client_master_handshake.md

Client/Master/Command handshake

 Client    Master    Command
1  ---------->                | Command, Arguments, Pid
2  ---------->                | Terminal IO
3            ----------->     | Terminal IO
4            ----------->     | Arguments, Pid
5            <-----------     | pid
6  <---------                 | pid
       (time passes)
7            <-----------     | exit status
8  <---------                 | exit status

1. Command & Arguments (Client -> Master)

The Master always has a UNIX domain server listening at a known socket path.

The Client connects to this server and sends a string indicating the command to run and any arguments to run with (ie. the ARGV). See message_format.md for more info.

2. Terminal IO (Client -> Master)

The Client then sends an IO over the server socket to be used for raw terminal IO.

3. Arguments (Master -> Command)

The Master sends the Client arguments from step 1 to the Command.

4. Terminal IO (Master -> Command)

The Master forks a new Command process and sends it the Terminal IO from the Client.

5. Pid (Command -> Master)

The Command process sends the Master its pid, using a Pid & Identifier message.

6. Pid (Master -> Client)

The Master responds to the client with the pid of the newly-forked Command process.

The Client is now connected to the Command process.

7. Exit status (Command -> Master)

When the command terminates, it must send its exit code to the master. This is normally easiest to implement as a wrapper process that does the setsid, then forks the command and waitpids on it.

The form of this message is {{code}}, eg: 1.

8. Exit status (Master -> Client)

Finally, the Master forwards the exit status to the Client. The command cycle is now complete.

The form of this message is {{code}}, eg: 1.

See message_format.md for more information on messages.