weldr: Return a JSON API error response for all unknown requests

This matches the lorax-composer behavior.

internal/client/client_test.go

@@ -29,10 +29,10 @@ func TestRequest(t *testing.T) {
 		t.Fatalf("Request bad route: %d != 404", resp.StatusCode)
 	}
 
-	// Test that apiError returns an error when trying to parse non-JSON response
+	// Test that apiError returns an error response
 	_, err = apiError(resp)
-	if err == nil {
+	if err != nil {
-		t.Fatalf("apiError of a 404 response did not return an error: %#v", resp)
+		t.Fatalf("apiError could not parse the response: %s", err)
 	}
 
 	// Make a request with a bad offset to trigger a JSON response with Status set to 400

internal/weldr/api.go

@@ -167,7 +167,12 @@ func methodNotAllowedHandler(writer http.ResponseWriter, request *http.Request)
 }
 
 func notFoundHandler(writer http.ResponseWriter, request *http.Request) {
-	writer.WriteHeader(http.StatusNotFound)
+	errors := responseError{
+		Code: http.StatusNotFound,
+		ID:   "HTTPError",
+		Msg:  "Not Found",
+	}
+	statusResponseError(writer, http.StatusNotFound, errors)
 }
 
 func notImplementedHandler(writer http.ResponseWriter, httpRequest *http.Request, _ httprouter.Params) {

internal/weldr/api_test.go

@@ -51,7 +51,7 @@ func TestBasic(t *testing.T) {
 
 		{"/api/v0/projects/source/list", http.StatusOK, `{"sources":["test-id"]}`},
 
-		{"/api/v0/projects/source/info", http.StatusNotFound, ``},
+		{"/api/v0/projects/source/info", http.StatusNotFound, `{"errors":[{"code":404,"id":"HTTPError","msg":"Not Found"}],"status":false}`},
 		{"/api/v0/projects/source/info/", http.StatusNotFound, `{"errors":[{"code":404,"id":"HTTPError","msg":"Not Found"}],"status":false}`},
 		{"/api/v0/projects/source/info/foo", http.StatusOK, `{"errors":[{"id":"UnknownSource","msg":"foo is not a valid source"}],"sources":{}}`},
 		{"/api/v0/projects/source/info/test-id", http.StatusOK, `{"sources":{"test-id":{"name":"test-id","type":"yum-baseurl","url":"http://example.com/test/os/x86_64","check_gpg":true,"check_ssl":true,"system":true}},"errors":[]}`},