Customize Log Format in LoggingHandlers Implementation in Gorilla Handlers In GO

Question

I want to customize logging format in gorilla handler implementation in LoggingHandler. Basically It gives Common Log format as a default.I want to customize based on the request headers. Assume I pass the tenantId value as a one request header.Then I want added it into the os.StdOut.

r := mux.NewRouter()
r.HandleFunc("/", func(w http.ResponseWriter, r *http.Request) {
    w.Write([]byte("This is a catch-all route"))
})
loggedRouter := handlers.LoggingHandler(os.Stdout, r)

127.0.0.1 - sandun [10/Oct/2018:13:55:36 -0700] "GET /api/request HTTP/1.0" 200 2326

Then Request Header

teanantId : 50

expected output

127.0.0.1 - sandun [10/Oct/2018:13:55:36 -0700] "GET /api/request HTTP/1.0" 200 2326 50

I want to add tenantid at the last on the log output.

How I do this without changing gorilla handlers liabry.

As more details: I can do it by changing inside code of gorilla handlers library.

// buildCommonLogLine builds a log entry for req in Apache Common Log Format.
// ts is the timestamp with which the entry should be logged.
// status and size are used to provide the response HTTP status and size.
func buildCommonLogLine(req *http.Request, url url.URL, ts time.Time, status int, size int) []byte {
    tenantId, err := strconv.Atoi(req.Header.Get("tenantid"))
    if err != nil {
        tenantId = 0
    }
    username := "-"
    if url.User != nil {
        if name := url.User.Username(); name != "" {
            username = name
        }
    }

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

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

    uri := req.RequestURI

    // Requests using the CONNECT method over HTTP/2.0 must use
    // the authority field (aka r.Host) to identify the target.
    // Refer: https://httpwg.github.io/specs/rfc7540.html#CONNECT
    if req.ProtoMajor == 2 && req.Method == "CONNECT" {
        uri = req.Host
    }
    if uri == "" {
        uri = url.RequestURI()
    }

    buf := make([]byte, 0, 3*(len(host)+len(username)+len(req.Method)+len(uri)+len(req.Proto)+50)/2)
    buf = append(buf, host...)
    buf = append(buf, " - "...)
    buf = append(buf, username...)
    buf = append(buf, " ["...)
    buf = append(buf, ts.Format("02/Jan/2006:15:04:05 -0700")...)
    buf = append(buf, `] "`...)
    buf = append(buf, req.Method...)
    buf = append(buf, " "...)
    buf = appendQuoted(buf, uri)
    buf = append(buf, " "...)
    buf = append(buf, req.Proto...)
    buf = append(buf, `" `...)
    buf = append(buf, strconv.Itoa(status)...)
    buf = append(buf, " "...)
    buf = append(buf, strconv.Itoa(size)...)
    buf = append(buf, " "...)
    buf = append(buf, strconv.Itoa(tenantId)...)
    return buf
}

But I think it is not good solution. I am expecting good solution from this community.

appreciate your help.

score 3 · Answer 1 · answered Jun 29 '18 at 08:17

3

Gorilla handlers library uses Apache Common Log Format. Changing of the output format makes your log messages absolutely unclear for everyone except you.

The idiomatic way: create you own middleware handler, that writes to output (or any other io.Writer) value of teanantId header.

The second (wrong in my opinion) way: fork repository, change behavior and use it.

answered Jun 29 '18 at 08:17

bayrinat

1,468
8
18

*Changing of the output format makes your log messages absolutely unclear for everyone except you* → ACLF is just one of several "standard" logging formats - a good default if someone does not care. You can have specific needs in terms of what is output in the log - the use-case of OP is actually very common, with the need to enrich the output. I would have gone for a structured log in his case, to make it easier to parse afterward. When you look at output logs of applications outside of a generic web server, it is a complete circus in terms of content. – WoJ Nov 02 '21 at 15:23

Customize Log Format in LoggingHandlers Implementation in Gorilla Handlers In GO

1 Answers1