fiber/docs/middleware/logger.md

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---
id: logger
---
# Logger
Logger middleware for [Fiber](https://github.com/gofiber/fiber) that logs HTTP request/response details.
## Signatures
```go
func New(config ...Config) fiber.Handler
```
## Examples
Import the middleware package that is part of the Fiber web framework
```go
import (
"github.com/gofiber/fiber/v3"
"github.com/gofiber/fiber/v3/middleware/logger"
)
```
:::tip
The order of registration plays a role. Only all routes that are registered after this one will be logged.
The middleware should therefore be one of the first to be registered.
:::
After you initiate your Fiber app, you can use the following possibilities:
```go
// Initialize default config
app.Use(logger.New())
// Or extend your config for customization
// Logging remote IP and Port
app.Use(logger.New(logger.Config{
Format: "[${ip}]:${port} ${status} - ${method} ${path}\n",
}))
// Logging Request ID
app.Use(requestid.New())
app.Use(logger.New(logger.Config{
// For more options, see the Config section
Format: "${pid} ${locals:requestid} ${status} - ${method} ${path}\n",
}))
// Changing TimeZone & TimeFormat
app.Use(logger.New(logger.Config{
Format: "${pid} ${status} - ${method} ${path}\n",
TimeFormat: "02-Jan-2006",
TimeZone: "America/New_York",
}))
// Custom File Writer
file, err := os.OpenFile("./123.log", os.O_RDWR|os.O_CREATE|os.O_APPEND, 0666)
if err != nil {
log.Fatalf("error opening file: %v", err)
}
defer file.Close()
app.Use(logger.New(logger.Config{
Output: file,
}))
// Add Custom Tags
app.Use(logger.New(logger.Config{
CustomTags: map[string]logger.LogFunc{
"custom_tag": func(output logger.Buffer, c fiber.Ctx, data *logger.Data, extraParam string) (int, error) {
return output.WriteString("it is a custom tag")
},
},
}))
// Callback after log is written
app.Use(logger.New(logger.Config{
TimeFormat: time.RFC3339Nano,
TimeZone: "Asia/Shanghai",
Done: func(c fiber.Ctx, logString []byte) {
if c.Response().StatusCode() != fiber.StatusOK {
reporter.SendToSlack(logString)
}
},
}))
// Disable colors when outputting to default format
app.Use(logger.New(logger.Config{
DisableColors: true,
}))
```
:::tip
Writing to os.File is goroutine-safe, but if you are using a custom Output that is not goroutine-safe, make sure to implement locking to properly serialize writes.
:::
## Config
### Config
| Property | Type | Description | Default |
|:-----------------|:---------------------------|:---------------------------------------------------------------------------------------------------------------------------------|:----------------------------------------------------------------------|
| Next | `func(fiber.Ctx) bool` | Next defines a function to skip this middleware when returned true. | `nil` |
| Done | `func(fiber.Ctx, []byte)` | Done is a function that is called after the log string for a request is written to Output, and pass the log string as parameter. | `nil` |
| CustomTags | `map[string]LogFunc` | tagFunctions defines the custom tag action. | `map[string]LogFunc` |
| Format | `string` | Format defines the logging tags. | `[${time}] ${ip} ${status} - ${latency} ${method} ${path} ${error}\n` |
| TimeFormat | `string` | TimeFormat defines the time format for log timestamps. | `15:04:05` |
| TimeZone | `string` | TimeZone can be specified, such as "UTC" and "America/New_York" and "Asia/Chongqing", etc | `"Local"` |
| TimeInterval | `time.Duration` | TimeInterval is the delay before the timestamp is updated. | `500 * time.Millisecond` |
| Output | `io.Writer` | Output is a writer where logs are written. | `os.Stdout` |
| DisableColors | `bool` | DisableColors defines if the logs output should be colorized. | `false` |
| enableColors | `bool` | Internal field for enabling colors in the log output. (This is not a user-configurable field) | - |
| enableLatency | `bool` | Internal field for enabling latency measurement in logs. (This is not a user-configurable field) | - |
| timeZoneLocation | `*time.Location` | Internal field for the time zone location. (This is not a user-configurable field) | - |
## Default Config
```go
var ConfigDefault = Config{
Next: nil,
Done: nil,
Format: "[${time}] ${ip} ${status} - ${latency} ${method} ${path} ${error}\n",
TimeFormat: "15:04:05",
TimeZone: "Local",
TimeInterval: 500 * time.Millisecond,
Output: os.Stdout,
DisableColors: false,
}
```
## Constants
```go
// Logger variables
const (
TagPid = "pid"
TagTime = "time"
TagReferer = "referer"
TagProtocol = "protocol"
TagPort = "port"
TagIP = "ip"
TagIPs = "ips"
TagHost = "host"
TagMethod = "method"
TagPath = "path"
TagURL = "url"
TagUA = "ua"
TagLatency = "latency"
TagStatus = "status" // response status
TagResBody = "resBody" // response body
TagReqHeaders = "reqHeaders"
TagQueryStringParams = "queryParams" // request query parameters
TagBody = "body" // request body
TagBytesSent = "bytesSent"
TagBytesReceived = "bytesReceived"
TagRoute = "route"
TagError = "error"
// DEPRECATED: Use TagReqHeader instead
TagHeader = "header:" // request header
TagReqHeader = "reqHeader:" // request header
TagRespHeader = "respHeader:" // response header
TagQuery = "query:" // request query
TagForm = "form:" // request form
TagCookie = "cookie:" // request cookie
TagLocals = "locals:"
// colors
TagBlack = "black"
TagRed = "red"
TagGreen = "green"
TagYellow = "yellow"
TagBlue = "blue"
TagMagenta = "magenta"
TagCyan = "cyan"
TagWhite = "white"
TagReset = "reset"
)
```