import "github.com/juju/loggo"
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 using the GetLogger function.
logger := loggo.GetLogger("foo.bar")
By default there is 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, loggo.TRACE)
const DefaultWriterName = "default"DefaultWriterName is the name of the writer default writer for a Context.
func ConfigureLoggers(specification string) errorConfigureLoggers 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(entry Entry) stringDefaultFormatter 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.
func LoggerInfo() stringLoggerInfo 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(name string, writer Writer) errorRegisterWriter adds the writer to the list of writers to the DefaultContext that get notified when logging. If there is already a registered writer with that name, an error is returned.
func ResetLoggers()ResetLogging iterates through the known modules and sets the levels of all to UNSPECIFIED, except for which is set to WARNING.
func ResetWriters()ResetWriters puts the list of writers back into the initial state.
type Config map[string]LevelConfig is a mapping of logger module names to logging severity levels.
func ParseConfigurationString(specification string) (Config, error)ParseConfigurationString 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.
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 "".
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 (c Config) String() stringString returns a logger configuration string that may be parsed using ParseLoggersConfig.
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() *ContextDefaultContext returns the global default logging context.
func NewContext(rootLevel Level, defaultWriter Writer) *ContextNewLoggers returns a new Context with a possible default writer set. If the root level is UNSPECIFIED, WARNING is used.
func (c *Context) AddWriter(name string, writer Writer) errorAddWriter adds an 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 (c *Context) ApplyConfig(config Config)ApplyConfig configures the logging modules according to the provided config.
func (c *Context) CompleteConfig() ConfigCompleteConfig returns all the loggers and their defined levels, even if that level is UNSPECIFIED.
func (c *Context) Config() ConfigConfig returns the current configuration of the Loggers. Loggers with UNSPECIFIED level will not be included.
func (c *Context) GetLogger(name string) LoggerGetLogger returns a Logger for the given module name, creating it and its parents if necessary.
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 (c *Context) ReplaceWriter(name string, writer Writer) (Writer, error)ReplaceWriter is a convenience function that does the equivalent of RemoveWriter followed by AddWriter with the same name. The replaced writer is returned.
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 (c *Context) ResetWriters()ResetWriters is generally only used in testing and removes all the writers, and adds back in the default writer if one was specified when the Context was created.
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 uint32Level 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(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 Level) String() stringString implements Stringer.
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(name string) LoggerGetLogger returns a Logger for the given module name, creating it and its parents if necessary.
func (logger Logger) Criticalf(message string, args ...interface{})Criticalf logs the printf-formatted message at critical level.
func (logger Logger) Debugf(message string, args ...interface{})Debugf logs the printf-formatted message at debug level.
func (logger Logger) EffectiveLogLevel() LevelEffectiveLogLevel 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 Logger) Errorf(message string, args ...interface{})Errorf logs the printf-formatted message at error level.
func (logger Logger) Infof(message string, args ...interface{})Infof logs the printf-formatted message at info level.
func (logger Logger) IsDebugEnabled() boolIsDebugEnabled returns whether debugging is enabled at debug level.
func (logger Logger) IsErrorEnabled() boolIsErrorEnabled returns whether debugging is enabled at error level.
func (logger Logger) IsInfoEnabled() boolIsInfoEnabled returns whether debugging is enabled at info level.
func (logger Logger) IsLevelEnabled(level Level) boolIsLevelEnabled returns whether debugging is enabled for the given log level.
func (logger Logger) IsTraceEnabled() boolIsTraceEnabled returns whether debugging is enabled at trace level.
func (logger Logger) IsWarningEnabled() boolIsWarningEnabled returns whether debugging is enabled at warning level.
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 Logger) LogLevel() LevelLogLevel returns the configured min log level of the logger.
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 Logger) Name() stringName returns the logger's module name.
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 Logger) Tracef(message string, args ...interface{})Tracef logs the printf-formatted message at trace level.
func (logger Logger) Warningf(message string, args ...interface{})Warningf logs the printf-formatted message at warning level.
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 (writer *TestWriter) Clear()Clear removes any saved log messages.
func (writer *TestWriter) Log() []EntryLog returns a copy of the current logged values.
func (writer *TestWriter) Write(entry Entry)Write saves the params as members in the TestLogValues struct appended to the Log array.
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(writer Writer, minLevel Level) WriterNewMinLevelWriter 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 minimul level.
func NewSimpleWriter(writer io.Writer, formatter func(entry Entry) string) WriterNewSimpleWriter returns a new writer that writes log messages to the given io.Writer formatting the messages with the given formatter.
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(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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