From 1beeba379ec0364d6a5a4cfd59a992c4bc40ce16 Mon Sep 17 00:00:00 2001
From: Jaglyser <joelwblomster@gmail.com>
Date: Thu, 6 Nov 2025 10:39:48 +0100
Subject: [PATCH] Added dynamic port allocation, GetPort helper, and test

---
 embedded_postgres.go      | 28 +++++++++++++++++++++
 embedded_postgres_test.go | 52 +++++++++++++++++++++++++++++++++++++++
 2 files changed, 80 insertions(+)

diff --git a/embedded_postgres.go b/embedded_postgres.go
index afe8497..cff0132 100644
--- a/embedded_postgres.go
+++ b/embedded_postgres.go
@@ -71,6 +71,15 @@ func (ep *EmbeddedPostgres) Start() error {
 		return ErrServerAlreadyStarted
 	}
 
+	if ep.config.port == 0 {
+		port, err := getFreePort()
+		if err != nil {
+			return err
+		}
+
+		ep.config.port = port
+	}
+
 	if err := ensurePortAvailable(ep.config.port); err != nil {
 		return err
 	}
@@ -147,6 +156,10 @@ func (ep *EmbeddedPostgres) Start() error {
 	return nil
 }
 
+func (ep *EmbeddedPostgres) GetPort() uint32 {
+	return ep.config.port
+}
+
 func (ep *EmbeddedPostgres) downloadAndExtractBinary(cacheExists bool, cacheLocation string) error {
 	// lock to prevent collisions with duplicate downloads
 	mu.Lock()
@@ -254,6 +267,21 @@ func ensurePortAvailable(port uint32) error {
 	return nil
 }
 
+func getFreePort() (uint32, error) {
+	addr, err := net.ResolveTCPAddr("tcp", "localhost:0")
+	if err != nil {
+		return 0, fmt.Errorf("failed to resolve TCP address: %w", err)
+	}
+
+	l, err := net.ListenTCP("tcp", addr)
+	if err != nil {
+		return 0, fmt.Errorf("failed to listen on TCP: %w", err)
+	}
+	defer l.Close()
+
+	return uint32(l.Addr().(*net.TCPAddr).Port), nil
+}
+
 func dataDirIsValid(dataDir string, version PostgresVersion) bool {
 	pgVersion := filepath.Join(dataDir, "PG_VERSION")
 
diff --git a/embedded_postgres_test.go b/embedded_postgres_test.go
index 6429a89..bead4d3 100644
--- a/embedded_postgres_test.go
+++ b/embedded_postgres_test.go
@@ -833,3 +833,55 @@ func Test_RunningInParallel(t *testing.T) {
 
 	waitGroup.Wait()
 }
+
+func Test_DynamicallyAllocatingPort(t *testing.T) {
+	tempDir, err := os.MkdirTemp("", "embedded_postgres_test")
+	if err != nil {
+		panic(err)
+	}
+
+	defer func() {
+		if err := os.RemoveAll(tempDir); err != nil {
+			panic(err)
+		}
+	}()
+
+	database := NewDatabase(DefaultConfig().
+		Username("gin").
+		Password("wine").
+		Database("beer").
+		Version(V15).
+		RuntimePath(tempDir).
+		Port(0).
+		StartTimeout(10 * time.Second).
+		Locale("C").
+		Encoding("UTF8").
+		Logger(nil))
+
+	if err := database.Start(); err != nil {
+		shutdownDBAndFail(t, err, database)
+	}
+
+	port := database.GetPort()
+
+	db, err := sql.Open("postgres", fmt.Sprintf("host=localhost port=%d user=gin password=wine dbname=beer sslmode=disable", port))
+	if err != nil {
+		shutdownDBAndFail(t, err, database)
+	}
+
+	if !strings.Contains(database.config.GetConnectionURL(), fmt.Sprint(port)) {
+		shutdownDBAndFail(t, errors.New("wrong port in connection url"), database)
+	}
+
+	if err = db.Ping(); err != nil {
+		shutdownDBAndFail(t, err, database)
+	}
+
+	if err := db.Close(); err != nil {
+		shutdownDBAndFail(t, err, database)
+	}
+
+	if err := database.Stop(); err != nil {
+		shutdownDBAndFail(t, err, database)
+	}
+}