Simple Socket Server in Bash

Simple Socket Server in Bash?

$ nc -k -l 4444 > filename.out

see nc(1)

Looking for simple socket server application that could be used to test socket applications?

For a simple TCP server you could use netcat:

Ncat is a feature-packed networking utility which reads and writes data across networks from the command line. Ncat was written for the Nmap Project and is the culmination of the currently splintered family of Netcat incarnations. It is designed to be a reliable back-end tool to instantly provide network connectivity to other applications and users. Ncat will not only work with IPv4 and IPv6 but provides the user with a virtually limitless number of potential uses.

It can provide bidirectional communication through TCP/UDP. There's even some HTTP server implementations using only netcat.

It'd be as easy as:

$ nc -l 0.0.0.0 9999

And voilá, you're now listening to the port 9999 in all interfaces and can connect from your device.

To test the communications you can also use netcat. In another bash session, try this:

$ nc 127.0.0.1 9999

Easy and available on all distros :)

Opening a socket to see output with bash

If you version of bash supports networking

#!/bin/bash
set -u
host="$1"
port="$2"
path="$3"
exec 3<>/dev/tcp/$host/$port
printf '%s\r\n' "$path" >&3
cat <&3

if you are hitting a HTTP server the probably you have to pass the GET requests as path, something like

script example.com 80 $'GET / HTTP/1.1\r\nConnection: close\r\n'

How to make an Echo server with Bash?

If you use ncat instead of nc your command line works fine with multiple connections but (as you pointed out) without -p.

ncat -l 2000 -k -c 'xargs -n1 echo'

ncat is available at http://nmap.org/ncat/.

P.S. with the original the Hobbit's netcat (nc) the -c flag is not supported.

Update: -k (--keep-open) is now required to handle multiple connections.

Want to create a TCP server

If your nc supports it, you can use the '-e' option: put your loop in a new file handle_client.sh, then start the server with

nc -l localhost 3000 -e ./handle_client.sh

C++ UNIX Help - simple TCP server socket connection

You problem is here:

else if(s.st_mode & S_IFREG)
{
    int fd = open(path, O_RDONLY);
    if(fd < 0) { perror("open"); exit(EXIT_FAILURE); }
    read(fd, buffer, strlen(buffer)); << Change strlen(buffer)
    strcat(buffer, "\n");
    if(write(connSock, buffer, strlen(buffer)) < 0)
    { perror("write"); exit(EXIT_FAILURE); }
    close(fd);
}

strlen(buffer) can be any value, because you are initializing buffer to 1024 bytes. The memory area is possibly being filled full of zeroes. strlen(buffer) would then be returning 0, because the first character is a null byte. Nothing is being written into the buffer because read will end up writing zero bytes.

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