registry: improve error for invalid search endpoints

Explain that search is not supported on v2 endpoints, and include the
offending endpoint in the error-message.

Signed-off-by: Sebastiaan van Stijn <github@gone.nl>

registry/endpoint_test.go

@@ -42,7 +42,7 @@ func TestV1EndpointParse(t *testing.T) {
 		},
 		{
 			address:     "https://0.0.0.0:5000/v2/",
-			expectedErr: "unsupported V1 version path v2",
+			expectedErr: "search is not supported on v2 endpoints: https://0.0.0.0:5000/v2/",
 		},
 	}
 	for _, tc := range tests {

registry/endpoint_v1.go

@@ -87,7 +87,7 @@ func validateEndpoint(endpoint *v1Endpoint) error {
 func trimV1Address(address string) (string, error) {
 	trimmed := strings.TrimSuffix(address, "/")
 	if strings.HasSuffix(trimmed, "/v2") {
-		return "", invalidParamf("unsupported V1 version path v2")
+		return "", invalidParamf("search is not supported on v2 endpoints: %s", address)
 	}
 	return strings.TrimSuffix(trimmed, "/v1"), nil
 }