http: Support non-JSON handlers

2 files changed, 58 insertions, 34 deletions

diff --git a/http/http.go b/http/http.go
index 8a219dc..d547010 100644
--- a/http/http.go
+++ b/http/http.go
@@ -2,6 +2,7 @@ package http
 
 import (
 	"context"
+	"encoding/json"
 	"fmt"
 	"log"
 	"net"
@@ -15,6 +16,10 @@ import (
 	"github.com/mpolden/zdns/sql"
 )
 
+const (
+	jsonMediaType = "application/json"
+)
+
 // A Server defines paramaters for running an HTTP server. The HTTP server serves an API for inspecting cache contents
 // and request log.
 type Server struct {
@@ -130,10 +135,22 @@ func resolutionFrom(r *http.Request) (time.Duration, error) {
 	return time.ParseDuration(param)
 }
 
-func (s *Server) cacheHandler(w http.ResponseWriter, r *http.Request) (interface{}, *httpError) {
+func writeJSONHeader(w http.ResponseWriter) { w.Header().Set("Content-Type", jsonMediaType) }
+
+func writeJSON(w http.ResponseWriter, data interface{}) {
+	b, err := json.Marshal(data)
+	if err != nil {
+		panic(err)
+	}
+	writeJSONHeader(w)
+	w.Write(b)
+}
+
+func (s *Server) cacheHandler(w http.ResponseWriter, r *http.Request) *httpError {
 	count, err := countFrom(r)
 	if err != nil {
-		return nil, newHTTPBadRequest(err)
+		writeJSONHeader(w)
+		return newHTTPBadRequest(err)
 	}
 	cacheValues := s.cache.List(count)
 	entries := make([]entry, 0, len(cacheValues))
@@ -147,24 +164,28 @@ func (s *Server) cacheHandler(w http.ResponseWriter, r *http.Request) (interface
 			Rcode:    dnsutil.RcodeToString[v.Rcode()],
 		})
 	}
-	return entries, nil
+	writeJSON(w, entries)
+	return nil
 }
 
-func (s *Server) cacheResetHandler(w http.ResponseWriter, r *http.Request) (interface{}, *httpError) {
+func (s *Server) cacheResetHandler(w http.ResponseWriter, r *http.Request) *httpError {
 	s.cache.Reset()
-	return struct {
+	writeJSON(w, struct {
 		Message string `json:"message"`
-	}{"Cleared cache."}, nil
+	}{"Cleared cache."})
+	return nil
 }
 
-func (s *Server) logHandler(w http.ResponseWriter, r *http.Request) (interface{}, *httpError) {
+func (s *Server) logHandler(w http.ResponseWriter, r *http.Request) *httpError {
 	count, err := countFrom(r)
 	if err != nil {
-		return nil, newHTTPBadRequest(err)
+		writeJSONHeader(w)
+		return newHTTPBadRequest(err)
 	}
 	logEntries, err := s.logger.Read(count)
 	if err != nil {
-		return nil, newHTTPError(err)
+		writeJSONHeader(w)
+		return newHTTPError(err)
 	}
 	entries := make([]entry, 0, len(logEntries))
 	for _, le := range logEntries {
@@ -178,17 +199,20 @@ func (s *Server) logHandler(w http.ResponseWriter, r *http.Request) (interface{}
 			Answers:    le.Answers,
 		})
 	}
-	return entries, nil
+	writeJSON(w, entries)
+	return nil
 }
 
-func (s *Server) basicMetricHandler(w http.ResponseWriter, r *http.Request) (interface{}, *httpError) {
+func (s *Server) basicMetricHandler(w http.ResponseWriter, r *http.Request) *httpError {
 	resolution, err := resolutionFrom(r)
 	if err != nil {
-		return nil, newHTTPBadRequest(err)
+		writeJSONHeader(w)
+		return newHTTPBadRequest(err)
 	}
 	lstats, err := s.logger.Stats(resolution)
 	if err != nil {
-		return nil, newHTTPError(err)
+		writeJSONHeader(w)
+		return newHTTPError(err)
 	}
 	requests := make([]request, 0, len(lstats.Events))
 	for _, e := range lstats.Events {
@@ -202,7 +226,7 @@ func (s *Server) basicMetricHandler(w http.ResponseWriter, r *http.Request) (int
 	if s.sqlCache != nil {
 		bstats = &backendStats{PendingTasks: s.sqlCache.Stats().PendingTasks}
 	}
-	return stats{
+	stats := stats{
 		Summary: summary{
 			Log: logStats{
 				Since:    lstats.Since.Format(time.RFC3339),
@@ -217,10 +241,12 @@ func (s *Server) basicMetricHandler(w http.ResponseWriter, r *http.Request) (int
 			},
 		},
 		Requests: requests,
-	}, nil
+	}
+	writeJSON(w, stats)
+	return nil
 }
 
-func (s *Server) metricHandler(w http.ResponseWriter, r *http.Request) (interface{}, *httpError) {
+func (s *Server) metricHandler(w http.ResponseWriter, r *http.Request) *httpError {
 	format := ""
 	if formatParams := r.URL.Query()["format"]; len(formatParams) > 0 {
 		format = formatParams[0]
@@ -229,7 +255,8 @@ func (s *Server) metricHandler(w http.ResponseWriter, r *http.Request) (interfac
 	case "", "basic":
 		return s.basicMetricHandler(w, r)
 	}
-	return nil, newHTTPBadRequest(fmt.Errorf("invalid metric format: %s", format))
+	writeJSONHeader(w)
+	return newHTTPBadRequest(fmt.Errorf("invalid metric format: %s", format))
 }
 
 // Close shuts down the HTTP server.
diff --git a/http/router.go b/http/router.go
index 27adc33..2e6b77b 100644
--- a/http/router.go
+++ b/http/router.go
@@ -15,32 +15,29 @@ type route struct {
 	handler appHandler
 }
 
-type appHandler func(http.ResponseWriter, *http.Request) (interface{}, *httpError)
+type appHandler func(http.ResponseWriter, *http.Request) *httpError
 
 func (fn appHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
-	data, e := fn(w, r)
-	w.Header().Set("Content-Type", "application/json")
-	if e != nil { // e is *Error, not os.Error.
+	if e := fn(w, r); e != nil { // e is *httpError, not os.Error.
 		if e.Message == "" {
 			e.Message = e.err.Error()
 		}
-		out, err := json.Marshal(e)
-		if err != nil {
-			panic(err)
-		}
 		w.WriteHeader(e.Status)
-		w.Write(out)
-	} else if data != nil {
-		out, err := json.Marshal(data)
-		if err != nil {
-			panic(err)
+		if w.Header().Get("Content-Type") == jsonMediaType {
+			out, err := json.Marshal(e)
+			if err != nil {
+				panic(err)
+			}
+			w.Write(out)
+		} else {
+			w.Write([]byte(e.Message))
 		}
-		w.Write(out)
 	}
 }
 
-func notFoundHandler(w http.ResponseWriter, r *http.Request) (interface{}, *httpError) {
-	return nil, &httpError{
+func notFoundHandler(w http.ResponseWriter, r *http.Request) *httpError {
+	writeJSONHeader(w)
+	return &httpError{
 		Status:  http.StatusNotFound,
 		Message: "Resource not found",
 	}
@@ -57,7 +54,7 @@ func (r *router) route(method, path string, handler appHandler) *route {
 }
 
 func (r *router) handler() http.Handler {
-	return appHandler(func(w http.ResponseWriter, req *http.Request) (interface{}, *httpError) {
+	return appHandler(func(w http.ResponseWriter, req *http.Request) *httpError {
 		for _, route := range r.routes {
 			if route.match(req) {
 				return route.handler(w, req)