Add syslog_formatter

The formatter enables remote(udp/tcp) syslog sink

example/example.cpp

@@ -27,6 +27,7 @@ void custom_flags_example();
 void file_events_example();
 void replace_default_logger_example();
 void mdc_example();
+void syslog_formatter_example();
 
 #include "spdlog/spdlog.h"
 #include "spdlog/cfg/env.h"   // support for loading levels from the environment variable
@@ -86,6 +87,7 @@ int main(int, char *[]) {
         file_events_example();
         replace_default_logger_example();
         mdc_example();
+        syslog_formatter_example();
 
         // Flush all *registered* loggers using a worker thread every 3 seconds.
         // note: registered loggers *must* be thread safe for this to work correctly!
@@ -391,3 +393,14 @@ void mdc_example()
     spdlog::set_pattern("[%H:%M:%S %z] [%^%L%$] [%&] %v");
     spdlog::info("Some log message with context");
 }
+
+#include "spdlog/syslog_formatter.h"
+void syslog_formatter_example()
+{
+    // run "nc -klu 514" to receive the syslog message
+    spdlog::sinks::udp_sink_config udp_sink_config("127.0.0.1", 514);
+    auto udp_logger = spdlog::udp_logger_mt("udp_logger", udp_sink_config);
+    spdlog::syslog_formatter syslog_formatter(spdlog::facility::user, "localhost", "example");
+    udp_logger->set_formatter(syslog_formatter.clone());
+    udp_logger->info("this message will be logged in local syslog receiver");
+}

include/spdlog/syslog_formatter-inl.h

@@ -0,0 +1,107 @@
+#pragma once
+
+#ifndef SPDLOG_HEADER_ONLY
+    #include <spdlog/syslog_formatter.h>
+#endif
+
+#include <spdlog/details/fmt_helper.h>
+
+namespace spdlog {
+namespace details {
+
+namespace severity {
+    enum severity_enum : int {
+        emergency = 0,
+        alert = 1,
+        critical = 2,
+        error = 3,
+        warning = 4,
+        notice = 5,
+        informational = 6,
+        debug = 7,
+    };
+}
+
+} // namespace details
+
+SPDLOG_INLINE syslog_formatter::syslog_formatter(int facility, std::string hostname, std::string appname)
+    : facility_(facility),
+      hostname_(std::move(hostname)),
+      appname_(std::move(appname)),
+      pattern_formatter_("%Y-%m-%dT%H:%M:%SZ", pattern_time_type::utc, "") {
+    pattern_formatter_.need_localtime();
+}
+
+SPDLOG_INLINE std::unique_ptr<formatter> syslog_formatter::clone() const {
+    auto cloned = details::make_unique<syslog_formatter>(facility_, hostname_, appname_);
+#if defined(__GNUC__) && __GNUC__ < 5
+    return std::move(cloned);
+#else
+    return cloned;
+#endif
+}
+
+SPDLOG_INLINE void syslog_formatter::format(const details::log_msg &msg, memory_buf_t &dest) {
+    details::severity::severity_enum severity;
+
+    switch (msg.level) {
+        case level::critical:
+            severity = details::severity::critical;
+
+        case level::err:
+            severity = details::severity::error;
+            break;
+
+        case level::warn:
+            severity = details::severity::warning;
+            break;
+
+        case level::info:
+            severity = details::severity::informational;
+            break;
+
+        default:
+            severity = details::severity::debug;
+            break;
+    }
+
+    dest.push_back('<');
+    details::fmt_helper::append_int((facility_ * 8) + severity, dest);
+    dest.push_back('>');
+    dest.push_back('1');
+
+    dest.push_back(' ');
+    pattern_formatter_.format(msg, dest);
+
+    dest.push_back(' ');
+    if (hostname_.empty()) {
+        dest.push_back('-');
+    } else {
+        details::fmt_helper::append_string_view(hostname_, dest);
+    }
+
+    dest.push_back(' ');
+    if (appname_.empty()) {
+        dest.push_back('-');
+    } else {
+        details::fmt_helper::append_string_view(appname_, dest);
+    }
+    
+    dest.push_back(' ');
+    details::fmt_helper::append_int(details::os::pid(), dest);
+
+    dest.push_back(' ');
+    if (msg.logger_name.size() == 0) {
+        dest.push_back('-');
+    } else {
+        details::fmt_helper::append_string_view(msg.logger_name, dest);
+    }
+
+    dest.push_back(' ');
+    dest.push_back('-'); // nil structured data
+
+    dest.push_back(' ');
+    details::fmt_helper::append_string_view(msg.payload, dest);
+}
+
+} // namespace spdlog

include/spdlog/syslog_formatter.h

@@ -0,0 +1,63 @@
+#pragma once
+
+#include <spdlog/common.h>
+#include <spdlog/formatter.h>
+#include <spdlog/pattern_formatter.h>
+#include <spdlog/details/log_msg.h>
+
+#include <memory>
+#include <string>
+
+namespace spdlog {
+
+namespace facility {
+    enum facility_enum : int {
+        kernel = 0,
+        user = 1,
+        mail = 2,
+        daemons = 3,
+        security = 4,
+        syslogd = 5,
+        printer = 6,
+        network = 7,
+        uucp = 8,
+        clock = 9,
+        security2 = 10,
+        ftp = 11,
+        ntp = 12,
+        audit = 13,
+        alert = 14,
+        clock2 = 15,
+        local0 = 16,
+        local1 = 17,
+        local2 = 18,
+        local3 = 19,
+        local4 = 20,
+        local5 = 21,
+        local6 = 22,
+        local7 = 23
+    };
+}
+
+class SPDLOG_API syslog_formatter : public formatter {
+public:
+    explicit syslog_formatter(int facility, std::string hostname, std::string appname);
+
+    syslog_formatter(const syslog_formatter &other) = delete;
+    syslog_formatter &operator=(const syslog_formatter &other) = delete;
+
+    std::unique_ptr<formatter> clone() const override;
+    void format(const details::log_msg &msg, memory_buf_t &dest) override;
+
+private:
+    int facility_;
+    std::string hostname_;
+    std::string appname_;
+    spdlog::pattern_formatter pattern_formatter_;
+};
+
+} // namespace spdlog
+
+#ifdef SPDLOG_HEADER_ONLY
+    #include "syslog_formatter-inl.h"
+#endif

src/spdlog.cpp

@@ -17,6 +17,7 @@
 #include <spdlog/sinks/base_sink-inl.h>
 #include <spdlog/sinks/sink-inl.h>
 #include <spdlog/spdlog-inl.h>
+#include <spdlog/syslog_formatter-inl.h>
 
 #include <mutex>