feat(logging): rotating log files (#5485)

tests/unit/test_logging.cpp

@@ -5,9 +5,14 @@
 #include "../tests_common.h"
 #include "../tests_log_checker.h"
 
+#include <filesystem>
 #include <format>
+#include <fstream>
+#include <iterator>
 #include <random>
 #include <src/logging.h>
+#include <string>
+#include <string_view>
 
 namespace {
   std::array log_levels = {
@@ -20,8 +25,103 @@ namespace {
   };
 
   constexpr auto log_file = "test_sunshine.log";
+
+  /**
+   * @brief Write test content to a log file.
+   *
+   * @param path Path to write.
+   * @param content Content to write.
+   */
+  void write_log_file(const std::filesystem::path &path, std::string_view content) {
+    std::ofstream output {path};
+    output << content;
+  }
+
+  /**
+   * @brief Read all content from a test log file.
+   *
+   * @param path Path to read.
+   * @return File content.
+   */
+  std::string read_log_file(const std::filesystem::path &path) {
+    std::ifstream input {path};
+    return {std::istreambuf_iterator<char> {input}, std::istreambuf_iterator<char> {}};
+  }
 }  // namespace
 
+/**
+ * @brief Test fixture for startup log rotation.
+ */
+class LogRotationTest: public BaseTest {
+protected:
+  /**
+   * @brief Create an empty directory for the current test.
+   */
+  void SetUp() override {
+    BaseTest::SetUp();
+    std::filesystem::remove_all(test_directory);
+    std::filesystem::create_directories(test_directory);
+  }
+
+  /**
+   * @brief Remove files created by the current test.
+   */
+  void TearDown() override {
+    std::filesystem::remove_all(test_directory);
+    BaseTest::TearDown();
+  }
+
+  /**
+   * @brief Build the path for a rotated test log.
+   *
+   * @param generation Rotated log generation number.
+   * @return Path with the generation suffix appended.
+   */
+  std::filesystem::path rotated_log_path(std::size_t generation) const {
+    auto path = log_path;
+    path += std::format(".{}", generation);
+    return path;
+  }
+
+  const std::filesystem::path test_directory {std::filesystem::path {SUNSHINE_TEST_BIN_DIR} / "log_rotation_tests"};  ///< Directory containing log rotation test files.
+  const std::filesystem::path log_path {test_directory / "custom.log"};  ///< Path to the current test log.
+};
+
+TEST_F(LogRotationTest, RotatesCurrentLogAndRetainsFivePreviousLogs) {
+  write_log_file(log_path, "current");
+  for (std::size_t generation = 1; generation <= logging::retained_log_file_count; ++generation) {
+    write_log_file(rotated_log_path(generation), std::to_string(generation));
+  }
+
+  EXPECT_FALSE(logging::rotate_log_file(log_path));
+
+  EXPECT_FALSE(std::filesystem::exists(log_path));
+  EXPECT_EQ(read_log_file(rotated_log_path(1)), "current");
+  EXPECT_EQ(read_log_file(rotated_log_path(2)), "1");
+  EXPECT_EQ(read_log_file(rotated_log_path(3)), "2");
+  EXPECT_EQ(read_log_file(rotated_log_path(4)), "3");
+  EXPECT_EQ(read_log_file(rotated_log_path(5)), "4");
+}
+
+TEST_F(LogRotationTest, SupportsMissingLogGenerations) {
+  write_log_file(rotated_log_path(2), "second");
+
+  EXPECT_FALSE(logging::rotate_log_file(log_path));
+
+  EXPECT_FALSE(std::filesystem::exists(log_path));
+  EXPECT_FALSE(std::filesystem::exists(rotated_log_path(1)));
+  EXPECT_FALSE(std::filesystem::exists(rotated_log_path(2)));
+  EXPECT_EQ(read_log_file(rotated_log_path(3)), "second");
+}
+
+TEST_F(LogRotationTest, ReportsFilesystemErrors) {
+  std::filesystem::create_directories(rotated_log_path(logging::retained_log_file_count) / "child");
+  write_log_file(log_path, "current");
+
+  EXPECT_TRUE(logging::rotate_log_file(log_path));
+  EXPECT_EQ(read_log_file(log_path), "current");
+}
+
 struct LogLevelsTest: BaseTest, testing::WithParamInterface<decltype(log_levels)::value_type> {};
 
 INSTANTIATE_TEST_SUITE_P(