fix(whatsmeow): reuse pooled authDB connection in StartClient (fixes #175)

[wilsonborba]

Problem

StartClient calls sqlstore.New(ctx, "postgres", config.PostgresAuthDB, ...) on every invocation, opening a brand new *sql.DB connection pool each time. container.Close() is never called, so the old pool (and every connection it opened) is simply dropped.

StartClient is re-entered on:

• ReconnectClient, which calls StartInstance -> StartClient again
• the kill-channel branch of StartClient's own select loop, which unconditionally restarts on any kill signal
• every QR pairing attempt that ends in a restart

Each path leaks one unbounded connection pool. Reproduced locally against a real Postgres instance: 15 consecutive POST /instance/reconnect calls grew evogo_auth connections from a baseline of 2 to 32, exceeding the app's own SetMaxOpenConns(25) cap, which confirms the leaked connections come from a pool outside the one the app manages. In production this exhausts max_connections under normal instance create/reconnect activity, surfacing as pq: sorry, too many clients already and QR pairing timeouts.

Closes #175.

Fix

Reuse the already-pooled, bounded authDB *sql.DB (whatsmeowService already holds it as a field, configured once in config.CreateAuthDB with SetMaxOpenConns/SetMaxIdleConns/SetConnMaxLifetime/SetConnMaxIdleTime) via sqlstore.NewWithDB(w.authDB, "postgres", dbLog) instead of opening a new pool per call, then run container.Upgrade(ctx) explicitly since NewWithDB does not auto-upgrade like sqlstore.New does.

Falls back to the previous sqlstore.New behavior if authDB is unexpectedly nil (it should always be set when PostgresAuthDB is configured, see main.go), so this can't introduce a nil-pointer panic.

No changes to the SQLite fallback path.

Verification

Tested against a real Postgres 192.168.x LAN instance with an actual WhatsApp session paired via QR:

	Before fix	After fix
Baseline connections	2	2
After 15x /instance/reconnect	32 (exceeds pool cap of 25)	2
Session state after cycling	Connected: true, LoggedIn: true	Connected: true, LoggedIn: true

go build ./... passes on top of develop with the whatsmeow-lib submodule initialized.

Notes

This is the same root cause already reported/attempted in #102, #117, #131, #168 and #174. This PR takes the smaller-diff approach from #168/#174 (reuse w.authDB via NewWithDB rather than introducing a new package-level singleton container), and additionally guards against a nil authDB per the review feedback left on #174.

Summary by Sourcery

Prevent WhatsApp client restarts from leaking PostgreSQL connection pools by reusing the configured authentication database connection.

Bug Fixes:

• Reuse the existing bounded PostgreSQL authentication database pool across WhatsApp client restarts to prevent connection-pool leaks and database connection exhaustion.
• Preserve a safe fallback to per-call PostgreSQL initialization when the shared authentication database is unexpectedly unavailable.

Enhancements:

• Explicitly upgrade reused WhatsApp database containers while retaining the existing SQLite fallback path.

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Reviewer's Guide

This PR changes how the WhatsMeow service initializes its SQL container in StartClient so that it reuses the existing pooled Postgres authDB connection when available, ensuring upgrades are run explicitly and keeping logging behavior consistent across Postgres and SQLite paths while preserving a safe fallback to the previous behavior.

File-Level Changes

Change	Details	Files
Reuse the existing pooled Postgres authDB connection in StartClient instead of creating a new connection pool on each call, with an explicit container upgrade.	Introduce a shared dbLog variable so it can be reused for both Postgres and SQLite container initialization. When PostgresAuthDB is configured and authDB is non-nil, call sqlstore.NewWithDB with w.authDB, the postgres driver, and dbLog. After creating the container via NewWithDB, explicitly call container.Upgrade with a background context and log and return early on error. If PostgresAuthDB is configured but authDB is nil, fall back to the previous sqlstore.New-based behavior instead of panicking. Keep the SQLite path but switch it to use dbLog when WaDebug is enabled instead of passing nil, and remove the duplicated branching that mixed debug and backend selection.	pkg/whatsmeow/service/whatsmeow.go

Possibly linked issues

• Postgres connection pool leak on every StartClient/reconnect cycle #175: PR reuses w.authDB via sqlstore.NewWithDB in StartClient, fixing the Postgres connection pool leak described.
• Postgres connection pool leak on every StartClient/reconnect cycle #175: PR reuses the existing pooled authDB via sqlstore.NewWithDB in StartClient, preventing the reported Postgres pool leak.
• Postgres connection pool leak on every StartClient/reconnect cycle #175: PR reuses shared authDB via NewWithDB in StartClient, preventing new pools on reconnect and fixing the leak.

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