add a filter function to let users filter out certain log messages

Readme.md

@@ -90,6 +90,12 @@ serializer instead of the default one which is using `req.originalUrl` instead.
 
 - A function receiving `req` and `res` as arguments returning an object. The elements in the returned object will be added to the fields in the `request finish` message.
 
+**`filter`** Default: `undefined`
+
+- A function receiving `req` and `res` as arguments returning a boolean.
+  If this functions return value is truthy it will skip all logging for
+  this request/response.
+
 **`logName`** Default: `'req_id'`
 
 - The name for the request id in the log output.

index.d.ts

@@ -13,6 +13,7 @@ interface Params {
   requestStart?: boolean
   verbose?: boolean
   level?: 'trace' | 'debug' | 'info' | 'warn' | 'error' | 'fatal'
+  filter?: { (req: Request, res: Response): boolean }
 }
 interface ParamsWithLogger extends Params {
   logger: Logger

index.js

@@ -22,6 +22,7 @@ module.exports = function (options, logger) {
     , excludeHeaders = options.excludeHeaders
     , requestStart = options.requestStart || false
     , verbose = options.verbose || false
+    , filter = options.filter
     , parentRequestSerializer = logger.serializers && logger.serializers.req
     , level = options.level || 'info'
 
@@ -79,6 +80,9 @@ module.exports = function (options, logger) {
   )
 
   return function (req, res, next) {
+    if (filter && filter(req, res))
+      return next()
+
     var id = req[propertyName]
           || req.headers[headerNameLower]
           || uuid()
@@ -97,6 +101,7 @@ module.exports = function (options, logger) {
       if (verbose) reqStartData.res = res
       req.log[level](reqStartData, 'request start')
     }
+
     res.on('finish', function() {
       var reqFinishData =
         { res: res
@@ -113,6 +118,7 @@ module.exports = function (options, logger) {
       }
       res.log[level](reqFinishData, 'request finish')
     })
+
     res.on('close', function () {
       res.log.warn(
           { req: req