3 files changed, 193 insertions, 0 deletions
diff --git a/src/change_log.cc b/src/change_log.cc
new file mode 100644
index 0000000..5ca0e8e
--- /dev/null
+++ b/src/change_log.cc
@@ -0,0 +1,104 @@
+#ifndef _GNU_SOURCE
+#define _GNU_SOURCE
+#endif
+
+#include <memory>
+#include <functional>
+#include <unordered_set>
+
+#include "io.h"
+#include "utility.h"
+
+static std::unique_ptr<std::unordered_set<std::string>> tracked_files;
+static std::unique_ptr<io::FileDescriptorGuard>         fd_guard;
+static std::unique_ptr<utility::Logger>                 log;
+
+template <class Result, typename... Arguments>
+std::function<Result(Arguments...)> get_real_function(
+	const std::string& symbol_name) {
+
+	Result (*real_function)(Arguments...) = nullptr;
+	const void* symbol_address = dlsym(RTLD_NEXT, symbol_name.c_str());
+
+	std::memcpy(&real_function, &symbol_address, sizeof(symbol_address));
+
+	return std::function<Result(Arguments...)>(real_function);
+}
+
+void init() __attribute__ ((constructor));
+void init() {
+	tracked_files = std::make_unique<std::unordered_set<std::string>>();
+
+	if ( getenv("CHANGE_LOG_TARGET") != NULL ) {
+		fd_guard = std::make_unique<io::FileDescriptorGuard>(
+			getenv("CHANGE_LOG_TARGET")
+		);
+		log      = std::make_unique<utility::Logger>(*fd_guard);
+	} else {
+		log      = std::make_unique<utility::Logger>(STDERR_FILENO);
+	}
+}
+
+void exit(int status) {
+	get_real_function<void, int>("exit")(status);
+}
+
+bool is_tracked_file(const std::string& file_name) {
+	return tracked_files->find(file_name) != tracked_files->end();
+}
+
+bool track_file(const std::string& file_name) {
+	return tracked_files->emplace(file_name).second;
+}
+
+ssize_t write(int fd, const void* buffer, size_t count) {
+	static auto real_write = get_real_function<ssize_t, int, const void*, size_t>("write");
+
+	if ( io::is_regular_file(fd) ) {
+		const std::string file_name{ io::get_file_name(fd) };
+
+		if ( !is_tracked_file(file_name) ) {
+			track_file(file_name);
+
+			log->append("wrote to '" + file_name + "'");
+		}
+	}
+
+	return real_write(fd, buffer, count);
+}
+
+int rename(const char* old_path, const char* new_path) {
+	static auto real_rename = get_real_function<int, const char*, const char*>("rename");
+
+	log->append("renamed '" + std::string(old_path) + "' to '" + std::string(new_path) + "'");
+
+	return real_rename(old_path, new_path);
+}
+
+int rmdir(const char* path) {
+	static auto real_rmdir = get_real_function<int, const char*>("rmdir");
+
+	log->append("removed directory '" + std::string(path) + "'");
+
+	return real_rmdir(path);
+}
+
+int unlink(const char* path) {
+	static auto real_unlink = get_real_function<int, const char*>("unlink");
+
+	log->append("removed '" + std::string(path) + "'");
+
+	return real_unlink(path);
+}
+
+int unlinkat(int dirfd, const char* path, int flags) {
+	static auto real_unlinkat = get_real_function<int, int, const char*, int>("unlinkat");
+
+	if ( dirfd == AT_FDCWD ) {
+		log->append("removed '" + std::string(path) + "'");
+	} else {
+		log->append("removed '" + io::get_file_name(dirfd) + path + "'");
+	}
+
+	return real_unlinkat(dirfd, path, flags);
+}
diff --git a/src/io.h b/src/io.h
new file mode 100644
index 0000000..87778ec
--- /dev/null
+++ b/src/io.h
@@ -0,0 +1,61 @@
+#ifndef CHANGE_IO_H_
+#define CHANGE_IO_H_
+
+#include <unistd.h>
+#include <dlfcn.h>
+#include <fcntl.h>
+#include <sys/stat.h>
+
+#include <cstring>
+
+namespace io {
+
+class FileDescriptorGuard {
+	public:
+		FileDescriptorGuard(const std::string& path) {
+			this->fd = open(path.c_str(), O_WRONLY | O_APPEND);
+
+			if ( !this->fd ) {
+				this->fd = STDERR_FILENO;
+			}
+		}
+
+		~FileDescriptorGuard() {
+			close(this->fd);
+		}
+
+		operator int() {
+			return this->fd;
+		}
+
+	private:
+		int fd;
+
+};
+
+std::string get_file_name(int fd) {
+	char proc_link[20];
+	char file_name[256];
+
+	snprintf(proc_link, sizeof(proc_link), "/proc/self/fd/%d", fd);
+	const ssize_t name_size = readlink(proc_link, file_name, sizeof(file_name));
+
+	if ( name_size > 0 ) {
+		file_name[name_size] = '\0';
+
+		return std::string(file_name);
+	} else {
+		return std::string();
+	}
+}
+
+bool is_regular_file(int fd) {
+	struct stat fd_stat;
+	fstat(fd, &fd_stat);
+
+	return S_ISREG(fd_stat.st_mode);
+}
+
+}
+
+#endif  // CHANGE_IO_H_
diff --git a/src/utility.h b/src/utility.h
new file mode 100644
index 0000000..27ce8e9
--- /dev/null
+++ b/src/utility.h
@@ -0,0 +1,28 @@
+#ifndef CHANGE_UTILITY_H_
+#define CHANGE_UTILITY_H_
+
+#include <ext/stdio_filebuf.h>
+
+#include <iostream>
+
+namespace utility {
+
+class Logger {
+	public:
+		Logger(const int target_fd):
+			buffer(target_fd, std::ios::out),
+			stream(&this->buffer) { }
+
+		void append(const std::string& msg) {
+			this->stream << msg << std::endl;
+		}
+
+	private:
+		__gnu_cxx::stdio_filebuf<char> buffer;
+		std::ostream                   stream;
+
+};
+
+}
+
+#endif  // CHANGE_UTILITY_H_