handlers: Add 'crossdomain.xml' handler. (#2305)

Fixes #2301

crossdomain-xml-handler.go

@@ -0,0 +1,49 @@
+/*
+ * Minio Cloud Storage, (C) 2016 Minio, 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 main
+
+import "net/http"
+
+// Standard cross domain policy information located at https://s3.amazonaws.com/crossdomain.xml
+var crossDomainXML = `<?xml version="1.0"?><!DOCTYPE cross-domain-policy SYSTEM "http://www.adobe.com/xml/dtds/cross-domain-policy.dtd"><cross-domain-policy><allow-access-from domain="*" secure="false" /></cross-domain-policy>`
+
+// Cross domain policy implements http.Handler interface, implementing a custom ServerHTTP.
+type crossDomainPolicy struct {
+	handler http.Handler
+}
+
+// A cross-domain policy file is an XML document that grants a web client, such as Adobe Flash Player
+// or Adobe Acrobat (though not necessarily limited to these), permission to handle data across domains.
+// When clients request content hosted on a particular source domain and that content make requests
+// directed towards a domain other than its own, the remote domain needs to host a cross-domain
+// policy file that grants access to the source domain, allowing the client to continue the transaction.
+func setCrossDomainPolicy(h http.Handler) http.Handler {
+	return crossDomainPolicy{handler: h}
+}
+
+func (c crossDomainPolicy) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Look for 'crossdomain.xml' in the incoming request.
+	switch r.URL.Path {
+	case "/crossdomain.xml":
+		// Write the standard cross domain policy xml.
+		w.Write([]byte(crossDomainXML))
+		// Request completed, no need to serve to other handlers.
+		return
+	}
+	// Continue to serve the request further.
+	c.handler.ServeHTTP(w, r)
+}

routers.go

@@ -71,8 +71,9 @@ func configureServerHandler(srvCmdConfig serverCmdConfig) http.Handler {
 	var handlerFns = []HandlerFunc{
 		// Limits the number of concurrent http requests.
 		setRateLimitHandler,
-		// Redirect some pre-defined browser request paths to a static
-		// location prefix.
+		// Adds 'crossdomain.xml' policy handler to serve legacy flash clients.
+		setCrossDomainPolicy,
+		// Redirect some pre-defined browser request paths to a static location prefix.
 		setBrowserRedirectHandler,
 		// Validates if incoming request is for restricted buckets.
 		setPrivateBucketHandler,