Do not reject unexpected content types during upload creation

See tus/tus-java-client#10

post_test.go

@@ -201,10 +201,16 @@ func TestPostWithUpload(t *testing.T) {
 		Method: "POST",
 		ReqHeader: map[string]string{
 			"Tus-Resumable":   "1.0.0",
+			"Upload-Length":   "300",
+			"Upload-Metadata": "foo aGVsbG8=, bar d29ybGQ=",
 			"Content-Type":    "application/false",
 		},
 		ReqBody: strings.NewReader("hello"),
-		Code:    http.StatusBadRequest,
+		Code:    http.StatusCreated,
+		ResHeader: map[string]string{
+			"Location":      "http://tus.io/files/foo",
+			"Upload-Offset": "",
+		},
 	}).Run(handler, t)
 
 	(&httpTest{

unrouted_handler.go

@@ -190,15 +190,10 @@ func (handler *UnroutedHandler) Middleware(h http.Handler) http.Handler {
 // PostFile creates a new file upload using the datastore after validating the
 // length and parsing the metadata.
 func (handler *UnroutedHandler) PostFile(w http.ResponseWriter, r *http.Request) {
-	// Check for presence of application/offset+octet-stream
-	containsChunk := false
-	if contentType := r.Header.Get("Content-Type"); contentType != "" {
-		if contentType != "application/offset+octet-stream" {
-			handler.sendError(w, r, ErrInvalidContentType)
-			return
-		}
-		containsChunk = true
-	}
+	// Check for presence of application/offset+octet-stream. If another content
+	// type is defined, it will be ignored and treated as none was set because
+	// some HTTP clients may enforce a default value for this header.
+	containsChunk := r.Header.Get("Content-Type") == "application/offset+octet-stream"
 
 	// Only use the proper Upload-Concat header if the concatenation extension
 	// is even supported by the data store.