Fix S3 scheme backwards compat

s3/client_test.go

@@ -52,6 +52,27 @@ func TestParseURL_EndpointHTTP(t *testing.T) {
 	require.True(t, cfg.PathStyle)
 }
 
+func TestParseURL_EndpointNoScheme(t *testing.T) {
+	// A bare host:port endpoint (no scheme) must default to https for backward compatibility.
+	// Without this, url.Parse treats the host as the scheme ("localhost:9000" -> scheme "localhost").
+	cfg, err := ParseURL("s3://AKID:SECRET@my-bucket?region=us-east-1&endpoint=localhost:9000")
+	require.Nil(t, err)
+	require.Equal(t, "https", cfg.Scheme)
+	require.Equal(t, "localhost:9000", cfg.Endpoint)
+	require.True(t, cfg.PathStyle)
+	require.Equal(t, "https://localhost:9000/my-bucket", cfg.BucketURL())
+}
+
+func TestParseURL_EndpointNoSchemeHostname(t *testing.T) {
+	// A dotted hostname with a port and no scheme must also default to https
+	// ("minio.example.com:9000" must not become scheme "minio.example.com").
+	cfg, err := ParseURL("s3://AKID:SECRET@my-bucket?region=us-east-1&endpoint=minio.example.com:9000")
+	require.Nil(t, err)
+	require.Equal(t, "https", cfg.Scheme)
+	require.Equal(t, "minio.example.com:9000", cfg.Endpoint)
+	require.Equal(t, "https://minio.example.com:9000/my-bucket", cfg.BucketURL())
+}
+
 func TestParseURL_EndpointTrailingSlash(t *testing.T) {
 	cfg, err := ParseURL("s3://AKID:SECRET@my-bucket?region=us-east-1&endpoint=https://s3.example.com/")
 	require.Nil(t, err)

s3/util.go

@@ -74,12 +74,13 @@ func ParseURL(s3URL string) (*Config, error) {
 	var endpoint string
 	var pathStyle bool
 	if endpointParam != "" {
-		// Custom endpoint: strip scheme prefix to extract host[:port]
-		uep, err := url.Parse(endpointParam)
-		if err != nil {
-			return nil, fmt.Errorf("s3: invalid endpoint URL: %w", err)
+		// Custom endpoint: derive the scheme from the prefix and strip it to extract host[:port].
+		// Default to https for backward compatibility, including bare "host:port" endpoints (no
+		// scheme) -- url.Parse would otherwise misread the host before the port colon as the scheme.
+		scheme = "https"
+		if strings.HasPrefix(endpointParam, "http://") {
+			scheme = "http"
 		}
-		scheme = uep.Scheme
 		ep := strings.TrimRight(endpointParam, "/")
 		ep = strings.TrimPrefix(ep, "https://")
 		ep = strings.TrimPrefix(ep, "http://")