bash socket utility

1. Listen

Binding an input creates a listening socket on a local port and binds the socket data to a local accessible buffer (accessible with the native read call).

bind-input $id $port;

Arguments:

• $id is a unique arbitrary name you must give to the listening binding
• $port is the number of the local port to listen to (between 1024 and 49151)

Execution:

• The bind-input execution will last until the socket is created, then it will move it to a background process and print its PID.
• In order to close properly the bind-input, you must kill its PID with one of the 3 following signals: SIGINT, SIGHUP, SIGTERM. Note that you must not use SIGKILL because it won't trigger the "proper closing" routine.

Exemple:

Let's say that you want to listen to port 9999, then read every second. You want to ignore empty messages (if nothing received), and end the program when you receive the message "END".

#/bin/bash

# 1. Create the listening socket + store PID in /tmp
bind-input input1 9999 > /tmp/get_bg_pid;

# 2. Store PID in a variable
bound_pid="`cat /tmp/get_bg_pid`";

# 3. Now the socket is listening, you can read every 1 sec
while true; do

    # 3.1. Read received data from port 9999
    message="`read input1`";

    # 3.2. Ignore empty messages
    [[ -z "$message" ]] && sleep 1 && continue;

    # 3.3. Exit while() loop if received "END"
    [[ "$message" = "END" ]] && break;

    # 3.4. Wait 1 sec
    sleep 1;

done;

# 4. Kill 'bind-input' with signal SIGINT, SIGHUP or SIGTERM
kill -INT $bound_pid;

2. Connect

Binding an output creates a local accessible buffer (accessible with the native write call) bound to a socket connecting to a certain host and port.

bind-output $id $host $port;

Arguments:

• $id is a unique arbitrary name you must give to the output binding
• $host is the hostname (IP addr. or resolvable) of the machine to connect to.
• $port is the number of the remote port to connect to (between 1024 and 49151)

Execution:

• The bind-output execution will last until the socket is created, then it will move it to a background process and print its PID.
• In order to close properly the bind-output, you must kill its PID with one of the 3 following signals: SIGINT, SIGHUP, SIGTERM. Note that you must not use SIGKILL because it won't trigger the "proper closing" routine.

Exemple:

Let's say that you want to connect to port 192.168.0.2 at port 9999, wait 2 seconds, send a message, wait 1 second and send the "END" message.

#/bin/bash

# 1. Create the connecting socket + store PID in /tmp
bind-output output1 192.168.0.2 9999 > /tmp/get_bg_pid;

# 2. Store PID in a variable
bound_pid="`cat /tmp/get_bg_pid`";

# 3. Wait for sending first message
sleep 2;
write output1 "some message\nwith\tescapable\e[1mcharaters\e[0m";

# 4. Wait for sending "END" message
sleep 1;
write output1 "END";

# 5. Kill 'bind-output' with signal SIGINT, SIGHUP or SIGTERM
kill -INT $bound_pid;

3. Network trigger

The programs trigger-send and trigger-wait allows signals to be send over the network (private or public).

• trigger-wait will wait for a signal to exit.
• trigger-send will send a signal to a remote host.

trigger-wait

trigger-wait $key $port

Arguments:

• $key is a secret string that the sender will have to match.
• $port is the local listening port (between 1024 and 49151).

Note: The reading delay is set to 0.5 seconds not to overuse the processor.

Exemple:

Let's say you want to wait for a signal on port 9999 then launch some command (for example read input1).

trigger-wait somekey123 9999; read input1;

trigger-send

trigger-wait $key $host $port

Arguments:

• $key is the same secret string used by the receiver.
• $host is the remote hostname (IP addr. or resolvable) to send the messag eto.
• $port is the remote port to send the message to (between 1024 and 49151).

Exemple:

Let's say you want to execute a long command (sleep 5), then send the trigger to 192.168.0.2 port 9999.

sleep 5; trigger-send somekey123 192.168.0.2 9999;

4. Daemon pool

This package includes a purpose-specific implementation:

• master pushes a pool of daemons (infinite scripts echoing things over time) bound to a pool receiver.
• pool waits for daemons to be started to bind input buffers.

Pool receiver

The pool commands allows you to wait for daemons on a port.

pool $key $port

Arguments:

• $key is the key for the pool receiver, the master must match it in order for the communication to be validated.
• $port is the number of the local port to listen on (between 1024 and 49151).

Execution:

1. Waits for incoming daemon_request from master (asks for binding an input for a daemon). If the END message is received, stop listening and wait for background bindings to stop.
2. For each daemon, open a free port (bind-input in background), then return its number to the master

Signals:

• If one of these signals: SIGHUP, SIGTERM, SIGINT is received, all processes, sockets and background routines will be properly (recursively) stopped.
• You must avoid SIGKILL, because nothing can be triggered (by definition), so all sockets and binding will remain active.

Pool creator (master)

The master commands allows you to bind daemons output to another machine.

master $key $host $port $ddir

Arguments:

• $key is the key for the pool receiver, if it does not match, it won't work.
• $host is the hostname (IP addr. or resolvable) of the machine powering the pool receiver.
• $port is the number of the remote port the pool is listening on (between 1024 and 49151).
• $ddir is the directory containing the daemon files (must be executable).

Execution:

1. Send daemon_request for each daemon, when open port received, start daemon in background bound to output on $host
2. Send the END message
3. Wait for daemons and output to end

Signals:

• If one of these signals: SIGHUP, SIGTERM, SIGINT is received, all processes, sockets and background routines will be properly (recursively) stopped.
• You must avoid SIGKILL, because nothing can be triggered (by definition), so all sockets and binding will remain active.

Exemple master-pool:

Let's say the master has 2 daemons: dem1 and dem2. Both contains a while loop echoing something each second. In this example, the key is "k12".

                   ip:      ipM                      ip:      ipP
                   listen:  pM                       listen:  pP

                   +--------+                        +--------+
                   | master |                        |  pool  |
                   +--------+                        +--------+
                       |                                 |
               ________|________                   ______|_______
              /                 \                 /              \
             | connect to ipP:pP | =============> | listen on pP |
              \_________________/                 \______________/
                       |                                 |
                      ...                               ...
                       |                                 |
                       | ------ k12:dem1:ipM:pM -------> | bind input on free port: p1
                       |                                 |
                       |                                 |
 start dem1 to ipP:p1  | <------------- p1 ------------- |
                       |                                 |
                      ...                               ...
                       |                                 |
                       | ------ k12:dem2:ipM:pM -------> | bind input on free port: p2
                       |                                 |
                       |                                 |
 start dem2 to ipP:p2  | <------------- p2 ------------- |
                       |                                 |
                      ...                               ...
                       |                                 |
                       | --------- ENDk12END ----------> x stop listening on pP,
                       |
disconnect from ipP:pP x


                wait dem1+dem2                      wait dem1+dem2