336 lines
9.0 KiB
Go
336 lines
9.0 KiB
Go
// Package mlog is a generic logging library. The log methods come in different
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// severities: Debug, Info, Warn, Error, and Fatal.
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//
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// The log methods take in a string describing the error, and a set of key/value
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// pairs giving the specific context around the error. The string is intended to
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// always be the same no matter what, while the key/value pairs give information
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// like which userID the error happened to, or any other relevant contextual
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// information.
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//
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// Examples:
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//
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// Info("Something important has occurred")
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// Error("Could not open file", llog.KV{"filename": filename}, llog.ErrKV(err))
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//
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package mlog
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import (
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"fmt"
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"io"
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"os"
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"sort"
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"strconv"
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"strings"
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"sync"
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)
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// Truncate is a helper function to truncate a string to a given size. It will
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// add 3 trailing elipses, so the returned string will be at most size+3
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// characters long
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func Truncate(s string, size int) string {
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if len(s) <= size {
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return s
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}
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return s[:size] + "..."
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}
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// Level describes the severity of a particular log message, and can be compared
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// to the severity of any other Level
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type Level interface {
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// String gives the string form of the level, e.g. "INFO" or "ERROR"
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String() string
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// Uint gives an integer indicator of the severity of the level, with zero
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// being most severe. If a Level with Uint of zero is logged then the Logger
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// implementation provided by this package will exit the process (i.e. zero
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// is used as Fatal).
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Uint() uint
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}
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type level struct {
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s string
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i uint
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}
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func (l level) String() string {
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return l.s
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}
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func (l level) Uint() uint {
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return l.i
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}
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// All pre-defined log levels
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var (
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DebugLevel Level = level{s: "DEBUG", i: 40}
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InfoLevel Level = level{s: "INFO", i: 30}
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WarnLevel Level = level{s: "WARN", i: 20}
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ErrorLevel Level = level{s: "ERROR", i: 10}
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FatalLevel Level = level{s: "FATAL", i: 0}
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)
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// LevelFromString parses a string, possibly lowercase, and returns the Level
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// identified by it, or an error.
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//
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// Note that this only works for the Levels pre-defined in this package, if
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// you've extended the package to use your own levels you'll have to implement
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// your own LevelFromString method.
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func LevelFromString(ls string) (Level, error) {
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var l Level
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switch strings.ToUpper(ls) {
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case "DEBUG":
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l = DebugLevel
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case "INFO":
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l = InfoLevel
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case "WARN":
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l = WarnLevel
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case "ERROR":
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l = ErrorLevel
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case "FATAL":
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l = FatalLevel
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default:
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return nil, fmt.Errorf("unknown log level %q", ls)
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}
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return l, nil
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}
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// KVer is used to provide context to a log entry in the form of a dynamic set
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// of key/value pairs which can be different for every entry.
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//
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// Each returned KV should be modifiable.
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type KVer interface {
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KV() KV
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}
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// KV is a set of key/value pairs which provides context for a log entry by a
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// KVer. KV is itself also a KVer.
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type KV map[string]interface{}
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// KV implements the KVer method by returning a copy of the KV
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func (kv KV) KV() KV {
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nkv := make(KV, len(kv))
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for k, v := range kv {
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nkv[k] = v
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}
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return nkv
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}
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// Set returns a copy of the KV being called on with the given key/val set on
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// it. The original KV is unaffected
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func (kv KV) Set(k string, v interface{}) KV {
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nkv := kv.KV()
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nkv[k] = v
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return nkv
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}
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// separate from Merge because it's convenient to not return a KVer if that KVer
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// is going to immediately have KV called on it (and thereby create a copy for
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// no reason).
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func merge(kvs ...KVer) KV {
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kvm := kvs[0].KV()
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for _, kv := range kvs[1:] {
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for k, v := range kv.KV() {
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kvm[k] = v
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}
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}
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return KV(kvm)
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}
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// Merge takes in multiple KVers and returns a single KVer which is the union of
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// all the passed in ones. Key/vals on the rightmost of the set take precedence
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// over conflicting ones to the left.
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func Merge(kvs ...KVer) KVer {
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return merge(kvs...)
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}
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// Message describes a message to be logged, after having already resolved the
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// KVer
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type Message struct {
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Level
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Msg string
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KV KV
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}
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// WriteFn describes a function which formats a single log message and writes it
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// to the given io.Writer. If the io.Writer returns an error this should return
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// that error.
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type WriteFn func(w io.Writer, msg Message) error
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func stringSlice(kv KV) [][2]string {
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slice := make([][2]string, 0, len(kv))
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for k, v := range kv {
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slice = append(slice, [2]string{
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k,
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strconv.QuoteToGraphic(fmt.Sprint(v)),
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})
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}
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sort.Slice(slice, func(i, j int) bool {
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return slice[i][0] < slice[j][0]
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})
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return slice
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}
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// DefaultWriteFn is the default implementation of WriteFn.
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func DefaultWriteFn(w io.Writer, msg Message) error {
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var err error
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write := func(s string, args ...interface{}) {
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if err == nil {
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_, err = fmt.Fprintf(w, s, args...)
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}
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}
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write("~ %s -- %s", msg.Level.String(), msg.Msg)
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if len(msg.KV) > 0 {
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write(" --")
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for _, kve := range stringSlice(msg.KV) {
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write(" %s=%s", kve[0], kve[1])
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}
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}
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write("\n")
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return err
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}
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// Logger wraps a WriteFn and an io.WriteCloser such that logging calls on the
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// Logger will use them (in a thread-safe manner) to write out log messages.
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//
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// Logger will auto-initialize itself on the first method call.
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type Logger struct {
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WriteFn // Defaults to DefaultWriteFn
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io.WriteCloser // Defaults to os.Stderr
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levelL sync.RWMutex
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maxLevel uint
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maxLevelSet bool
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init sync.Once
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msgCh chan Message
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testMsgWrittenCh chan struct{} // only initialized/used in tests
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}
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func (l *Logger) getMaxLevel() uint {
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l.levelL.RLock()
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defer l.levelL.RUnlock()
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if !l.maxLevelSet {
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return InfoLevel.Uint()
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}
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return l.maxLevel
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}
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// SetMaxLevelUint sets the maximum (up-to-and-including) level priority which
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// the Logger will output a log for. Any Levels with an Uint value higher than
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// this will not be logged. This may be called at any time.
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func (l *Logger) SetMaxLevelUint(i uint) {
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l.levelL.Lock()
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l.maxLevel = i
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l.maxLevelSet = true
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l.levelL.Unlock()
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}
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// SetMaxLevel sets the maximum (up-to-and-including) Level which the Logger
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// will output a log for. Any Levels whose Uint value is higher than this one's
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// will not be logged. This may be called at any time.
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func (l *Logger) SetMaxLevel(lvl Level) {
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l.SetMaxLevelUint(lvl.Uint())
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}
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func (l *Logger) spin() {
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for msg := range l.msgCh {
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if err := l.WriteFn(l.WriteCloser, msg); err != nil {
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go l.Error("could not write to Logger.WriteCloser", ErrKV(err))
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}
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if l.testMsgWrittenCh != nil {
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l.testMsgWrittenCh <- struct{}{}
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}
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if msg.Level.Uint() == 0 {
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l.WriteCloser.Close()
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os.Exit(1)
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}
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}
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l.WriteCloser.Close()
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}
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func (l *Logger) initDo() {
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l.init.Do(func() {
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if l.WriteFn == nil {
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l.WriteFn = DefaultWriteFn
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}
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if l.WriteCloser == nil {
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l.WriteCloser = os.Stderr
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}
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// maxLevel's default is implicitly handled by getMaxLevel
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l.msgCh = make(chan Message, 1000)
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go l.spin()
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})
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}
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// Stop stops and cleans up any running go-routines and resources held by the
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// Logger, allowing it to be garbage-collected. The Logger should not be used
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// after Stop is called
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func (l *Logger) Stop() {
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l.initDo()
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close(l.msgCh)
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}
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// Log can be used to manually log a message of some custom defined Level. kvs
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// will be Merge'd automatically. If the Level is a fatal (Uint() == 0) then
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// calling this will never return, and the process will have os.Exit(1) called.
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func (l *Logger) Log(lvl Level, msg string, kvs ...KVer) {
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if maxLevel := l.getMaxLevel(); maxLevel < lvl.Uint() {
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return
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}
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var kv KV
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if len(kvs) > 0 {
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kv = merge(kvs...)
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}
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l.initDo()
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l.msgCh <- Message{Level: lvl, Msg: msg, KV: kv}
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// if a Fatal is logged then we're merely waiting here for spin to call
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// os.Exit, and this go-routine shouldn't be allowed to continue
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if lvl.Uint() == 0 {
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select {}
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}
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}
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// Debug logs a DebugLevel message, merging the KVers together first
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func (l *Logger) Debug(msg string, kvs ...KVer) {
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l.Log(DebugLevel, msg, kvs...)
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}
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// Info logs a InfoLevel message, merging the KVers together first
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func (l *Logger) Info(msg string, kvs ...KVer) {
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l.Log(InfoLevel, msg, kvs...)
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}
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// Warn logs a WarnLevel message, merging the KVers together first
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func (l *Logger) Warn(msg string, kvs ...KVer) {
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l.Log(WarnLevel, msg, kvs...)
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}
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// Error logs a ErrorLevel message, merging the KVers together first
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func (l *Logger) Error(msg string, kvs ...KVer) {
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l.Log(ErrorLevel, msg, kvs...)
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}
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// Fatal logs a FatalLevel message, merging the KVers together first. A Fatal
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// message automatically stops the process with an os.Exit(1)
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func (l *Logger) Fatal(msg string, kvs ...KVer) {
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l.Log(FatalLevel, msg, kvs...)
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}
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// DefaultLogger is a Logger using the default configuration (which will log to
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// stderr). The Debug, Info, Warn, etc... methods from DefaultLogger are exposed
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// as global functions for convenience. Because Logger is not truly initialized
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// till the first time it is called any of DefaultLogger's fields may be
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// modified before using one of the Debug, Info, Warn, etc... global functions.
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var (
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DefaultLogger = new(Logger)
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Debug = DefaultLogger.Debug
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Info = DefaultLogger.Info
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Warn = DefaultLogger.Warn
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Error = DefaultLogger.Error
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Fatal = DefaultLogger.Fatal
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)
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