File monitoring (inotify) support

CMakeLists.txt

@@ -76,6 +76,7 @@ file(
   ${PROJECT_SOURCE_DIR}/src/utils/BaseServerStats.cpp
   ${PROJECT_SOURCE_DIR}/src/utils/ConfigParser.cpp
   ${PROJECT_SOURCE_DIR}/src/utils/ErrorHelpers.cpp
+  ${PROJECT_SOURCE_DIR}/src/utils/FileHelpers.cpp
   ${PROJECT_SOURCE_DIR}/src/utils/Tracer.cpp
   ${PROJECT_SOURCE_DIR}/src/zeromq/ZeroMQ.cpp
   ${PROJECT_SOURCE_DIR}/src/zeromq/ZeroMQMonitor.cpp
@@ -135,7 +136,7 @@ target_compile_options(${PROJECT_NAME}-lib PRIVATE -Wall -Wextra -g -Wl,--build-
 target_include_directories(${PROJECT_NAME}-lib PRIVATE ${PROJECT_BINARY_DIR})
 target_link_libraries(
   ${PROJECT_NAME}-lib
-  PUBLIC cppzmq crashpad::client CURL::libcurl prometheus-cpp::pull sentry::sentry spdlog::spdlog
+  PUBLIC cppzmq crashpad::client CURL::libcurl prometheus-cpp::pull sentry::sentry spdlog::spdlog stdc++fs
 )
 enable_security_flags_for_target(${PROJECT_NAME}-lib)
 

include/utils/FileHelpers.hpp

@@ -1,8 +1,12 @@
 #pragma once
 
+#include <atomic>
+#include <filesystem>
 #include <fstream>
 #include <regex>
 #include <string>
+#include <sys/inotify.h>
+#include <thread>
 #include <vector>
 
 /**
@@ -51,3 +55,66 @@ inline std::vector<std::string> findFromFile(const std::string &filePath, const
 	std::string lastWord;
 	return findFromFile(filePath, pattern, lastWord);
 }
+
+/// Callback function for file notifications
+using FNotifyCallback = std::function<void(const void *)>;
+
+/**
+ * Invokes functions for a file for given notify events
+ */
+class FileMonitor {
+  private:
+	/// File descriptor
+	int _fDescriptor{-1};
+	/// Watch descriptor
+	int _wDescriptor{-1};
+	/// File path
+	std::filesystem::path _filePath;
+	/// Callback function
+	FNotifyCallback _notifyCallback;
+	/// Notify types
+	uint32_t _notifyEvents;
+	/// User pointer
+	const void *_userPtr = nullptr;
+
+	/// Thread
+	std::unique_ptr<std::thread> _thread;
+	/// Flag to stop monitoring
+	std::atomic_flag _shouldStop{false};
+
+	void threadFunc() const noexcept;
+
+  public:
+	/**
+	 * Constructor
+	 * @param[in] filePath Path to the file
+	 * @param[in] notifyEvents Events to notify
+	 */
+	explicit FileMonitor(std::filesystem::path filePath, uint32_t notifyEvents = IN_MODIFY);
+
+	/// @brief Copy constructor
+	FileMonitor(const FileMonitor & /*unused*/) = delete;
+
+	/// @brief Move constructor
+	FileMonitor(FileMonitor && /*unused*/) = delete;
+
+	/// @brief Copy assignment operator
+	FileMonitor &operator=(FileMonitor /*unused*/) = delete;
+
+	/// @brief Move assignment operator
+	FileMonitor &operator=(FileMonitor && /*unused*/) = delete;
+
+	[[nodiscard]] FNotifyCallback notifyCallback() const { return _notifyCallback; }
+	void notifyCallback(FNotifyCallback func) { _notifyCallback = std::move(func); }
+
+	/**
+	 * Sets user pointer
+	 * @param[in] ptr User pointer
+	 */
+	void userPtr(const void *ptr) { _userPtr = ptr; }
+
+	/**
+	 * Destructor
+	 */
+	~FileMonitor();
+};

src/utils/FileHelpers.cpp

@@ -0,0 +1,125 @@
+#include "utils/FileHelpers.hpp"
+
+#include "utils/ErrorHelpers.hpp"
+
+#include <fcntl.h>
+#include <iostream>
+#include <sys/file.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+#include <spdlog/spdlog.h>
+
+/// Sleep interval for the file monitor
+constexpr int SLEEP_INTERVAL_MS = 50;
+
+void FileMonitor::threadFunc() const noexcept
+{
+	while (!_shouldStop._M_i)
+	{
+		// Buffer for reading events
+		unsigned int nBytes = 0;
+		if (ioctl(_fDescriptor, FIONREAD, &nBytes) < 0)
+		{
+			spdlog::error("Failed to get available events for file monitoring: {}", getErrnoString(errno));
+		}
+
+		auto buffer = std::vector<char>(nBytes + 1, '\0');
+		auto nRead = read(_fDescriptor, buffer.data(), nBytes);
+		if (nRead < 0)
+		{
+			spdlog::error("Failed to read events for file monitoring: {}", getErrnoString(errno));
+		}
+		else if (nRead == 0)
+		{
+			spdlog::debug("No events read for file monitoring");
+		}
+
+		ssize_t idx = 0;
+		while (_notifyCallback && idx < nRead)
+		{
+			const auto *event = reinterpret_cast<inotify_event *>(&buffer[static_cast<size_t>(idx)]);
+
+			// Check if file notify type matches
+			if ((event->mask & _notifyEvents) != 0)
+			{
+				_notifyCallback(_userPtr);
+				break;
+			}
+
+			idx += static_cast<ssize_t>(sizeof(inotify_event) + event->len);
+		}
+
+		std::this_thread::sleep_for(std::chrono::milliseconds(SLEEP_INTERVAL_MS));
+	}
+}
+
+FileMonitor::FileMonitor(std::filesystem::path filePath, uint32_t notifyEvents)
+	: _fDescriptor(inotify_init()), _filePath(std::move(filePath)), _notifyEvents(notifyEvents)
+{
+	if (_fDescriptor < 0)
+	{
+		throw std::ios_base::failure("Failed to initialize inotify");
+	}
+
+	_wDescriptor = inotify_add_watch(_fDescriptor, _filePath.c_str(), notifyEvents);
+	if (_wDescriptor < 0)
+	{
+		close(_fDescriptor);
+		throw std::ios_base::failure("Failed to add watch descriptor");
+	}
+
+	if (fcntl(_fDescriptor, F_SETFL, fcntl(_fDescriptor, F_GETFL) | O_NONBLOCK) < 0)
+	{
+		close(_fDescriptor);
+		throw std::ios_base::failure("Failed to set file descriptor to non-blocking mode");
+	}
+
+	_thread = std::make_unique<std::thread>(&FileMonitor::threadFunc, this);
+}
+
+FileMonitor::~FileMonitor()
+{
+	_shouldStop.test_and_set();
+	if (_thread && _thread->joinable())
+	{
+		_thread->join();
+		_thread.reset();
+	}
+
+	// Remove watch descriptor first
+	if (_wDescriptor >= 0)
+	{
+		if (inotify_rm_watch(_fDescriptor, _wDescriptor) < 0)
+		{
+			try
+			{
+				spdlog::error("Failed to remove watch descriptor: {}", getErrnoString(errno));
+			}
+			catch (const std::exception &e)
+			{
+				std::cerr << "Failed to remove watch descriptor and also logger thrown an exception: "
+						  << getErrnoString(errno) << " " << e.what() << '\n';
+			}
+		}
+		_wDescriptor = -1;
+	}
+
+	// Then close the file descriptor
+	if (_fDescriptor >= 0)
+	{
+		if (close(_fDescriptor) < 0)
+		{
+			try
+			{
+				spdlog::error("Failed to close file descriptor: {}", getErrnoString(errno));
+			}
+			catch (const std::exception &e)
+			{
+				std::cerr << "Failed to close file descriptor and also logger thrown an exception: "
+						  << getErrnoString(errno) << " " << e.what() << '\n';
+			}
+		}
+		_fDescriptor = -1;
+	}
+}

tests/unittests/Utils_UnitTests.cpp

@@ -71,6 +71,27 @@ TEST(Utils_Tests, FileHelpersUnitTests)
 
 	readLines = findFromFile(TEST_DATA_READ_PATH, "^dummy", word);
 	ASSERT_TRUE(readLines.empty());
+
+	FileMonitor monitor(TEST_DATA_READ_PATH, IN_OPEN);
+	int val = 0xFF;
+	monitor.userPtr(&val);
+
+	bool isInvoked = false;
+	bool isAccessed = false;
+	monitor.notifyCallback([&isInvoked, &isAccessed](const void *ptr) {
+		isInvoked = true;
+		if (ptr)
+		{
+			isAccessed = *(static_cast<const int *>(ptr)) == 0xFF;
+		}
+	});
+
+	std::ifstream file(TEST_DATA_READ_PATH);
+	ASSERT_TRUE(file.is_open());
+
+	std::this_thread::sleep_for(std::chrono::milliseconds(300));
+	ASSERT_TRUE(isInvoked);
+	ASSERT_TRUE(isAccessed);
 }
 
 TEST(Utils_Tests, InputParserUnitTests)