Use fmt::string_view when logging a C string to avoid unnecessary copy

bench/bench.cpp

@@ -29,6 +29,7 @@ using namespace utils;
 void bench(int howmany, std::shared_ptr<spdlog::logger> log);
 void bench_mt(int howmany, std::shared_ptr<spdlog::logger> log, int thread_count);
 void bench_default_api(int howmany, std::shared_ptr<spdlog::logger> log);
+void bench_c_string(int howmany, std::shared_ptr<spdlog::logger> log);
 
 int main(int argc, char *argv[])
 {
@@ -81,6 +82,21 @@ int main(int argc, char *argv[])
 
         bench_default_api(howmany, spdlog::create<null_sink_st>("null_st"));
 
+        spdlog::info("**************************************************************");
+        spdlog::info("C-string. Single thread, {:n} iterations", howmany);
+        spdlog::info("**************************************************************");
+
+        basic_st = spdlog::basic_logger_st("basic_st", "logs/basic_cs.log", true);
+        bench_c_string(howmany, std::move(basic_st));
+
+        rotating_st = spdlog::rotating_logger_st("rotating_st", "logs/rotating_cs.log", file_size, rotating_files);
+        bench_c_string(howmany, std::move(rotating_st));
+
+        daily_st = spdlog::daily_logger_st("daily_st", "logs/daily_cs.log");
+        bench_c_string(howmany, std::move(daily_st));
+
+        bench_c_string(howmany, spdlog::create<null_sink_st>("null_st"));
+
         spdlog::info("**************************************************************");
         spdlog::info("{:n} threads sharing same logger, {:n} iterations", threads, howmany);
         spdlog::info("**************************************************************");
@@ -173,3 +189,26 @@ void bench_default_api(int howmany, std::shared_ptr<spdlog::logger> log)
     spdlog::set_default_logger(std::move(orig_default));
     spdlog::info("{:<16} Elapsed: {:0.2f} secs {:>16n}/sec", log->name(), delta_d, int(howmany / delta_d));
 }
+
+void bench_c_string(int howmany, std::shared_ptr<spdlog::logger> log)
+{
+    const char *msg = "Lorem ipsum dolor sit amet, consectetur adipiscing elit. Vestibulum pharetra metus cursus " \
+        "lacus placerat congue. Nulla egestas, mauris a tincidunt tempus, enim lectus volutpat mi, eu consequat sem " \
+        "libero nec massa. In dapibus ipsum a diam rhoncus gravida. Etiam non dapibus eros. Donec fringilla dui sed " \
+        "augue pretium, nec scelerisque est maximus. Nullam convallis, sem nec blandit maximus, nisi turpis ornare " \
+        "nisl, sit amet volutpat neque massa eu odio. Maecenas malesuada quam ex, posuere congue nibh turpis duis.";
+    using std::chrono::high_resolution_clock;
+    auto orig_default = spdlog::default_logger();
+    spdlog::set_default_logger(log);
+    auto start = high_resolution_clock::now();
+    for (auto i = 0; i < howmany; ++i)
+    {
+        spdlog::log(level::info, msg);
+    }
+
+    auto delta = high_resolution_clock::now() - start;
+    auto delta_d = duration_cast<duration<double>>(delta).count();
+    spdlog::drop(log->name());
+    spdlog::set_default_logger(std::move(orig_default));
+    spdlog::info("{:<16} Elapsed: {:0.2f} secs {:>16n}/sec", log->name(), delta_d, int(howmany / delta_d));
+}

include/spdlog/details/fmt_helper.h

@@ -5,6 +5,7 @@
 #pragma once
 
 #include "chrono"
+#include "spdlog/details/log_msg.h"
 #include "spdlog/fmt/fmt.h"
 
 // Some fmt helpers to efficiently format and pad ints and strings
@@ -40,6 +41,17 @@ inline void append_int(T n, fmt::basic_memory_buffer<char, Buffer_Size> &dest)
     dest.append(i.data(), i.data() + i.size());
 }
 
+template<size_t Buffer_Size>
+inline void append_msg(const details::log_msg &msg, fmt::basic_memory_buffer<char, Buffer_Size> &dest)
+{
+    auto *c_buf = msg.c_string.data();
+    if (c_buf != nullptr) {
+        dest.append(c_buf, c_buf + msg.c_string.size());
+    } else {
+        append_buf(msg.raw, dest);
+    }
+}
+
 template<size_t Buffer_Size>
 inline void pad2(int n, fmt::basic_memory_buffer<char, Buffer_Size> &dest)
 {

include/spdlog/details/log_msg.h

@@ -39,6 +39,9 @@ struct log_msg
     log_clock::time_point time;
     size_t thread_id;
     fmt::memory_buffer raw;
+    // if c_string.data() is not nullptr, c_string should be used as the message
+    // instead of raw above 
+    fmt::string_view c_string;
     size_t msg_id;
 
     // info about wrapping the formatted text with color (updated by pattern_formatter).

include/spdlog/details/logger_impl.h

@@ -20,7 +20,7 @@ inline spdlog::logger::logger(std::string logger_name, It begin, It end)
     , flush_level_(level::off)
     , last_err_time_(0)
     , msg_counter_(1) // message counter will start from 1. 0-message id will be
-                      // reserved for controll messages
+                      // reserved for control messages
 {
     err_handler_ = [this](const std::string &msg) { this->default_err_handler_(msg); };
 }
@@ -70,8 +70,12 @@ inline void spdlog::logger::log(level::level_enum lvl, const char *fmt, const Ar
     SPDLOG_CATCH_AND_HANDLE
 }
 
-template<typename... Args>
 inline void spdlog::logger::log(level::level_enum lvl, const char *msg)
+{
+    logn(lvl, msg, std::char_traits<char>::length(msg));
+}
+
+inline void spdlog::logger::logn(level::level_enum lvl, const char *msg, size_t msg_len)
 {
     if (!should_log(lvl))
     {
@@ -80,7 +84,7 @@ inline void spdlog::logger::log(level::level_enum lvl, const char *msg)
     try
     {
         details::log_msg log_msg(&name_, lvl);
-        details::fmt_helper::append_c_str(msg, log_msg.raw);
+        log_msg.c_string = fmt::string_view(msg, msg_len);
         sink_it_(log_msg);
     }
     SPDLOG_CATCH_AND_HANDLE

include/spdlog/details/pattern_formatter.h

@@ -401,7 +401,7 @@ class v_formatter final : public flag_formatter
 {
     void format(const details::log_msg &msg, const std::tm &, fmt::memory_buffer &dest) override
     {
-        fmt_helper::append_buf(msg.raw, dest);
+        fmt_helper::append_msg(msg, dest);
     }
 };
 
@@ -524,7 +524,7 @@ class full_formatter final : public flag_formatter
         msg.color_range_end = dest.size();
         dest.push_back(']');
         dest.push_back(' ');
-        fmt_helper::append_buf(msg.raw, dest);
+        fmt_helper::append_msg(msg, dest);
     }
 
 private:

include/spdlog/details/thread_pool.h

@@ -1,5 +1,6 @@
 #pragma once
 
+#include "spdlog/details/fmt_helper.h"
 #include "spdlog/details/log_msg.h"
 #include "spdlog/details/mpmc_blocking_q.h"
 #include "spdlog/details/os.h"
@@ -77,7 +78,7 @@ struct async_msg
         , msg_id(m.msg_id)
         , worker_ptr(std::move(worker))
     {
-        fmt_helper::append_buf(m.raw, raw);
+        fmt_helper::append_msg(m, raw);
     }
 
     async_msg(async_logger_ptr &&worker, async_msg_type the_type)

include/spdlog/logger.h

@@ -46,9 +46,10 @@ public:
     template<typename... Args>
     void log(level::level_enum lvl, const char *fmt, const Args &... args);
 
-    template<typename... Args>
     void log(level::level_enum lvl, const char *msg);
 
+    void logn(level::level_enum lvl, const char *msg, size_t msg_len);
+
     template<typename... Args>
     void trace(const char *fmt, const Args &... args);
 

include/spdlog/sinks/android_sink.h

@@ -47,7 +47,7 @@ protected:
         fmt::memory_buffer formatted;
         if (use_raw_msg_)
         {
-            details::fmt_helper::append_buf(msg.raw, formatted);
+            details::fmt_helper::append_msg(msg, formatted);
         }
         else
         {

include/spdlog/sinks/syslog_sink.h

@@ -53,7 +53,12 @@ public:
 protected:
     void sink_it_(const details::log_msg &msg) override
     {
-        ::syslog(syslog_prio_from_level(msg), "%s", fmt::to_string(msg.raw).c_str());
+        if (msg.c_string.data() != nullptr)
+        {
+            ::syslog(syslog_prio_from_level(msg), "%.*s", static_cast<int>(msg.c_string.size()), msg.c_string.data());
+        } else {
+            ::syslog(syslog_prio_from_level(msg), "%s", fmt::to_string(msg.raw).c_str());
+        }
     }
 
     void flush_() override {}

tests/test_misc.cpp

@@ -231,3 +231,22 @@ TEST_CASE("default logger API", "[default logger]")
     spdlog::drop_all();
     spdlog::set_pattern("%v");
 }
+
+TEST_CASE("C string", "[c_string]")
+{
+    std::ostringstream oss;
+    auto oss_sink = std::make_shared<spdlog::sinks::ostream_sink_mt>(oss);
+
+    spdlog::logger oss_logger("oss", oss_sink);
+    oss_logger.set_level(spdlog::level::debug);
+    oss_logger.set_pattern("*** %v");
+
+    const char *test_string = "Lorem ipsum dolor sit amet, consectetur adipiscing elit massa nunc";
+
+    oss_logger.log(spdlog::level::debug, test_string);
+    REQUIRE(oss.str() == "*** " + std::string(test_string) + std::string(spdlog::details::os::default_eol));
+
+    oss.str("");
+    oss_logger.logn(spdlog::level::debug, test_string, 11);
+    REQUIRE(oss.str() == "*** " + std::string(test_string, 11) + std::string(spdlog::details::os::default_eol));
+}