Custom Error Pages (#1675)

* custom error pages

middlewares/error_pages.go

@@ -0,0 +1,77 @@
+package middlewares
+
+import (
+	"net/http"
+	"strconv"
+	"strings"
+
+	"github.com/containous/traefik/log"
+	"github.com/containous/traefik/types"
+	"github.com/vulcand/oxy/forward"
+	"github.com/vulcand/oxy/utils"
+)
+
+//ErrorPagesHandler is a middleware that provides the custom error pages
+type ErrorPagesHandler struct {
+	HTTPCodeRanges     [][2]int
+	BackendURL         string
+	errorPageForwarder *forward.Forwarder
+}
+
+//NewErrorPagesHandler initializes the utils.ErrorHandler for the custom error pages
+func NewErrorPagesHandler(errorPage types.ErrorPage, backendURL string) (*ErrorPagesHandler, error) {
+	fwd, err := forward.New()
+	if err != nil {
+		return nil, err
+	}
+
+	//Break out the http status code ranges into a low int and high int
+	//for ease of use at runtime
+	var blocks [][2]int
+	for _, block := range errorPage.Status {
+		codes := strings.Split(block, "-")
+		//if only a single HTTP code was configured, assume the best and create the correct configuration on the user's behalf
+		if len(codes) == 1 {
+			codes = append(codes, codes[0])
+		}
+		lowCode, err := strconv.Atoi(codes[0])
+		if err != nil {
+			return nil, err
+		}
+		highCode, err := strconv.Atoi(codes[1])
+		if err != nil {
+			return nil, err
+		}
+		blocks = append(blocks, [2]int{lowCode, highCode})
+	}
+	return &ErrorPagesHandler{
+			HTTPCodeRanges:     blocks,
+			BackendURL:         backendURL + errorPage.Query,
+			errorPageForwarder: fwd},
+		nil
+}
+
+func (ep *ErrorPagesHandler) ServeHTTP(w http.ResponseWriter, req *http.Request, next http.HandlerFunc) {
+	recorder := newRetryResponseRecorder()
+	recorder.responseWriter = w
+	next.ServeHTTP(recorder, req)
+
+	w.WriteHeader(recorder.Code)
+	//check the recorder code against the configured http status code ranges
+	for _, block := range ep.HTTPCodeRanges {
+		if recorder.Code >= block[0] && recorder.Code <= block[1] {
+			log.Errorf("Caught HTTP Status Code %d, returning error page", recorder.Code)
+			finalURL := strings.Replace(ep.BackendURL, "{status}", strconv.Itoa(recorder.Code), -1)
+			if newReq, err := http.NewRequest(http.MethodGet, finalURL, nil); err != nil {
+				w.Write([]byte(http.StatusText(recorder.Code)))
+			} else {
+				ep.errorPageForwarder.ServeHTTP(w, newReq)
+			}
+			return
+		}
+	}
+
+	//did not catch a configured status code so proceed with the request
+	utils.CopyHeaders(w.Header(), recorder.Header())
+	w.Write(recorder.Body.Bytes())
+}