feat: add application_name_add_host setting

[Nihal-Pandey-2302]

Closes #253

What

Adds application_name_add_host setting to [general] config, matching PgBouncer's behavior.

When enabled, PgDog appends the client's IP address and port to the
application_name parameter when connecting to the backend. This makes
it easy to trace which client is behind which backend connection in
pg_stat_activity.

Example: myapp becomes myapp (192.168.1.5:54321)

Behavior

• Disabled by default (false)
• Only applied at connection start, not on subsequent SET application_name commands
• Silently skipped if peer address is unavailable (e.g. Unix sockets)

Config

[general]
application_name_add_host = true

Changes

• pgdog-config/src/general.rs -> added application_name_add_host: bool field to General struct
• src/frontend/client/query_engine/connect.rs -> appends client addr to application_name before link_client is called

[CLAassistant]

All committers have signed the CLA.

[codecov]

Codecov Report

❌ Patch coverage is 37.50000% with 10 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
pgdog/src/frontend/client/query_engine/connect.rs	33.33%	10 Missing ⚠️

📢 Thoughts on this report? Let us know!

[levkk]

If you want to replicate pgbouncer behavior, I would recommend handling it here:

pgdog/pgdog/src/frontend/listener.rs

Line 172 in b9fb98f

let startup = match Startup::from_stream(&mut stream).await {

The config is already available and you can mutate the params, i.e., if application_name is indeed in the startup params, you can add the peer_addr() there once.

Your current implementation will actually update the application_name with the IP address even if the client uses SET. This is probably how we want it to work actually; I find pgbouncer's implementation arbitrarily limited (probably because they don't parse / handle SET statements).

If we go with this, I would recommend handling this here:

pgdog/pgdog/src/frontend/client/mod.rs

Line 520 in b9fb98f

let config = config::config();

and only doing this operation if it hasn't been done before; this avoids unnecessary allocations (format! creates a new string).