From 8a56c9fa0c32d370ba5b599f98868d3f41a2b86f Mon Sep 17 00:00:00 2001
From: CoolCoolTomato <2983315455@qq.com>
Date: Fri, 5 Jun 2026 20:48:04 +0800
Subject: [PATCH] fix(setup): bootstrap postgres connection with maintenance db

---
 backend/internal/setup/setup.go      | 25 +++++++++++++++----------
 backend/internal/setup/setup_test.go | 23 +++++++++++++++++++++++
 2 files changed, 38 insertions(+), 10 deletions(-)

diff --git a/backend/internal/setup/setup.go b/backend/internal/setup/setup.go
index 9256d24575..51baf3dfe6 100644
--- a/backend/internal/setup/setup.go
+++ b/backend/internal/setup/setup.go
@@ -160,13 +160,23 @@ func NeedsSetup() bool {
 	return true
 }
 
+func buildPostgresDSN(cfg *DatabaseConfig, dbName string) string {
+	return fmt.Sprintf(
+		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
+		cfg.Host, cfg.Port, cfg.User, cfg.Password, dbName, cfg.SSLMode,
+	)
+}
+
+func buildDatabaseConnectionDSNs(cfg *DatabaseConfig) (bootstrapDSN, targetDSN string) {
+	return buildPostgresDSN(cfg, "postgres"), buildPostgresDSN(cfg, cfg.DBName)
+}
+
 // TestDatabaseConnection tests the database connection and creates database if not exists
 func TestDatabaseConnection(cfg *DatabaseConfig) error {
-	// First, connect to the default 'postgres' database to check/create target database
-	defaultDSN := fmt.Sprintf(
-		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
-		cfg.Host, cfg.Port, cfg.User, cfg.Password, cfg.DBName, cfg.SSLMode,
-	)
+	// First, connect to the default 'postgres' database to check/create target database.
+	// Connecting to cfg.DBName here fails when the target database has not been
+	// created yet, so the bootstrap connection must use PostgreSQL's maintenance DB.
+	defaultDSN, targetDSN := buildDatabaseConnectionDSNs(cfg)
 
 	db, err := sql.Open("postgres", defaultDSN)
 	if err != nil {
@@ -214,11 +224,6 @@ func TestDatabaseConnection(cfg *DatabaseConfig) error {
 	}
 	db = nil
 
-	targetDSN := fmt.Sprintf(
-		"host=%s port=%d user=%s password=%s dbname=%s sslmode=%s",
-		cfg.Host, cfg.Port, cfg.User, cfg.Password, cfg.DBName, cfg.SSLMode,
-	)
-
 	targetDB, err := sql.Open("postgres", targetDSN)
 	if err != nil {
 		return fmt.Errorf("failed to connect to database '%s': %w", cfg.DBName, err)
diff --git a/backend/internal/setup/setup_test.go b/backend/internal/setup/setup_test.go
index a01dd00c4d..a2aa2f4cc1 100644
--- a/backend/internal/setup/setup_test.go
+++ b/backend/internal/setup/setup_test.go
@@ -87,3 +87,26 @@ func TestWriteConfigFileKeepsDefaultUserConcurrency(t *testing.T) {
 		t.Fatalf("config missing default user concurrency, got:\n%s", string(data))
 	}
 }
+
+func TestBuildDatabaseConnectionDSNsUsesPostgresForBootstrap(t *testing.T) {
+	cfg := &DatabaseConfig{
+		Host:     "db",
+		Port:     5432,
+		User:     "sub2api",
+		Password: "secret",
+		DBName:   "sub2api",
+		SSLMode:  "disable",
+	}
+
+	bootstrapDSN, targetDSN := buildDatabaseConnectionDSNs(cfg)
+
+	if !strings.Contains(bootstrapDSN, "dbname=postgres") {
+		t.Fatalf("bootstrap DSN = %q, want default postgres database", bootstrapDSN)
+	}
+	if strings.Contains(bootstrapDSN, "dbname=sub2api") {
+		t.Fatalf("bootstrap DSN = %q, should not connect to target database before checking/creating it", bootstrapDSN)
+	}
+	if !strings.Contains(targetDSN, "dbname=sub2api") {
+		t.Fatalf("target DSN = %q, want configured database", targetDSN)
+	}
+}