocket: an WebSocket implementation in Go
    Server:
    

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22. websocket.Conn implementation
    websocket.Conn has net.Conn in the unexported field.
    The return value of http.Hijack will be set to the field conn.
    https://github.com/gorilla/websocket/blob/eeb877e8a1fd26c449b7af3cb1d71879287d724c/server.go#L125
    

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23. Agenda
    HTTP(S)
    Client
    WebSocket
    server
    WebSocket
    client
    HTTP(S)
    Server
    1. HTTP Tunneling
    2. Establish bidirectional connection using WebSocket
    3. HTTP Tunneling over WebSocket
    

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24. HTTP Tunneling over WebSocket
    HTTP(S)
    Client
    HTTP(S)
    Server
    WebSocket
    server
    WebSocket
    client
    WebSocket
    Conn
    WebSocket
    Conn
    TCP
    Conn
    TCP
    Conn
    $ curl -Lv -x http://websocket-server https://target.local
    WebSocket server and WebSocket client jointly act as a
    proxy(gateway).
    https://target.local
    http://websocket-server
    streaming streaming
    

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25. How HTTP Tunneling over WebSocket
    

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26. How HTTP Tunneling with WebSocket
    WebSocket server tells the address of
    destination to WebSocket client.
    WebSocket client open a TCP connection to
    the destination server.
    

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27. How HTTP Tunneling with WebSocket
    Bidirectional message over
    an established WebSocket
    connection.
    

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28. WebSocket server implementation
    A sample code available on
    github.com/hgsgtk/go-snippets
    

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29. WebSocket server implementation
    1
    2
    3
    

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30. Step 1: Write messages to WebSocket connection
    Send a TCP handshake request
    with the destination address.
    

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31. Distinguish several types of messages
    This design transfers several kinds of message over a
    single WebSocket connection
    ● Request to open TCP connections
    ● Notify to establish TCP connections
    ● Streaming raw packets of data
    ● etc
    

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32. A case study: Chrome Devtools Protocol
    CDP defines the JSON protocol, which is used to communicate in the
    WebSocket connection.
    Request
    Members: id, method, params
    Response
    Members: id, result, (error)
    

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33. Define own protocol for WebSocket communication
    A small example of methods
    ● Handshake:
    Request to open TCP connections
    ● Completed:
    Notify to establish TCP connections
    ● Communication:
    Streaming raw packets of data
    

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34. Step 2: Take over the proxy connection
    2
    Take over the connection
    using http.Hijacker.
    

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35. Step 3: Streaming
    3
    Use io.Copy to combine
    WebSocket connection
    and TCP connection.
    

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36. Notes on net.Conn returned from http.Hijack
    ● http.Hijacker returns net.Conn and
    bufio.ReadWriter.
    [Code comment on http.Hijack]
    The returned bufio.Reader may contain
    unprocessed buffered data from the
    client.
    ● Reading net.Conn alone may cause data
    to be dropped.
    ● Read buffers from bufio.Reader.
    

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37. Wrap websocket.Conn to use in io.Copy: io.Writer
    Pack incoming packets to defined JSON format
    ﾝu��(gT��!"�.
    ��ҠF��0�Q��Yl/��L�E8/���c<��>���C�
    ��m$�X�Ax�Y%^��J�v�[�o�U�a���U�t
    �u��5��k��m��&|Ǜq����)�z7����?�…
    {
    "method": 3,
    "data": "ﾝu��(gT��!"�.
    ��ҠF��0�Q��Yl/��L�E8/���c<��>�
    ��C���m$�X�Ax�Y%^��J�v�
    [�o�U�a���U�t
    �u��5��k��m��&|Ǜq����)
    �z7����?�…
    "
    }
    

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38. Wrap websocket.Conn to use in io.Copy: io.Reader
    Read packets from a decoded JSON message
    ﾝu��(gT��!"�.
    ��ҠF��0�Q��Yl/��L�E8/���c<��>���C�
    ��m$�X�Ax�Y%^��J�v�[�o�U�a���U�t
    �u��5��k��m��&|Ǜq����)�z7����?�…
    {
    "method": 3,
    "data": "ﾝu��(gT��!"�.
    ��ҠF��0�Q��Yl/��L�E8/���c<��>�
    ��C���m$�X�Ax�Y%^��J�v�
    [�o�U�a���U�t
    �u��5��k��m��&|Ǜq����)
    �z7����?�…
    "
    }
    

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39. WebSocket client implementation
    

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40. Open a TCP connection to the given destination
    Dial to the destination address
    conn, err := net.Dial("tcp",
    “autify.com:443”)
    

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41. Key takeaways
    ● HTTP Tunneling over WebSocket
    ● Define own protocol for WebSocket communication and
    create a wrap struct for streaming with io.Copy
    ● Should read both net.Conn and bufio.ReadWriter
    returned from http.Hijacker
    

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42. Resources
    ● RFC 6455 The WebSocket Protocol
    ● IETF: Tunneling TCP based protocols through Web proxy servers
    ● Mmdn web doc: Proxy servers and tunneling
    ● Mmdn web doc: CONNECT
    ● Wikipedia: HTTP Tunnel
    ● Wikipedia: WebSocket
    ● HTTP: The Definitive Guide / 8.5 Tunnels
    ● Cloudflare: What happens in a TLS handshake? | SSL handshake
    ● Chrome DevTools Protocol
    

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43. Resources
    ● elazarl/goproxy
    ● gorilla/websocket
    ● github.com/hgsgtk/go-snippets/gocon2022spring/tcpws
    

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44. Thank you for your watching
    We are taking demo requests https://autify.com/
    Autify for Web Autify for Mobile
    

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