Create checkHeader func, add env vars and update documentation

README.md

@@ -46,6 +46,14 @@ console.log(parsed);
 Parses the given link header containing [web links](http://tools.ietf.org/html/rfc5988) and returns an object keyed by
 the `rel` property that contains information about each link.
 
+### Environmental Variables
+
+To avoid redundantly parsing of extremely long (invalid) input, the package uses 2 env variabes:
+
+`MAX_LINKHEADER_LENGTH` - Sets the number of characters the input should be limited to - longer inputs will not be handled. Defaults to `2000`.
+
+`PARSE_LINK_HEADER_THROW_ON_MAXLEN_EXCEEDED` - Defines behavior for when the `MAX_LINKHEADER_LENGTH` parameter is exceeded. if `true`, an error will be thrown; if `false`, the function fails silently by returning `null`. Defaults to `false`.
+
 ### Formatting a link header
 
 The purpose of this module is to parse the link header information. To format an object generated by this module back to the link header string, use the [format-link-header](https://github.com/jonathansamines/format-link-header) module.

index.js

@@ -4,6 +4,8 @@ var qs = require('querystring')
   , url = require('url')
   , xtend = require('xtend');
 
+
+
 function hasRel(x) {
   return x && x.rel;
 }
@@ -46,13 +48,22 @@ function parseLink(link) {
   }
 }
 
-module.exports = function (linkHeader) {
-  if (!linkHeader) return null;
-  const MAX_LINKHEADER_LENGTH = 2000;
+function checkHeader(linkHeader){
+  if (!linkHeader) return false;
+  const MAX_LINKHEADER_LENGTH = process.env.MAX_LINKHEADER_LENGTH || 2000;
+  const PARSE_LINK_HEADER_THROW_ON_MAXLEN_EXCEEDED = process.env.PARSE_LINK_HEADER_THROW_ON_MAXLEN_EXCEEDED || false
   if (linkHeader.length > MAX_LINKHEADER_LENGTH) {
+    if (PARSE_LINK_HEADER_THROW_ON_MAXLEN_EXCEEDED) {
     throw new Error('Input string too long, it should be under ' + MAX_LINKHEADER_LENGTH + ' characters.');
+    }
+    else return false;
   }
-
+  return true;
+}
+
+module.exports = function (linkHeader) {
+  if (!checkHeader(linkHeader)) return null;
+
   return linkHeader.split(/,\s*</)
    .map(parseLink)
    .filter(hasRel)

test/parse-link-header.js

@@ -186,3 +186,21 @@ test('parsing a proper link header with matrix parameters', function (t) {
   )
   t.end()
 })
+
+test('parsing an extremely long link header', function (t) {
+  function payload (n) {
+    var ret = ""
+    for (var i = 0; i < n; i++) {
+    ret += " "
+    }
+    return ret
+    }
+  var linkHeader = '; rel="' + payload(10000) + '",'
+
+  t.equal(
+      parse(linkHeader)
+    , null
+    , 'correctly returns null when dealing with an extremely long link header'
+  )
+  t.end()
+})