fix(whatsmeow): reuse pooled authDB connection in StartClient instead of leaking a new pool per call

[fmedeiros95]

Problem

StartClient (pkg/whatsmeow/service/whatsmeow.go) opens a brand new *sql.DB connection pool on every call, via:

container, err = sqlstore.New(context.Background(), "postgres", w.config.PostgresAuthDB, dbLog)

sqlstore.New internally does sql.Open(dialect, address) — a fresh, completely unbounded pool (no SetMaxOpenConns/SetMaxIdleConns/SetConnMaxLifetime), independent from the properly-configured GORM pool set up in pkg/config/config.go. The container variable is local to StartClient and is never closed (container.Close() is not called anywhere in the file), so every call leaks the entire underlying connection pool.

StartClient is called repeatedly during normal operation, not just once per process lifetime:

• on the LoggedOut event auto-restart (whatsmeow.go, "restart client")
• on CONNECT_ON_STARTUP
• when updating settings of an already-running instance
• on manual reconnect (POST /instance/connect) — note this path only calls client.Disconnect() on the old whatsmeow.Client, it never closes the old sqlstore.Container/pool before creating a new one

In production, with only a couple of WhatsApp instances reconnecting periodically (WhatsApp forces session logout for various reasons on its own, no user action required), this accumulated ~95 idle Postgres connections over about 2 days and exhausted max_connections, taking down the whole app with remaining connection slots are reserved for roles with the SUPERUSER attribute — including breaking evolution-go's own ability to open new connections, so instances got stuck in a reconnect-fail loop.

Fix

whatsmeowService already holds authDB *sql.DB — the same GORM-backed, properly pool-limited connection injected via NewWhatsmeowService. sqlstore exposes NewWithDB(db *sql.DB, dialect string, log) exactly for reusing an existing connection instead of opening a new one. This PR switches the Postgres branches of StartClient to:

container = sqlstore.NewWithDB(w.authDB, "postgres", dbLog)
err = container.Upgrade(context.Background())

NewWithDB doesn't run Upgrade automatically like New does, so the Upgrade call is made explicitly right after, preserving the original behavior (schema stays up to date) while reusing the bounded pool instead of leaking a new one per call.

The SQLite branches are untouched — w.sqliteDB wraps a different file (dbdata/users.db vs. the whatsmeow store's dbdata/main.db), so blindly reusing it there would point at the wrong database; fixing that path would need separate investigation and is out of scope for this fix.

Testing

• CGO_ENABLED=1 go build ./cmd/evolution-go — builds cleanly.
• Deployed the patched binary to a production instance (2 workspaces, Postgres-backed POSTGRES_AUTH_DB, max_connections=100 shared with other apps on the same server). Before the fix, pg_stat_activity showed the evolution role accumulating idle connections on every instance reconnect/restart, with recurring Failed to create container: failed to upgrade database: ... remaining connection slots are reserved for roles with the SUPERUSER attribute in the logs. After deploying the fix and restarting, idle connections for the evolution role stayed at 1-2 across multiple reconnect cycles, with no recurrence of the pool-exhaustion error.

Summary by Sourcery

Bug Fixes:

• Fix Postgres connection pool leaks caused by StartClient creating a new unbounded sql.DB on each invocation instead of reusing the shared authDB pool.

[sourcery-ai]

Reviewer's guide (collapsed on small PRs)

Reviewer's Guide

This PR changes StartClient to reuse the existing, bounded Postgres authDB connection pool instead of opening and leaking a new *sql.DB pool on every call, while preserving the automatic schema upgrade behavior; SQLite handling is left unchanged.

Sequence diagram for StartClient Postgres container initialization

sequenceDiagram
    participant caller
    participant whatsmeowService
    participant sqlstore
    participant Postgres

    caller->>whatsmeowService: StartClient(cd)
    alt PostgresAuthDB configured
        whatsmeowService->>sqlstore: NewWithDB(authDB, postgres, dbLog)
        sqlstore-->>whatsmeowService: container
        whatsmeowService->>sqlstore: container.Upgrade(context.Background)
        sqlstore->>Postgres: apply schema migrations using authDB pool
        sqlstore-->>whatsmeowService: upgrade result
    else SQLite
        whatsmeowService->>sqlstore: New(context.Background, sqlite, dsn, dbLog)
        sqlstore-->>whatsmeowService: container
    end

Loading

File-Level Changes

Change	Details	Files
Reuse the existing Postgres authDB *sql.DB pool in StartClient via sqlstore.NewWithDB and explicitly run Upgrade, fixing a severe connection leak.	Replace sqlstore.New(...) Postgres calls in StartClient with sqlstore.NewWithDB(w.authDB, "postgres", ...) so that the existing GORM-managed pool is used. Add explicit container.Upgrade(context.Background()) calls after NewWithDB because NewWithDB does not auto-run schema upgrades. Keep SQLite branches as-is, continuing to open a dedicated sqlstore container using a file-based DSN for dbdata/main.db.	pkg/whatsmeow/service/whatsmeow.go

Possibly linked issues

• #: PR replaces sqlstore.New with NewWithDB in StartClient, reusing the shared Postgres pool and stopping leaks.
• #(unknown): The PR changes StartClient to use sqlstore.NewWithDB(authDB), fixing the Postgres connection pool leak described.
• #(unknown): PR changes StartClient to use NewWithDB on w.authDB, fixing the Postgres pool leak described in the issue.

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[sourcery-ai]

Hey - I've left some high level feedback:

• Consider guarding the Postgres branches with a nil check on w.authDB so that NewWithDB doesn’t panic if the shared connection wasn’t initialized as expected.
• The explanatory comment added above the Postgres NewWithDB call is quite long and in Portuguese; you might shorten it and align the language with the rest of the codebase for consistency.

Prompt for AI Agents

Please address the comments from this code review:

## Overall Comments
- Consider guarding the Postgres branches with a nil check on `w.authDB` so that `NewWithDB` doesn’t panic if the shared connection wasn’t initialized as expected.
- The explanatory comment added above the Postgres `NewWithDB` call is quite long and in Portuguese; you might shorten it and align the language with the rest of the codebase for consistency.

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