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// Copyright 2009 The Go Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.

// Package syslog provides a simple interface to the system log service. It
// can send messages to the syslog daemon using UNIX domain sockets, UDP, or
// TCP connections.
package syslog

import (
        "errors"
        "fmt"
        "log"
        "net"
        "os"
)

type Priority int

const (
        // From /usr/include/sys/syslog.h.
        // These are the same on Linux, BSD, and OS X.
        LOG_EMERG Priority = iota
        LOG_ALERT
        LOG_CRIT
        LOG_ERR
        LOG_WARNING
        LOG_NOTICE
        LOG_INFO
        LOG_DEBUG
)

// A Writer is a connection to a syslog server.
type Writer struct {
        priority Priority
        prefix   string
        conn     serverConn
}

type serverConn interface {
        writeBytes(p Priority, prefix string, b []byte) (int, error)
        writeString(p Priority, prefix string, s string) (int, error)
        close() error
}

type netConn struct {
        conn net.Conn
}

// New establishes a new connection to the system log daemon.
// Each write to the returned writer sends a log message with
// the given priority and prefix.
func New(priority Priority, prefix string) (w *Writer, err error) {
        return Dial("", "", priority, prefix)
}

// Dial establishes a connection to a log daemon by connecting
// to address raddr on the network net.
// Each write to the returned writer sends a log message with
// the given priority and prefix.
func Dial(network, raddr string, priority Priority, prefix string) (w *Writer, err error) {
        if prefix == "" {
                prefix = os.Args[0]
        }
        var conn serverConn
        if network == "" {
                conn, err = unixSyslog()
        } else {
                var c net.Conn
                c, err = net.Dial(network, raddr)
                conn = netConn{c}
        }
        return &Writer{priority, prefix, conn}, err
}

// Write sends a log message to the syslog daemon.
func (w *Writer) Write(b []byte) (int, error) {
        if w.priority > LOG_DEBUG || w.priority < LOG_EMERG {
                return 0, errors.New("log/syslog: invalid priority")
        }
        return w.conn.writeBytes(w.priority, w.prefix, b)
}

func (w *Writer) writeString(p Priority, s string) (int, error) {
        return w.conn.writeString(p, w.prefix, s)
}

func (w *Writer) Close() error { return w.conn.close() }

// Emerg logs a message using the LOG_EMERG priority.
func (w *Writer) Emerg(m string) (err error) {
        _, err = w.writeString(LOG_EMERG, m)
        return err
}

// Alert logs a message using the LOG_ALERT priority.
func (w *Writer) Alert(m string) (err error) {
        _, err = w.writeString(LOG_ALERT, m)
        return err
}

// Crit logs a message using the LOG_CRIT priority.
func (w *Writer) Crit(m string) (err error) {
        _, err = w.writeString(LOG_CRIT, m)
        return err
}

// Err logs a message using the LOG_ERR priority.
func (w *Writer) Err(m string) (err error) {
        _, err = w.writeString(LOG_ERR, m)
        return err
}

// Warning logs a message using the LOG_WARNING priority.
func (w *Writer) Warning(m string) (err error) {
        _, err = w.writeString(LOG_WARNING, m)
        return err
}

// Notice logs a message using the LOG_NOTICE priority.
func (w *Writer) Notice(m string) (err error) {
        _, err = w.writeString(LOG_NOTICE, m)
        return err
}

// Info logs a message using the LOG_INFO priority.
func (w *Writer) Info(m string) (err error) {
        _, err = w.writeString(LOG_INFO, m)
        return err
}

// Debug logs a message using the LOG_DEBUG priority.
func (w *Writer) Debug(m string) (err error) {
        _, err = w.writeString(LOG_DEBUG, m)
        return err
}

func (n netConn) writeBytes(p Priority, prefix string, b []byte) (int, error) {
        return fmt.Fprintf(n.conn, "<%d>%s: %s\n", p, prefix, b)
}

func (n netConn) writeString(p Priority, prefix string, s string) (int, error) {
        return fmt.Fprintf(n.conn, "<%d>%s: %s\n", p, prefix, s)
}

func (n netConn) close() error {
        return n.conn.Close()
}

// NewLogger provides an object that implements the full log.Logger interface,
// but sends messages to Syslog instead; flag is passed as is to Logger;
// priority will be used for all messages sent using this interface.
// All messages are logged with priority p.
func NewLogger(p Priority, flag int) *log.Logger {
        s, err := New(p, "")
        if err != nil {
                return nil
        }
        return log.New(s, "", flag)
}