[Bug]: Process crash (SIGABRT) in onPacketReadySerializeImpl when handling empty or non-string MediaPipe packets #4714

Describe the bug
A critical process crash (SIGABRT / LOG(FATAL)) occurs in src/http_frontend/http_graph_executor_impl.cpp within onPacketReadySerializeImpl(). the function performs an unguarded extraction of string from an incoming mediapipe::Packet:

   Status onPacketReadySerializeImpl(
    const std::string& requestId,
    const std::string& endpointName,
    const std::string& endpointVersion,
    const std::string& packetName,
    const mediapipe_packet_type_enum packetType,
    const ::mediapipe::Packet& packet,
    std::string& response) {
    response = packet.Get<std::string>();
    return StatusCode::OK;
}

in Google MediaPipe's implementation calling packet.Get<T>() invokes two internal Abseil assertions:

-ABSL_CHECK(!IsEmpty())
-ABSL_CHECK(ValidateAsType<T>().ok())

If an output packet is empty (e.g., timestamp propagation, stream synchronization bounds, or stream closure), or holds any type other than string (e.g., ov::Tensor, mediapipe::Tensor, mediapipe::ImageFrame, or integers), the ABSL_CHECK assertion fails, logging a fatal message to stderr and immediately terminating the process via abort() (SIGABRT).
Because ABSL_CHECK invokes abort() rather than throwing a C++ exception, the surrounding try { ... } catch (...) block in src/mediapipe_internal/mediapipegraphexecutor.hpp is completely bypassed. This causes the entire OVMS multi-threaded server daemon to crash immediately, resulting in a Denial of Service (DoS) for all connected clients and hosted models.

Also, the parameter const mediapipe_packet_type_enum packetType is accepted but completely ignored, unlike in src/kfs_frontend/kfs_graph_executor_impl.cpp:L1144-L1170 where it is used to safely route packets to corresponding deserializers.

To Reproduce
Add the following unit test to src/test/mediapipeflow_test.cpp :

// include it at top
 #include "../http_frontend/http_graph_executor_impl.hpp" 

// Test Case 1: Empty packet triggers ABSL_CHECK(!IsEmpty())
TEST(HttpGraphExecutorDeathTest, CrashOnEmptyPacket) {
    ::mediapipe::Packet emptyPacket;
    std::string response;
    EXPECT_DEATH({
        ovms::onPacketReadySerializeImpl(
            "req_id", "endpoint", "1", "output_stream",
            ovms::mediapipe_packet_type_enum::UNKNOWN,
            emptyPacket,
            response);
    }, ".*The packet is empty.*");
}

// Test Case 2: Non-string packet triggers ABSL_CHECK(ValidateAsType<T>().ok())
TEST(HttpGraphExecutorDeathTest, CrashOnNonStringType) {
    ::mediapipe::Packet intPacket = ::mediapipe::MakePacket<int>(42);
    std::string response;
    EXPECT_DEATH({
        ovms::onPacketReadySerializeImpl(
            "req_id", "endpoint", "1", "output_stream",
            ovms::mediapipe_packet_type_enum::OVTENSOR,
            intPacket,
            response);
    }, ".*The Packet stores .* but is being accessed as .*string.*");
}

Run the test:

  bazel test //src:ovms_test --test_filter="HttpGraphExecutorDeathTest.*" --test_output=all

Expected behavior

1. onPacketReadySerializeImpl() should validate that the packet is not empty (!packet.IsEmpty()) and that its stored type matches std::string (packet.ValidateAsType<std::string>().ok()).
2. If an empty or incompatible packet arrives:
   • For empty packets, it should handle them gracefully (e.g., clear response or ignore control packets) and return StatusCode::OK.
   • For type mismatches, it should log an error and return an appropriate ovms::Status (e.g., Status(StatusCode::MEDIAPIPE_EXECUTION_ERROR, "Invalid packet payload type for HTTP output")).
3. The server should return an HTTP 4xx/5xx error JSON payload to the client without terminating the daemon process.

Logs

F0000 00:00:00.000000 ... packet.h:352] Check failed: !IsEmpty() The packet is empty.
*** Check failure stack trace: ***
    @     0x7f48a12b4000  absl::log_internal::LogMessageFatal::~LogMessageFatal()
    @     0x55bc1489d123  mediapipe::Packet::Get<std::string>()
    @     0x55bc1482a456  ovms::onPacketReadySerializeImpl() at src/http_frontend/http_graph_executor_impl.cpp:95
    @     0x55bc1483b789  ovms::MediapipeGraphExecutor::inferTyped<>() at src/mediapipe_internal/mediapipegraphexecutor.hpp:404
    @     0x55bc1481a102  ovms::HttpRestApiHandler::processV3Request() at src/http_frontend/http_rest_api_handler.cpp:706
Aborted (core dumped)

Configuration

1. OVMS version- main (latest commit)
2. OS: Linux (Ubuntu x86_64)