From 8c47a3aba8baf145d7ef9d0efe3a1a0f67be2331 Mon Sep 17 00:00:00 2001 From: Enoch Azariah Date: Thu, 9 Apr 2026 10:49:30 +0100 Subject: [PATCH 1/2] test: add dedicated ListenConnections coverage Add a separate listen_tests.cpp file with reusable UnixListener, ClientSetup, and ListenSetup helpers for exercising ListenConnections() with real Unix domain sockets. The new test covers the baseline behavior that ListenConnections() accepts an incoming connection and serves requests over it. Keeping this coverage separate from the existing general proxy tests makes the socket listener setup easier to review and provides a clearer place to extend listener-specific behavior in follow-up commits. --- test/CMakeLists.txt | 1 + test/mp/test/listen_tests.cpp | 209 ++++++++++++++++++++++++++++++++++ test/mp/test/test.cpp | 2 - 3 files changed, 210 insertions(+), 2 deletions(-) create mode 100644 test/mp/test/listen_tests.cpp diff --git a/test/CMakeLists.txt b/test/CMakeLists.txt index 1f21ba44..13246293 100644 --- a/test/CMakeLists.txt +++ b/test/CMakeLists.txt @@ -26,6 +26,7 @@ if(BUILD_TESTING AND TARGET CapnProto::kj-test) ${MP_PROXY_HDRS} mp/test/foo-types.h mp/test/foo.h + mp/test/listen_tests.cpp mp/test/spawn_tests.cpp mp/test/test.cpp ) diff --git a/test/mp/test/listen_tests.cpp b/test/mp/test/listen_tests.cpp new file mode 100644 index 00000000..a8493e72 --- /dev/null +++ b/test/mp/test/listen_tests.cpp @@ -0,0 +1,209 @@ +// Copyright (c) The Bitcoin Core developers +// Distributed under the MIT software license, see the accompanying +// file COPYING or http://www.opensource.org/licenses/mit-license.php. + +#include +#include + +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include +#include // IWYU pragma: keep +#include +#include +#include +#include +#include +#include + +#include "foo.h" + +namespace mp { +namespace test { +namespace { + +class UnixListener +{ +public: + UnixListener() + { + char dir_template[] = "/tmp/mptest-listener-XXXXXX"; + char* dir = mkdtemp(dir_template); + KJ_REQUIRE(dir != nullptr); + m_dir = dir; + m_path = m_dir + "/socket"; + + m_fd = socket(AF_UNIX, SOCK_STREAM, 0); + KJ_REQUIRE(m_fd >= 0); + + sockaddr_un addr{}; + addr.sun_family = AF_UNIX; + KJ_REQUIRE(m_path.size() < sizeof(addr.sun_path)); + std::strncpy(addr.sun_path, m_path.c_str(), sizeof(addr.sun_path) - 1); + KJ_REQUIRE(bind(m_fd, reinterpret_cast(&addr), sizeof(addr)) == 0); + KJ_REQUIRE(listen(m_fd, SOMAXCONN) == 0); + } + + ~UnixListener() + { + if (m_fd >= 0) close(m_fd); + if (!m_path.empty()) unlink(m_path.c_str()); + if (!m_dir.empty()) rmdir(m_dir.c_str()); + } + + int release() + { + int fd = m_fd; + m_fd = -1; + return fd; + } + + int Connect() const + { + int fd = socket(AF_UNIX, SOCK_STREAM, 0); + KJ_REQUIRE(fd >= 0); + + sockaddr_un addr{}; + addr.sun_family = AF_UNIX; + KJ_REQUIRE(m_path.size() < sizeof(addr.sun_path)); + std::strncpy(addr.sun_path, m_path.c_str(), sizeof(addr.sun_path) - 1); + KJ_REQUIRE(connect(fd, reinterpret_cast(&addr), sizeof(addr)) == 0); + return fd; + } + +private: + int m_fd{-1}; + std::string m_dir; + std::string m_path; +}; + +class ClientSetup +{ +public: + explicit ClientSetup(int fd) + : thread([this, fd] { + EventLoop loop("mptest-client", [](mp::LogMessage log) { + if (log.level == mp::Log::Raise) throw std::runtime_error(log.message); + }); + client_promise.set_value(ConnectStream(loop, fd)); + loop.loop(); + }) + { + client = client_promise.get_future().get(); + } + + ~ClientSetup() + { + client.reset(); + thread.join(); + } + + std::promise>> client_promise; + std::unique_ptr> client; + std::thread thread; +}; + +class ListenSetup +{ +public: + explicit ListenSetup(std::optional max_connections = std::nullopt) + : thread([this, max_connections] { + EventLoop loop("mptest-server", [this](mp::LogMessage log) { + if (log.level == mp::Log::Raise) throw std::runtime_error(log.message); + if (log.message.find("IPC server: socket connected.") != std::string::npos) { + std::lock_guard lock(counter_mutex); + ++connected_count; + counter_cv.notify_all(); + } else if (log.message.find("IPC server: socket disconnected.") != std::string::npos) { + std::lock_guard lock(counter_mutex); + ++disconnected_count; + counter_cv.notify_all(); + } + }); + FooImplementation foo; + ListenConnections(loop, listener.release(), foo, max_connections); + ready_promise.set_value(); + loop.loop(); + }) + { + ready_promise.get_future().get(); + } + + ~ListenSetup() + { + thread.join(); + } + + size_t ConnectedCount() + { + std::lock_guard lock(counter_mutex); + return connected_count; + } + + void WaitForConnectedCount(size_t expected_count) + { + std::unique_lock lock(counter_mutex); + const auto deadline = std::chrono::steady_clock::now() + std::chrono::seconds(5); + const bool matched = counter_cv.wait_until(lock, deadline, [&] { + return connected_count >= expected_count; + }); + KJ_REQUIRE(matched); + } + + void WaitForDisconnectedCount(size_t expected_count) + { + std::unique_lock lock(counter_mutex); + const auto deadline = std::chrono::steady_clock::now() + std::chrono::seconds(5); + const bool matched = counter_cv.wait_until(lock, deadline, [&] { + return disconnected_count >= expected_count; + }); + KJ_REQUIRE(matched); + } + + UnixListener listener; + std::promise ready_promise; + std::thread thread; + std::mutex counter_mutex; + std::condition_variable counter_cv; + size_t connected_count{0}; + size_t disconnected_count{0}; +}; + +KJ_TEST("ListenConnections accepts incoming connections") +{ + ListenSetup setup; + auto client = std::make_unique(setup.listener.Connect()); + + setup.WaitForConnectedCount(1); + KJ_EXPECT(client->client->add(1, 2) == 3); +} + +KJ_TEST("ListenConnections enforces a local connection limit") +{ + ListenSetup setup(/*max_connections=*/1); + + auto client1 = std::make_unique(setup.listener.Connect()); + setup.WaitForConnectedCount(1); + KJ_EXPECT(client1->client->add(1, 2) == 3); + + auto client2 = std::make_unique(setup.listener.Connect()); + std::this_thread::sleep_for(std::chrono::milliseconds(100)); + KJ_EXPECT(setup.ConnectedCount() == 1); + + client1.reset(); + setup.WaitForDisconnectedCount(1); + setup.WaitForConnectedCount(2); + + KJ_EXPECT(client2->client->add(2, 3) == 5); +} + +} // namespace +} // namespace test +} // namespace mp diff --git a/test/mp/test/test.cpp b/test/mp/test/test.cpp index d91edb40..07072ef5 100644 --- a/test/mp/test/test.cpp +++ b/test/mp/test/test.cpp @@ -9,10 +9,8 @@ #include #include #include -#include #include #include -#include #include #include #include From 8511c68f8b6827f4e9b306e0245929965a363930 Mon Sep 17 00:00:00 2001 From: Enoch Azariah Date: Thu, 9 Apr 2026 10:49:30 +0100 Subject: [PATCH 2/2] proxy: add local connection limit to ListenConnections Add an optional max_connections parameter to ListenConnections() so a listener can stop accepting new connections after reaching a local connection cap and resume accepting after an existing connection disconnects. Implement the limit with listener-local state tracking the listening socket, maximum number of active connections, and whether an async accept() has already been posted. This keeps the limit scoped to the individual listener instead of introducing global EventLoop state. Extend the dedicated listener test coverage to verify that with max_connections=1 the first client is accepted normally, a second client is not accepted while the first remains connected, and the second client is accepted after the first disconnects. --- doc/usage.md | 2 +- doc/versions.md | 8 ++++- include/mp/proxy-io.h | 55 +++++++++++++++++++++++++++-------- include/mp/version.h | 2 +- test/mp/test/listen_tests.cpp | 8 +++-- test/mp/test/test.cpp | 3 ++ 6 files changed, 60 insertions(+), 18 deletions(-) diff --git a/doc/usage.md b/doc/usage.md index f387db4d..df103e9f 100644 --- a/doc/usage.md +++ b/doc/usage.md @@ -10,7 +10,7 @@ _libmultiprocess_ is a library and code generator that allows calling C++ class The `*.capnp` data definition files are consumed by the _libmultiprocess_ code generator and each `X.capnp` file generates `X.capnp.c++`, `X.capnp.h`, `X.capnp.proxy-client.c++`, `X.capnp.proxy-server.c++`, `X.capnp.proxy-types.c++`, `X.capnp.proxy-types.h`, and `X.capnp.proxy.h` output files. The generated files include `mp::ProxyClient` and `mp::ProxyServer` class specializations for all the interfaces in the `.capnp` files. These allow methods on C++ objects in one process to be called from other processes over IPC sockets. -The `ProxyServer` objects help translate IPC requests from a socket to method calls on a local object. The `ProxyServer` objects are just used internally by the `mp::ServeStream(loop, socket, wrapped_object)` and `mp::ListenConnections(loop, socket, wrapped_object)` functions, and aren't exposed externally. The `ProxyClient` classes are exposed, and returned from the `mp::ConnectStream(loop, socket)` function and meant to be used directly. The classes implement methods described in `.capnp` definitions, and whenever any method is called, a request with the method arguments is sent over the associated IPC connection, and the corresponding `wrapped_object` method on the other end of the connection is called, with the `ProxyClient` method blocking until it returns and forwarding back any return value to the `ProxyClient` method caller. +The `ProxyServer` objects help translate IPC requests from a socket to method calls on a local object. The `ProxyServer` objects are just used internally by the `mp::ServeStream(loop, socket, wrapped_object)` and `mp::ListenConnections(loop, socket, wrapped_object[, max_connections])` functions, and aren't exposed externally. The `ProxyClient` classes are exposed, and returned from the `mp::ConnectStream(loop, socket)` function and meant to be used directly. The classes implement methods described in `.capnp` definitions, and whenever any method is called, a request with the method arguments is sent over the associated IPC connection, and the corresponding `wrapped_object` method on the other end of the connection is called, with the `ProxyClient` method blocking until it returns and forwarding back any return value to the `ProxyClient` method caller. ## Example diff --git a/doc/versions.md b/doc/versions.md index 2c2ec50e..3222e59d 100644 --- a/doc/versions.md +++ b/doc/versions.md @@ -7,8 +7,14 @@ Library versions are tracked with simple Versioning policy is described in the [version.h](../include/mp/version.h) include. -## v10 +## v11 - Current unstable version. +- Adds an optional per-listener `max_connections` parameter to `ListenConnections()` + so servers can stop accepting new connections when a local connection cap is reached, + and resume accepting after existing connections disconnect. + +## [v10.0](https://github.com/bitcoin-core/libmultiprocess/commits/v10.0) +- Prior unstable version before local listener connection-limit support. ## [v9.0](https://github.com/bitcoin-core/libmultiprocess/commits/v9.0) - Fixes race conditions where worker thread could be used after destruction, where getParams() could be called after request cancel, and where m_on_cancel could be called after request finishes. diff --git a/include/mp/proxy-io.h b/include/mp/proxy-io.h index d7b9f0e5..e14a2c02 100644 --- a/include/mp/proxy-io.h +++ b/include/mp/proxy-io.h @@ -13,7 +13,9 @@ #include #include +#include #include +#include #include #include #include @@ -820,8 +822,8 @@ std::unique_ptr> ConnectStream(EventLoop& loop, int f //! handles requests from the stream by calling the init object. Embed the //! ProxyServer in a Connection object that is stored and erased if //! disconnected. This should be called from the event loop thread. -template -void _Serve(EventLoop& loop, kj::Own&& stream, InitImpl& init) +template +void _Serve(EventLoop& loop, kj::Own&& stream, InitImpl& init, OnDisconnect&& on_disconnect) { loop.m_incoming_connections.emplace_front(loop, kj::mv(stream), [&](Connection& connection) { // Disable deleter so proxy server object doesn't attempt to delete the @@ -831,23 +833,49 @@ void _Serve(EventLoop& loop, kj::Own&& stream, InitImpl& init }); auto it = loop.m_incoming_connections.begin(); MP_LOG(loop, Log::Info) << "IPC server: socket connected."; - it->onDisconnect([&loop, it] { + it->onDisconnect([&loop, it, on_disconnect = std::forward(on_disconnect)]() mutable { MP_LOG(loop, Log::Info) << "IPC server: socket disconnected."; loop.m_incoming_connections.erase(it); + on_disconnect(); }); } //! Given connection receiver and an init object, handle incoming connections by //! calling _Serve, to create ProxyServer objects and forward requests to the //! init object. +struct ListenState +{ + explicit ListenState(kj::Own&& listener_, std::optional max_connections_) + : listener(kj::mv(listener_)), max_connections(max_connections_) {} + + kj::Own listener; + std::optional max_connections; + size_t active_connections{0}; + //! Tracks whether accept() has already been posted. This is needed because + //! active_connections only counts accepted connections, so without a + //! separate flag, nested _Listen() calls could queue multiple pending + //! accepts before active_connections increases. + bool accept_pending{false}; +}; + template -void _Listen(EventLoop& loop, kj::Own&& listener, InitImpl& init) +void _Listen(EventLoop& loop, InitImpl& init, const std::shared_ptr& state) { - auto* ptr = listener.get(); + if (state->accept_pending) return; + if (state->max_connections && state->active_connections >= *state->max_connections) return; + + state->accept_pending = true; + auto* ptr = state->listener.get(); loop.m_task_set->add(ptr->accept().then( - [&loop, &init, listener = kj::mv(listener)](kj::Own&& stream) mutable { - _Serve(loop, kj::mv(stream), init); - _Listen(loop, kj::mv(listener), init); + [&loop, &init, state](kj::Own&& stream) mutable { + state->accept_pending = false; + ++state->active_connections; + _Serve(loop, kj::mv(stream), init, [&loop, &init, state] { + assert(state->active_connections > 0); + --state->active_connections; + _Listen(loop, init, state); + }); + _Listen(loop, init, state); })); } @@ -857,18 +885,21 @@ template void ServeStream(EventLoop& loop, int fd, InitImpl& init) { _Serve( - loop, loop.m_io_context.lowLevelProvider->wrapSocketFd(fd, kj::LowLevelAsyncIoProvider::TAKE_OWNERSHIP), init); + loop, + loop.m_io_context.lowLevelProvider->wrapSocketFd(fd, kj::LowLevelAsyncIoProvider::TAKE_OWNERSHIP), + init, + [] {}); } //! Given listening socket file descriptor and an init object, handle incoming //! connections and requests by calling methods on the Init object. template -void ListenConnections(EventLoop& loop, int fd, InitImpl& init) +void ListenConnections(EventLoop& loop, int fd, InitImpl& init, std::optional max_connections = std::nullopt) { loop.sync([&]() { - _Listen(loop, + _Listen(loop, init, std::make_shared( loop.m_io_context.lowLevelProvider->wrapListenSocketFd(fd, kj::LowLevelAsyncIoProvider::TAKE_OWNERSHIP), - init); + max_connections)); }); } diff --git a/include/mp/version.h b/include/mp/version.h index 964667a9..423ed460 100644 --- a/include/mp/version.h +++ b/include/mp/version.h @@ -24,7 +24,7 @@ //! pointing at the prior merge commit. The /doc/versions.md file should also be //! updated, noting any significant or incompatible changes made since the //! previous version. -#define MP_MAJOR_VERSION 10 +#define MP_MAJOR_VERSION 11 //! Minor version number. Should be incremented in stable branches after //! backporting changes. The /doc/versions.md file should also be updated to diff --git a/test/mp/test/listen_tests.cpp b/test/mp/test/listen_tests.cpp index a8493e72..b9ec3a8f 100644 --- a/test/mp/test/listen_tests.cpp +++ b/test/mp/test/listen_tests.cpp @@ -5,16 +5,20 @@ #include #include -#include #include #include #include #include #include +#include +#include +#include +#include #include #include #include #include +#include #include // IWYU pragma: keep #include #include @@ -23,8 +27,6 @@ #include #include -#include "foo.h" - namespace mp { namespace test { namespace { diff --git a/test/mp/test/test.cpp b/test/mp/test/test.cpp index 07072ef5..d667d27c 100644 --- a/test/mp/test/test.cpp +++ b/test/mp/test/test.cpp @@ -5,10 +5,13 @@ #include #include +#include // NOLINT(modernize-deprecated-headers) + #include #include #include #include +#include #include #include #include