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Msgfs
=====

Jeff Read <[email protected]>

Msgfs is a little proof of concept of a multicast publish-subscribe
bus that uses inotify to alert listening processes. It is not a file
system in its own right, but rather a protocol which uses the file
system to achieve a form of inter-process communication.

The protocol is as follows: To send a message, write to a file in a
directory that has msgfs listeners watching it via inotify, and then
close the file.

To receive messages, add an inotify watch to the directory with event
mask IN_CLOSE_WRITE with inotify_add_watch(2). When you receive an
event on this watch, it means a message has been sent; the file's
contents are the body of the message; you can open(2) the file and
read(2) or mmap(2) it to get at its contents.

A new file should be created (with UUIDs, mkstemp, or similar) for
every message sent. Senders are responsible for cleaning up the
messages they create (perhaps after a timeout).

Advantages
----------

1. Multicast-capable, publish-subscribe messaging. Unix permissions
determine who may send and who may receive messages on a particular
"bus".

2. Serialization-agnostic. Ship XML, JSON, text, binary, whatever you
like.

3. Message size limited by file size. Want to alert a group of
processes about a cool new lolcat JPEG? Send it as-is in a message!

4. Send messages with 'echo' :)

Drawbacks
---------

1. It's probably insecure as all get-out. Anyone with read access to
the msgfs message can see it; anyone with write access can clobber
existing messages before their intended consumers can open them in a
race condition, etc. DO NOT transmit sensitive information with this
version of msgfs. :)

2. The API presented in msgfs.h does not support asynchronous polling
for msgfs events.