Introduction

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.

Examples

With UNIX domain 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

With TCP socket

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.

Wire protocol

The protocol is very simple, similar somewhat to HTTP:

Request format:

<command-line>\r\n
<stdin-byte-count>\r\n
<stdin-data>

The <command-line> length cannot exceed 2040 characters.

Response format:

status:<process-exit-code>\r\n
<stdout-byte-count>\r\n
<stdout-data>
<stderr-byte-count>\r\n
<stderr-data>

License

The MIT License (MIT)