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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 log implements a simple logging package. It defines a type, Logger,

// with methods for formatting output. It also has a predefined 'standard'

// Logger accessible through helper functions Print[f|ln], Fatal[f|ln], and

// Panic[f|ln], which are easier to use than creating a Logger manually.

// That logger writes to standard error and prints the date and time

// of each logged message.

// The Fatal functions call os.Exit(1) after writing the log message.

// The Panic functions call panic after writing the log message.

package log

import (

        "bytes"

        "fmt"

        "io"

        "os"

        "runtime"

        "sync"

        "time"

)

// These flags define which text to prefix to each log entry generated by the Logger.

const (

        // Bits or'ed together to control what's printed. There is no control over the

        // order they appear (the order listed here) or the format they present (as

        // described in the comments).  A colon appears after these items:

        //      2009/0123 01:23:23.123123 /a/b/c/d.go:23: message

        Ldate         = 1 << iota     // the date: 2009/0123

        Ltime                         // the time: 01:23:23

        Lmicroseconds                 // microsecond resolution: 01:23:23.123123.  assumes Ltime.

        Llongfile                     // full file name and line number: /a/b/c/d.go:23

        Lshortfile                    // final file name element and line number: d.go:23. overrides Llongfile

        LstdFlags     = Ldate | Ltime // initial values for the standard logger

)

// A Logger represents an active logging object that generates lines of

// output to an io.Writer.  Each logging operation makes a single call to

// the Writer's Write method.  A Logger can be used simultaneously from

// multiple goroutines; it guarantees to serialize access to the Writer.

type Logger struct {

        mu     sync.Mutex   // ensures atomic writes; protects the following fields

        prefix string       // prefix to write at beginning of each line

        flag   int          // properties

        out    io.Writer    // destination for output

        buf    bytes.Buffer // for accumulating text to write

}

// New creates a new Logger.   The out variable sets the

// destination to which log data will be written.

// The prefix appears at the beginning of each generated log line.

// The flag argument defines the logging properties.

func New(out io.Writer, prefix string, flag int) *Logger {

        return &Logger{out: out, prefix: prefix, flag: flag}

}

var std = New(os.Stderr, "", LstdFlags)

// Cheap integer to fixed-width decimal ASCII.  Give a negative width to avoid zero-padding.

// Knows the buffer has capacity.

func itoa(buf *bytes.Buffer, i int, wid int) {

        var u uint = uint(i)

        if u == 0 && wid <= 1 {

                buf.WriteByte('0')

                return

        }

        // Assemble decimal in reverse order.

        var b [32]byte

        bp := len(b)

        for ; u > 0 || wid > 0; u /= 10 {

                bp--

                wid--

                b[bp] = byte(u%10) + '0'

        }

        // avoid slicing b to avoid an allocation.

        for bp < len(b) {

                buf.WriteByte(b[bp])

                bp++

        }

}

func (l *Logger) formatHeader(buf *bytes.Buffer, t time.Time, file string, line int) {

        buf.WriteString(l.prefix)

        if l.flag&(Ldate|Ltime|Lmicroseconds) != 0 {

                if l.flag&Ldate != 0 {

                        year, month, day := t.Date()

                        itoa(buf, year, 4)

                        buf.WriteByte('/')

                        itoa(buf, int(month), 2)

                        buf.WriteByte('/')

                        itoa(buf, day, 2)

                        buf.WriteByte(' ')

                }

                if l.flag&(Ltime|Lmicroseconds) != 0 {

                        hour, min, sec := t.Clock()

                        itoa(buf, hour, 2)

                        buf.WriteByte(':')

                        itoa(buf, min, 2)

                        buf.WriteByte(':')

                        itoa(buf, sec, 2)

                        if l.flag&Lmicroseconds != 0 {

                                buf.WriteByte('.')

                                itoa(buf, t.Nanosecond()/1e3, 6)

                        }

                        buf.WriteByte(' ')

                }

        }

        if l.flag&(Lshortfile|Llongfile) != 0 {

                if l.flag&Lshortfile != 0 {

                        short := file

                        for i := len(file) - 1; i > 0; i-- {

                                if file[i] == '/' {

                                        short = file[i+1:]

                                        break

                                }

                        }

                        file = short

                }

                buf.WriteString(file)

                buf.WriteByte(':')

                itoa(buf, line, -1)

                buf.WriteString(": ")

        }

}

// Output writes the output for a logging event.  The string s contains

// the text to print after the prefix specified by the flags of the

// Logger.  A newline is appended if the last character of s is not

// already a newline.  Calldepth is used to recover the PC and is

// provided for generality, although at the moment on all pre-defined

// paths it will be 2.

func (l *Logger) Output(calldepth int, s string) error {

        now := time.Now() // get this early.

        var file string

        var line int

        l.mu.Lock()

        defer l.mu.Unlock()

        if l.flag&(Lshortfile|Llongfile) != 0 {

                // release lock while getting caller info - it's expensive.

                l.mu.Unlock()

                var ok bool

                _, file, line, ok = runtime.Caller(calldepth)

                if !ok {

                        file = "???"

                        line = 0

                }

                l.mu.Lock()

        }

        l.buf.Reset()

        l.formatHeader(&l.buf, now, file, line)

        l.buf.WriteString(s)

        if len(s) > 0 && s[len(s)-1] != '\n' {

                l.buf.WriteByte('\n')

        }

        _, err := l.out.Write(l.buf.Bytes())

        return err

}

// Printf calls l.Output to print to the logger.

// Arguments are handled in the manner of fmt.Printf.

func (l *Logger) Printf(format string, v ...interface{}) {

        l.Output(2, fmt.Sprintf(format, v...))

}

// Print calls l.Output to print to the logger.

// Arguments are handled in the manner of fmt.Print.

func (l *Logger) Print(v ...interface{}) { l.Output(2, fmt.Sprint(v...)) }

// Println calls l.Output to print to the logger.

// Arguments are handled in the manner of fmt.Println.

func (l *Logger) Println(v ...interface{}) { l.Output(2, fmt.Sprintln(v...)) }

// Fatal is equivalent to l.Print() followed by a call to os.Exit(1).

func (l *Logger) Fatal(v ...interface{}) {

        l.Output(2, fmt.Sprint(v...))

        os.Exit(1)

}

// Fatalf is equivalent to l.Printf() followed by a call to os.Exit(1).

func (l *Logger) Fatalf(format string, v ...interface{}) {

        l.Output(2, fmt.Sprintf(format, v...))

        os.Exit(1)

}

// Fatalln is equivalent to l.Println() followed by a call to os.Exit(1).

func (l *Logger) Fatalln(v ...interface{}) {

        l.Output(2, fmt.Sprintln(v...))

        os.Exit(1)

}

// Panic is equivalent to l.Print() followed by a call to panic().

func (l *Logger) Panic(v ...interface{}) {

        s := fmt.Sprint(v...)

        l.Output(2, s)

        panic(s)

}

// Panicf is equivalent to l.Printf() followed by a call to panic().

func (l *Logger) Panicf(format string, v ...interface{}) {

        s := fmt.Sprintf(format, v...)

        l.Output(2, s)

        panic(s)

}

// Panicln is equivalent to l.Println() followed by a call to panic().

func (l *Logger) Panicln(v ...interface{}) {

        s := fmt.Sprintln(v...)

        l.Output(2, s)

        panic(s)

}

// Flags returns the output flags for the logger.

func (l *Logger) Flags() int {

        l.mu.Lock()

        defer l.mu.Unlock()

        return l.flag

}

// SetFlags sets the output flags for the logger.

func (l *Logger) SetFlags(flag int) {

        l.mu.Lock()

        defer l.mu.Unlock()

        l.flag = flag

}

// Prefix returns the output prefix for the logger.

func (l *Logger) Prefix() string {

        l.mu.Lock()

        defer l.mu.Unlock()

        return l.prefix

}

// SetPrefix sets the output prefix for the logger.

func (l *Logger) SetPrefix(prefix string) {

        l.mu.Lock()

        defer l.mu.Unlock()

        l.prefix = prefix

}

// SetOutput sets the output destination for the standard logger.

func SetOutput(w io.Writer) {

        std.mu.Lock()

        defer std.mu.Unlock()

        std.out = w

}

// Flags returns the output flags for the standard logger.

func Flags() int {

        return std.Flags()

}

// SetFlags sets the output flags for the standard logger.

func SetFlags(flag int) {

        std.SetFlags(flag)

}

// Prefix returns the output prefix for the standard logger.

func Prefix() string {

        return std.Prefix()

}

// SetPrefix sets the output prefix for the standard logger.

func SetPrefix(prefix string) {

        std.SetPrefix(prefix)

}

// These functions write to the standard logger.

// Print calls Output to print to the standard logger.

// Arguments are handled in the manner of fmt.Print.

func Print(v ...interface{}) {

        std.Output(2, fmt.Sprint(v...))

}

// Printf calls Output to print to the standard logger.

// Arguments are handled in the manner of fmt.Printf.

func Printf(format string, v ...interface{}) {

        std.Output(2, fmt.Sprintf(format, v...))

}

// Println calls Output to print to the standard logger.

// Arguments are handled in the manner of fmt.Println.

func Println(v ...interface{}) {

        std.Output(2, fmt.Sprintln(v...))

}

// Fatal is equivalent to Print() followed by a call to os.Exit(1).

func Fatal(v ...interface{}) {

        std.Output(2, fmt.Sprint(v...))

        os.Exit(1)

}

// Fatalf is equivalent to Printf() followed by a call to os.Exit(1).

func Fatalf(format string, v ...interface{}) {

        std.Output(2, fmt.Sprintf(format, v...))

        os.Exit(1)

}

// Fatalln is equivalent to Println() followed by a call to os.Exit(1).

func Fatalln(v ...interface{}) {

        std.Output(2, fmt.Sprintln(v...))

        os.Exit(1)

}

// Panic is equivalent to Print() followed by a call to panic().

func Panic(v ...interface{}) {

        s := fmt.Sprint(v...)

        std.Output(2, s)

        panic(s)

}

// Panicf is equivalent to Printf() followed by a call to panic().

func Panicf(format string, v ...interface{}) {

        s := fmt.Sprintf(format, v...)

        std.Output(2, s)

        panic(s)

}

// Panicln is equivalent to Println() followed by a call to panic().

func Panicln(v ...interface{}) {

        s := fmt.Sprintln(v...)

        std.Output(2, s)

        panic(s)

}