URL encode username/password fields

Fixes #188.

cmd/postgres_exporter/postgres_exporter.go

@@ -1086,8 +1086,9 @@ func getDataSource() string {
 			pass = os.Getenv("DATA_SOURCE_PASS")
 		}
+		ui := url.UserPassword(user, pass).String()
 		uri := os.Getenv("DATA_SOURCE_URI")
-		dsn = "postgresql://" + user + ":" + pass + "@" + uri
+		dsn = "postgresql://" + ui + "@" + uri
 	}
 	return dsn

cmd/postgres_exporter/postgres_exporter_test.go

@@ -105,7 +105,7 @@ func (s *FunctionalSuite) TestEnvironmentSettingWithSecretsFiles(c *C) {
 	c.Assert(err, IsNil)
 	defer UnsetEnvironment(c, "DATA_SOURCE_URI")
-	var expected = "postgresql://custom_username:custom_password@localhost:5432/?sslmode=disable"
+	var expected = "postgresql://custom_username$&+,%2F%3A;=%3F%40:custom_password$&+,%2F%3A;=%3F%40@localhost:5432/?sslmode=disable"
 	dsn := getDataSource()
 	if dsn != expected {

cmd/postgres_exporter/tests/username_file

-custom_username
+custom_username$&+,/:;=?@

cmd/postgres_exporter/tests/userpass_file

-custom_password
+custom_password$&+,/:;=?@