A logging library for Go. Doesn't use the built in go log standard library, but instead offers a replacement.
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README.md

loggo

import "github.com/juju/loggo"

GoDoc

Module level logging for Go

This package provides an alternative to the standard library log package.

The actual logging functions never return errors. If you are logging something, you really don't want to be worried about the logging having trouble.

Modules have names that are defined by dotted strings.

"first.second.third"

There is a root module that has the name "". Each module (except the root module) has a parent, identified by the part of the name without the last dotted value.

  • the parent of "first.second.third" is "first.second"
  • the parent of "first.second" is "first"
  • the parent of "first" is "" (the root module)

Each module can specify its own severity level. Logging calls that are of a lower severity than the module's effective severity level are not written out.

Loggers are created through their Context. There is a default global context that is used if you just want simple use. Contexts are used where you may want different sets of writers for different loggers. Most use cases are fine with just using the default global context.

Loggers are created using the GetLogger function.

logger := loggo.GetLogger("foo.bar")

The default global context has one writer registered, which will write to Stderr, and the root module, which will only emit warnings and above. If you want to continue using the default logger, but have it emit all logging levels you need to do the following.

writer, err := loggo.RemoveWriter("default")
// err is non-nil if and only if the name isn't found.
loggo.RegisterWriter("default", writer)

To make loggo produce colored output, you can do the following, having imported github.com/juju/loggo/loggocolor:

loggo.ReplaceDefaultWriter(loggocolor.NewWriter(os.Stderr))

Constants

const DefaultWriterName = "default"

DefaultWriterName is the name of the default writer for a Context.

Variables

var TimeFormat = initTimeFormat()

TimeFormat is the time format used for the default writer. This can be set with the environment variable LOGGO_TIME_FORMAT.

func ConfigureLoggers

func ConfigureLoggers(specification string) error

ConfigureLoggers configures loggers according to the given string specification, which specifies a set of modules and their associated logging levels. Loggers are colon- or semicolon-separated; each module is specified as =. White space outside of module names and levels is ignored. The root module is specified with the name "".

An example specification:

`<root>=ERROR; foo.bar=WARNING`

func DefaultFormatter

func DefaultFormatter(entry Entry) string

DefaultFormatter returns the parameters separated by spaces except for filename and line which are separated by a colon. The timestamp is shown to second resolution in UTC. For example:

2016-07-02 15:04:05

func LoggerInfo

func LoggerInfo() string

LoggerInfo returns information about the configured loggers and their logging levels. The information is returned in the format expected by ConfigureLoggers. Loggers with UNSPECIFIED level will not be included.

func RegisterWriter

func RegisterWriter(name string, writer Writer) error

RegisterWriter adds the writer to the list of writers in the DefaultContext that get notified when logging. If there is already a registered writer with that name, an error is returned.

func ResetLogging

func ResetLogging()

ResetLogging iterates through the known modules and sets the levels of all to UNSPECIFIED, except for which is set to WARNING. The call also removes all writers in the DefaultContext and puts the original default writer back as the only writer.

func ResetWriters

func ResetWriters()

ResetWriters puts the list of writers back into the initial state.

type Config

type Config map[string]Level

Config is a mapping of logger module names to logging severity levels.

func ParseConfigString

func ParseConfigString(specification string) (Config, error)

ParseConfigString parses a logger configuration string into a map of logger names and their associated log level. This method is provided to allow other programs to pre-validate a configuration string rather than just calling ConfigureLoggers.

Logging modules are colon- or semicolon-separated; each module is specified as =. White space outside of module names and levels is ignored. The root module is specified with the name "".

As a special case, a log level may be specified on its own. This is equivalent to specifying the level of the root module, so "DEBUG" is equivalent to <root>=DEBUG

An example specification:

`<root>=ERROR; foo.bar=WARNING`

func (Config) String

func (c Config) String() string

String returns a logger configuration string that may be parsed using ParseConfigurationString.

type Context

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

Context produces loggers for a hierarchy of modules. The context holds a collection of hierarchical loggers and their writers.

func DefaultContext

func DefaultContext() *Context

DefaultContext returns the global default logging context.

func NewContext

func NewContext(rootLevel Level) *Context

NewLoggers returns a new Context with no writers set. If the root level is UNSPECIFIED, WARNING is used.

func (*Context) AddWriter

func (c *Context) AddWriter(name string, writer Writer) error

AddWriter adds a writer to the list to be called for each logging call. The name cannot be empty, and the writer cannot be nil. If an existing writer exists with the specified name, an error is returned.

func (*Context) ApplyConfig

func (c *Context) ApplyConfig(config Config)

ApplyConfig configures the logging modules according to the provided config.

func (*Context) CompleteConfig

func (c *Context) CompleteConfig() Config

CompleteConfig returns all the loggers and their defined levels, even if that level is UNSPECIFIED.

func (*Context) Config

func (c *Context) Config() Config

Config returns the current configuration of the Loggers. Loggers with UNSPECIFIED level will not be included.

func (*Context) GetLogger

func (c *Context) GetLogger(name string) Logger

GetLogger returns a Logger for the given module name, creating it and its parents if necessary.

func (*Context) RemoveWriter

func (c *Context) RemoveWriter(name string) (Writer, error)

RemoveWriter remotes the specified writer. If a writer is not found with the specified name an error is returned. The writer that was removed is also returned.

func (*Context) ReplaceWriter

func (c *Context) ReplaceWriter(name string, writer Writer) (Writer, error)

ReplaceWriter is a convenience method that does the equivalent of RemoveWriter followed by AddWriter with the same name. The replaced writer is returned.

func (*Context) ResetLoggerLevels

func (c *Context) ResetLoggerLevels()

ResetLoggerLevels iterates through the known logging modules and sets the levels of all to UNSPECIFIED, except for which is set to WARNING.

func (*Context) ResetWriters

func (c *Context) ResetWriters()

ResetWriters is generally only used in testing and removes all the writers.

func (*Context) Writer

func (c *Context) Writer(name string) Writer

Writer returns the named writer if one exists. If there is not a writer with the specified name, nil is returned.

type Entry

type Entry struct {
    // Level is the severity of the log message.
    Level Level
    // Module is the dotted module name from the logger.
    Module string
    // Filename is the full path the file that logged the message.
    Filename string
    // Line is the line number of the Filename.
    Line int
    // Timestamp is when the log message was created
    Timestamp time.Time
    // Message is the formatted string from teh log call.
    Message string
}

Entry represents a single log message.

type Level

type Level uint32

Level holds a severity level.

const (
    UNSPECIFIED Level = iota
    TRACE
    DEBUG
    INFO
    WARNING
    ERROR
    CRITICAL
)

The severity levels. Higher values are more considered more important.

func ParseLevel

func ParseLevel(level string) (Level, bool)

ParseLevel converts a string representation of a logging level to a Level. It returns the level and whether it was valid or not.

func (Level) Short

func (level Level) Short() string

Short returns a five character string to use in aligned logging output.

func (Level) String

func (level Level) String() string

String implements Stringer.

type Logger

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

A Logger represents a logging module. It has an associated logging level which can be changed; messages of lesser severity will be dropped. Loggers have a hierarchical relationship - see the package documentation.

The zero Logger value is usable - any messages logged to it will be sent to the root Logger.

func GetLogger

func GetLogger(name string) Logger

GetLogger returns a Logger for the given module name, creating it and its parents if necessary.

func (Logger) Child

func (logger Logger) Child(name string) Logger

Child returns the Logger whose module name is the composed of this Logger's name and the specified name.

func (Logger) Criticalf

func (logger Logger) Criticalf(message string, args ...interface{})

Criticalf logs the printf-formatted message at critical level.

func (Logger) Debugf

func (logger Logger) Debugf(message string, args ...interface{})

Debugf logs the printf-formatted message at debug level.

func (Logger) EffectiveLogLevel

func (logger Logger) EffectiveLogLevel() Level

EffectiveLogLevel returns the effective min log level of the receiver - that is, messages with a lesser severity level will be discarded.

If the log level of the receiver is unspecified, it will be taken from the effective log level of its parent.

func (Logger) Errorf

func (logger Logger) Errorf(message string, args ...interface{})

Errorf logs the printf-formatted message at error level.

func (Logger) Infof

func (logger Logger) Infof(message string, args ...interface{})

Infof logs the printf-formatted message at info level.

func (Logger) IsDebugEnabled

func (logger Logger) IsDebugEnabled() bool

IsDebugEnabled returns whether debugging is enabled at debug level.

func (Logger) IsErrorEnabled

func (logger Logger) IsErrorEnabled() bool

IsErrorEnabled returns whether debugging is enabled at error level.

func (Logger) IsInfoEnabled

func (logger Logger) IsInfoEnabled() bool

IsInfoEnabled returns whether debugging is enabled at info level.

func (Logger) IsLevelEnabled

func (logger Logger) IsLevelEnabled(level Level) bool

IsLevelEnabled returns whether debugging is enabled for the given log level.

func (Logger) IsTraceEnabled

func (logger Logger) IsTraceEnabled() bool

IsTraceEnabled returns whether debugging is enabled at trace level.

func (Logger) IsWarningEnabled

func (logger Logger) IsWarningEnabled() bool

IsWarningEnabled returns whether debugging is enabled at warning level.

func (Logger) LogCallf

func (logger Logger) LogCallf(calldepth int, level Level, message string, args ...interface{})

LogCallf logs a printf-formatted message at the given level. The location of the call is indicated by the calldepth argument. A calldepth of 1 means the function that called this function. A message will be discarded if level is less than the the effective log level of the logger. Note that the writers may also filter out messages that are less than their registered minimum severity level.

func (Logger) LogLevel

func (logger Logger) LogLevel() Level

LogLevel returns the configured min log level of the logger.

func (Logger) Logf

func (logger Logger) Logf(level Level, message string, args ...interface{})

Logf logs a printf-formatted message at the given level. A message will be discarded if level is less than the the effective log level of the logger. Note that the writers may also filter out messages that are less than their registered minimum severity level.

func (Logger) Name

func (logger Logger) Name() string

Name returns the logger's module name.

func (Logger) Parent

func (logger Logger) Parent() Logger

Parent returns the Logger whose module name is the same as this logger without the last period and suffix. For example the parent of the logger that has the module "a.b.c" is "a.b". The Parent of the root logger is still the root logger.

func (Logger) SetLogLevel

func (logger Logger) SetLogLevel(level Level)

SetLogLevel sets the severity level of the given logger. The root logger cannot be set to UNSPECIFIED level. See EffectiveLogLevel for how this affects the actual messages logged.

func (Logger) Tracef

func (logger Logger) Tracef(message string, args ...interface{})

Tracef logs the printf-formatted message at trace level.

func (Logger) Warningf

func (logger Logger) Warningf(message string, args ...interface{})

Warningf logs the printf-formatted message at warning level.

type TestWriter

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

TestWriter is a useful Writer for testing purposes. Each component of the logging message is stored in the Log array.

func (*TestWriter) Clear

func (writer *TestWriter) Clear()

Clear removes any saved log messages.

func (*TestWriter) Log

func (writer *TestWriter) Log() []Entry

Log returns a copy of the current logged values.

func (*TestWriter) Write

func (writer *TestWriter) Write(entry Entry)

Write saves the params as members in the TestLogValues struct appended to the Log array.

type Writer

type Writer interface {
    // Write writes a message to the Writer with the given level and module
    // name. The filename and line hold the file name and line number of the
    // code that is generating the log message; the time stamp holds the time
    // the log message was generated, and message holds the log message
    // itself.
    Write(entry Entry)
}

Writer is implemented by any recipient of log messages.

func NewMinimumLevelWriter

func NewMinimumLevelWriter(writer Writer, minLevel Level) Writer

NewMinLevelWriter returns a Writer that will only pass on the Write calls to the provided writer if the log level is at or above the specified minimum level.

func NewSimpleWriter

func NewSimpleWriter(writer io.Writer, formatter func(entry Entry) string) Writer

NewSimpleWriter returns a new writer that writes log messages to the given io.Writer formatting the messages with the given formatter.

func RemoveWriter

func RemoveWriter(name string) (Writer, error)

RemoveWriter removes the Writer identified by 'name' and returns it. If the Writer is not found, an error is returned.

func ReplaceDefaultWriter

func ReplaceDefaultWriter(writer Writer) (Writer, error)

ReplaceDefaultWriter is a convenience method that does the equivalent of RemoveWriter and then RegisterWriter with the name "default". The previous default writer, if any is returned.


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