http2: track memory allocated by nghttp2

Provide a custom memory allocator for nghttp2, and track
memory allocated by the library with it.

This makes the used-memory-per-session estimate more
accurate, and allows us to track memory leaks either
in nghttp2 itself or, more likely, through faulty
usage on our end.

It also allows us to make the per-session memory limit
more accurate in the future; currently, we are not
handling this in an ideal way, and instead let nghttp2
allocate what it wants, even if that goes over our limit.

Backport-PR-URL: #22850
PR-URL: #21374
Refs: #21373
Refs: #21336
Reviewed-By: James M Snell <[email protected]>
Reviewed-By: Anatoli Papirovski <[email protected]>
Reviewed-By: Tiancheng "Timothy" Gu <[email protected]>

src/node_http2.cc

@@ -486,6 +486,92 @@ Http2Session::Callbacks::~Callbacks() {
   nghttp2_session_callbacks_del(callbacks);
 }
 
+// Track memory allocated by nghttp2 using a custom allocator.
+class Http2Session::MemoryAllocatorInfo {
+ public:
+  explicit MemoryAllocatorInfo(Http2Session* session)
+      : info({ session, H2Malloc, H2Free, H2Calloc, H2Realloc }) {}
+
+  static void* H2Malloc(size_t size, void* user_data) {
+    return H2Realloc(nullptr, size, user_data);
+  }
+
+  static void* H2Calloc(size_t nmemb, size_t size, void* user_data) {
+    size_t real_size = MultiplyWithOverflowCheck(nmemb, size);
+    void* mem = H2Malloc(real_size, user_data);
+    if (mem != nullptr)
+      memset(mem, 0, real_size);
+    return mem;
+  }
+
+  static void H2Free(void* ptr, void* user_data) {
+    if (ptr == nullptr) return;  // free(null); happens quite often.
+    void* result = H2Realloc(ptr, 0, user_data);
+    CHECK_EQ(result, nullptr);
+  }
+
+  static void* H2Realloc(void* ptr, size_t size, void* user_data) {
+    Http2Session* session = static_cast<Http2Session*>(user_data);
+    size_t previous_size = 0;
+    char* original_ptr = nullptr;
+
+    // We prepend each allocated buffer with a size_t containing the full
+    // size of the allocation.
+    if (size > 0) size += sizeof(size_t);
+
+    if (ptr != nullptr) {
+      // We are free()ing or re-allocating.
+      original_ptr = static_cast<char*>(ptr) - sizeof(size_t);
+      previous_size = *reinterpret_cast<size_t*>(original_ptr);
+      // This means we called StopTracking() on this pointer before.
+      if (previous_size == 0) {
+        // Fall back to the standard Realloc() function.
+        char* ret = UncheckedRealloc(original_ptr, size);
+        if (ret != nullptr)
+          ret += sizeof(size_t);
+        return ret;
+      }
+    }
+    CHECK_GE(session->current_nghttp2_memory_, previous_size);
+
+    // TODO(addaleax): Add the following, and handle NGHTTP2_ERR_NOMEM properly
+    // everywhere:
+    //
+    // if (size > previous_size &&
+    //     !session->IsAvailableSessionMemory(size - previous_size)) {
+    //  return nullptr;
+    //}
+
+    char* mem = UncheckedRealloc(original_ptr, size);
+
+    if (mem != nullptr) {
+      // Adjust the memory info counter.
+      session->current_nghttp2_memory_ += size - previous_size;
+      *reinterpret_cast<size_t*>(mem) = size;
+      mem += sizeof(size_t);
+    } else if (size == 0) {
+      session->current_nghttp2_memory_ -= previous_size;
+    }
+
+    return mem;
+  }
+
+  static void StopTracking(Http2Session* session, void* ptr) {
+    size_t* original_ptr = reinterpret_cast<size_t*>(
+        static_cast<char*>(ptr) - sizeof(size_t));
+    session->current_nghttp2_memory_ -= *original_ptr;
+    *original_ptr = 0;
+  }
+
+  inline nghttp2_mem* operator*() { return &info; }
+
+  nghttp2_mem info;
+};
+
+void Http2Session::StopTrackingRcbuf(nghttp2_rcbuf* buf) {
+  MemoryAllocatorInfo::StopTracking(this, buf);
+}
+
 Http2Session::Http2Session(Environment* env,
                            Local<Object> wrap,
                            nghttp2_session_type type)
@@ -517,15 +603,17 @@ Http2Session::Http2Session(Environment* env,
       = callback_struct_saved[hasGetPaddingCallback ? 1 : 0].callbacks;
 
   auto fn = type == NGHTTP2_SESSION_SERVER ?
-      nghttp2_session_server_new2 :
-      nghttp2_session_client_new2;
+      nghttp2_session_server_new3 :
+      nghttp2_session_client_new3;
+
+  MemoryAllocatorInfo allocator_info(this);
 
   // This should fail only if the system is out of memory, which
   // is going to cause lots of other problems anyway, or if any
   // of the options are out of acceptable range, which we should
   // be catching before it gets this far. Either way, crash if this
   // fails.
-  CHECK_EQ(fn(&session_, callbacks, this, *opts), 0);
+  CHECK_EQ(fn(&session_, callbacks, this, *opts, *allocator_info), 0);
 
   outgoing_storage_.reserve(4096);
   outgoing_buffers_.reserve(32);
@@ -553,6 +641,7 @@ Http2Session::~Http2Session() {
   Unconsume();
   DEBUG_HTTP2SESSION(this, "freeing nghttp2 session");
   nghttp2_session_del(session_);
+  CHECK_EQ(current_nghttp2_memory_, 0);
 }
 
 inline bool HasHttp2Observer(Environment* env) {
@@ -1160,9 +1249,9 @@ inline void Http2Session::HandleHeadersFrame(const nghttp2_frame* frame) {
       nghttp2_header item = headers[n++];
       // The header name and value are passed as external one-byte strings
       name_str =
-          ExternalHeader::New<true>(env(), item.name).ToLocalChecked();
+          ExternalHeader::New<true>(this, item.name).ToLocalChecked();
       value_str =
-          ExternalHeader::New<false>(env(), item.value).ToLocalChecked();
+          ExternalHeader::New<false>(this, item.value).ToLocalChecked();
       argv[j * 2] = name_str;
       argv[j * 2 + 1] = value_str;
       j++;

src/node_http2.h

@@ -797,6 +797,7 @@ class Http2Session : public AsyncWrap {
 
   class Http2Ping;
   class Http2Settings;
+  class MemoryAllocatorInfo;
 
   inline void EmitStatistics();
 
@@ -934,13 +935,15 @@ class Http2Session : public AsyncWrap {
     current_session_memory_ -= amount;
   }
 
-  // Returns the current session memory including the current size of both
-  // the inflate and deflate hpack headers, the current outbound storage
-  // queue, and pending writes.
+  // Tell our custom memory allocator that this rcbuf is independent of
+  // this session now, and may outlive it.
+  void StopTrackingRcbuf(nghttp2_rcbuf* buf);
+
+  // Returns the current session memory including memory allocated by nghttp2,
+  // the current outbound storage queue, and pending writes.
   uint64_t GetCurrentSessionMemory() {
     uint64_t total = current_session_memory_ + sizeof(Http2Session);
-    total += nghttp2_session_get_hd_deflate_dynamic_table_size(session_);
-    total += nghttp2_session_get_hd_inflate_dynamic_table_size(session_);
+    total += current_nghttp2_memory_;
     total += outgoing_storage_.size();
     return total;
   }
@@ -1072,6 +1075,8 @@ class Http2Session : public AsyncWrap {
   // The maximum amount of memory allocated for this session
   uint64_t max_session_memory_ = DEFAULT_MAX_SESSION_MEMORY;
   uint64_t current_session_memory_ = 0;
+  // The amount of memory allocated by nghttp2 internals
+  uint64_t current_nghttp2_memory_ = 0;
 
   // The collection of active Http2Streams associated with this session
   std::unordered_map<int32_t, Http2Stream*> streams_;
@@ -1274,7 +1279,8 @@ class ExternalHeader :
   }
 
   template<bool may_internalize>
-  static MaybeLocal<String> New(Environment* env, nghttp2_rcbuf* buf) {
+  static MaybeLocal<String> New(Http2Session* session, nghttp2_rcbuf* buf) {
+    Environment* env = session->env();
     if (nghttp2_rcbuf_is_static(buf)) {
       auto& static_str_map = env->isolate_data()->http2_static_strs;
       v8::Eternal<v8::String>& eternal = static_str_map[buf];
@@ -1301,6 +1307,7 @@ class ExternalHeader :
       return GetInternalizedString(env, vec);
     }
 
+    session->StopTrackingRcbuf(buf);
     ExternalHeader* h_str = new ExternalHeader(buf);
     MaybeLocal<String> str = String::NewExternalOneByte(env->isolate(), h_str);
     if (str.IsEmpty())

src/util-inl.h

@@ -345,8 +345,9 @@ bool StringEqualNoCaseN(const char* a, const char* b, size_t length) {
   return true;
 }
 
-inline size_t MultiplyWithOverflowCheck(size_t a, size_t b) {
-  size_t ret = a * b;
+template <typename T>
+inline T MultiplyWithOverflowCheck(T a, T b) {
+  auto ret = a * b;
   if (a != 0)
     CHECK_EQ(b, ret / a);
 

src/util.h

@@ -65,6 +65,9 @@ inline char* Calloc(size_t n);
 inline char* UncheckedMalloc(size_t n);
 inline char* UncheckedCalloc(size_t n);
 
+template <typename T>
+inline T MultiplyWithOverflowCheck(T a, T b);
+
 // Used by the allocation functions when allocation fails.
 // Thin wrapper around v8::Isolate::LowMemoryNotification() that checks
 // whether V8 is initialized.