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;