response_logger.go

package httpd

import (
	"fmt"
	"net"
	"net/http"
	"strconv"
	"strings"
	"time"
)

type loggingResponseWriter interface {
	http.ResponseWriter
	Status() int
	Size() int
}

// responseLogger is wrapper of http.ResponseWriter that keeps track of its HTTP status
// code and body size
type responseLogger struct {
	w      http.ResponseWriter
	status int
	size   int
}

func (l *responseLogger) Header() http.Header {
	return l.w.Header()
}

func (l *responseLogger) Write(b []byte) (int, error) {
	if l.status == 0 {
		// Set status if WriteHeader has not been called
		l.status = http.StatusOK
	}
	size, err := l.w.Write(b)
	l.size += size
	return size, err
}

func (l *responseLogger) WriteHeader(s int) {
	l.w.WriteHeader(s)
	l.status = s
}

func (l *responseLogger) Status() int {
	if l.status == 0 {
		// This can happen if we never actually write data, but only set response headers.
		l.status = http.StatusOK
	}
	return l.status
}

func (l *responseLogger) Size() int {
	return l.size
}

// Common Log Format: http://en.wikipedia.org/wiki/Common_Log_Format

// buildLogLine creates a common log format
// in addittion to the common fields, we also append referrer, user agent and request ID
func buildLogLine(l *responseLogger, r *http.Request, start time.Time) string {
	username := parseUsername(r)

	host, _, err := net.SplitHostPort(r.RemoteAddr)

	if err != nil {
		host = r.RemoteAddr
	}

	uri := r.URL.RequestURI()

	referer := r.Referer()

	userAgent := r.UserAgent()

	fields := []string{
		host,
		"-",
		detect(username, "-"),
		fmt.Sprintf("[%s]", start.Format("02/Jan/2006:15:04:05 -0700")),
		r.Method,
		uri,
		r.Proto,
		detect(strconv.Itoa(l.Status()), "-"),
		strconv.Itoa(l.Size()),
		detect(referer, "-"),
		detect(userAgent, "-"),
		r.Header.Get("Request-Id"),
		fmt.Sprintf("%s", time.Since(start)),
	}

	return strings.Join(fields, " ")
}

// detect detects the first presense of a non blank string and returns it
func detect(values ...string) string {
	for _, v := range values {
		if v != "" {
			return v
		}
	}
	return ""
}

// parses the uesrname either from the url or auth header
func parseUsername(r *http.Request) string {
	var (
		username = ""
		url      = r.URL
	)

	// get username from the url if passed there
	if url.User != nil {
		if name := url.User.Username(); name != "" {
			username = name
		}
	}

	// Try to get it from the authorization header if set there
	if username == "" {
		if u, _, ok := r.BasicAuth(); ok {
			username = u
		}
	}
	return username
}