1/*
  2Copyright 2019 The logr Authors.
  3
  4Licensed under the Apache License, Version 2.0 (the "License");
  5you may not use this file except in compliance with the License.
  6You may obtain a copy of the License at
  7
  8    http://www.apache.org/licenses/LICENSE-2.0
  9
 10Unless required by applicable law or agreed to in writing, software
 11distributed under the License is distributed on an "AS IS" BASIS,
 12WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 13See the License for the specific language governing permissions and
 14limitations under the License.
 15*/
 16
 17// This design derives from Dave Cheney's blog:
 18//     http://dave.cheney.net/2015/11/05/lets-talk-about-logging
 19
 20// Package logr defines a general-purpose logging API and abstract interfaces
 21// to back that API.  Packages in the Go ecosystem can depend on this package,
 22// while callers can implement logging with whatever backend is appropriate.
 23//
 24// # Usage
 25//
 26// Logging is done using a Logger instance.  Logger is a concrete type with
 27// methods, which defers the actual logging to a LogSink interface.  The main
 28// methods of Logger are Info() and Error().  Arguments to Info() and Error()
 29// are key/value pairs rather than printf-style formatted strings, emphasizing
 30// "structured logging".
 31//
 32// With Go's standard log package, we might write:
 33//
 34//	log.Printf("setting target value %s", targetValue)
 35//
 36// With logr's structured logging, we'd write:
 37//
 38//	logger.Info("setting target", "value", targetValue)
 39//
 40// Errors are much the same.  Instead of:
 41//
 42//	log.Printf("failed to open the pod bay door for user %s: %v", user, err)
 43//
 44// We'd write:
 45//
 46//	logger.Error(err, "failed to open the pod bay door", "user", user)
 47//
 48// Info() and Error() are very similar, but they are separate methods so that
 49// LogSink implementations can choose to do things like attach additional
 50// information (such as stack traces) on calls to Error(). Error() messages are
 51// always logged, regardless of the current verbosity.  If there is no error
 52// instance available, passing nil is valid.
 53//
 54// # Verbosity
 55//
 56// Often we want to log information only when the application in "verbose
 57// mode".  To write log lines that are more verbose, Logger has a V() method.
 58// The higher the V-level of a log line, the less critical it is considered.
 59// Log-lines with V-levels that are not enabled (as per the LogSink) will not
 60// be written.  Level V(0) is the default, and logger.V(0).Info() has the same
 61// meaning as logger.Info().  Negative V-levels have the same meaning as V(0).
 62// Error messages do not have a verbosity level and are always logged.
 63//
 64// Where we might have written:
 65//
 66//	if flVerbose >= 2 {
 67//	    log.Printf("an unusual thing happened")
 68//	}
 69//
 70// We can write:
 71//
 72//	logger.V(2).Info("an unusual thing happened")
 73//
 74// # Logger Names
 75//
 76// Logger instances can have name strings so that all messages logged through
 77// that instance have additional context.  For example, you might want to add
 78// a subsystem name:
 79//
 80//	logger.WithName("compactor").Info("started", "time", time.Now())
 81//
 82// The WithName() method returns a new Logger, which can be passed to
 83// constructors or other functions for further use.  Repeated use of WithName()
 84// will accumulate name "segments".  These name segments will be joined in some
 85// way by the LogSink implementation.  It is strongly recommended that name
 86// segments contain simple identifiers (letters, digits, and hyphen), and do
 87// not contain characters that could muddle the log output or confuse the
 88// joining operation (e.g. whitespace, commas, periods, slashes, brackets,
 89// quotes, etc).
 90//
 91// # Saved Values
 92//
 93// Logger instances can store any number of key/value pairs, which will be
 94// logged alongside all messages logged through that instance.  For example,
 95// you might want to create a Logger instance per managed object:
 96//
 97// With the standard log package, we might write:
 98//
 99//	log.Printf("decided to set field foo to value %q for object %s/%s",
100//	    targetValue, object.Namespace, object.Name)
101//
102// With logr we'd write:
103//
104//	// Elsewhere: set up the logger to log the object name.
105//	obj.logger = mainLogger.WithValues(
106//	    "name", obj.name, "namespace", obj.namespace)
107//
108//	// later on...
109//	obj.logger.Info("setting foo", "value", targetValue)
110//
111// # Best Practices
112//
113// Logger has very few hard rules, with the goal that LogSink implementations
114// might have a lot of freedom to differentiate.  There are, however, some
115// things to consider.
116//
117// The log message consists of a constant message attached to the log line.
118// This should generally be a simple description of what's occurring, and should
119// never be a format string.  Variable information can then be attached using
120// named values.
121//
122// Keys are arbitrary strings, but should generally be constant values.  Values
123// may be any Go value, but how the value is formatted is determined by the
124// LogSink implementation.
125//
126// Logger instances are meant to be passed around by value. Code that receives
127// such a value can call its methods without having to check whether the
128// instance is ready for use.
129//
130// The zero logger (= Logger{}) is identical to Discard() and discards all log
131// entries. Code that receives a Logger by value can simply call it, the methods
132// will never crash. For cases where passing a logger is optional, a pointer to Logger
133// should be used.
134//
135// # Key Naming Conventions
136//
137// Keys are not strictly required to conform to any specification or regex, but
138// it is recommended that they:
139//   - be human-readable and meaningful (not auto-generated or simple ordinals)
140//   - be constant (not dependent on input data)
141//   - contain only printable characters
142//   - not contain whitespace or punctuation
143//   - use lower case for simple keys and lowerCamelCase for more complex ones
144//
145// These guidelines help ensure that log data is processed properly regardless
146// of the log implementation.  For example, log implementations will try to
147// output JSON data or will store data for later database (e.g. SQL) queries.
148//
149// While users are generally free to use key names of their choice, it's
150// generally best to avoid using the following keys, as they're frequently used
151// by implementations:
152//   - "caller": the calling information (file/line) of a particular log line
153//   - "error": the underlying error value in the `Error` method
154//   - "level": the log level
155//   - "logger": the name of the associated logger
156//   - "msg": the log message
157//   - "stacktrace": the stack trace associated with a particular log line or
158//     error (often from the `Error` message)
159//   - "ts": the timestamp for a log line
160//
161// Implementations are encouraged to make use of these keys to represent the
162// above concepts, when necessary (for example, in a pure-JSON output form, it
163// would be necessary to represent at least message and timestamp as ordinary
164// named values).
165//
166// # Break Glass
167//
168// Implementations may choose to give callers access to the underlying
169// logging implementation.  The recommended pattern for this is:
170//
171//	// Underlier exposes access to the underlying logging implementation.
172//	// Since callers only have a logr.Logger, they have to know which
173//	// implementation is in use, so this interface is less of an abstraction
174//	// and more of way to test type conversion.
175//	type Underlier interface {
176//	    GetUnderlying() <underlying-type>
177//	}
178//
179// Logger grants access to the sink to enable type assertions like this:
180//
181//	func DoSomethingWithImpl(log logr.Logger) {
182//	    if underlier, ok := log.GetSink().(impl.Underlier); ok {
183//	       implLogger := underlier.GetUnderlying()
184//	       ...
185//	    }
186//	}
187//
188// Custom `With*` functions can be implemented by copying the complete
189// Logger struct and replacing the sink in the copy:
190//
191//	// WithFooBar changes the foobar parameter in the log sink and returns a
192//	// new logger with that modified sink.  It does nothing for loggers where
193//	// the sink doesn't support that parameter.
194//	func WithFoobar(log logr.Logger, foobar int) logr.Logger {
195//	   if foobarLogSink, ok := log.GetSink().(FoobarSink); ok {
196//	      log = log.WithSink(foobarLogSink.WithFooBar(foobar))
197//	   }
198//	   return log
199//	}
200//
201// Don't use New to construct a new Logger with a LogSink retrieved from an
202// existing Logger. Source code attribution might not work correctly and
203// unexported fields in Logger get lost.
204//
205// Beware that the same LogSink instance may be shared by different logger
206// instances. Calling functions that modify the LogSink will affect all of
207// those.
208package logr
209
210// New returns a new Logger instance.  This is primarily used by libraries
211// implementing LogSink, rather than end users.  Passing a nil sink will create
212// a Logger which discards all log lines.
213func New(sink LogSink) Logger {
214	logger := Logger{}
215	logger.setSink(sink)
216	if sink != nil {
217		sink.Init(runtimeInfo)
218	}
219	return logger
220}
221
222// setSink stores the sink and updates any related fields. It mutates the
223// logger and thus is only safe to use for loggers that are not currently being
224// used concurrently.
225func (l *Logger) setSink(sink LogSink) {
226	l.sink = sink
227}
228
229// GetSink returns the stored sink.
230func (l Logger) GetSink() LogSink {
231	return l.sink
232}
233
234// WithSink returns a copy of the logger with the new sink.
235func (l Logger) WithSink(sink LogSink) Logger {
236	l.setSink(sink)
237	return l
238}
239
240// Logger is an interface to an abstract logging implementation.  This is a
241// concrete type for performance reasons, but all the real work is passed on to
242// a LogSink.  Implementations of LogSink should provide their own constructors
243// that return Logger, not LogSink.
244//
245// The underlying sink can be accessed through GetSink and be modified through
246// WithSink. This enables the implementation of custom extensions (see "Break
247// Glass" in the package documentation). Normally the sink should be used only
248// indirectly.
249type Logger struct {
250	sink  LogSink
251	level int
252}
253
254// Enabled tests whether this Logger is enabled.  For example, commandline
255// flags might be used to set the logging verbosity and disable some info logs.
256func (l Logger) Enabled() bool {
257	// Some implementations of LogSink look at the caller in Enabled (e.g.
258	// different verbosity levels per package or file), but we only pass one
259	// CallDepth in (via Init).  This means that all calls from Logger to the
260	// LogSink's Enabled, Info, and Error methods must have the same number of
261	// frames.  In other words, Logger methods can't call other Logger methods
262	// which call these LogSink methods unless we do it the same in all paths.
263	return l.sink != nil && l.sink.Enabled(l.level)
264}
265
266// Info logs a non-error message with the given key/value pairs as context.
267//
268// The msg argument should be used to add some constant description to the log
269// line.  The key/value pairs can then be used to add additional variable
270// information.  The key/value pairs must alternate string keys and arbitrary
271// values.
272func (l Logger) Info(msg string, keysAndValues ...any) {
273	if l.sink == nil {
274		return
275	}
276	if l.sink.Enabled(l.level) { // see comment in Enabled
277		if withHelper, ok := l.sink.(CallStackHelperLogSink); ok {
278			withHelper.GetCallStackHelper()()
279		}
280		l.sink.Info(l.level, msg, keysAndValues...)
281	}
282}
283
284// Error logs an error, with the given message and key/value pairs as context.
285// It functions similarly to Info, but may have unique behavior, and should be
286// preferred for logging errors (see the package documentations for more
287// information). The log message will always be emitted, regardless of
288// verbosity level.
289//
290// The msg argument should be used to add context to any underlying error,
291// while the err argument should be used to attach the actual error that
292// triggered this log line, if present. The err parameter is optional
293// and nil may be passed instead of an error instance.
294func (l Logger) Error(err error, msg string, keysAndValues ...any) {
295	if l.sink == nil {
296		return
297	}
298	if withHelper, ok := l.sink.(CallStackHelperLogSink); ok {
299		withHelper.GetCallStackHelper()()
300	}
301	l.sink.Error(err, msg, keysAndValues...)
302}
303
304// V returns a new Logger instance for a specific verbosity level, relative to
305// this Logger.  In other words, V-levels are additive.  A higher verbosity
306// level means a log message is less important.  Negative V-levels are treated
307// as 0.
308func (l Logger) V(level int) Logger {
309	if l.sink == nil {
310		return l
311	}
312	if level < 0 {
313		level = 0
314	}
315	l.level += level
316	return l
317}
318
319// GetV returns the verbosity level of the logger. If the logger's LogSink is
320// nil as in the Discard logger, this will always return 0.
321func (l Logger) GetV() int {
322	// 0 if l.sink nil because of the if check in V above.
323	return l.level
324}
325
326// WithValues returns a new Logger instance with additional key/value pairs.
327// See Info for documentation on how key/value pairs work.
328func (l Logger) WithValues(keysAndValues ...any) Logger {
329	if l.sink == nil {
330		return l
331	}
332	l.setSink(l.sink.WithValues(keysAndValues...))
333	return l
334}
335
336// WithName returns a new Logger instance with the specified name element added
337// to the Logger's name.  Successive calls with WithName append additional
338// suffixes to the Logger's name.  It's strongly recommended that name segments
339// contain only letters, digits, and hyphens (see the package documentation for
340// more information).
341func (l Logger) WithName(name string) Logger {
342	if l.sink == nil {
343		return l
344	}
345	l.setSink(l.sink.WithName(name))
346	return l
347}
348
349// WithCallDepth returns a Logger instance that offsets the call stack by the
350// specified number of frames when logging call site information, if possible.
351// This is useful for users who have helper functions between the "real" call
352// site and the actual calls to Logger methods.  If depth is 0 the attribution
353// should be to the direct caller of this function.  If depth is 1 the
354// attribution should skip 1 call frame, and so on.  Successive calls to this
355// are additive.
356//
357// If the underlying log implementation supports a WithCallDepth(int) method,
358// it will be called and the result returned.  If the implementation does not
359// support CallDepthLogSink, the original Logger will be returned.
360//
361// To skip one level, WithCallStackHelper() should be used instead of
362// WithCallDepth(1) because it works with implementions that support the
363// CallDepthLogSink and/or CallStackHelperLogSink interfaces.
364func (l Logger) WithCallDepth(depth int) Logger {
365	if l.sink == nil {
366		return l
367	}
368	if withCallDepth, ok := l.sink.(CallDepthLogSink); ok {
369		l.setSink(withCallDepth.WithCallDepth(depth))
370	}
371	return l
372}
373
374// WithCallStackHelper returns a new Logger instance that skips the direct
375// caller when logging call site information, if possible.  This is useful for
376// users who have helper functions between the "real" call site and the actual
377// calls to Logger methods and want to support loggers which depend on marking
378// each individual helper function, like loggers based on testing.T.
379//
380// In addition to using that new logger instance, callers also must call the
381// returned function.
382//
383// If the underlying log implementation supports a WithCallDepth(int) method,
384// WithCallDepth(1) will be called to produce a new logger. If it supports a
385// WithCallStackHelper() method, that will be also called. If the
386// implementation does not support either of these, the original Logger will be
387// returned.
388func (l Logger) WithCallStackHelper() (func(), Logger) {
389	if l.sink == nil {
390		return func() {}, l
391	}
392	var helper func()
393	if withCallDepth, ok := l.sink.(CallDepthLogSink); ok {
394		l.setSink(withCallDepth.WithCallDepth(1))
395	}
396	if withHelper, ok := l.sink.(CallStackHelperLogSink); ok {
397		helper = withHelper.GetCallStackHelper()
398	} else {
399		helper = func() {}
400	}
401	return helper, l
402}
403
404// IsZero returns true if this logger is an uninitialized zero value
405func (l Logger) IsZero() bool {
406	return l.sink == nil
407}
408
409// RuntimeInfo holds information that the logr "core" library knows which
410// LogSinks might want to know.
411type RuntimeInfo struct {
412	// CallDepth is the number of call frames the logr library adds between the
413	// end-user and the LogSink.  LogSink implementations which choose to print
414	// the original logging site (e.g. file & line) should climb this many
415	// additional frames to find it.
416	CallDepth int
417}
418
419// runtimeInfo is a static global.  It must not be changed at run time.
420var runtimeInfo = RuntimeInfo{
421	CallDepth: 1,
422}
423
424// LogSink represents a logging implementation.  End-users will generally not
425// interact with this type.
426type LogSink interface {
427	// Init receives optional information about the logr library for LogSink
428	// implementations that need it.
429	Init(info RuntimeInfo)
430
431	// Enabled tests whether this LogSink is enabled at the specified V-level.
432	// For example, commandline flags might be used to set the logging
433	// verbosity and disable some info logs.
434	Enabled(level int) bool
435
436	// Info logs a non-error message with the given key/value pairs as context.
437	// The level argument is provided for optional logging.  This method will
438	// only be called when Enabled(level) is true. See Logger.Info for more
439	// details.
440	Info(level int, msg string, keysAndValues ...any)
441
442	// Error logs an error, with the given message and key/value pairs as
443	// context.  See Logger.Error for more details.
444	Error(err error, msg string, keysAndValues ...any)
445
446	// WithValues returns a new LogSink with additional key/value pairs.  See
447	// Logger.WithValues for more details.
448	WithValues(keysAndValues ...any) LogSink
449
450	// WithName returns a new LogSink with the specified name appended.  See
451	// Logger.WithName for more details.
452	WithName(name string) LogSink
453}
454
455// CallDepthLogSink represents a LogSink that knows how to climb the call stack
456// to identify the original call site and can offset the depth by a specified
457// number of frames.  This is useful for users who have helper functions
458// between the "real" call site and the actual calls to Logger methods.
459// Implementations that log information about the call site (such as file,
460// function, or line) would otherwise log information about the intermediate
461// helper functions.
462//
463// This is an optional interface and implementations are not required to
464// support it.
465type CallDepthLogSink interface {
466	// WithCallDepth returns a LogSink that will offset the call
467	// stack by the specified number of frames when logging call
468	// site information.
469	//
470	// If depth is 0, the LogSink should skip exactly the number
471	// of call frames defined in RuntimeInfo.CallDepth when Info
472	// or Error are called, i.e. the attribution should be to the
473	// direct caller of Logger.Info or Logger.Error.
474	//
475	// If depth is 1 the attribution should skip 1 call frame, and so on.
476	// Successive calls to this are additive.
477	WithCallDepth(depth int) LogSink
478}
479
480// CallStackHelperLogSink represents a LogSink that knows how to climb
481// the call stack to identify the original call site and can skip
482// intermediate helper functions if they mark themselves as
483// helper. Go's testing package uses that approach.
484//
485// This is useful for users who have helper functions between the
486// "real" call site and the actual calls to Logger methods.
487// Implementations that log information about the call site (such as
488// file, function, or line) would otherwise log information about the
489// intermediate helper functions.
490//
491// This is an optional interface and implementations are not required
492// to support it. Implementations that choose to support this must not
493// simply implement it as WithCallDepth(1), because
494// Logger.WithCallStackHelper will call both methods if they are
495// present. This should only be implemented for LogSinks that actually
496// need it, as with testing.T.
497type CallStackHelperLogSink interface {
498	// GetCallStackHelper returns a function that must be called
499	// to mark the direct caller as helper function when logging
500	// call site information.
501	GetCallStackHelper() func()
502}
503
504// Marshaler is an optional interface that logged values may choose to
505// implement. Loggers with structured output, such as JSON, should
506// log the object return by the MarshalLog method instead of the
507// original value.
508type Marshaler interface {
509	// MarshalLog can be used to:
510	//   - ensure that structs are not logged as strings when the original
511	//     value has a String method: return a different type without a
512	//     String method
513	//   - select which fields of a complex type should get logged:
514	//     return a simpler struct with fewer fields
515	//   - log unexported fields: return a different struct
516	//     with exported fields
517	//
518	// It may return any value of any type.
519	MarshalLog() any
520}