feat: implemented consumer thread, all tests pass

Reviewed-on: #5

CMakeLists.txt

@@ -8,12 +8,22 @@ project(azkoyen_ipc_test LANGUAGES CXX)
 set(CMAKE_CXX_STANDARD 17)
 set(CMAKE_CXX_STANDARD_REQUIRED ON)
 
+# Qt Setup — AUTOMOC runs moc automatically on Q_OBJECT headers
+find_package(Qt5 REQUIRED COMPONENTS Core Widgets Test)
+set(CMAKE_AUTOMOC ON)
+set(CMAKE_INCLUDE_CURRENT_DIR ON)
+
 # Core library
 add_library(core
     src/core/SysfsRead.cxx
+    src/core/UnixIpcBridge.cxx
+    src/core/Producer.cxx
+    src/core/Consumer.cxx
+    include/Consumer.hpp
 )
 
 target_include_directories(core PUBLIC ${CMAKE_CURRENT_SOURCE_DIR}/include)
+target_link_libraries(core PUBLIC Qt5::Core)
 
 #tests
 enable_testing()

README.md

@@ -21,3 +21,27 @@ A Test-Driven Development (TDD) workflow was followed throughout the project. Ev
 The reader never throws on I/O errors; every outcome is expressed through the enum so callers can react without exception handling. A helper `trim_in_place` strips trailing whitespace and newlines before comparison.
 
 **Tests:** [tests/test_sysfs_read.cxx](tests/test_sysfs_read.cxx) — covers all five status branches by writing controlled content to a temporary file.
+
+## Producer class / thread
+
+`Producer` ([include/Producer.hpp](include/Producer.hpp), [src/core/Producer.cxx](src/core/Producer.cxx)) runs a worker `std::thread` that periodically polls the `SysfsReader` and, when the status is `Enabled`, generates a random integer and forwards it through an injected `send_fn` callback. The polling interval is 1 second under normal conditions and 7 seconds when the sysfs file reports `ErrorTempTooHigh` (cool-down).
+
+## UnixIpcBridge
+
+>[!note]
+>why unix domain sockets? Because I have more experience with them under linux than with posix shared memmory and semaphore, and I find them easier to unit-test.
+
+`UnixIpcBridge` ([include/UnixIpcBridge.hpp](include/UnixIpcBridge.hpp), [src/core/UnixIpcBridge.cxx](src/core/UnixIpcBridge.cxx)) is a small helper that connects to a UNIX domain socket and sends a single `int` per call. It opens a new connection for each value, which keeps the protocol stateless and simple.
+
+**Tests:** [tests/test_unix_ipc.cxx](tests/test_unix_ipc.cxx) — spins up a fake socket server, sends values through the bridge, and asserts they arrive correctly.
+
+## ConsumerThread
+
+`ConsumerThread` ([include/ConsumerThread.hpp](include/ConsumerThread.hpp), [src/core/ConsumerThread.cxx](src/core/ConsumerThread.cxx)) is a `QObject` that listens on a UNIX domain socket in a background `std::thread`. On each received integer it:
+
+1. Prints the value to `stdout`.
+2. Emits the `valueReceived(int)` Qt signal.
+
+The server socket is created and bound inside `start()` **before** the thread is spawned, so the socket is guaranteed to be ready by the time `start()` returns — eliminating race conditions with the producer. Graceful shutdown is handled by `stop()`, which shuts down the file descriptor to unblock the blocking `accept()` call.
+
+**Tests:** [tests/test_consumer_thread.cxx](tests/test_consumer_thread.cxx) — uses `QSignalSpy` to verify single-value, multi-value, negative, and zero reception.

include/Consumer.hpp

@@ -0,0 +1,44 @@
+#pragma once
+// ConsumerThread.hpp
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+#include <QObject>
+#include <atomic>
+#include <string>
+#include <thread>
+
+/// @brief Listens on a UNIX domain socket, receives integers from the
+///        producer via IPC, prints them to console, and emits a Qt signal.
+class ConsumerThread : public QObject
+{
+  Q_OBJECT
+
+ public:
+  /// @brief Construct the consumer bound to a socket path.
+  /// @param socket_path UNIX domain socket path to listen on.
+  /// @param parent Optional QObject parent for memory management.
+  explicit ConsumerThread(const std::string& socket_path,
+                          QObject* parent = nullptr);
+
+  ~ConsumerThread() override;
+
+  /// @brief Start the listener thread. The server socket is ready
+  ///        when this function returns.
+  void start();
+
+  /// @brief Stop the listener thread gracefully. Safe to call multiple times.
+  void stop();
+
+ signals:
+  /// @brief Emitted every time an integer is received from the producer.
+  void valueReceived(int value);
+
+ private:
+  /// @brief Main loop: accept → recv → print → emit. Runs in m_thread.
+  void run_loop();
+
+  std::string m_socket_path;
+  int m_server_fd = -1;
+  std::atomic<bool> m_running{false};
+  std::thread m_thread;
+};

include/Producer.hpp

@@ -0,0 +1,48 @@
+#pragma once
+// Producer.hpp
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+#include <atomic>
+#include <chrono>
+#include <filesystem>
+#include <functional>
+#include <thread>
+
+#include "SysfsRead.hpp"
+
+using RandomFn = std::function<int()>;
+using LogFn = std::function<void(const std::string&)>;
+using SleepFn = std::function<void(std::chrono::milliseconds)>;
+class Producer
+{
+ public:
+  /// @brief Construct a Producer bound to a sysfs-like control file.
+  /// @param sysfs_path Path to the control file (e.g. "./fake_sysfs_input").
+  /// @param send_fn    Function called whenever a new integer should be sent.
+  Producer(const std::filesystem::path& sysfs_path,
+           std::function<void(int)> send_fn, RandomFn random_fn,
+           LogFn log_fn = nullptr, SleepFn sleep_fn = default_sleep);
+
+  /// @brief Start the worker thread. Safe to call only once.
+  void start();
+
+  /// @brief Request the worker thread to stop and wait for it to finish.
+  void stop();
+
+ private:
+  /// @brief Main loop executed by the worker thread.
+  void run_loop();
+
+  std::thread m_thread;
+  std::atomic<bool> m_running;
+  SysfsReader m_reader;
+  RandomFn m_random;
+  SleepFn m_sleep;
+  static void default_sleep(std::chrono::milliseconds d)
+  {
+    std::this_thread::sleep_for(d);
+  }
+  LogFn m_log;
+  std::function<void(int)> m_send;
+  std::chrono::milliseconds compute_delay(SysfsStatus status) const;
+};

include/UnixIpcBridge.hpp

@@ -0,0 +1,31 @@
+// UnixIpcBridge.hpp
+// SPDX-License-Identifier: GPL-3.0-only
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#pragma once
+#include <fcntl.h>  // non‑blocking
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>  // close()
+
+#include <string>
+
+///@brief Small bridge to allow the producer class to send data over UNIX domain
+/// sockets
+class UnixIpcBridge
+{
+ public:
+  ///@brief constructor
+  ///@param socket path pointing the socket
+  explicit UnixIpcBridge(const std::string& socket_path);
+
+  ///@brief sending function, this goes into the producer
+  ///@param integer to send over the socket
+  void send(int value);
+
+ private:
+  std::string m_socket_path;
+  int m_socket_fd = -1;
+
+  void connect_to_consumer();
+};

src/core/Consumer.cxx

@@ -0,0 +1,104 @@
+// ConsumerThread.cxx
+// SPDX-License-Identifier: GPL-3.0-or-later
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#include "Consumer.hpp"
+
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include <cstring>
+#include <iostream>
+#include <stdexcept>
+
+ConsumerThread::ConsumerThread(const std::string& socket_path, QObject* parent)
+    : QObject(parent), m_socket_path(socket_path)
+{
+}
+
+ConsumerThread::~ConsumerThread() { stop(); }
+
+void ConsumerThread::start()
+{
+  // Remove stale socket from previous runs
+  unlink(m_socket_path.c_str());
+
+  // Create, bind and listen BEFORE spawning the thread so the socket
+  // is guaranteed ready when start() returns — no race with the producer.
+  m_server_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  if (m_server_fd < 0)
+  {
+    throw std::runtime_error("ConsumerThread: socket() failed");
+  }
+
+  struct sockaddr_un addr = {};
+  addr.sun_family = AF_UNIX;
+  std::strncpy(addr.sun_path, m_socket_path.c_str(), sizeof(addr.sun_path) - 1);
+
+  if (bind(m_server_fd, reinterpret_cast<sockaddr*>(&addr), sizeof(addr)) < 0)
+  {
+    close(m_server_fd);
+    m_server_fd = -1;
+    throw std::runtime_error("ConsumerThread: bind() failed");
+  }
+
+  if (listen(m_server_fd, 5) < 0)
+  {
+    close(m_server_fd);
+    m_server_fd = -1;
+    throw std::runtime_error("ConsumerThread: listen() failed");
+  }
+
+  m_running.store(true);
+  m_thread = std::thread(&ConsumerThread::run_loop, this);
+}
+
+void ConsumerThread::stop()
+{
+  if (!m_running.exchange(false))
+  {
+    return;  // already stopped or never started
+  }
+
+  // Shutdown the server fd to unblock the blocking accept() call
+  if (m_server_fd >= 0)
+  {
+    shutdown(m_server_fd, SHUT_RDWR);
+    close(m_server_fd);
+    m_server_fd = -1;
+  }
+
+  if (m_thread.joinable())
+  {
+    m_thread.join();
+  }
+
+  unlink(m_socket_path.c_str());
+}
+
+void ConsumerThread::run_loop()
+{
+  while (m_running.load())
+  {
+    int client_fd = accept(m_server_fd, nullptr, nullptr);
+    if (client_fd < 0)
+    {
+      // accept() failed — most likely stop() closed the fd
+      break;
+    }
+
+    int value = 0;
+    ssize_t n = recv(client_fd, &value, sizeof(value), MSG_WAITALL);
+    close(client_fd);
+
+    if (n == static_cast<ssize_t>(sizeof(value)))
+    {
+      // 1) Print to console (spec requirement)
+      std::cout << "ConsumerThread received: " << value << std::endl;
+
+      // 2) Emit Qt signal (spec requirement)
+      emit valueReceived(value);
+    }
+  }
+}

src/core/Producer.cxx

@@ -0,0 +1,84 @@
+// Producer.cxx
+// SPDX-License-Identifier: GPL-3.0-only
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+
+#include "Producer.hpp"
+
+#include "SysfsRead.hpp"
+
+Producer::Producer(const std::filesystem::path& sysfs_path,
+                   std::function<void(int)> send_fn, RandomFn random_fn,
+                   LogFn log_fn, SleepFn sleep_fn)
+    : m_reader(sysfs_path),
+      m_send(std::move(send_fn)),
+      m_random(std::move(random_fn)),
+      m_log(std::move(log_fn)),
+      m_sleep(std::move(sleep_fn))
+{
+}
+std::chrono::milliseconds Producer::compute_delay(SysfsStatus status) const
+{
+  using namespace std::chrono_literals;
+
+  auto standard = 1000ms;  // example: 1s, must be < 7s
+  auto hot = 7000ms;       // exactly 7s
+
+  if (status == SysfsStatus::ErrorTempTooHigh)
+  {  // when error = temp too high
+    return hot;
+  }
+  else
+  {
+    return standard;
+  }
+}
+
+void Producer::start()
+{
+  m_running.store(true);
+  m_thread = std::thread(&Producer::run_loop, this);
+}
+
+void Producer::stop()
+{
+  m_running.store(false);
+  if (m_thread.joinable())
+  {
+    m_thread.join();
+  }
+}
+
+void Producer::run_loop()
+{
+  while (m_running.load())
+  {
+    auto status = m_reader.read_status();
+    switch (status)
+    {
+      case SysfsStatus::Enabled:
+        m_send(m_random());
+        if (m_log) m_log("Producer: Enabled");
+        break;
+
+      case SysfsStatus::Unreachable:
+        // do nothing for now
+        if (m_log) m_log("Producer: SysfsFile Unreachable");
+        break;
+
+      case SysfsStatus::Empty:
+        if (m_log) m_log("Producer: SysfsFile Empty");
+        break;
+
+      case SysfsStatus::ErrorTempTooHigh:
+        if (m_log) m_log("Producer: Error temp too high!!");
+        break;
+
+      case SysfsStatus::UnexpectedValue:
+        if (m_log) m_log("Producer: UnexpectedValue");
+        break;
+    }
+    auto delay = compute_delay(status);
+    m_sleep(delay);
+    // Thread will end here (for now) stop will join it
+  }
+}

src/core/UnixIpcBridge.cxx

@@ -0,0 +1,49 @@
+// UnixIpcBridge.cxx
+// SPDX-License-Identifier: GPL-3.0-only
+// Author: Unai Blazquez <unaibg2000@gmail.com>
+#include "UnixIpcBridge.hpp"
+
+#include <cstring>
+#include <stdexcept>
+
+UnixIpcBridge::UnixIpcBridge(const std::string& socket_path)
+    : m_socket_path(socket_path)
+{
+}
+
+void UnixIpcBridge::send(int value)
+{
+  connect_to_consumer();
+
+  ssize_t n = ::send(m_socket_fd, &value, sizeof(value), 0);
+  if (n != sizeof(value))
+  {
+    close(m_socket_fd);
+    m_socket_fd = -1;
+    throw std::runtime_error("UnixIpcBridge::send: failed to write value");
+  }
+
+  close(m_socket_fd);
+  m_socket_fd = -1;
+}
+
+void UnixIpcBridge::connect_to_consumer()
+{
+  m_socket_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+  if (m_socket_fd < 0)
+  {
+    throw std::runtime_error("UnixIpcBridge: socket() failed");
+  }
+
+  struct sockaddr_un addr = {};
+  addr.sun_family = AF_UNIX;
+  std::strncpy(addr.sun_path, m_socket_path.c_str(), sizeof(addr.sun_path) - 1);
+
+  if (connect(m_socket_fd, reinterpret_cast<sockaddr*>(&addr), sizeof(addr)) <
+      0)
+  {
+    close(m_socket_fd);
+    m_socket_fd = -1;
+    throw std::runtime_error("UnixIpcBridge: connect() failed");
+  }
+}

tests/CMakeLists.txt

@@ -12,4 +12,44 @@ target_link_libraries(test_sysfs_reader
         gtest_main
 )
 add_test(NAME test_sysfs_reader COMMAND test_sysfs_reader)
+add_executable(test_producer
+    test_producer.cxx
+)
 
+target_link_libraries(test_producer
+    PRIVATE
+        core
+        gtest
+        gtest_main
+)
+
+add_test(NAME test_producer COMMAND test_producer)
+
+add_executable(test_ipc
+    test_unix_ipc.cxx
+)
+
+target_link_libraries(test_ipc
+    PRIVATE
+        core
+        gtest
+        gtest_main
+)
+
+add_test(NAME test_ipc COMMAND test_ipc)
+
+
+add_executable(test_consumer
+    test_consumer.cxx
+)
+
+target_link_libraries(test_consumer
+    PRIVATE
+        core
+        gtest
+        gtest_main
+        Qt5::Core
+        Qt5::Test
+)
+
+add_test(NAME test_consumer COMMAND test_consumer)

tests/test_consumer.cxx

@@ -0,0 +1,120 @@
+#include <gtest/gtest.h>
+
+#include <QCoreApplication>
+#include <QSignalSpy>
+
+#include "Consumer.hpp"
+#include "UnixIpcBridge.hpp"
+
+// QSignalSpy needs a QCoreApplication to dispatch queued signals
+static int argc_ = 0;
+static QCoreApplication app_(argc_, nullptr);
+
+TEST(ConsumerThreadTest, ReceivesSingleValue)
+{
+  const std::string sock = "/tmp/test_ct_single.sock";
+
+  ConsumerThread consumer(sock);
+
+  // QSignalSpy records every emission of the given signal
+  QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+  consumer.start();
+
+  UnixIpcBridge bridge(sock);
+  bridge.send(42);
+
+  // spy.wait() pumps the event loop for up to 1s until a signal arrives
+  spy.wait(1000);
+  consumer.stop();
+
+  ASSERT_EQ(spy.count(), 1);
+  EXPECT_EQ(spy.at(0).at(0).toInt(), 42);
+}
+
+TEST(ConsumerThreadTest, ReceivesMultipleValues)
+{
+  const std::string sock = "/tmp/test_ct_multi.sock";
+
+  ConsumerThread consumer(sock);
+  QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+  consumer.start();
+
+  constexpr int kMessages = 5;
+  for (int i = 0; i < kMessages; ++i)
+  {
+    UnixIpcBridge bridge(sock);
+    bridge.send(i * 10);
+    // Small delay so the consumer can re-enter accept() between sends
+    std::this_thread::sleep_for(std::chrono::milliseconds(10));
+  }
+
+  // Wait until all signals arrive (or timeout after 5s)
+  for (int attempt = 0; spy.count() < kMessages && attempt < 50; ++attempt)
+  {
+    spy.wait(100);
+  }
+
+  consumer.stop();
+
+  ASSERT_EQ(spy.count(), kMessages);
+  for (int i = 0; i < kMessages; ++i)
+  {
+    EXPECT_EQ(spy.at(i).at(0).toInt(), i * 10);
+  }
+}
+
+TEST(ConsumerThreadTest, ReceivesNegativeAndZero)
+{
+  // Zero
+  {
+    const std::string sock = "/tmp/test_ct_zero.sock";
+    ConsumerThread consumer(sock);
+    QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(0);
+
+    spy.wait(1000);
+    consumer.stop();
+
+    ASSERT_EQ(spy.count(), 1);
+    EXPECT_EQ(spy.at(0).at(0).toInt(), 0);
+  }
+
+  // Negative
+  {
+    const std::string sock = "/tmp/test_ct_neg.sock";
+    ConsumerThread consumer(sock);
+    QSignalSpy spy(&consumer, &ConsumerThread::valueReceived);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(-999);
+
+    spy.wait(1000);
+    consumer.stop();
+
+    ASSERT_EQ(spy.count(), 1);
+    EXPECT_EQ(spy.at(0).at(0).toInt(), -999);
+  }
+}
+
+TEST(ConsumerThreadTest, StopsCleanlyWithoutDeadlock)
+{
+  const std::string sock = "/tmp/test_ct_stop.sock";
+
+  ConsumerThread consumer(sock);
+  consumer.start();
+  // stop() must return without hanging, even with no connections
+  consumer.stop();
+}
+
+TEST(ConsumerThreadTest, StopsCleanlyWhenNeverStarted)
+{
+  const std::string sock = "/tmp/test_ct_nostart.sock";
+
+  ConsumerThread consumer(sock);
+  // stop() on a consumer that was never started must not crash
+  consumer.stop();
+}

tests/test_producer.cxx

@@ -0,0 +1,124 @@
+#include <gtest/gtest.h>
+
+#include <chrono>
+#include <fstream>
+
+#include "Producer.hpp"
+
+TEST(ProducerTest, ProducerCallsBackWhenEnabled)
+{
+  // Arrange create the file and write "1\n" into it.
+  {
+    std::ofstream out("fake_sysfs_input");
+    out << "1\n";
+  }
+  // create a fake callback function
+  std::vector<int> outputs;
+  std::vector<std::string> logs;
+
+  // construct a producer with fake file and callback
+  Producer producer{"fake_sysfs_input", [&outputs](int value)
+                    { outputs.push_back(value); }, []() { return 42; },
+                    [&logs](const std::string& msg) { logs.push_back(msg); }};
+  // Act: initialize producer and stop it.
+  producer.start();
+  std::this_thread::sleep_for(std::chrono::milliseconds(1));
+  producer.stop();
+
+  // Assert: we expect one output being 42
+  EXPECT_EQ(outputs[0], 42);
+  EXPECT_NE(logs[0].find("Enabled"), std::string::npos);
+}
+
+TEST(ProducerTest, ProducerDoesNotCallWhenUnexpectedValue)
+{
+  // Arrange create the file and write "0\n" into it.
+  {
+    std::ofstream out("fake_sysfs_input");
+    out << "0\n";
+  }
+
+  std::vector<int> outputs;
+  std::vector<std::string> logs;
+
+  Producer producer{"fake_sysfs_input", [&outputs](int value)
+                    { outputs.push_back(value); }, []() { return 42; },
+                    [&logs](const std::string& msg) { logs.push_back(msg); },
+                    [](std::chrono::milliseconds) {}};
+
+  producer.start();
+  std::this_thread::sleep_for(std::chrono::milliseconds(1));  // ← 1ms window
+  producer.stop();
+
+  // Assert: we expect no output
+  EXPECT_TRUE(outputs.empty());
+  EXPECT_NE(logs[0].find("UnexpectedValue"), std::string::npos);
+}
+
+TEST(ProducerTest, ProducerDoesNotCallWhenEmpty)
+{
+  // Arrange create the file and write "0\n" into it.
+  {
+    std::ofstream out("fake_sysfs_input");
+    out << " ";
+  }
+
+  std::vector<int> outputs;
+  std::vector<std::string> logs;
+
+  Producer producer{"fake_sysfs_input", [&outputs](int value)
+                    { outputs.push_back(value); }, []() { return 42; },
+                    [&logs](const std::string& msg) { logs.push_back(msg); },
+                    [](std::chrono::milliseconds) {}};
+
+  producer.start();
+  std::this_thread::sleep_for(std::chrono::milliseconds(1));  // ← 1ms window
+  producer.stop();
+
+  // Assert: we expect no output
+  EXPECT_TRUE(outputs.empty());
+  EXPECT_NE(logs[0].find("Empty"), std::string::npos);
+}
+
+TEST(ProducerTest, ProducerDoesNotCallWhenUnreachable)
+{
+  std::vector<int> outputs;
+  std::vector<std::string> logs;
+
+  Producer producer{"nonexistant_sysfs_input", [&outputs](int value)
+                    { outputs.push_back(value); }, []() { return 42; },
+                    [&logs](const std::string& msg) { logs.push_back(msg); },
+                    [](std::chrono::milliseconds) {}};
+
+  producer.start();
+  std::this_thread::sleep_for(std::chrono::milliseconds(1));  // ← 1ms window
+  producer.stop();
+
+  // Assert: we expect no output
+  EXPECT_TRUE(outputs.empty());
+  EXPECT_NE(logs[0].find("Unreachable"), std::string::npos);
+}
+
+TEST(ProducerTest, ProducerDoesNotCallWhenTempTooHigh)
+{
+  // create  a file that contains error
+  {
+    std::ofstream out("fake_sysfs_input");
+    out << "error: temp too high";
+  }
+  std::vector<int> outputs;
+  std::vector<std::string> logs;
+
+  Producer producer{"fake_sysfs_input", [&outputs](int value)
+                    { outputs.push_back(value); }, []() { return 42; },
+                    [&logs](const std::string& msg) { logs.push_back(msg); },
+                    [](std::chrono::milliseconds) {}};
+
+  producer.start();
+  std::this_thread::sleep_for(std::chrono::milliseconds(1));  // ← 1ms window
+  producer.stop();
+
+  // Assert: we expect no output
+  EXPECT_TRUE(outputs.empty());
+  EXPECT_NE(logs[0].find("Error"), std::string::npos);
+}

tests/test_unix_ipc.cxx

@@ -0,0 +1,220 @@
+#include <gtest/gtest.h>
+#include <sys/socket.h>
+#include <sys/un.h>
+#include <unistd.h>
+
+#include <atomic>
+#include <chrono>
+#include <cstring>
+#include <stdexcept>
+#include <string>
+#include <thread>
+#include <vector>
+
+#include "UnixIpcBridge.hpp"
+
+// ---------------------------------------------------------------------------
+// Helper: a minimal UNIX-domain socket server that accepts one connection,
+// reads `count` ints, then tears down cleanly.  Uses a ready-flag so the
+// client never races against bind/listen.
+// ---------------------------------------------------------------------------
+class FakeConsumer
+{
+ public:
+  explicit FakeConsumer(const std::string& path, int count = 1)
+      : m_path(path), m_count(count)
+  {
+    // Remove stale socket from any previous failed run
+    unlink(m_path.c_str());
+  }
+
+  /// Start the server on a background thread.
+  void start()
+  {
+    m_thread = std::thread([this] { run(); });
+
+    // Spin until the server signals it is listening (bounded wait).
+    auto deadline = std::chrono::steady_clock::now() + std::chrono::seconds(5);
+    while (!m_ready.load(std::memory_order_acquire))
+    {
+      if (std::chrono::steady_clock::now() > deadline)
+      {
+        throw std::runtime_error("FakeConsumer: server failed to start");
+      }
+      std::this_thread::sleep_for(std::chrono::milliseconds(1));
+    }
+  }
+
+  /// Block until the server thread finishes.
+  void join() { m_thread.join(); }
+
+  /// Values received in order.
+  const std::vector<int>& received() const { return m_received; }
+
+  ~FakeConsumer() { unlink(m_path.c_str()); }
+
+ private:
+  void run()
+  {
+    m_server_fd = socket(AF_UNIX, SOCK_STREAM, 0);
+    ASSERT_GE(m_server_fd, 0) << "socket() failed: " << strerror(errno);
+
+    struct sockaddr_un addr = {};
+    addr.sun_family = AF_UNIX;
+    std::strncpy(addr.sun_path, m_path.c_str(), sizeof(addr.sun_path) - 1);
+
+    ASSERT_EQ(
+        bind(m_server_fd, reinterpret_cast<sockaddr*>(&addr), sizeof(addr)), 0)
+        << "bind() failed: " << strerror(errno);
+    ASSERT_EQ(listen(m_server_fd, 1), 0)
+        << "listen() failed: " << strerror(errno);
+
+    // Signal that we are ready to accept connections.
+    m_ready.store(true, std::memory_order_release);
+
+    int client_fd = accept(m_server_fd, nullptr, nullptr);
+    ASSERT_GE(client_fd, 0) << "accept() failed: " << strerror(errno);
+
+    for (int i = 0; i < m_count; ++i)
+    {
+      int value = 0;
+      ssize_t n = recv(client_fd, &value, sizeof(value), MSG_WAITALL);
+      ASSERT_EQ(n, static_cast<ssize_t>(sizeof(value)))
+          << "recv() short read on message " << i;
+      m_received.push_back(value);
+    }
+
+    close(client_fd);
+    close(m_server_fd);
+  }
+
+  std::string m_path;
+  int m_count;
+  int m_server_fd = -1;
+  std::atomic<bool> m_ready{false};
+  std::thread m_thread;
+  std::vector<int> m_received;
+};
+
+// ---------------------------------------------------------------------------
+// Tests
+// ---------------------------------------------------------------------------
+
+/// Sends a single integer value and verifies the consumer receives it.
+TEST(UnixIpcBridgeTest, SendsSingleInt)
+{
+  const std::string sock = "/tmp/test_ipc_single.sock";
+
+  FakeConsumer consumer(sock, /*count=*/1);
+  consumer.start();
+
+  UnixIpcBridge bridge(sock);
+  bridge.send(42);
+
+  consumer.join();
+
+  ASSERT_EQ(consumer.received().size(), 1u);
+  EXPECT_EQ(consumer.received()[0], 42);
+}
+
+/// Sends zero and a negative value — makes sure sign bits survive.
+TEST(UnixIpcBridgeTest, SendsZeroAndNegativeValues)
+{
+  // Zero
+  {
+    const std::string sock = "/tmp/test_ipc_zero.sock";
+    FakeConsumer consumer(sock, 1);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(0);
+
+    consumer.join();
+    ASSERT_EQ(consumer.received().size(), 1u);
+    EXPECT_EQ(consumer.received()[0], 0);
+  }
+
+  // Negative
+  {
+    const std::string sock = "/tmp/test_ipc_neg.sock";
+    FakeConsumer consumer(sock, 1);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(-1);
+
+    consumer.join();
+    ASSERT_EQ(consumer.received().size(), 1u);
+    EXPECT_EQ(consumer.received()[0], -1);
+  }
+}
+
+/// Sends INT_MAX / INT_MIN to check for truncation or overflow.
+TEST(UnixIpcBridgeTest, SendsExtremeBoundaryValues)
+{
+  {
+    const std::string sock = "/tmp/test_ipc_max.sock";
+    FakeConsumer consumer(sock, 1);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(std::numeric_limits<int>::max());
+
+    consumer.join();
+    ASSERT_EQ(consumer.received().size(), 1u);
+    EXPECT_EQ(consumer.received()[0], std::numeric_limits<int>::max());
+  }
+
+  {
+    const std::string sock = "/tmp/test_ipc_min.sock";
+    FakeConsumer consumer(sock, 1);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(std::numeric_limits<int>::min());
+
+    consumer.join();
+    ASSERT_EQ(consumer.received().size(), 1u);
+    EXPECT_EQ(consumer.received()[0], std::numeric_limits<int>::min());
+  }
+}
+
+/// Connecting to a non-existent socket must throw, not silently fail.
+TEST(UnixIpcBridgeTest, ThrowsWhenNoConsumerListening)
+{
+  const std::string sock = "/tmp/test_ipc_noserver.sock";
+  unlink(sock.c_str());  // make sure nothing is there
+
+  UnixIpcBridge bridge(sock);
+  EXPECT_THROW(bridge.send(99), std::runtime_error);
+}
+
+/// Multiple sequential sends (each reopens the connection).
+TEST(UnixIpcBridgeTest, MultipleSendsSequentially)
+{
+  const std::string sock = "/tmp/test_ipc_multi.sock";
+  constexpr int kMessages = 5;
+
+  // Server expects exactly kMessages ints from kMessages connections.
+  // Because the bridge reconnects every send(), we run kMessages
+  // single-message consumers sequentially.
+  std::vector<int> all_received;
+  for (int i = 0; i < kMessages; ++i)
+  {
+    FakeConsumer consumer(sock, 1);
+    consumer.start();
+
+    UnixIpcBridge bridge(sock);
+    bridge.send(i * 10);
+
+    consumer.join();
+    ASSERT_EQ(consumer.received().size(), 1u);
+    all_received.push_back(consumer.received()[0]);
+  }
+
+  ASSERT_EQ(all_received.size(), static_cast<size_t>(kMessages));
+  for (int i = 0; i < kMessages; ++i)
+  {
+    EXPECT_EQ(all_received[i], i * 10);
+  }
+}