pkg: move cors.go to /pkg/cors.go

pkg/cors.go

@@ -0,0 +1,93 @@
+/*
+Copyright 2013 CoreOS Inc.
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+     http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+*/
+
+package pkg
+
+import (
+	"fmt"
+	"net/http"
+	"net/url"
+	"strings"
+)
+
+type CORSInfo map[string]bool
+
+// CORSInfo implements the flag.Value interface to allow users to define a list of CORS origins
+func (ci *CORSInfo) Set(s string) error {
+	m := make(map[string]bool)
+	for _, v := range strings.Split(s, ",") {
+		v = strings.TrimSpace(v)
+		if v == "" {
+			continue
+		}
+		if v != "*" {
+			if _, err := url.Parse(v); err != nil {
+				return fmt.Errorf("Invalid CORS origin: %s", err)
+			}
+		}
+		m[v] = true
+
+	}
+	*ci = CORSInfo(m)
+	return nil
+}
+
+func (ci *CORSInfo) String() string {
+	o := make([]string, 0)
+	for k, _ := range *ci {
+		o = append(o, k)
+	}
+	return strings.Join(o, ",")
+}
+
+// OriginAllowed determines whether the server will allow a given CORS origin.
+func (c CORSInfo) OriginAllowed(origin string) bool {
+	return c["*"] || c[origin]
+}
+
+type CORSHandler struct {
+	Handler http.Handler
+	Info    *CORSInfo
+}
+
+// addHeader adds the correct cors headers given an origin
+func (h *CORSHandler) addHeader(w http.ResponseWriter, origin string) {
+	w.Header().Add("Access-Control-Allow-Methods", "POST, GET, OPTIONS, PUT, DELETE")
+	w.Header().Add("Access-Control-Allow-Origin", origin)
+	w.Header().Add("Access-Control-Allow-Headers", "accept, content-type")
+}
+
+// ServeHTTP adds the correct CORS headers based on the origin and returns immediately
+// with a 200 OK if the method is OPTIONS.
+func (h *CORSHandler) ServeHTTP(w http.ResponseWriter, req *http.Request) {
+	// It is important to flush before leaving the goroutine.
+	// Or it may miss the latest info written.
+	defer w.(http.Flusher).Flush()
+
+	// Write CORS header.
+	if h.Info.OriginAllowed("*") {
+		h.addHeader(w, "*")
+	} else if origin := req.Header.Get("Origin"); h.Info.OriginAllowed(origin) {
+		h.addHeader(w, origin)
+	}
+
+	if req.Method == "OPTIONS" {
+		w.WriteHeader(http.StatusOK)
+		return
+	}
+
+	h.Handler.ServeHTTP(w, req)
+}