Avoid startup overhead by automagically serverizing your scripts.

Video introduction

video, slides

What it does

Have a Unix command-line program that you call frequently with small input and output? Does it take a long time to start up, e.g. because it needs to read large parameter files? Turn it into a server process that keeps running in the background while handling multiple inputs and outputs.

How it works

For example, instead of this:

$ cat file1.txt | ./parse -m model > file1.parse
$ cat file2.txt | ./parse -m model > file2.parse
$ cat file3.txt | ./parse -m model > file3.parse

Do this:

$ cat file1.txt | viasock run ./parse -m model > file1.parse
$ cat file2.txt | viasock run ./parse -m model > file2.parse
$ cat file3.txt | viasock run ./parse -m model > file3.parse

All it takes is to insert viasock run before the command. The first time this is called, it will spin up the parse program as a server in the background. On every subsequent call, it will just use that server. If the parse program takes a long time to start up, e.g. reading in its model, this now happens only once, not every time it is used.

Viasock will also

• shut down the server if it is not used for a while (currently 15 seconds),
• start a new server if any of the files the command might need (such as ./parse or model) are updated, making sure you use the current version.

There are similar projects that use TCP sockets, which may expose your program to security threats. Viasock uses Unix domain sockets, which are more secure because they are protected by file system permissions.

Input/output format and limitations

Programs that can be called through Viasock must

• accept input from STDIN,
• write output to STDOUT,
• output exactly one output record for each input record, and output it before it blocks waiting for the next input record.

Every record must end with \n (the line feed character). A record is a single line by default, but this can be configured with the -t and -T options.

The output may contain a number of extra records at the beginning which don’t correspond to any input records and should be repeated at the beginning of the output for every client. Specify the number of such “prelude” records using the -P option.

If the process does not follow the protocol properly, it may happen that viasock gets deadlocked after sending an input record, waiting for an output record that never comes. To fail more gracefully in such situations, specify a timeout using the -w option. This is the maximum number of seconds the process is allowed to take for sending the output record.

Run viasock run -h for help and details.

Getting involved

• Check out the list of issues or submit your own at https://github.com/texttheater/viasock/issues

Acknowledgments

The Viasock logo was designed by Valerio Basile.