fix(httputil): improve error handling

Errors are now returned in the best matching format for the
HTTP Accept header.

cmd/manager/router/router.go

@@ -31,6 +31,7 @@ package router
 import (
 	"log"
 	"net/http"
+	"reflect"
 
 	"github.com/Masterminds/httputil"
 	helmhttp "github.com/kubernetes/helm/pkg/httputil"
@@ -68,6 +69,7 @@ func NewHandler(c *Context) *Handler {
 //
 // The route name is "VERB /ENPOINT/PATH", e.g. "GET /foo".
 func (h *Handler) Add(route string, fn HandlerFunc) {
+	log.Printf("Map %q to %s", route, reflect.ValueOf(fn).Type().Name())
 	h.routes[route] = fn
 	h.paths = append(h.paths, route)
 	h.resolver = httputil.NewResolver(h.paths)
@@ -84,6 +86,7 @@ func (h *Handler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 
 	fn, ok := h.routes[route]
 	if !ok {
+		// This is a 500 because the route was registered, but not here.
 		helmhttp.Fatal(w, r, "route %s missing", route)
 	}
 

pkg/httputil/encoder.go

@@ -28,6 +28,9 @@ import (
 	"github.com/ghodss/yaml"
 )
 
+// DefaultEncoder is an *AcceptEncoder with the default application/json encoding.
+var DefaultEncoder = &AcceptEncoder{DefaultEncoding: "application/json"}
+
 // Encoder takes input and translate it to an expected encoded output.
 //
 // Implementations of encoders may use details of the HTTP request and response
@@ -40,7 +43,9 @@ type Encoder interface {
 	//
 	// When an encoder fails, it logs any necessary data and then responds to
 	// the client.
-	Encode(http.ResponseWriter, *http.Request, interface{})
+	//
+	// The integer must be a valid http.Status* status code.
+	Encode(http.ResponseWriter, *http.Request, interface{}, int)
 }
 
 // AcceptEncoder uses the accept headers on a request to determine the response type.
@@ -56,7 +61,7 @@ type AcceptEncoder struct {
 }
 
 // Encode encodeds the given interface to the first available type in the Accept header.
-func (e *AcceptEncoder) Encode(w http.ResponseWriter, r *http.Request, out interface{}) {
+func (e *AcceptEncoder) Encode(w http.ResponseWriter, r *http.Request, out interface{}, statusCode int) {
 	a := r.Header.Get("accept")
 	fn := encoders[e.DefaultEncoding]
 	mt := e.DefaultEncoding
@@ -70,6 +75,7 @@ func (e *AcceptEncoder) Encode(w http.ResponseWriter, r *http.Request, out inter
 		return
 	}
 	w.Header().Add("content-type", mt)
+	w.WriteHeader(statusCode)
 	w.Write(data)
 }
 

pkg/httputil/encoder_test.go

@@ -77,7 +77,7 @@ func TestAcceptEncoder(t *testing.T) {
 		DefaultEncoding: "application/json",
 	}
 	fn := func(w http.ResponseWriter, r *http.Request) {
-		enc.Encode(w, r, []string{"hello", "world"})
+		enc.Encode(w, r, []string{"hello", "world"}, http.StatusOK)
 	}
 	s := httptest.NewServer(http.HandlerFunc(fn))
 	defer s.Close()

pkg/httputil/httperrors.go

@@ -30,27 +30,46 @@ const (
 	// LogFatal is for logging 500 errors. Form: Internal Server Error r.Method r.URL message
 	LogFatal = "Internal Server Error: %s %s %s"
 	// LogBadRequest logs 400 errors.
-	LogBadRequest = "Bad Request: %s %s"
+	LogBadRequest = "Bad Request: %s %s %s"
 )
 
+// Error represents an HTTP error that can be converted to structured types.
+//
+// For example, and error can be serialized to JSON or YAML. Likewise, the
+// string marshal can convert it to a string.
+type Error struct {
+	Msg    string `json:"message, omitempty"`
+	Status string `json:"status"`
+}
+
+// Error implements the error interface.
+func (e *Error) Error() string {
+	return fmt.Sprintf("%s: %s", e.Status, e.Msg)
+}
+
 // NotFound writes a 404 error to the client and logs an error.
 func NotFound(w http.ResponseWriter, r *http.Request) {
-	log.Printf(LogNotFound, r.Method, r.URL)
-	w.WriteHeader(http.StatusNotFound)
-	fmt.Fprintln(w, "File Not Found")
+	msg := fmt.Sprintf(LogNotFound, r.Method, r.URL)
+	log.Println(msg)
+	writeErr(w, r, msg, http.StatusNotFound)
+}
+
+// BadRequest writes an HTTP 400.
+func BadRequest(w http.ResponseWriter, r *http.Request, err error) {
+	log.Printf(LogBadRequest, r.Method, r.URL, err)
+	writeErr(w, r, err.Error(), http.StatusBadRequest)
 }
 
-func BadRequest(w http.ResponseWriter, r *http.Request) {
-	log.Printf(LogNotFound, r.Method, r.URL)
-	w.WriteHeader(http.StatusBadRequest)
-	fmt.Fprintln(w, "Bad Request")
+// writeErr formats and writes the error using the default encoder.
+func writeErr(w http.ResponseWriter, r *http.Request, msg string, status int) {
+	DefaultEncoder.Encode(w, r, &Error{Status: http.StatusText(status), Msg: msg}, status)
 }
 
 // Fatal writes a 500 response to the client and logs the message.
 //
 // Additional arguments are past into the the formatter as params to msg.
 func Fatal(w http.ResponseWriter, r *http.Request, msg string, v ...interface{}) {
-	log.Printf(LogFatal, r.Method, r.URL, fmt.Sprintf(msg, v...))
-	w.WriteHeader(http.StatusInternalServerError)
-	fmt.Fprintln(w, "Internal Server Error")
+	m := fmt.Sprintf(msg, v...)
+	log.Printf(LogFatal, r.Method, r.URL, m)
+	writeErr(w, r, m, http.StatusInternalServerError)
 }