Fix panic on parsing DSN with trailing '='

Also correctly return error with leading '='.

fixes #47

config.go

@@ -497,7 +497,8 @@ func parseDSNSettings(s string) (map[string]string, error) {
 
 		key = strings.Trim(s[:eqIdx], " \t\n\r\v\f")
 		s = strings.TrimLeft(s[eqIdx+1:], " \t\n\r\v\f")
-		if s[0] != '\'' {
+		if len(s) == 0 {
+		} else if s[0] != '\'' {
 			end := 0
 			for ; end < len(s); end++ {
 				if asciiSpace[s[end]] == 1 {
@@ -539,6 +540,10 @@ func parseDSNSettings(s string) (map[string]string, error) {
 			key = k
 		}
 
+		if key == "" {
+			return nil, errors.New("invalid dsn")
+		}
+
 		settings[key] = val
 	}
 

config_test.go

@@ -528,6 +528,17 @@ func TestParseConfig(t *testing.T) {
 	}
 }
 
+// https://github.com/jackc/pgconn/issues/47
+func TestParseConfigDSNWithTrailingEmptyEqualDoesNotPanic(t *testing.T) {
+	_, err := pgconn.ParseConfig("host= user= password= port= database=")
+	require.NoError(t, err)
+}
+
+func TestParseConfigDSNLeadingEqual(t *testing.T) {
+	_, err := pgconn.ParseConfig("= user=jack")
+	require.Error(t, err)
+}
+
 func TestConfigCopyReturnsEqualConfig(t *testing.T) {
 	connString := "postgres://jack:secret@localhost:5432/mydb?application_name=pgxtest&search_path=myschema&connect_timeout=5"
 	original, err := pgconn.ParseConfig(connString)