add "show help" command

[sebastianwebber]

Hey Everyone, I'm new to Rust and this is an attempt to implement the show help command.

Currently, it has a bug in the package that I'm trying to figure out:

❯ PGPASSWORD=postgres psql -h 127.0.0.1 -p 6432 -U postgres pgbouncer -c 'show help'; NOTICE: Console usage DETAIL:	SHOW HELP|CONFIG|DATABASES|POOLS|CLIENTS|SERVERS|USERS|VERSION	SHOW LISTS	SHOW STATS	SET key = arg	RELOAD	PAUSE [<db>, <user>]	RESUME [<db>, <user>]	SHUTDOWN message contents do not agree with length in message type "N" SHOW 

I've understood that pgcat is a replacement for pgbouncer, so I copied the help in the same format as pgbouncer does in admin.c.

Currently trying to figure what is the cause of the error below:

message contents do not agree with length in message type "N" 

[levkk]

Subtract one (-1). The length of the message does not include the message identifier (N).

[sebastianwebber]

when chaging to +3, like this:

diff --git a/src/messages.rs b/src/messages.rs index cb3b595..b1cd3f9 100644 --- a/src/messages.rs +++ b/src/messages.rs @@ -541,7 +541,7 @@ pub fn notify(message: &str, details: String) -> BytesMut { let mut res = BytesMut::new(); res.put_u8(b'N'); - res.put_i32(notify_cmd.len() as i32 + 4); + res.put_i32(notify_cmd.len() as i32 + 3); res.put(notify_cmd); res 

it drops the connection:

 ❯ PGPASSWORD=postgres psql -h 127.0.0.1 -p 6432 -U postgres pgbouncer -c 'show help'; NOTICE: Console usage DETAIL:	SHOW HELP|CONFIG|DATABASES|POOLS|CLIENTS|SERVERS|USERS|VERSION	SHOW LISTS	SHOW STATS	SET key = arg	RELOAD	PAUSE [<db>, <user>]	RESUME [<db>, <user>]	SHUTDOWN message contents do not agree with length in message type "N" lost synchronization with server: got message type " connection to server was lost 

[sebastianwebber]

From the log:

[2023-07-13T20:43:36.328145Z WARN pgcat] Client disconnected with error SocketError("Error reading message code from socket - Error Kind(UnexpectedEof)") 

[levkk]

Ah nevermind, it must be something else. From the looks of it, your implementation seems correct.

[sebastianwebber]

do you have any idea how to troubleshoot this?

[levkk]

Ahh! I think there is a missing NULL byte. This is how we format the error message (same format as notice): https://github.com/postgresml/pgcat/blob/main/src/messages.rs#L357-L358

[sebastianwebber]

It worked! 💪

I've rebased and added a better commit message.

Is there anything else that you need me to change?

[levkk]

looks great!