Merge pull request #642 from CartoDB/resources-urls-crc-hash

Use crc32 instead of md5 for computing subdomain candidate

lib/cartodb/models/resource-locator.js

@@ -1,5 +1,3 @@
-var crypto = require('crypto');
-
 var dot = require('dot');
 dot.templateSettings.strip = false;
 
@@ -91,9 +89,31 @@ function getCdnDomain(serverMetadata, resource) {
     return null;
 }
 
+// ref https://jsperf.com/js-crc32
+function crcTable() {
+    var c;
+    var table = [];
+    for (var n = 0; n < 256; n++) {
+      c = n;
+      for (var k = 0; k < 8; k++) {
+        c = ((c & 1) ? (0xEDB88320 ^ (c >>> 1)) : (c >>> 1));
+      }
+      table[n] = c;
+    }
+    return table;
+}
+var CRC_TABLE = crcTable();
+
+function crc32(str) {
+    var crc = 0 ^ (-1);
+    for (var i = 0; i < str.length; i++) {
+      crc = (crc >>> 8) ^ CRC_TABLE[(crc ^ str.charCodeAt(i)) & 0xFF];
+    }
+    return (crc ^ (-1)) >>> 0;
+}
+
 function subdomain(subdomains, resource) {
-    var resourceHash = crypto.createHash('md5').update(resource, 'binary').digest('hex');
-    var index = parseInt(resourceHash, 16) % subdomains.length;
+    var index = crc32(resource) % subdomains.length;
     return subdomains[index];
 }
-module.exports.subdomain = subdomain;
+module.exports.subdomain = subdomain;