nghttpx: Fix bug that server push from mruby script did not work

src/shrpx_http2_upstream.cc

@@ -1893,7 +1893,8 @@ bool Http2Upstream::push_enabled() const {
 int Http2Upstream::initiate_push(Downstream *downstream, const StringRef &uri) {
   int rv;
 
-  if (uri.empty() || !push_enabled() || (downstream->get_stream_id() % 2)) {
+  if (uri.empty() || !push_enabled() ||
+      (downstream->get_stream_id() % 2) == 0) {
     return 0;
   }
 

src/shrpx_upstream.h

@@ -68,6 +68,9 @@ public:
   virtual int send_reply(Downstream *downstream, const uint8_t *body,
                          size_t bodylen) = 0;
 
+  // Starts server push.  The |downstream| is an associated stream for
+  // the pushed resource.  This function returns 0 if it succeeds,
+  // otherwise -1.
   virtual int initiate_push(Downstream *downstream, const StringRef &uri) = 0;
 
   // Fills response data in |iov| whose capacity is |iovcnt|.  Returns