PoC: Add mozc_client_cli

[kou]

Description

Add a CLI client command.

This is for decoupling third party Mozc clients such as uim and Fcitx5.

Mozc doesn't provide a client library. So third party Mozc clients can't be implemented without bundling Mozc. If we provide a CLI client command, third party Mozc clients can be implemented out of Mozc source.

This just:

1. accepts mozc.commands.Input as input from stdin,
2. sends the input to mozc_server as-is,
3. receives mozc.commands.Output as output from mozc_server and
4. outputs the output to stdout.

This may convert the protobuf binary format to/from something such as JSON Lines. This PoC just implements JSON Lines input/output. (No the protobuf binary format support.)

mozc_emacs_helper manages a client pool but this doesn't manage a client pool. If users need it, they must spawn multiple mozc_client_cli processes by themselves.

If there is any input error, mozc_client_cli exits with non-0 (1 in this implementation). Users can get error message from stderr.

Issue IDs

#1362 (comment) as a related discussion.

Steps to test new behaviors (if any)

A clear and concise description about how to verify new behaviors (if any).

• OS: Debian GNU/Linux sid
• Steps:
  1. bazelisk build package --config oss_linux --config release_build
  2. bazel-bin/unix/cli/mozc_client_cli
  3. Input mozc.commands.Input as JSON Lines to stdin

Example:

$ bazel-bin/unix/cli/mozc_client_cli
{"type": "GET_CONFIG"}
{"id":"0",...(GET_CONFIG response in JSON)}
{"type": "CREATE_SESSION"}
{"id":"1968337769025405287"}
^D
$

$ bazel-bin/unix/cli/mozc_client_cli
"X"
Failed to parse an input JSON as mozc.commands.Input: <"X">: INVALID_ARGUMENT: invalid JSON in mozc.commands.Input, near 1:1 (offset 0): unexpected character: '"'; expected '{'
$ echo $?
1

Additional context

This is just a PoC to discuss this direction.