database: add FormatDSN

Signed-off-by: Vasiliy Tolstov <v.tolstov@unistack.org>

database/dsn.go

@@ -15,7 +15,6 @@ var (
 )
 
 type Config struct {
-	Params    map[string]string
 	TLSConfig *tls.Config
 	Username  string
 	Password  string
@@ -23,6 +22,50 @@ type Config struct {
 	Host      string
 	Port      string
 	Database  string
+	Params    []string
+}
+
+func (cfg *Config) FormatDSN() string {
+	var s strings.Builder
+
+	if len(cfg.Scheme) > 0 {
+		s.WriteString(cfg.Scheme + "://")
+	}
+	// [username[:password]@]
+	if len(cfg.Username) > 0 {
+		s.WriteString(cfg.Username)
+		if len(cfg.Password) > 0 {
+			s.WriteByte(':')
+			s.WriteString(url.PathEscape(cfg.Password))
+		}
+		s.WriteByte('@')
+	}
+
+	// [host:port]
+	if len(cfg.Host) > 0 {
+		s.WriteString(cfg.Host)
+		if len(cfg.Port) > 0 {
+			s.WriteByte(':')
+			s.WriteString(cfg.Port)
+		}
+	}
+
+	// /dbname
+	s.WriteByte('/')
+	s.WriteString(url.PathEscape(cfg.Database))
+
+	for i := 0; i < len(cfg.Params); i += 2 {
+		if i == 0 {
+			s.WriteString("?")
+		} else {
+			s.WriteString("&")
+		}
+		s.WriteString(cfg.Params[i])
+		s.WriteString("=")
+		s.WriteString(cfg.Params[i+1])
+	}
+
+	return s.String()
 }
 
 func ParseDSN(dsn string) (*Config, error) {
@@ -84,13 +127,13 @@ func ParseDSN(dsn string) (*Config, error) {
 			for j = i + 1; j < len(dsn); j++ {
 				if dsn[j] == '?' {
 					parts := strings.Split(dsn[j+1:], "&")
-					cfg.Params = make(map[string]string, len(parts))
+					cfg.Params = make([]string, 0, len(parts)*2)
 					for _, p := range parts {
 						k, v, found := strings.Cut(p, "=")
 						if !found {
 							continue
 						}
-						cfg.Params[k] = v
+						cfg.Params = append(cfg.Params, k, v)
 					}
 
 					break

database/dsn_test.go

@@ -1,6 +1,7 @@
 package database
 
 import (
+	"net/url"
 	"testing"
 )
 
@@ -13,3 +14,18 @@ func TestParseDSN(t *testing.T) {
 		t.Fatalf("parsing error")
 	}
 }
+
+func TestFormatDSN(t *testing.T) {
+	src := "postgres://username:p@ssword#@host:12345/dbname?key1=val2&key2=val2"
+	cfg, err := ParseDSN(src)
+	if err != nil {
+		t.Fatal(err)
+	}
+	dst, err := url.PathUnescape(cfg.FormatDSN())
+	if err != nil {
+		t.Fatal(err)
+	}
+	if src != dst {
+		t.Fatalf("\n%s\n%s", src, dst)
+	}
+}