support error templates for text/xml (#3392)

(cherry picked from commit d88e9a5)

gateway/handler_error.go

@@ -70,6 +70,9 @@ func (e *ErrorHandler) HandleError(w http.ResponseWriter, r *http.Request, errMs
 		case headers.ApplicationXML:
 			templateExtension = "xml"
 			contentType = headers.ApplicationXML
+		case headers.TextXML:
+			templateExtension = "xml"
+			contentType = headers.TextXML
 		default:
 			templateExtension = "json"
 			contentType = headers.ApplicationJSON

gateway/handler_error_test.go

@@ -0,0 +1,53 @@
+package gateway
+
+import (
+	"bytes"
+	"io/ioutil"
+	"net/http"
+	"net/http/httptest"
+	"os"
+	"path/filepath"
+	"strings"
+	"testing"
+
+	"github.com/TykTechnologies/tyk/config"
+	"github.com/TykTechnologies/tyk/headers"
+	"github.com/TykTechnologies/tyk/test"
+)
+
+func TestHandleError_text_xml(t *testing.T) {
+	file := filepath.Join(config.Global().TemplatePath, "error_500.xml")
+	xml := `<error>
+	<code>500</code>
+	<message>{{.Message}}</message>
+</error>`
+	err := ioutil.WriteFile(file, []byte(xml), 0600)
+	if err != nil {
+		t.Fatal(err)
+	}
+	defer os.Remove(file)
+	expect := `
+<error>
+	<code>500</code>
+	<message>There was a problem proxying the request</message>
+</error>
+	`
+	ts := StartTest()
+	defer ts.Close()
+	h := httptest.NewServer(http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {}))
+	h.Close()
+	BuildAndLoadAPI(func(spec *APISpec) {
+		spec.Proxy.ListenPath = "/"
+		spec.Proxy.TargetURL = ts.URL
+	})
+	ts.Run(t, test.TestCase{
+		Path: "/",
+		Code: http.StatusInternalServerError,
+		Headers: map[string]string{
+			headers.ContentType: headers.TextXML,
+		},
+		BodyMatchFunc: func(b []byte) bool {
+			return strings.TrimSpace(expect) == string(bytes.TrimSpace(b))
+		},
+	})
+}

headers/headers.go

@@ -20,6 +20,7 @@ const (
 	TykHookshot     = "Tyk-Hookshot"
 	ApplicationJSON = "application/json"
 	ApplicationXML  = "application/xml"
+	TextXML         = "text/xml"
 )
 
 const (