README
¶
go-hclog
go-hclog is a package for Go that provides a simple key/value logging
interface for use in development and production environments.
It provides logging levels that provide decreased output based upon the
desired amount of output, unlike the standard library log package.
It provides Printf style logging of values via hclog.Fmt().
It provides a human readable output mode for use in development as well as JSON output mode for production.
Stability Note
While this library is fully open source and HashiCorp will be maintaining it (since we are and will be making extensive use of it), the API and output format is subject to minor changes as we fully bake and vet it in our projects. This notice will be removed once it's fully integrated into our major projects and no further changes are anticipated.
Installation and Docs
Install using go get github.com/hashicorp/go-hclog.
Full documentation is available at http://godoc.org/github.com/hashicorp/go-hclog
Usage
Use the global logger
hclog.Default().Info("hello world")
2017-07-05T16:15:55.167-0700 [INFO ] hello world
(Note timestamps are removed in future examples for brevity.)
Create a new logger
appLogger := hclog.New(&hclog.LoggerOptions{
Name: "my-app",
Level: hclog.LevelFromString("DEBUG"),
})
Emit an Info level message with 2 key/value pairs
input := "5.5"
_, err := strconv.ParseInt(input, 10, 32)
if err != nil {
appLogger.Info("Invalid input for ParseInt", "input", input, "error", err)
}
... [INFO ] my-app: Invalid input for ParseInt: input=5.5 error="strconv.ParseInt: parsing "5.5": invalid syntax"
Create a new Logger for a major subsystem
subsystemLogger := appLogger.Named("transport")
subsystemLogger.Info("we are transporting something")
... [INFO ] my-app.transport: we are transporting something
Notice that logs emitted by subsystemLogger contain my-app.transport,
reflecting both the application and subsystem names.
Create a new Logger with fixed key/value pairs
Using With() will include a specific key-value pair in all messages emitted
by that logger.
requestID := "5fb446b6-6eba-821d-df1b-cd7501b6a363"
requestLogger := subsystemLogger.With("request", requestID)
requestLogger.Info("we are transporting a request")
... [INFO ] my-app.transport: we are transporting a request: request=5fb446b6-6eba-821d-df1b-cd7501b6a363
This allows sub Loggers to be context specific without having to thread that into all the callers.
Using hclog.Fmt()
var int totalBandwidth = 200
appLogger.Info("total bandwidth exceeded", "bandwidth", hclog.Fmt("%d GB/s", totalBandwidth))
... [INFO ] my-app: total bandwidth exceeded: bandwidth="200 GB/s"
Use this with code that uses the standard library logger
If you want to use the standard library's log.Logger interface you can wrap
hclog.Logger by calling the StandardLogger() method. This allows you to use
it with the familiar Println(), Printf(), etc. For example:
stdLogger := appLogger.StandardLogger(&hclog.StandardLoggerOptions{
InferLevels: true,
})
// Printf() is provided by stdlib log.Logger interface, not hclog.Logger
stdLogger.Printf("[DEBUG] %+v", stdLogger)
... [DEBUG] my-app: &{mu:{state:0 sema:0} prefix: flag:0 out:0xc42000a0a0 buf:[]}
Alternatively, you may configure the system-wide logger:
// log the standard logger from 'import "log"'
log.SetOutput(appLogger.Writer(&hclog.StandardLoggerOptions{InferLevels: true}))
log.SetPrefix("")
log.SetFlags(0)
log.Printf("[DEBUG] %d", 42)
... [DEBUG] my-app: 42
Notice that if appLogger is initialized with the INFO log level and you
specify InferLevels: true, you will not see any output here. You must change
appLogger to DEBUG to see output. See the docs for more information.
Documentation
¶
Index ¶
Constants ¶
const TimeFormat = "2006-01-02T15:04:05.000Z0700"
TimeFormat to use for logging. This is a version of RFC3339 that contains contains millisecond precision
Variables ¶
var ( //DefaultOutput is used as the default log output. DefaultOutput io.Writer = os.Stderr // DefaultLevel is used as the default log level. DefaultLevel = Info )
var ( // DefaultOptions is used to create the Default logger. These are read // only when the Default logger is created, so set them as soon as the // process starts. DefaultOptions = &LoggerOptions{ Level: DefaultLevel, Output: DefaultOutput, } )
Functions ¶
func WithContext ¶ added in v0.9.1
WithContext inserts a logger into the context and is retrievable with FromContext. The optional args can be set with the same syntax as Logger.With to set fields on the inserted logger. This will not modify the logger argument in-place.
Types ¶
type CapturedStacktrace ¶
type CapturedStacktrace string
CapturedStacktrace represents a stacktrace captured by a previous call to log.Stacktrace. If passed to a logging function, the stacktrace will be appended.
func Stacktrace ¶
func Stacktrace() CapturedStacktrace
Stacktrace captures a stacktrace of the current goroutine and returns it to be passed to a logging function.
type Format ¶
type Format []interface{}
Format is a simple convience type for when formatting is required. When processing a value of this type, the logger automatically treats the first argument as a Printf formatting string and passes the rest as the values to be formatted. For example: L.Info(Fmt{"%d beans/day", beans}).
type Level ¶
type Level int32
Level represents a log level.
const ( // NoLevel is a special level used to indicate that no level has been // set and allow for a default to be used. NoLevel Level = 0 // Trace is the most verbose level. Intended to be used for the tracing // of actions in code, such as function enters/exits, etc. Trace Level = 1 // Debug information for programmer lowlevel analysis. Debug Level = 2 // Info information about steady state operations. Info Level = 3 // Warn information about rare but handled events. Warn Level = 4 // Error information about unrecoverable events. Error Level = 5 )
func LevelFromString ¶
LevelFromString returns a Level type for the named log level, or "NoLevel" if the level string is invalid. This facilitates setting the log level via config or environment variable by name in a predictable way.
type LevelWriter ¶ added in v0.8.0
LevelWriter is the interface that wraps the LevelWrite method.
type LeveledWriter ¶ added in v0.8.0
type LeveledWriter struct {
// contains filtered or unexported fields
}
LeveledWriter writes all log messages to the standard writer, except for log levels that are defined in the overrides map.
func NewLeveledWriter ¶ added in v0.8.0
NewLeveledWriter returns an initialized LeveledWriter.
standard will be used as the default writer for all log levels, except for log levels that are defined in the overrides map.
func (*LeveledWriter) LevelWrite ¶ added in v0.8.0
func (lw *LeveledWriter) LevelWrite(level Level, p []byte) (int, error)
LevelWrite implements LevelWriter.
type Logger ¶
type Logger interface {
// Args are alternating key, val pairs
// keys must be strings
// vals can be any type, but display is implementation specific
// Emit a message and key/value pairs at the TRACE level
Trace(msg string, args ...interface{})
// Emit a message and key/value pairs at the DEBUG level
Debug(msg string, args ...interface{})
// Emit a message and key/value pairs at the INFO level
Info(msg string, args ...interface{})
// Emit a message and key/value pairs at the WARN level
Warn(msg string, args ...interface{})
// Emit a message and key/value pairs at the ERROR level
Error(msg string, args ...interface{})
// Indicate if TRACE logs would be emitted. This and the other Is* guards
// are used to elide expensive logging code based on the current level.
IsTrace() bool
// Indicate if DEBUG logs would be emitted. This and the other Is* guards
IsDebug() bool
// Indicate if INFO logs would be emitted. This and the other Is* guards
IsInfo() bool
// Indicate if WARN logs would be emitted. This and the other Is* guards
IsWarn() bool
// Indicate if ERROR logs would be emitted. This and the other Is* guards
IsError() bool
// Creates a sublogger that will always have the given key/value pairs
With(args ...interface{}) Logger
// Create a logger that will prepend the name string on the front of all messages.
// If the logger already has a name, the new value will be appended to the current
// name. That way, a major subsystem can use this to decorate all it's own logs
// without losing context.
Named(name string) Logger
// Create a logger that will prepend the name string on the front of all messages.
// This sets the name of the logger to the value directly, unlike Named which honor
// the current name as well.
ResetNamed(name string) Logger
// Updates the level. This should affect all sub-loggers as well. If an
// implementation cannot update the level on the fly, it should no-op.
SetLevel(level Level)
// Return a value that conforms to the stdlib log.Logger interface
StandardLogger(opts *StandardLoggerOptions) *log.Logger
// Return a value that conforms to io.Writer, which can be passed into log.SetOutput()
StandardWriter(opts *StandardLoggerOptions) io.Writer
}
Logger describes the interface that must be implemeted by all loggers.
func Default ¶
func Default() Logger
Default returns a globally held logger. This can be a good starting place, and then you can use .With() and .Name() to create sub-loggers to be used in more specific contexts.
func FromContext ¶ added in v0.9.1
FromContext returns a logger from the context. This will return L() (the default logger) if no logger is found in the context. Therefore, this will never return a nil value.
func NewNullLogger ¶
func NewNullLogger() Logger
NewNullLogger instantiates a Logger for which all calls will succeed without doing anything. Useful for testing purposes.
func SetDefault ¶ added in v0.9.2
SetDefault changes the logger to be returned by Default()and L() to the one given. This allows packages to use the default logger and have higher level packages change it to match the execution environment. It returns any old default if there is one.
type LoggerOptions ¶
type LoggerOptions struct {
// Name of the subsystem to prefix logs with
Name string
// The threshold for the logger. Anything less severe is supressed
Level Level
// Where to write the logs to. Defaults to os.Stderr if nil
Output io.Writer
// An optional mutex pointer in case Output is shared
Mutex *sync.Mutex
// Control if the output should be in JSON.
JSONFormat bool
// Include file and line information in each log line
IncludeLocation bool
// The time format to use instead of the default
TimeFormat string
}
LoggerOptions can be used to configure a new logger.
type StandardLoggerOptions ¶
type StandardLoggerOptions struct {
// Indicate that some minimal parsing should be done on strings to try
// and detect their level and re-emit them.
// This supports the strings like [ERROR], [ERR] [TRACE], [WARN], [INFO],
// [DEBUG] and strip it off before reapplying it.
InferLevels bool
// ForceLevel is used to force all output from the standard logger to be at
// the specified level. Similar to InferLevels, this will strip any level
// prefix contained in the logged string before applying the forced level.
// If set, this override InferLevels.
ForceLevel Level
}
StandardLoggerOptions can be used to configure a new standard logger.
Source Files
Directories