Publish ITWorx Pulse source

cmd/agent/store.go

@@ -0,0 +1,70 @@
+package main
+
+import (
+	"context"
+	"errors"
+	"fmt"
+	"time"
+
+	"github.com/itworx/pulse/internal/agentstore"
+	"github.com/itworx/pulse/internal/database"
+	"github.com/itworx/pulse/internal/runtimeconfig"
+	"github.com/jackc/pgx/v5/pgxpool"
+)
+
+const (
+	// storeConnectTimeout bounds the start-up reachability check. The healthcheck
+	// contract wants the first heartbeat written after the database is reachable, so
+	// this must stay far below the 45 second staleness threshold.
+	storeConnectTimeout = 5 * time.Second
+	// agentPoolMaxConns keeps the agent's footprint on the shared database small: it
+	// issues one small write per capability per interval and never reads.
+	agentPoolMaxConns = 2
+)
+
+// errStoreNotLinked is returned by every write while no snapshot store implementation
+// is compiled into this binary. It is deliberately an error on the write path rather
+// than a silent drop: the reader turns a missing snapshot into Unknown, and the agent
+// log states plainly why nothing arrives.
+var errStoreNotLinked = errors.New("no agent snapshot store is linked into this build")
+
+// openStore connects to PostgreSQL and returns the narrow Writer the agent publishes
+// through, plus a close function.
+//
+// The agent depends on the agentstore.Writer interface only; the concrete PostgreSQL
+// store owns migration 0016 and the agent_snapshots table.
+func openStore(ctx context.Context, config runtimeconfig.AgentConfig) (agentstore.Writer, func(), error) {
+	pool, err := database.NewPool(ctx, database.Config{
+		URL:      config.DatabaseURL,
+		MaxConns: agentPoolMaxConns,
+		MinConns: 1,
+	})
+	if err != nil {
+		// Never wrap the URL itself into the error: it carries the database password.
+		return nil, nil, errors.New("agent database pool could not be created")
+	}
+	reachable, cancel := context.WithTimeout(ctx, storeConnectTimeout)
+	defer cancel()
+	if err := database.Ping(reachable, pool); err != nil {
+		pool.Close()
+		return nil, nil, fmt.Errorf("agent database is unreachable: %w", err)
+	}
+	writer, err := newSnapshotWriter(pool)
+	if err != nil {
+		pool.Close()
+		return nil, nil, err
+	}
+	return writer, pool.Close, nil
+}
+
+// newSnapshotWriter builds the store the agent writes through. A nil pool would make
+// every publish fail silently at the driver, so it is refused here instead: the agent
+// must either have a real store or fail to start.
+func newSnapshotWriter(pool *pgxpool.Pool) (agentstore.Writer, error) {
+	if pool == nil {
+		return nil, errStoreNotLinked
+	}
+	return agentstore.PostgresStore{Pool: pool}, nil
+}
+
+var _ agentstore.Writer = agentstore.PostgresStore{}