IPC: support sending config and dependent files

[indutny]

n/t

[odeke-em]

Quoting from @indutny:
Bud has a master->workers architecture. Each worker has a pipe shared with master (the pipe is technically a socketpair()). The master sends IPC messages on this pipe, which are usually just a one-byte kBudIPCBalance messages. However this channel may (and should) be used for transferring the config file and the keys too, and this is a blocker for a stdin configuration file.

Here is a relevant header file and some lines of it:

https://github.com/indutny/bud/blob/master/src/ipc.h#L25-L29

So, on a technical note, what needs to be performed (at least this how I see it):

Master sends some files on which the JSON configuration does depend (like keys, certs).
Worker stores them in some hashmap in memory
Master sends the configuration file itself
Worker loads it and, instead of loading files from disc, loads files from that hashmap (see config.c for all details)

[indutny]

I think it is done now.

[odeke-em]

👍 good stuff.