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)

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 LoggerInfo() string

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

func ParseConfigurationString(specification string) (map[string]Level, 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 RegisterWriter(name string, writer Writer, minLevel Level) error

RegisterWriter adds the writer to the list of writers that get notified when logging. When registering, the caller specifies the minimum logging level that will be written, and a name for the writer. 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.

func WillWrite(level Level) bool

WillWrite returns whether there are any writers registered at or above the given severity level. If it returns false, a log message at the given level will be discarded.

type DefaultFormatter struct{}

DefaultFormatter provides a simple concatenation of all the components.

func (*DefaultFormatter) Format(level Level, module, filename string, line int, timestamp time.Time, message string) string

Format 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.

type ColorFormatter struct{}

ColorFormatter provides a compact formatter with colored output, ideal for terminals

func (*ColorFormatter) Format(level Level, module, filename string, line int, timestamp time.Time, message string) string

Format returns the parameters separated by spaces except for filename and line which are separated by a colon. The time is shown to second resolution in UTC.

type Formatter interface {
    Format(level Level, module, filename string, line int, timestamp time.Time, message string) string
}

Formatter defines the single method Format, which takes the logging information, and converts it to a string.

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(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() string

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) Logger

GetLogger 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() Level

EffectiveLogLevel returns the effective 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() bool

IsDebugEnabled returns whether debugging is enabled at debug level.

func (logger Logger) IsErrorEnabled() bool

IsErrorEnabled returns whether debugging is enabled at error level.

func (logger Logger) IsInfoEnabled() bool

IsInfoEnabled returns whether debugging is enabled at info level.

func (logger Logger) IsLevelEnabled(level Level) bool

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

func (logger Logger) IsTraceEnabled() bool

IsTraceEnabled returns whether debugging is enabled at trace level.

func (logger Logger) IsWarningEnabled() bool

IsWarningEnabled 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() Level

LogLevel returns the configured 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() string

Name 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 TestLogValues struct {
    Level     Level
    Module    string
    Filename  string
    Line      int
    Timestamp time.Time
    Message   string
}

TestLogValues represents a single logging call.

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() []TestLogValues

Log returns a copy of the current logged values.

func (writer *TestWriter) Write(level Level, module, filename string, line int, timestamp time.Time, message string)

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(level Level, name, filename string, line int, timestamp time.Time, message string)
}

Writer is implemented by any recipient of log messages.

func NewSimpleWriter(writer io.Writer, formatter Formatter) Writer

NewSimpleWriter 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, Level, 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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