#1 : SCHEMA VALIDATION

“Good code is its own best documentation.”(Steve McConnell)

Mobile Server – JSON Processor

Mobile Server with Schema Validation

Mobile Client

Validation layer

Mobile Server

• Every request / response goes through validation with schema.• In case of response validation failure, the response is a 500• In case of request validation failure, the response is a 400.

How?

Avro Schema{ "type" : "record", "name" : ”Person", "namespace": "com.linkedin.mobileserver.templates", "doc" : ”Represents all the data fields for a person.", "fields" : [ { "name" : "firstName", "type" : "string", "doc" : "First name of the person" }, { "name" : "lastName", "type" : "string", "doc" : "Last name of the person" }], "version" : 1}

{ firstName: “Deepank”, lastName: “Gupta”}

How can I use it?

• Avro is open-source, available in Apache. Schema details: http://avro.apache.org/docs/current/spec.html

• Node module for helping with Avro:https://npmjs.org/package/avro-schema

#2: FUNCTIONAL PROGRAMMING

"It is better to have 100 functions operate on one data structure than 10 functions on 10 data structures."

—Alan Perlis

Pure vs Impure Functions

function add(a, b) { return a + b;}

function getFirst(name) { return name.slice(0, 1)[0];}

var x;function add() { x = this.a + this.b;}

function getFirst(name) { return name.splice(0, 1)[0];}

Why?

• Easy to use & understand• Simple to test. No before clauses required to

setup big objects.• No coupling

Higher Order Functions

• What?– Functions that accept functions as parameters or

return functions– Yes… functions are just like any other data

• Why?– Code Reuse– Terse, beautiful code

Functions that take a function as input

var res = [];var l = arr.length; for (var i = 0, i < l; ++i) { res.push(arr[i]);}

var res = _.map(arr, function(e){ return e;});

Example without Higher Level functionsfunction getProfile(req, res) { ProfileHelper.get(req, function(err, result) { if (err) { var error = getError(500, {msg: err}); Util.sendError(req, res, error); } else { Util.sendJsonResponse(req, res, result); } });}

function getUpdates(req, res) { UpdatesHelper.get(req, function(err, result) { if (err) { var error = getError(500, {msg: err}); Util.sendError(req, res, error); } else { Util.sendJsonResponse(req, res, result); } });}

Example with higher order functionfunction getProfile(req, res) { ProfileHelper.get(req, jsonResponder(req, res, 500));}

function getUpdates(req, res) { UpdatesHelper.get(req, jsonResponder(req, res, 400));}

function jsonResponder(req, res, errorKey) { return function(err, result) { if (err) { var error = getError(errorKey, {msg: err}); Util.sendError(req, res, error); } else { Util.sendJsonResponse(req, res, result); } });}

Functional libraries & resources

• Underscore.js (http://underscorejs.org )• lodash.js (http://lodash.com )• Wu.js (http://fitzgen.github.com/wu.js )