Feature/custom errors

README.md

@@ -30,6 +30,7 @@
 	  - [Force HTTPS](#forcessl)
 	  - [Status](#status)
 	  - [Status Auth](#status-auth)
+	  - [Custom Error Responses](#custom-error-responses)
   - [Advanced](#advanced)
 	  - [JWT](#jwt)
 	  - [Streaming](#streaming)
@@ -444,6 +445,79 @@ func (u *Users) DeleteUser(w rest.ResponseWriter, r *rest.Request) {
 ```
 
 
+#### Custom Error Responses
+
+Demonstrate how to send custom error responses in go-json-rest
+
+curl demo:
+```sh
+curl -i http://127.0.0.1:8080/square/8675309
+```
+
+
+code:
+``` go
+package main
+
+import (
+	"./rest"
+	"log"
+	"net/http"
+	"strconv"
+)
+
+func MyCustomError(r *rest.Request, error string, code int) interface{} {
+	var header string
+	switch code {
+	case 400:
+		header = "Bad Input"
+		break
+	default:
+		header = "API Error"
+	}
+
+	// do whatever needed with the caught error
+	go log.Println("Error from", r.RemoteAddr, r.Method, r.URL)
+
+	return map[string]interface{}{
+		"error": map[string]interface{}{
+			"header":  header,
+			"code":    code,
+			"message": error,
+		},
+	}
+}
+
+func main() {
+	api := rest.NewApi()
+	api.Use(rest.DefaultDevStack...)
+	router, err := rest.MakeRouter(
+		rest.Get("/square/:number", Square),
+	)
+	if err != nil {
+		log.Fatal(err)
+	}
+
+	api.SetApp(router)
+	rest.ErrorFunc = MyCustomError
+
+	log.Fatal(http.ListenAndServe(":8081", api.MakeHandler()))
+}
+
+func Square(w rest.ResponseWriter, r *rest.Request) {
+	// parse 8-bit signed decimal
+	// -128 <= n <= 127
+	n, err := strconv.ParseInt(r.PathParam("number"), 10, 8)
+	if err != nil {
+		rest.ErrorWithRequest(r, w, err.Error(), http.StatusBadRequest)
+		return
+	}
+
+	w.WriteJson(n * n)
+}
+
+```
+
 ### Applications
 
 Common use cases, found in many applications.

rest/response.go

@@ -11,7 +11,6 @@ import (
 // Note, the responseWriter object instantiated by the framework also implements many other interfaces
 // accessible by type assertion: http.ResponseWriter, http.Flusher, http.CloseNotifier, http.Hijacker.
 type ResponseWriter interface {
-
 	// Identical to the http.ResponseWriter interface
 	Header() http.Header
 
@@ -34,12 +33,34 @@ type ResponseWriter interface {
 // eg: rest.ErrorFieldName = "errorMessage"
 var ErrorFieldName = "Error"
 
+// This allows to customize the error messages used in the error response payload.
+// It defaults to the ErrorFieldName method for compatibility reasons (only recieves error string and http code),
+// but can be changed before starting the server.
+//
+// Sends a json payload of the struct given. Be sure to define the json keys in the struct.
+// eg: rest.CustomErrorStruct = &MyCustomStruct{}
+var ErrorFunc func(*Request, string, int) interface{}
+
 // Error produces an error response in JSON with the following structure, '{"Error":"My error message"}'
 // The standard plain text net/http Error helper can still be called like this:
 // http.Error(w, "error message", code)
 func Error(w ResponseWriter, error string, code int) {
+	// Call new method to support backwards compat
+	ErrorWithRequest(nil, w, error, code)
+}
+
+// Error produces an error response in JSON with context of the request
+func ErrorWithRequest(r *Request, w ResponseWriter, error string, code int) {
 	w.WriteHeader(code)
-	err := w.WriteJson(map[string]string{ErrorFieldName: error})
+
+	var errPayload interface{}
+	if ErrorFunc != nil {
+		errPayload = ErrorFunc(r, error, code)
+	} else {
+		errPayload = map[string]string{ErrorFieldName: error}
+	}
+
+	err := w.WriteJson(errPayload)
 	if err != nil {
 		panic(err)
 	}

rest/response_test.go

@@ -6,6 +6,29 @@ import (
 	"github.com/ant0ine/go-json-rest/rest/test"
 )
 
+func CustomError(r *Request, error string, code int) interface{} {
+	// r = nil when using test requests
+	var header string
+	switch code {
+	case 400:
+		header = "Bad Input"
+		break
+	case 404:
+		header = "Not Found"
+		break
+	default:
+		header = "API Error"
+	}
+
+	return map[string]interface{}{
+		"error": map[string]interface{}{
+			"header":  header,
+			"code":    code,
+			"message": error,
+		},
+	}
+}
+
 func TestResponseNotIndent(t *testing.T) {
 
 	writer := responseWriter{
@@ -24,7 +47,7 @@ func TestResponseNotIndent(t *testing.T) {
 	}
 }
 
-// The following tests could instantiate only the reponseWriter,
+// The following tests could instantiate only the responseWriter,
 // but using the Api object allows to use the rest/test utilities,
 // and make the tests easier to write.
 
@@ -54,6 +77,24 @@ func TestErrorResponse(t *testing.T) {
 	recorded.BodyIs("{\"Error\":\"test\"}")
 }
 
+func TestCustomErrorResponse(t *testing.T) {
+
+	api := NewApi()
+	ErrorFunc = CustomError
+
+	api.SetApp(AppSimple(func(w ResponseWriter, r *Request) {
+		Error(w, "test", 500)
+	}))
+
+	recorded := test.RunRequest(t, api.MakeHandler(), test.MakeSimpleRequest("GET", "http://localhost/", nil))
+	recorded.CodeIs(500)
+	recorded.ContentTypeIsJson()
+	recorded.BodyIs(`{"error":{"code":500,"header":"API Error","message":"test"}}`)
+
+	// reset the package variable to not effect other tests
+	ErrorFunc = nil
+}
+
 func TestNotFoundResponse(t *testing.T) {
 
 	api := NewApi()
@@ -66,3 +107,21 @@ func TestNotFoundResponse(t *testing.T) {
 	recorded.ContentTypeIsJson()
 	recorded.BodyIs("{\"Error\":\"Resource not found\"}")
 }
+
+func TestCustomNotFoundResponse(t *testing.T) {
+
+	api := NewApi()
+	ErrorFunc = CustomError
+
+	api.SetApp(AppSimple(func(w ResponseWriter, r *Request) {
+		NotFound(w, r)
+	}))
+
+	recorded := test.RunRequest(t, api.MakeHandler(), test.MakeSimpleRequest("GET", "http://localhost/", nil))
+	recorded.CodeIs(404)
+	recorded.ContentTypeIsJson()
+	recorded.BodyIs(`{"error":{"code":404,"header":"Not Found","message":"Resource not found"}}`)
+
+	// reset the package variable to not effect other tests
+	ErrorFunc = nil
+}