grpc: Add support for max frame length in gPRC frame decoding

source/common/grpc/codec.cc

@@ -32,13 +32,17 @@ void Encoder::prependFrameHeader(uint8_t flags, Buffer::Instance& buffer, uint32
 }
 
 bool Decoder::decode(Buffer::Instance& input, std::vector<Frame>& output) {
+  // Make sure those flags are set to initial state.
   decoding_error_ = false;
+  is_frame_oversized_ = false;
   output_ = &output;
   inspect(input);
   output_ = nullptr;
-  if (decoding_error_) {
+
+  if (decoding_error_ || is_frame_oversized_) {
     return false;
   }
+
   input.drain(input.length());
   return true;
 }
@@ -102,6 +106,12 @@ uint64_t FrameInspector::inspect(const Buffer::Instance& data) {
       case State::FhLen3:
         length_as_bytes_[3] = c;
         length_ = absl::big_endian::Load32(length_as_bytes_);
+        // Compares the frame length against maximum length when `max_frame_length_` is configured,
+        if (max_frame_length_ != 0 && length_ > max_frame_length_) {
+          // Set the flag to indicate the over-limit error and return.
+          is_frame_oversized_ = true;
+          return delta;
+        }
         frameDataStart();
         if (length_ == 0) {
           frameDataEnd();

source/common/grpc/codec.h

@@ -113,6 +113,11 @@ class FrameInspector {
     uint8_t length_as_bytes_[4];
   };
   uint64_t count_{0};
+  // Default value 0 means there is no limitation on maximum frame length.
+  uint32_t max_frame_length_{0};
+  // When `max_frame_length_` is configured, this flag will be true if frame length is larger than
+  // `max_frame_length_`.
+  bool is_frame_oversized_{false};
 };
 
 class Decoder : public FrameInspector {
@@ -134,6 +139,9 @@ class Decoder : public FrameInspector {
   // Indicates whether it has buffered any partial data.
   bool hasBufferedData() const { return state_ != State::FhFlag; }
 
+  // Configures the maximum frame length.
+  void setMaxFrameLength(uint32_t max_frame_length) { max_frame_length_ = max_frame_length; }
+
 protected:
   bool frameStart(uint8_t) override;
   void frameDataStart() override;

test/common/grpc/codec_test.cc

@@ -221,6 +221,68 @@ TEST(GrpcCodecTest, decodeMultipleFrame) {
   }
 }
 
+TEST(GrpcCodecTest, decodeSingleFrameOverLimit) {
+  helloworld::HelloRequest request;
+  std::string test_str = std::string(64 * 1024, 'a');
+  request.set_name(test_str);
+
+  Buffer::OwnedImpl buffer;
+  std::array<uint8_t, 5> header;
+  Encoder encoder;
+  encoder.newFrame(GRPC_FH_DEFAULT, request.ByteSize(), header);
+  buffer.add(header.data(), 5);
+  buffer.add(request.SerializeAsString());
+  size_t size = buffer.length();
+
+  std::vector<Frame> frames;
+  // Configure decoder with 32kb max_frame_length.
+  Decoder decoder;
+  decoder.setMaxFrameLength(32 * 1024);
+
+  // The decoder doesn't successfully decode due to oversized frame.
+  EXPECT_FALSE(decoder.decode(buffer, frames));
+  EXPECT_EQ(buffer.length(), size);
+}
+
+TEST(GrpcCodecTest, decodeMultipleFramesOverLimit) {
+  Buffer::OwnedImpl buffer;
+  std::array<uint8_t, 5> header;
+  Encoder encoder;
+
+  // First frame is valid (i.e. within max_frame_length limit).
+  helloworld::HelloRequest request;
+  request.set_name("hello");
+  encoder.newFrame(GRPC_FH_DEFAULT, request.ByteSize(), header);
+  buffer.add(header.data(), 5);
+  buffer.add(request.SerializeAsString());
+
+  // Second frame is invalid (i.e. exceeds max_frame_length).
+  helloworld::HelloRequest overlimit_request;
+  std::string test_str = std::string(64 * 1024, 'a');
+  overlimit_request.set_name(test_str);
+  encoder.newFrame(GRPC_FH_DEFAULT, overlimit_request.ByteSize(), header);
+  buffer.add(header.data(), 5);
+  buffer.add(overlimit_request.SerializeAsString());
+
+  size_t size = buffer.length();
+
+  std::vector<Frame> frames;
+  Decoder decoder;
+  decoder.setMaxFrameLength(32 * 1024);
+
+  EXPECT_FALSE(decoder.decode(buffer, frames));
+  // When the decoder doesn't successfully decode, it puts valid frames up until
+  // an oversized frame into output frame vector.
+  ASSERT_EQ(frames.size(), 1);
+  // First frame is successfully decoded.
+  EXPECT_EQ(frames[0].length_, request.ByteSize());
+  // Buffer does not get drained due to it returning false.
+  EXPECT_EQ(buffer.length(), size);
+  // Only part of the buffer represented a valid frame. Thus, the frame length should not equal the
+  // buffer length.
+  EXPECT_NE(frames[0].length_, size);
+}
+
 TEST(GrpcCodecTest, FrameInspectorTest) {
   {
     Buffer::OwnedImpl buffer;