Add support of JSON API via network socket

[ligurio]

Currently, unreliablefs supports a single interface of setting fault injections - plain text file with INI-style configuration options. It would be quite convenient to have yet another interface with access via network socket and JSON API.

New command-line option

Add a new option socket that allows to specify a path to a control UNIX socket.
Mount with socket:

$ unreliablefs /tmp/fs -base_dir=/tmp -seed=1618680646 -socket=/tmp/unreliablefs.socket

JSON API:

JSON API has the same keywords as used in a configuration file.

# Show current fault-injections:
$ cat /tmp/unreliablefs.socket
{ "err-injections":[] }
...
# Set an error injection with `noop`:
$ echo '{ "err-injections": [ {"name": "errinj_noop", "path_regexp": "", "op_regexp": "", "probability": 5 } ] }' >  /tmp/unreliablefs.socket
...
# Set two error injections: `errinj_kill_caller` and `errinj_errno`:
$ echo '{ "err-injections":[ { "name": "errinj_kill_caller", "path_regexp": "" }, { "name": "errinj_errno", "path_regexp": "" } ] }' >  /tmp/unreliablefs.socket
...
# Cleanup all fault-injections:
$ echo '{ "err-injections": [] }' >  /tmp/unreliablefs.socket

Setting options using jo(1):

$ jo err_injections[]=$(jo name=errinj_errno) err_injections[]=$(jo name=errinj_noop)
{"err_injections":[{"name":"errinj_errno"},{"name":"errinj_noop"}]}
$ jo err_injections[]=$(jo name=errinj_errno) err_injections[]=$(jo name=errinj_noop) > /tmp/unreliablefs.socket

References

• https://en.wikipedia.org/wiki/JSON-RPC
• Specification: https://www.jsonrpc.org/specification
• toda API: https://github.com/chaos-mesh/toda/tree/master/config-examples
• JSON library to be considered:
  • https://github.com/hmng/jsonrpc-c
  • https://github.com/json-c/json-c/tree/json-c-0.16
  • https://github.com/DaveGamble/cJSON
  • https://github.com/udp/json-parser