gwsocket.1

.TH gwsocket 1 "MARCH 2023" Linux "User Manuals"
.SH NAME
gwsocket is a standalone, simple, yet powerful rfc6455 compliant WebSocket Server.
.SH SYNOPSIS
.LP
.B gwsocket -p [--addr][--origin][gwsocket options ...]
.SH DESCRIPTION
.B gwsocket
is a free (MIT Licensed), standalone, WebSocket Server. It sits
between your application and the client's browser, giving the ability for
bidirectional communication between these two with ease and flexibility.
.SH Start the Server
.P
You can run gwsocket without passing any options to the command line. By
default, it will listen on port 7890 on all the interfaces, e.g., 127.0.0.1,
::1, etc. For instance:
.LP
.B # gwsocket --access-log=/tmp/access.log
.I Note:
See a basic client-side example at the bottom of the man page.
.SH OPTIONS
.TP
\fB\-p \-\-port
Specifies the port to bind.
.TP
\fB\-h \-\-help
Command line help.
.TP
\fB\-V \-\-version
Display version information and exit.
.TP
\fB\-\-access-log=<path/file>
Specifies the path/file for the access log.
.TP
\fB\-\-addr=<addr>
Specifies the address to bind.
.TP
\fB\-\-echo-mode
Set the server to echo all received messages.
.TP
\fB\-\-max-frame-size=<bytes>
Maximum size of a websocket frame. This includes received frames from the
client and messages through the named pipe.
.TP
\fB\-\-origin=<origin>
Ensure clients send the specified origin header upon the WebSocket handshake.
.TP
\fB\-\-pipein=<path/file>
Creates a named pipe (FIFO) that reads from on the given path/file.
.TP
\fB\-\-pipeout=<path/file>
Creates a named pipe (FIFO) that writes to the given path/file.
.TP
\fB\-\-std
Enable --stdin and --stdout. By default named pipes are used for I/O. This adds the option to use stdin / stdout as well. For example, this allows:
    
    ./gwsocket --std > log.txt

    tail -F /var/log/syslog | ./gwsocket --std
    
    --stdin and --stdout are added for fine grained control.
.TP
\fB\-\-stdin
Send stdin to the websocket.
.TP
\fB\-\-stdout
Send received websocket data to stdout.
.TP
\fB\-\-strict
Parse messages using strict mode. See below for more details.
.TP
\fB\-\-ssl-cert=<cert.crt>
Path to TLS/SSL certificate.
.TP
\fB\-\-ssl-key=<priv.key>
Path to TLS/SSL private key.
.TP
\fB\-\-unix-socket=<addr>
Specify UNIX-domain socket address to bind server to.

.SH CONFIGURATION
.TP
\fB\-\-enable-debug
Compile with debugging symbols and turn off compiler optimizations.
.TP
\fB\-\-with-openssl
Compile gwsocket with OpenSSL support for its WebSocket server.
.SH DATA MODES
.P
In order to establish a channel between your application and the client's
browser, gwsocket provides two methods that allow the user to send data in and
out. The first one is through the use of the standard input
.I (stdin)
,and the standard output
.I (stdout)
.The second method is through a fixed-size header
followed by the payload. See options below for more details.
.SS
.I
1. stdin/stdout
.P
The standard input/output is the simplest way of sending/receiving data to/from
a client. However, it's limited to broadcasting messages to all clients. To
send messages to or receive from a specific client, use the strict mode in
section 2.
.SS
.I
1.1 Sending Data to all Clients — stdout
.P
If you need to broadcast data from your application to all clients connected to
gwsocket, then, the simplest way of doing it is by piping your application
output into a named pipe (also known as FIFO) that gwsocket makes use of. Once
gwsocket receives the payload, then it will automatically broadcast the message
to all connected clients.
.SS
.BR
1.1. Examples

  #include <fcntl.h>
  #include <sys/stat.h>
  #include <sys/types.h>
  #include <unistd.h>

  int main() {
      int fd;
      char *myfifo = "/tmp/wspipein.fifo";
      const char *msg = "Message to broadcast";

      fd = open(myfifo, O_WRONLY);
      write(fd, msg, strlen(msg));
      close(fd);

      return 0;
  }

.P
.I Note:
You can send as many bytes
.I PIPE_BUF
can hold. If a message is greater than PIPE_BUF, it would send the rest on a
second message or third, and so on. See strict mode below for more control over
messages.
.SS
.I
1.2 Receiving Data from Clients — stdin
.P
When a client sends a message to the server, it is possible to capture that
message in your application. To do this, your application simply needs to read
from a named pipe. By default, gwsocket creates a FIFO under
.I /tmp/wspipeout.fifo.
.SS
.BR
1.2. Examples
.P
Receiving data can be as simple as doing a
.I # cat /tmp/wspipeout.fifo
or you can do it in the language of your choice. See examples below.

  #include <stdio.h>
  #include <stdlib.h>
  #include <fcntl.h>
  #include <limits.h>

  static void read_message (int fd, fd_set set) {
    int bytes = 0;
    char buf[PIPE_BUF] = { 0 };

    FD_ZERO (&set);
    FD_SET (fd, &set);

    if ((select (fd + 1, &set, NULL, NULL, NULL)) < 1)
      exit (1);
    if (!FD_ISSET (fd, &set))
      return;

    if (read (fd, buf, PIPE_BUF) > 0)
      printf ("%s\n", buf);
  }

  int main (void) {
    fd_set set;
    char *fifo = "/tmp/wspipeout.fifo";
    int fd = 0;

    if ((fd = open (fifo, O_RDWR | O_NONBLOCK)) < 0)
      exit (1);
    while (1)
      read_message(fd, set);

    return 0;
  }

.I
Note:
Make sure the reader in your application is set as non-blocking to get a
constant feed.
.P
.I Tip
If you need to know which client sent the message, for example, in a chat
application, please see the strict mode below.

.SS
.I
2. Strict Mode
.P
gwsocket implements its own tiny protocol for sending/receiving data. In
contrast to the stdin/stdout mode, the strict mode allows you to send/receive
data to/from specific connected clients as well as to keep track of who
opened/closed a WebSocket connection. It also gives you the ability to pack and
send as much data as you would like on a single message.
.P
2. Data Format
.P
The message header is a fixed-size header. The first 12 bytes (uint32_t) are
packed in network byte order and contain the "meta-data" of the message we are
sending/receiving. The rest of it is the actual message.
.P
  0            1               2                3
  +---------------------------------------------+
  |        Client Socket Id (listener)          |
  +---------------------------------------------+
  |    Message Type (binary: 0x2 / text: 0x1)   |
  +---------------------------------------------+
  |             Payload length                  |
  +---------------------------------------------+
  |              Payload Data                   |
  +---------------------------------------------+
.SS
.I
2.1 Sending Data — Strict Mode
.P
If you need to send a message to a specific client, then you can do so by
specifying the client id in the message header. If set to 0, the message will
be broadcasted to all clients. The first 4 bytes are reserved for the client id
or listener. The following 4 bytes are reserved for the message type. 0x01 for
a text message, and 0x02 for a binary message. And the last 4 bytes are
reserved for the payload's length.
.P
Once the header has been written to the pipe, you may now write the message.
.SS
.BR
2.1. Examples
.P
First, start the server in strict-mode.
.LP
.B # gwsocket --strict-mode
  #include <stdio.h>
  #include <stdlib.h>
  #include <string.h>
  #include <fcntl.h>

  size_t pack_uint32(void* buf, uint32_t val) {
    uint32_t v32 = htonl(val);
    memcpy(buf, &v32, sizeof(uint32_t));
    return sizeof(uint32_t);
  }

  int main() {
    char *p = calloc (sizeof(uint32_t) * 3, sizeof(char)), *ptr;
    const char *msg = "Message to broadcast";
    const char *fifo = "/tmp/wspipein.fifo";
    int fd;

    ptr = p;
    ptr += pack_uint32(ptr, 0);
    ptr += pack_uint32(ptr, 0x01);
    ptr += pack_uint32(ptr, strlen(msg));

    fd = open(fifo, O_WRONLY);
    write(fd, p, sizeof(uint32_t) * 3);
    write(fd, msg, strlen(msg));
    close(fd);
    free (p);

    return 0;
  }
.SS
.I
2.2 Receiving Data from Clients — Strict Mode
.P
Now, to get a message from a specific client and route it to another client,
you just need to do the opposite of sending data. First you unpack the header
from network byte order to host byte order and then read the payload.
.SS
.BR
2.2. Examples
.P
First, start the server in strict-mode.
.LP
.B # gwsocket --strict-mode
  #include <stdio.h>
  #include <stdlib.h>
  #include <fcntl.h>
  #include <limits.h>
  #include <int.h>

  static size_t unpack_uint32 (const void *b, uint32_t * val) {
    uint32_t v32 = 0;
    memcpy (&v32, b, sizeof (uint32_t));
    *val = ntohl (v32);
    return sizeof (uint32_t);
  }

  static void read_message (int fd, fd_set set) {
    int bytes = 0;
    uint32_t size = 0, listener = 0, type = 0;
    char hdr[PIPE_BUF] = { 0 }, buf[PIPE_BUF] = {0};
    char *ptr = NULL;

    FD_ZERO (&set);
    FD_SET (fd, &set);

    if ((select (fd + 1, &set, NULL, NULL, NULL)) < 1)
      exit (1);
    if (!FD_ISSET (fd, &set))
      return;

    if (hdr[0] == '\0') {
      if (read (fd, hdr, sizeof (uint32_t) * 3) < 1)
        return;
    }

    ptr = hdr;
    ptr += unpack_uint32(ptr, &listener);
    ptr += unpack_uint32(ptr, &type);
    ptr += unpack_uint32(ptr, &size);

    if (read (fd, buf, size) < 1)
      return;

    printf ("client: %d, msg: %s\n", listener, buf);
  }

  int main (void) {
    fd_set set;
    char *fifo = "/tmp/wspipeout.fifo";
    int fd = 0;

    if ((fd = open (fifo, O_RDWR | O_NONBLOCK)) < 0)
      exit (1);
    while (1)
      read_message(fd, set);

    return 0;
  }
.P
.I Note:
If you read/write to a stream, be aware that they do not necessarily read/write
the full amount of data you have requested. Your application will need to
handle the case where only a single byte is read or written. Examples above do
not handle this.
.SH OBLIGATORY CLIENT EXAMPLE
.P
Here's the basic example, client and server side. First start the server and
set it in echo mode.
.LP
.B # gwsocket --echo-mode
.P
Now, let's create the client side.

  <!DOCTYPE html>
  <html lang="en">
  <style>
  pre {
      background: #EEE;
      border: 1px solid #CCC;
      padding: 10px;
  }
  #page-wrapper {
      border-top: 5px solid #69c773;
      margin: 1em auto;
      width: 950px;
  }
  </style>
  <script>
  window.onload = function() {
      function $(selector) {
          return document.querySelector(selector);
      }
      var socket = new WebSocket('ws://localhost:7890');
      socket.onopen = function(event) {
          $('#messages').innerHTML = 'Connected<br>';
      };
      socket.onmessage = function(event) {
          $('#messages').innerHTML += 'Received:<br>' + event.data + '<br>';
      };
      socket.onclose = function(event) {
          $('#messages').innerHTML = 'Disconnected ' + event.reason;
      };
      $('#submit').onclick = function(e) {
          socket.send($('input').value);
          $('#messages').innerHTML += 'Sent:<br>' + $('input').value + '<br>';
          $('input').value = '';
      };
  };
  </script>

  <div id="page-wrapper">
      <pre id="messages">Connecting...</pre>
      <input id="message" required>
      <button id="submit">Send Message</button>
  </div>

.SH BUGS
.P
If you think you have found a bug, please send me an email to hello [@at]
goaccess.io.
.SH AUTHOR
.P
Gerardo Orellana. For more details about it, or new releases, please visit
http://gwsocket.io