Allow basic_file_sink to open a file in text mode

Added an optional `bool` parameter to the explicit `basic_file_sink`
constructor, allowing to open the file in in text mode, instead of in binary
mode.

Enables automatic conversion of '\n' characters _inside_ a message string to a
platform specific eol representation. (`\r\n` on Windows.)

include/spdlog/details/file_helper-inl.h

@@ -29,13 +29,13 @@ SPDLOG_INLINE file_helper::~file_helper()
     close();
 }
 
-SPDLOG_INLINE void file_helper::open(const filename_t &fname, bool truncate)
+SPDLOG_INLINE void file_helper::open(const filename_t &fname, bool truncate, bool text_mode)
 {
     close();
     filename_ = fname;
 
-    auto *mode = SPDLOG_FILENAME_T("ab");
-    auto *trunc_mode = SPDLOG_FILENAME_T("wb");
+    auto *mode = text_mode ? SPDLOG_FILENAME_T("a") : SPDLOG_FILENAME_T("ab");
+    auto *trunc_mode = text_mode ? SPDLOG_FILENAME_T("w") : SPDLOG_FILENAME_T("wb");
 
     if (event_handlers_.before_open)
     {
@@ -47,8 +47,8 @@ SPDLOG_INLINE void file_helper::open(const filename_t &fname, bool truncate)
         os::create_dir(os::dir_name(fname));
         if (truncate)
         {
-            // Truncate by opening-and-closing a tmp file in "wb" mode, always
-            // opening the actual log-we-write-to in "ab" mode, since that
+            // Truncate by opening-and-closing a tmp file in trunc mode, always
+            // opening the actual log-we-write-to in append mode, since that
             // interacts more politely with eternal processes that might
             // rotate/truncate the file underneath us.
             std::FILE *tmp;

include/spdlog/details/file_helper.h

@@ -23,7 +23,7 @@ public:
     file_helper &operator=(const file_helper &) = delete;
     ~file_helper();
 
-    void open(const filename_t &fname, bool truncate = false);
+    void open(const filename_t &fname, bool truncate = false, bool text_mode = false);
     void reopen(bool truncate);
     void flush();
     void sync();

include/spdlog/details/os-inl.h

@@ -142,7 +142,7 @@ SPDLOG_INLINE bool fopen_s(FILE **fp, const filename_t &filename, const filename
 #    endif
 #else // unix
 #    if defined(SPDLOG_PREVENT_CHILD_FD)
-    const int mode_flag = mode == SPDLOG_FILENAME_T("ab") ? O_APPEND : O_TRUNC;
+    const int mode_flag = (mode.find('a') == filename_t::npos) ? O_TRUNC : O_APPEND;
     const int fd = ::open((filename.c_str()), O_CREAT | O_WRONLY | O_CLOEXEC | mode_flag, mode_t(0644));
     if (fd == -1)
     {

include/spdlog/sinks/base_sink-inl.h

@@ -53,7 +53,16 @@ void SPDLOG_INLINE spdlog::sinks::base_sink<Mutex>::set_formatter(std::unique_pt
 template<typename Mutex>
 void SPDLOG_INLINE spdlog::sinks::base_sink<Mutex>::set_pattern_(const std::string &pattern)
 {
-    set_formatter_(details::make_unique<spdlog::pattern_formatter>(pattern));
+    const auto current_pattern_formatter = dynamic_cast<spdlog::pattern_formatter *>(formatter_.get());
+
+    if (current_pattern_formatter)
+    {
+        current_pattern_formatter->set_pattern(pattern);
+    }
+    else
+    {
+        set_formatter_(details::make_unique<spdlog::pattern_formatter>(pattern));
+    }
 }
 
 template<typename Mutex>

include/spdlog/sinks/basic_file_sink-inl.h

@@ -9,15 +9,18 @@
 
 #include <spdlog/common.h>
 #include <spdlog/details/os.h>
+#include <spdlog/pattern_formatter.h>
 
 namespace spdlog {
 namespace sinks {
 
 template<typename Mutex>
-SPDLOG_INLINE basic_file_sink<Mutex>::basic_file_sink(const filename_t &filename, bool truncate, const file_event_handlers &event_handlers)
-    : file_helper_{event_handlers}
+SPDLOG_INLINE basic_file_sink<Mutex>::basic_file_sink(
+    const filename_t &filename, bool truncate, const file_event_handlers &event_handlers, bool text_mode)
+    : base_sink<Mutex>{details::make_unique<pattern_formatter>(pattern_time_type::local, text_mode ? "\n" : details::os::default_eol)}
+    , file_helper_{event_handlers}
 {
-    file_helper_.open(filename, truncate);
+    file_helper_.open(filename, truncate, text_mode);
 }
 
 template<typename Mutex>

include/spdlog/sinks/basic_file_sink.h

@@ -20,7 +20,8 @@ template<typename Mutex>
 class basic_file_sink final : public base_sink<Mutex>
 {
 public:
-    explicit basic_file_sink(const filename_t &filename, bool truncate = false, const file_event_handlers &event_handlers = {});
+    explicit basic_file_sink(
+        const filename_t &filename, bool truncate = false, const file_event_handlers &event_handlers = {}, bool text_mode = false);
     const filename_t &filename() const;
 
 protected:

tests/test_file_logging.cpp

@@ -23,6 +23,28 @@ TEST_CASE("simple_file_logger", "[simple_logger]]")
     REQUIRE(file_contents(SIMPLE_LOG) == spdlog::fmt_lib::format("Test message 1{}Test message 2{}", default_eol, default_eol));
 }
 
+TEST_CASE("text_file_logger", "[text_file_logger]]")
+{
+    spdlog::filename_t filename = SPDLOG_FILENAME_T(SIMPLE_LOG);
+
+    for (const bool text_mode : {false, true})
+    {
+        prepare_logdir();
+
+        auto sink = std::make_shared<spdlog::sinks::basic_file_sink_mt>(filename, false, spdlog::file_event_handlers{}, text_mode);
+        sink->set_pattern("%v");
+        spdlog::logger logger("logger", sink);
+
+        logger.info("Test line {}\nTest line {}", 1, 2);
+
+        logger.flush();
+        require_message_count(SIMPLE_LOG, 2);
+        using spdlog::details::os::default_eol;
+        REQUIRE(file_contents(SIMPLE_LOG) ==
+                spdlog::fmt_lib::format("Test line 1{}Test line 2{}", text_mode ? default_eol : "\n", default_eol));
+    }
+}
+
 TEST_CASE("flush_on", "[flush_on]]")
 {
     prepare_logdir();