nghttpx: Remember which resource is pushed

Remember which resource is pushed in order to conform to the semantics
described in RFC 8297.

src/shrpx_downstream.h

@@ -32,6 +32,7 @@
 #include <string>
 #include <memory>
 #include <chrono>
+#include <algorithm>
 
 #include <ev.h>
 
@@ -207,7 +208,40 @@ struct Response {
     unconsumed_body_length -= len;
   }
 
+  // returns true if a resource denoted by scheme, authority, and path
+  // has already been pushed.
+  bool is_resource_pushed(const StringRef &scheme, const StringRef &authority,
+                          const StringRef &path) const {
+    if (!pushed_resources) {
+      return false;
+    }
+    return std::find(std::begin(*pushed_resources), std::end(*pushed_resources),
+                     std::make_tuple(scheme, authority, path)) !=
+           std::end(*pushed_resources);
+  }
+
+  // remember that a resource denoted by scheme, authority, and path
+  // is pushed.
+  void resource_pushed(const StringRef &scheme, const StringRef &authority,
+                       const StringRef &path) {
+    if (!pushed_resources) {
+      pushed_resources = make_unique<
+          std::vector<std::tuple<StringRef, StringRef, StringRef>>>();
+    }
+    pushed_resources->emplace_back(scheme, authority, path);
+  }
+
   FieldStore fs;
+  // array of the tuple of scheme, authority, and path of pushed
+  // resource.  This is required because RFC 8297 says that server
+  // typically includes header fields appeared in non-final response
+  // header fields in final response header fields.  Without checking
+  // that a particular resource has already been pushed, or not, we
+  // end up pushing the same resource at least twice.  It is unknown
+  // that we should use more complex data structure (e.g., std::set)
+  // to find the resources faster.
+  std::unique_ptr<std::vector<std::tuple<StringRef, StringRef, StringRef>>>
+      pushed_resources;
   // the length of response body received so far
   int64_t recv_body_length;
   // The number of bytes not consumed by the application yet.  This is

src/shrpx_http2_upstream.cc

@@ -2039,7 +2039,7 @@ int Http2Upstream::prepare_push_promise(Downstream *downstream) {
   int rv;
 
   const auto &req = downstream->request();
-  const auto &resp = downstream->response();
+  auto &resp = downstream->response();
 
   auto base = http2::get_pure_path_component(req.path);
   if (base.empty()) {
@@ -2069,10 +2069,16 @@ int Http2Upstream::prepare_push_promise(Downstream *downstream) {
         authority = req.authority;
       }
 
+      if (resp.is_resource_pushed(scheme, authority, path)) {
+        continue;
+      }
+
       rv = submit_push_promise(scheme, authority, path, downstream);
       if (rv != 0) {
         return -1;
       }
+
+      resp.resource_pushed(scheme, authority, path);
     }
   }
   return 0;
@@ -2182,12 +2188,20 @@ int Http2Upstream::initiate_push(Downstream *downstream, const StringRef &uri) {
     authority = req.authority;
   }
 
+  auto &resp = downstream->response();
+
+  if (resp.is_resource_pushed(scheme, authority, path)) {
+    return 0;
+  }
+
   rv = submit_push_promise(scheme, authority, path, downstream);
 
   if (rv != 0) {
     return -1;
   }
 
+  resp.resource_pushed(scheme, authority, path);
+
   return 0;
 }