logger.go

package logger

import (
	"io"
	"net/http"
	"os"
	"regexp"
	"time"

	"github.com/gin-gonic/gin"
	"github.com/mattn/go-isatty"
	"github.com/rs/zerolog"
)

// Fn is a function type that takes a gin.Context and a zerolog.Logger as parameters,
// and returns a zerolog.Logger. It is typically used to modify or enhance the logger
// within the context of a Gin HTTP request.
type Fn func(*gin.Context, zerolog.Logger) zerolog.Logger

// Skipper defines a function to skip middleware. It takes a gin.Context as input
// and returns a boolean indicating whether to skip the middleware for the given context.
type Skipper func(c *gin.Context) bool

// config holds the configuration for the logger middleware.
type config struct {
	// logger is a function that defines the logging behavior.
	logger Fn
	// utc is a boolean stating whether to use UTC time zone or local.
	utc bool
	// skipPath is a list of paths to be skipped from logging.
	skipPath []string
	// skipPathRegexps is a list of regular expressions to match paths to be skipped from logging.
	skipPathRegexps []*regexp.Regexp
	// skip is a Skipper that indicates which logs should not be written. Optional.
	skip Skipper
	// output is a writer where logs are written. Optional. Default value is gin.DefaultWriter.
	output io.Writer
	// defaultLevel is the log level used for requests with status code < 400.
	defaultLevel zerolog.Level
	// clientErrorLevel is the log level used for requests with status code between 400 and 499.
	clientErrorLevel zerolog.Level
	// serverErrorLevel is the log level used for requests with status code >= 500.
	serverErrorLevel zerolog.Level
	// pathLevels is a map of specific paths to log levels for requests with status code < 400.
	pathLevels map[string]zerolog.Level
}

const loggerKey = "_gin-contrib/logger_"

var isTerm bool = isatty.IsTerminal(os.Stdout.Fd())

// SetLogger returns a gin.HandlerFunc (middleware) that logs requests using zerolog.
// It accepts a variadic number of Option functions to customize the logger's behavior.
//
// The logger configuration includes:
// - defaultLevel: the default logging level (default: zerolog.InfoLevel).
// - clientErrorLevel: the logging level for client errors (default: zerolog.WarnLevel).
// - serverErrorLevel: the logging level for server errors (default: zerolog.ErrorLevel).
// - output: the output writer for the logger (default: gin.DefaultWriter).
// - skipPath: a list of paths to skip logging.
// - skipPathRegexps: a list of regular expressions to skip logging for matching paths.
// - logger: a custom logger function to use instead of the default logger.
//
// The middleware logs the following request details:
// - method: the HTTP method of the request.
// - path: the URL path of the request.
// - ip: the client's IP address.
// - user_agent: the User-Agent header of the request.
// - status: the HTTP status code of the response.
// - latency: the time taken to process the request.
// - body_size: the size of the response body.
//
// The logging level for each request is determined based on the response status code:
// - clientErrorLevel for 4xx status codes.
// - serverErrorLevel for 5xx status codes.
// - defaultLevel for other status codes.
// - Custom levels can be set for specific paths using the pathLevels configuration.
func SetLogger(opts ...Option) gin.HandlerFunc {
	cfg := &config{
		defaultLevel:     zerolog.InfoLevel,
		clientErrorLevel: zerolog.WarnLevel,
		serverErrorLevel: zerolog.ErrorLevel,
		output:           gin.DefaultWriter,
	}

	// Loop through each option
	for _, o := range opts {
		// Call the option giving the instantiated
		o.apply(cfg)
	}

	var skip map[string]struct{}
	if length := len(cfg.skipPath); length > 0 {
		skip = make(map[string]struct{}, length)
		for _, path := range cfg.skipPath {
			skip[path] = struct{}{}
		}
	}

	l := zerolog.New(cfg.output).
		Output(
			zerolog.ConsoleWriter{
				Out:     cfg.output,
				NoColor: !isTerm,
			},
		).
		With().
		Timestamp().
		Logger()
	return func(c *gin.Context) {
		rl := l
		if cfg.logger != nil {
			rl = cfg.logger(c, l)
		}

		start := time.Now()
		path := c.Request.URL.Path
		raw := c.Request.URL.RawQuery
		if raw != "" {
			path = path + "?" + raw
		}

		track := true

		if _, ok := skip[path]; ok || (cfg.skip != nil && cfg.skip(c)) {
			track = false
		}

		if track && len(cfg.skipPathRegexps) > 0 {
			for _, reg := range cfg.skipPathRegexps {
				if !reg.MatchString(path) {
					continue
				}

				track = false
				break
			}
		}

		// Use a separate logger to save to the context, as we want to avoid mutating the original logger.
		contextLogger := rl
		if track {
			contextLogger = rl.With().
				Str("method", c.Request.Method).
				Str("path", path).
				Str("ip", c.ClientIP()).
				Str("user_agent", c.Request.UserAgent()).Logger()
		}
		c.Set(loggerKey, contextLogger)

		c.Next()

		if track {
			end := time.Now()
			if cfg.utc {
				end = end.UTC()
			}
			latency := end.Sub(start)

			msg := "Request"
			if len(c.Errors) > 0 {
				msg = c.Errors.String()
			}

			var evt *zerolog.Event
			level, hasLevel := cfg.pathLevels[path]

			switch {
			case c.Writer.Status() >= http.StatusBadRequest && c.Writer.Status() < http.StatusInternalServerError:
				evt = rl.WithLevel(cfg.clientErrorLevel).Ctx(c)
			case c.Writer.Status() >= http.StatusInternalServerError:
				evt = rl.WithLevel(cfg.serverErrorLevel).Ctx(c)
			case hasLevel:
				evt = rl.WithLevel(level).Ctx(c)
			default:
				evt = rl.WithLevel(cfg.defaultLevel).Ctx(c)
			}
			evt.
				Int("status", c.Writer.Status()).
				Str("method", c.Request.Method).
				Str("path", path).
				Str("ip", c.ClientIP()).
				Dur("latency", latency).
				Str("user_agent", c.Request.UserAgent()).
				Int("body_size", c.Writer.Size()).
				Msg(msg)
		}
	}
}

// ParseLevel parses a string representation of a log level and returns the corresponding zerolog.Level.
// It takes a single argument:
//   - levelStr: a string representing the log level (e.g., "debug", "info", "warn", "error").
//
// It returns:
//   - zerolog.Level: the parsed log level.
//   - error: an error if the log level string is invalid.
func ParseLevel(levelStr string) (zerolog.Level, error) {
	return zerolog.ParseLevel(levelStr)
}

// Get retrieves the zerolog.Logger instance from the given gin.Context.
// It assumes that the logger has been previously set in the context with the key loggerKey.
// If the logger is not found, it will panic.
//
// Parameters:
//
//	c - the gin.Context from which to retrieve the logger.
//
// Returns:
//
//	zerolog.Logger - the logger instance stored in the context.
func Get(c *gin.Context) zerolog.Logger {
	return c.MustGet(loggerKey).(zerolog.Logger)
}