app: return MethodNotAllowed for non-POST requests

Change-Id: I6053506d2eeac54e46f2ebd8a82e79121ff1da9b
Reviewed-on: https://go-review.googlesource.com/27076
Reviewed-by: Brad Fitzpatrick <bradfitz@golang.org>
diff --git a/app/goplay/compile.go b/app/goplay/compile.go
index f5bed89..499b505 100644
--- a/app/goplay/compile.go
+++ b/app/goplay/compile.go
@@ -20,6 +20,11 @@
 }
 
 func compile(w http.ResponseWriter, r *http.Request) {
+	if r.Method != "POST" {
+		code := http.StatusMethodNotAllowed
+		http.Error(w, http.StatusText(code), code)
+		return
+	}
 	if err := passThru(w, r); err != nil {
 		w.WriteHeader(http.StatusInternalServerError)
 		fmt.Fprintln(w, "Compile server error.")