properly respect file flag for protoc-gen-swagger

protoc-gen-swagger/main.go

@@ -16,7 +16,7 @@ import (
 
 var (
 	importPrefix = flag.String("import_prefix", "", "prefix to be added to go package paths for imported proto files")
-	file         = flag.String("file", "stdin", "where to load data from")
+	file         = flag.String("file", "-", "where to load data from")
 )
 
 func parseReq(r io.Reader) (*plugin.CodeGeneratorRequest, error) {
@@ -43,8 +43,11 @@ func main() {
 
 	glog.V(1).Info("Processing code generator request")
 	f := os.Stdin
-	if *file != "stdin" {
-		f, _ = os.Open("input.txt")
+	if *file != "-" {
+		f, err := os.Open(*file)
+		if err != nil {
+			glog.Fatal(err)
+		}
 	}
 	req, err := parseReq(f)
 	if err != nil {