Memoize url.resolve

Why:

* Resolve is an expensive API call

This change addresses the need by:

* Cache results of last evaluation.

lib/helpers.js

@@ -1,6 +1,6 @@
 'use strict';
 
-var uri = require('url');
+var memoizedResolve = require('./memoizedResolve');
 
 var ValidationError = exports.ValidationError = function ValidationError (message, instance, schema, path, name, argument) {
   if(Array.isArray(path)){
@@ -129,13 +129,13 @@ var SchemaContext = exports.SchemaContext = function SchemaContext (schema, opti
 };
 
 SchemaContext.prototype.resolve = function resolve (target) {
-  return uri.resolve(this.base, target);
+  return memoizedResolve(this.base, target);
 };
 
 SchemaContext.prototype.makeChild = function makeChild(schema, propertyName){
   var path = (propertyName===undefined) ? this.path : this.path.concat([propertyName]);
   var id = schema.$id || schema.id;
-  var base = uri.resolve(this.base, id||'');
+  var base = memoizedResolve(this.base, id||'');
   var ctx = new SchemaContext(schema, this.options, path, base, Object.create(this.schemas));
   if(id && !ctx.schemas[base]){
     ctx.schemas[base] = schema;

lib/memoizedResolve.js

@@ -0,0 +1,20 @@
+var uri = require('url');
+
+function memoizeLastCall(func) {
+  var lastArg1 = -1;
+  var lastArg2 = -1;
+  var lastResult = null;
+  return function() {
+    //return func.apply(null, arguments);
+    if (lastArg1 === arguments[0] && lastArg2 === arguments[1]) {
+      return lastResult;
+    } else {
+      lastResult = func.apply(null, arguments);
+      lastArg1 = arguments[0];
+      lastArg2 = arguments[1];
+      return lastResult;
+    }
+  };
+}
+
+module.exports = memoizeLastCall(uri.resolve);

lib/validator.js

@@ -1,5 +1,6 @@
 'use strict';
 
+var memoizedResolve = require('./memoizedResolve');
 var urilib = require('url');
 
 var attribute = require('./attribute');
@@ -115,7 +116,7 @@ Validator.prototype.validate = function validate (instance, schema, options, ctx
   // This section indexes subschemas in the provided schema, so they don't need to be added with Validator#addSchema
   // This will work so long as the function at uri.resolve() will resolve a relative URI to a relative URI
   var id = schema.$id || schema.id;
-  var base = urilib.resolve(options.base||anonymousBase, id||'');
+  var base = memoizedResolve(options.base||anonymousBase, id||'');
   if(!ctx){
     ctx = new SchemaContext(schema, options, [], base, Object.create(this.schemas));
     if (!ctx.schemas[base]) {

test/Validator.test.js

@@ -28,6 +28,47 @@ describe('Validator', function () {
       assert.deepStrictEqual(validator.unresolvedRefs, ['http://example.com/item.json']);
     });
   });
+  describe('Performance test', function(){
+    function measureTime(iterations, label, arg, fn) {
+      const startTime = new Date().getTime();
+      for (let x = 0; x < iterations; ++x) {
+        fn(arg);
+      }
+      const elapsed = new Date().getTime() - startTime;
+      console.log("Time to do " + iterations + "* " + label + " = " + elapsed+ ", " + elapsed * 1.0 / iterations + " ms/call");
+    }
+    it.only('Perf test', function (){
+      const schema = {
+        type: "object",
+        properties: {
+          field1: { type: "string"},
+          field2: { type: "string"},
+          field3: { type: "string"},
+          field4: { type: "string"},
+          field5: { type: "string"},
+          field6: { type: "string"},
+          field7: { type: "string"},
+          field8: { type: "string"},
+          field9: { type: "string"},
+          field10: { type: "integer"},
+          field11: { type: "integer"},
+          field12: { type: "integer"},
+          field13: { type: "integer"},
+          field14: { type: "integer"},
+          field15: { type: "integer"},
+          field16: { type: "integer"},
+          field17: { type: "integer"},
+          field18: { type: "integer"},
+          field19: { type: "integer"},
+          field20: { type: "integer"}
+        }
+      };
+      var values = {field1:"a", field2:"a", field3:"a", field4:"a", field5:"a",field6:"a", field7:"a", field8:"a", field9:"a",
+        field10: 0,field11: 0,field12: 0,field13: 0,field14: 0,field15: 0,field16: 0,field17: 0,field18: 0, field19: 0, field20: 0};
+
+      measureTime(10000, "validate", null, function() {return validator.validate(values, schema)});
+    });
+  });
   describe('Validator#addSchema', function () {
     it('argument schema must be a schema: object', function(){
       validator.addSchema({}, 'http://example.com/base.json');