Sockproc daemon is a simple server for executing shell commands or processes. It can be useful in the situations, where a typical system call to launch a child process and wait for its completion is unacceptable, due to its blocking nature. Instead, a socket can be opened to sockproc, a command written to it, and then once child process completes, its exit code, output stream data and error stream data can be read back from the socket.
Launch sockproc on a UNIX domain socket:
$ ./sockproc /tmp/shell.sock
On Mac telnet works with both tcp sockets and unix-domain sockets, but on most Linux distributions, the telnet command is not as versatile. So we can employ a socat utility instead, using "crlf" flag to enforce the '\r\n' line-endings for standard input.
Connect to socket and type in a command line to execute, followed by a line that contains the number 0:
$ socat - /tmp/shell.sock,crlf
uname -a
0
status:0
98
Linux a569cf4d3a74 4.9.27-moby #1 SMP Thu May 11 04:01:18 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
0
Launch sockproc on a TCP socket:
$ ./sockproc 13000
Connect to socket and type in a command line to execute, followed by a line that contains the number 0:
$ telnet 127.0.0.1 13000
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
uname -a
0
status:0
98
Linux a569cf4d3a74 4.9.27-moby #1 SMP Thu May 11 04:01:18 UTC 2017 x86_64 x86_64 x86_64 GNU/Linux
0
Connection closed by foreign host.
Execute a bad command:
$ telnet 127.0.0.1 13000
Trying 127.0.0.1...
Connected to 127.0.0.1.
Escape character is '^]'.
foobar
0
status:32512
0
37
/bin/bash: foobar: command not found
Connection closed by foreign host.
The protocol is very simple, similar somewhat to HTTP:
<command-line>\r\n
<stdin-byte-count>\r\n
<stdin-data>
The <command-line> length cannot exceed 2040 characters.
status:<process-exit-code>\r\n
<stdout-byte-count>\r\n
<stdout-data>
<stderr-byte-count>\r\n
<stderr-data>
The MIT License (MIT)