Logging request headers with njs

README.md

Logging request headers with njs

This configuration can be used to log all of the request headers presented by a client. We use the JavaScript (njs) module to iterate over each header, returning a list of JSON key-value pairs which are then included in a JSON log format.

nginx.conf

js_include functions.js;
js_set $headers_json headers_to_json;

log_format json escape=none '{"timestamp":"$time_iso8601",'
                             '"client":"$remote_addr",'
                             '"uri":"$request_uri",'
                             '"status":$status,'
                             '"size":$bytes_sent,'
                             '"request headers":{$headers_json}}';
…
server {
   listen 80;
   access_log /var/log/nginx/access.log json;
   …
}

Example log output: $ tail -1 access.log | jq

{
   "timestamp": "2018-10-04T22:51:20+01:00",
   "client": "172.16.52.1",
   "uri": "/api/f1/current/last",
   "status": 200,
   "size": 681,
   "request headers": {
      "host": "api.example.com",
      "cache-control": "max-age=0",
      "upgrade-insecure-requests": 1,
      "user-agent": "Mozilla/5.0 (Macintosh; Intel Mac OS X 10_13_6) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/69.0.3497.100 Safari/537.36",
      "accept": "text/html,application/xhtml+xml,application/xml;q=0.9,image/webp,image/apng,*/*;q=0.8",
      "accept-encoding": "gzip, deflate, br",
      "accept-language": "en-GB,en-US;q=0.9,en;q=0.8"
   }
}

headers.js

function headers_to_json(r) {
    var kvpairs = '';
    for (var h in req.headers) {
        if ( kvpairs.length ) {
            kvpairs += ',';
        }
        kvpairs += '"' + h + '":';
        if ( isNaN(r.headers[h]) ) {
            kvpairs += '"' + r.headers[h] + '"';
        } else {
            kvpairs += req.headers[h];
        }
    }
    return kvpairs;
}

Dear lcrilly,
js_include functions.js;
I have an error nginx: [emerg] unknown directive "js_include"
Can you help me?
Thank you so much

Hi! You need to install and load the njs module. See https://docs.nginx.com/nginx/admin-guide/dynamic-modules/nginscript/#configuration

Dear lcrilly,
I added to my config nginx.conf :(

Why the sad-face?

Presumably not working? Did you also install the module?
https://nginx.org/en/docs/njs/install.html

Wasn't js_include removed as far back as 0.7.1?

js_import functions.js;
js_set $headers_json functions.headers_to_json;

should work.

@btdahl you are correct. This Gist is from 2018.

A more sophisticated way to do this is captured in https://www.f5.com/company/blog/nginx/diagnostic-logging-nginx-javascript-module but I’ll update this too. Thanks for catching it.