log

package module
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 Go to latest Published: Sep 12, 2023 License: Apache-2.0 Imports: 19 Imported by: 0

README

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log15 godoc reference Build Status

Package log15 provides an opinionated, simple toolkit for best-practice logging in Go (golang) that is both human and machine readable. It is modeled after the Go standard library's io and net/http packages and is an alternative to the standard library's log package.

Features

  • A simple, easy-to-understand API
  • Promotes structured logging by encouraging use of key/value pairs
  • Child loggers which inherit and add their own private context
  • Lazy evaluation of expensive operations
  • Simple Handler interface allowing for construction of flexible, custom logging configurations with a tiny API.
  • Color terminal support
  • Built-in support for logging to files, streams, syslog, and the network
  • Support for forking records to multiple handlers, buffering records for output, failing over from failed handler writes, + more

Versioning

The API of the master branch of log15 should always be considered unstable. If you want to rely on a stable API, you must vendor the library.

Importing

import log "github.com/inconshreveable/log15"

Examples

// all loggers can have key/value context
srvlog := log.New("module", "app/server")

// all log messages can have key/value context
srvlog.Warn("abnormal conn rate", "rate", curRate, "low", lowRate, "high", highRate)

// child loggers with inherited context
connlog := srvlog.New("raddr", c.RemoteAddr())
connlog.Info("connection open")

// lazy evaluation
connlog.Debug("ping remote", "latency", log.Lazy{pingRemote})

// flexible configuration
srvlog.SetHandler(log.MultiHandler(
    log.StreamHandler(os.Stderr, log.LogfmtFormat()),
    log.LvlFilterHandler(
        log.LvlError,
        log.Must.FileHandler("errors.json", log.JSONFormat()))))

Will result in output that looks like this:

WARN[06-17|21:58:10] abnormal conn rate                       module=app/server rate=0.500 low=0.100 high=0.800
INFO[06-17|21:58:10] connection open                          module=app/server raddr=10.0.0.1

Breaking API Changes

The following commits broke API stability. This reference is intended to help you understand the consequences of updating to a newer version of log15.

  • 57a084d014d4150152b19e4e531399a7145d1540 - Added a Get() method to the Logger interface to retrieve the current handler
  • 93404652ee366648fa622b64d1e2b67d75a3094a - Record field Call changed to stack.Call with switch to github.com/go-stack/stack
  • a5e7613673c73281f58e15a87d2cf0cf111e8152 - Restored syslog.Priority argument to the SyslogXxx handler constructors

FAQ

The varargs style is brittle and error prone! Can I have type safety please?

Yes. Use log.Ctx:

srvlog := log.New(log.Ctx{"module": "app/server"})
srvlog.Warn("abnormal conn rate", log.Ctx{"rate": curRate, "low": lowRate, "high": highRate})

License

Apache

Documentation

Index

Constants

This section is empty.

Variables

View Source 
var Must muster

Must provides the following Handler creation functions which instead of returning an error parameter only return a Handler and panic on failure: FileHandler, NetHandler, SyslogHandler, SyslogNetHandler

Functions

func Crit 

func Crit(msg string, ctx ...interface{})

Crit is a convenient alias for Root().Crit

func Debug 

func Debug(msg string, ctx ...interface{})

Debug is a convenient alias for Root().Debug

func Error 

func Error(msg string, ctx ...interface{})

Error is a convenient alias for Root().Error

func Info 

func Info(msg string, ctx ...interface{})

Info is a convenient alias for Root().Info

func Output 

func Output(msg string, lvl Lvl, calldepth int, ctx ...interface{})

Output is a convenient alias for write, allowing for the modification of the calldepth (number of stack frames to skip). calldepth influences the reported line number of the log message. A calldepth of zero reports the immediate caller of Output. Non-zero calldepth skips as many stack frames.

func PrintOrigins 

func PrintOrigins(print bool)

PrintOrigins sets or unsets log location (file:line) printing for terminal format output.

func SetLogFile 

func SetLogFile(filePath string)

func Trace 

func Trace(msg string, ctx ...interface{})

Trace is a convenient alias for Root().Trace

func Warn 

func Warn(msg string, ctx ...interface{})

Warn is a convenient alias for Root().Warn

Types

type Ctx 

type Ctx map[string]interface{}

Ctx is a map of key/value pairs to pass as context to a log function Use this only if you really need greater safety around the arguments you pass to the logging functions.

type Format 

type Format interface {
	Format(r *Record) []byte
}

func FormatFunc 

func FormatFunc(f func(*Record) []byte) Format

FormatFunc returns a new Format object which uses the given function to perform record formatting.

func JSONFormat 

func JSONFormat() Format

JSONFormat formats log records as JSON objects separated by newlines. It is the equivalent of JSONFormatEx(false, true).

func JSONFormatEx 

func JSONFormatEx(pretty, lineSeparated bool) Format

JSONFormatEx formats log records as JSON objects. If pretty is true, records will be pretty-printed. If lineSeparated is true, records will be logged with a new line between each record.

func JSONFormatOrderedEx 

func JSONFormatOrderedEx(pretty, lineSeparated bool) Format

JSONFormatOrderedEx formats log records as JSON arrays. If pretty is true, records will be pretty-printed. If lineSeparated is true, records will be logged with a new line between each record.

func LogfmtFormat 

func LogfmtFormat() Format

LogfmtFormat prints records in logfmt format, an easy machine-parseable but human-readable format for key/value pairs.

For more details see: http://godoc.org/github.com/kr/logfmt

func TerminalFormat 

func TerminalFormat(usecolor bool) Format

TerminalFormat formats log records optimized for human readability on a terminal with color-coded level output and terser human friendly timestamp. This format should only be used for interactive programs or while developing. 

[LEVEL] [TIME] MESSAGE key=value key=value ...

Example: 

[DBUG] [May 16 20:58:45] remove route ns=haproxy addr=127.0.0.1:50002

type GlogHandler 

type GlogHandler struct {
	// contains filtered or unexported fields
}

GlogHandler is a log handler that mimics the filtering features of Google's glog logger: setting global log levels; overriding with callsite pattern matches; and requesting backtraces at certain positions.

func NewGlogHandler 

func NewGlogHandler(h Handler) *GlogHandler

NewGlogHandler creates a new log handler with filtering functionality similar to Google's glog logger. The returned handler implements Handler.

func (*GlogHandler) BacktraceAt 

func (h *GlogHandler) BacktraceAt(location string) error

BacktraceAt sets the glog backtrace location. When set to a file and line number holding a logging statement, a stack trace will be written to the Info log whenever execution hits that statement.

Unlike with Vmodule, the ".go" must be present.

func (*GlogHandler) Log 

func (h *GlogHandler) Log(r *Record) error

Log implements Handler.Log, filtering a log record through the global, local and backtrace filters, finally emitting it if either allow it through.

func (*GlogHandler) SetHandler 

func (h *GlogHandler) SetHandler(nh Handler)

SetHandler updates the handler to write records to the specified sub-handler.

func (*GlogHandler) Verbosity 

func (h *GlogHandler) Verbosity(level Lvl)

Verbosity sets the glog verbosity ceiling. The verbosity of individual packages and source files can be raised using Vmodule.

func (*GlogHandler) Vmodule 

func (h *GlogHandler) Vmodule(ruleset string) error

Vmodule sets the glog verbosity pattern.

The syntax of the argument is a comma-separated list of pattern=N, where the pattern is a literal file name or "glob" pattern matching and N is a V level.

For instance: 

pattern="gopher.go=3"
 sets the V level to 3 in all Go files named "gopher.go"

pattern="foo=3"
 sets V to 3 in all files of any packages whose import path ends in "foo"

pattern="foo/*=3"
 sets V to 3 in all files of any packages whose import path contains "foo"

type Handler 

type Handler interface {
	Log(r *Record) error
}

Handler defines where and how log records are written. A Logger prints its log records by writing to a Handler. Handlers are composable, providing you great flexibility in combining them to achieve the logging structure that suits your applications.

func BufferedHandler 

func BufferedHandler(bufSize int, h Handler) Handler

BufferedHandler writes all records to a buffered channel of the given size which flushes into the wrapped handler whenever it is available for writing. Since these writes happen asynchronously, all writes to a BufferedHandler never return an error and any errors from the wrapped handler are ignored.

func CallerFileHandler 

func CallerFileHandler(h Handler) Handler

CallerFileHandler returns a Handler that adds the line number and file of the calling function to the context with key "caller".

func CallerFuncHandler 

func CallerFuncHandler(h Handler) Handler

CallerFuncHandler returns a Handler that adds the calling function name to the context with key "fn".

func CallerStackHandler 

func CallerStackHandler(format string, h Handler) Handler

CallerStackHandler returns a Handler that adds a stack trace to the context with key "stack". The stack trace is formatted as a space separated list of call sites inside matching []'s. The most recent call site is listed first. Each call site is formatted according to format. See the documentation of package github.com/go-stack/stack for the list of supported formats.

func ChannelHandler 

func ChannelHandler(recs chan<- *Record) Handler

ChannelHandler writes all records to the given channel. It blocks if the channel is full. Useful for async processing of log messages, it's used by BufferedHandler.

func DiscardHandler 

func DiscardHandler() Handler

DiscardHandler reports success for all writes but does nothing. It is useful for dynamically disabling logging at runtime via a Logger's SetHandler method.

func FailoverHandler 

func FailoverHandler(hs ...Handler) Handler

FailoverHandler writes all log records to the first handler specified, but will failover and write to the second handler if the first handler has failed, and so on for all handlers specified. For example you might want to log to a network socket, but failover to writing to a file if the network fails, and then to standard out if the file write fails: 

log.FailoverHandler(
    log.Must.NetHandler("tcp", ":9090", log.JSONFormat()),
    log.Must.FileHandler("/var/log/app.log", log.LogfmtFormat()),
    log.StdoutHandler)

All writes that do not go to the first handler will add context with keys of the form "failover_err_{idx}" which explain the error encountered while trying to write to the handlers before them in the list.

func FileHandler 

func FileHandler(path string, fmtr Format) (Handler, error)

FileHandler returns a handler which writes log records to the give file using the given format. If the path already exists, FileHandler will append to the given file. If it does not, FileHandler will create the file with mode 0644.

func FilterHandler 

func FilterHandler(fn func(r *Record) bool, h Handler) Handler

FilterHandler returns a Handler that only writes records to the wrapped Handler if the given function evaluates true. For example, to only log records where the 'err' key is not nil: 

logger.SetHandler(FilterHandler(func(r *Record) bool {
    for i := 0; i < len(r.Ctx); i += 2 {
        if r.Ctx[i] == "err" {
            return r.Ctx[i+1] != nil
        }
    }
    return false
}, h))

func FuncHandler 

func FuncHandler(fn func(r *Record) error) Handler

FuncHandler returns a Handler that logs records with the given function.

func LazyHandler 

func LazyHandler(h Handler) Handler

LazyHandler writes all values to the wrapped handler after evaluating any lazy functions in the record's context. It is already wrapped around StreamHandler and SyslogHandler in this library, you'll only need it if you write your own Handler.

func LvlFilterHandler 

func LvlFilterHandler(maxLvl Lvl, h Handler) Handler

LvlFilterHandler returns a Handler that only writes records which are less than the given verbosity level to the wrapped Handler. For example, to only log Error/Crit records: 

log.LvlFilterHandler(log.LvlError, log.StdoutHandler)

func MatchFilterHandler 

func MatchFilterHandler(key string, value interface{}, h Handler) Handler

MatchFilterHandler returns a Handler that only writes records to the wrapped Handler if the given key in the logged context matches the value. For example, to only log records from your ui package: 

log.MatchFilterHandler("pkg", "app/ui", log.StdoutHandler)

func MultiHandler 

func MultiHandler(hs ...Handler) Handler

MultiHandler dispatches any write to each of its handlers. This is useful for writing different types of log information to different locations. For example, to log to a file and standard error: 

log.MultiHandler(
    log.Must.FileHandler("/var/log/app.log", log.LogfmtFormat()),
    log.StderrHandler)

func NetHandler 

func NetHandler(network, addr string, fmtr Format) (Handler, error)

NetHandler opens a socket to the given address and writes records over the connection.

func StreamHandler 

func StreamHandler(wr io.Writer, fmtr Format) Handler

StreamHandler writes log records to an io.Writer with the given format. StreamHandler can be used to easily begin writing log records to other outputs.

StreamHandler wraps itself with LazyHandler and SyncHandler to evaluate Lazy objects and perform safe concurrent writes.

func SyncHandler 

func SyncHandler(h Handler) Handler

SyncHandler can be wrapped around a handler to guarantee that only a single Log operation can proceed at a time. It's necessary for thread-safe concurrent writes.

func SyslogHandler 

func SyslogHandler(priority syslog.Priority, tag string, fmtr Format) (Handler, error)

SyslogHandler opens a connection to the system syslog daemon by calling syslog.New and writes all records to it.

func SyslogNetHandler 

func SyslogNetHandler(net, addr string, priority syslog.Priority, tag string, fmtr Format) (Handler, error)

SyslogNetHandler opens a connection to a log daemon over the network and writes all log records to it.

type Lazy 

type Lazy struct {
	Fn interface{}
}

Lazy allows you to defer calculation of a logged value that is expensive to compute until it is certain that it must be evaluated with the given filters.

Lazy may also be used in conjunction with a Logger's New() function to generate a child logger which always reports the current value of changing state.

You may wrap any function which takes no arguments to Lazy. It may return any number of values of any type.

type Logger 

type Logger interface {
	// New returns a new Logger that has this logger's context plus the given context
	New(ctx ...interface{}) Logger

	// GetHandler gets the handler associated with the logger.
	GetHandler() Handler

	// SetHandler updates the logger to write records to the specified handler.
	SetHandler(h Handler)

	// Log a message at the given level with context key/value pairs
	Trace(msg string, ctx ...interface{})
	Debug(msg string, ctx ...interface{})
	Info(msg string, ctx ...interface{})
	Warn(msg string, ctx ...interface{})
	Error(msg string, ctx ...interface{})
	Crit(msg string, ctx ...interface{})
}

A Logger writes key/value pairs to a Handler

func New 

func New(ctx ...interface{}) Logger

New returns a new logger with the given context. New is a convenient alias for Root().New

func NewModule 

func NewModule(module string, ctx ...interface{}) Logger

func Root 

func Root() Logger

Root returns the root logger

type Lvl 

type Lvl int
const (
	LvlCrit Lvl = iota
	LvlError
	LvlWarn
	LvlInfo
	LvlDebug
	LvlTrace
)

func LvlFromString 

func LvlFromString(lvlString string) (Lvl, error)

LvlFromString returns the appropriate Lvl from a string name. Useful for parsing command line args and configuration files.

func (Lvl) AlignedString 

func (l Lvl) AlignedString() string

AlignedString returns a 5-character string containing the name of a Lvl.

func (Lvl) String 

func (l Lvl) String() string

Strings returns the name of a Lvl.

type Record 

type Record struct {
	Time     time.Time
	Lvl      Lvl
	Msg      string
	Ctx      []interface{}
	Call     stack.Call
	KeyNames RecordKeyNames
}

A Record is what a Logger asks its handler to write

type RecordKeyNames 

type RecordKeyNames struct {
	Time string
	Msg  string
	Lvl  string
	Ctx  string
}

RecordKeyNames gets stored in a Record when the write function is executed.

type TerminalStringer 

type TerminalStringer interface {
	TerminalString() string
}

TerminalStringer is an analogous interface to the stdlib stringer, allowing own types to have custom shortened serialization formats when printed to the screen.

Source Files

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