Adding upstream version 2.52.6.

Signed-off-by: Daniel Baumann <daniel@debian.org>

docs/api/log.md

@@ -0,0 +1,155 @@
+---
+id: log
+title: 📃 Log
+description: Fiber's built-in log package
+sidebar_position: 6
+---
+
+We can use logs to observe program behavior, diagnose problems, or configure corresponding alarms.
+And defining a well structured log can improve search efficiency and facilitate handling of problems.
+
+Fiber provides a default way to print logs in the standard output. 
+It also provides several global functions, such as `log.Info`, `log.Errorf`, `log.Warnw`, etc. 
+
+## Log levels
+
+```go
+const (
+	LevelTrace Level = iota
+	LevelDebug
+	LevelInfo
+	LevelWarn
+	LevelError
+	LevelFatal
+	LevelPanic
+)
+```
+
+## Custom log
+
+Fiber provides the `AllLogger` interface for adapting the various log libraries.
+
+```go
+type CommonLogger interface {
+    Logger
+    FormatLogger
+    WithLogger
+}
+
+type AllLogger interface {
+    CommonLogger
+    ControlLogger
+    WithLogger
+}
+```
+
+## Print log
+Note: The method of calling the Fatal level will interrupt the program running after printing the log, please use it with caution. 
+Directly print logs of different levels, which will be entered into messageKey, the default is msg.
+
+```go
+log.Info("Hello, World!")
+log.Debug("Are you OK?")
+log.Info("42 is the answer to life, the universe, and everything")
+log.Warn("We are under attack!")
+log.Error("Houston, we have a problem.")
+log.Fatal("So Long, and Thanks for All the Fislog.")
+log.Panic("The system is down.")
+```
+Format and print logs of different levels, all methods end with f
+
+```go
+log.Debugf("Hello %s", "boy")
+log.Infof("%d is the answer to life, the universe, and everything", 233)
+log.Warnf("We are under attack %s!", "boss")
+log.Errorf("%s, we have a problem.", "Master Shifu")
+log.Fatalf("So Long, and Thanks for All the %s.", "banana")
+```
+
+Print a message with the key and value, or `KEYVALS UNPAIRED` if the key and value are not a pair.
+
+```go
+log.Debugw("", "Hello", "boy")
+log.Infow("", "number", 233)
+log.Warnw("", "job", "boss")
+log.Errorw("", "name", "Master Shifu")
+log.Fatalw("", "fruit", "banana")
+```
+
+## Global log
+If you are in a project and just want to use a simple log function that can be printed at any time in the global, we provide a global log.
+
+```go
+import "github.com/gofiber/fiber/v2/log"
+
+log.Info("info")
+log.Warn("warn")
+```
+
+The above is using the default `log.DefaultLogger` standard output. 
+You can also find an already implemented adaptation under contrib, or use your own implemented Logger and use `log.SetLogger` to set the global log logger.
+
+```go
+import (
+    "log"
+    fiberlog "github.com/gofiber/fiber/v2/log"
+)
+
+var _ log.AllLogger = (*customLogger)(nil)
+
+type customLogger struct {
+    stdlog *log.Logger
+}
+
+// ...
+// inject your custom logger
+fiberlog.SetLogger(customLogger)
+```
+
+## Set Level
+`log.SetLevel` sets the level of logs below which logs will not be output.
+The default logger is LevelTrace.
+
+Note that this method is not **concurrent-safe**.
+
+```go
+import "github.com/gofiber/fiber/v2/log"
+
+log.SetLevel(log.LevelInfo)
+```
+## Set output
+
+`log.SetOutput` sets the output destination of the logger. The default logger types the log in the console.
+
+```go
+var logger AllLogger = &defaultLogger{
+    stdlog: log.New(os.Stderr, "", log.LstdFlags|log.Lshortfile|log.Lmicroseconds),
+    depth:  4,
+}
+```
+
+Set the output destination to the file.
+
+```go
+// Output to ./test.log file
+f, err := os.OpenFile("test.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
+if err != nil {
+    return
+}
+log.SetOutput(f)
+```
+Set the output destination to the console and file.
+
+```go
+// Output to ./test.log file
+file, _ := os.OpenFile("test.log", os.O_CREATE|os.O_WRONLY|os.O_APPEND, 0666)
+iw := io.MultiWriter(os.Stdout, file)
+log.SetOutput(iw)
+```
+## Bind context
+Set the context, using the following method will return a `CommonLogger` instance bound to the specified context
+```go
+commonLogger := log.WithContext(ctx)
+commonLogger.Info("info")
+```
+