Building RESTful Web Services with Go Learn how to build powerful RESTful APIs with Golang that scale gracefully Naren Yellavula BIRMINGHAM - MUMBAI Building RESTful Web Services with Go Copyright © 2017 Packt Publishing All rights reserved. No part of this book may be reproduced, stored in a retrieval system, or transmitted in any form or by any means, without the prior written permission of the publisher, except in the case of brief quotations embedded in critical articles or reviews. Every effort has been made in the preparation of this book to ensure the accuracy of the information presented. However, the information contained in this book is sold without warranty, either express or implied. Neither the author, nor Packt Publishing, and its dealers and distributors will be held liable for any damages caused or alleged to be caused directly or indirectly by this book. Packt Publishing has endeavored to provide trademark information about all of the companies and products mentioned in this book by the appropriate use of capitals. However, Packt Publishing cannot guarantee the accuracy of this information. First published: December 2017 Production reference: 1261217 Published by Packt Publishing Ltd. Livery Place 35 Livery Street Birmingham B3 2PB, UK. ISBN 978-1-78829-428-7 www.packtpub.com Credits Copy Editors Author Dhanya Baburaj Naren Yellavula Safis Editing Reviewer Project Coordinator Anshul Joshi Sheejal Shah Commissioning Editor Proofreader Aaron Lazar Safis Editing Acquisition Editor Indexer Denim Pinto Rekha Nair Content Development Editor Graphics Sreeja Nair Jason Monteiro Technical Editor Production Coordinator Rutuja Vaze Nilesh Mohite About the Author Naren Yellavula—fondly called by the developer community as Naren Arya—started his programming career in the funniest way. He ditched mechanical engineering for computer science after watching The Matrix for the first time. With dreams of coding a mini world, he continuously sharpened his practical skills. Initially, he built few a mobile applications. Then, he completely moved into the space of full stack development. He always believed that computers and software can help make this world a better place. He wrote 120+ development articles on various open source technologies, including Go and Python. He is also one of the few young speakers at the PyCon India conference (he spoke at Bangalore in 2015 and Delhi in 2017). With detailed knowledge of web scraping and REST APIs, he dived into multiple domains such as cloud telephony and cloud-based web services. On this journey, he bathed in a lot of design decisions. He currently works as a software engineer for Citrix R&D, India. Naren is a great fan of Go personally because of the speed and intuitiveness of the language. In his spare time, he tries to educate the youth in programming and software development. He loves reading nonfiction most of the time, and Victorian and Russian fiction sometimes. Acknowledgments I would like to thank my grandmother, Tayamma, for raising me to be helpful to others by sharing my knowledge in every possible way. She was the one who always taught me how to put in serious effort with 100% dedication, and not worry much about results. Therefore, I dedicate this book to her, to my inspiration. I also cannot understate the support given by my father, Venkataiah Yellavula; mother, ShobaRani Dasyam; and lovely younger brother Saikiran, who understood the value of the time I spent on this book and always encouraged me with their positive wishes. I am grateful to my mentor, Chandrashekar MuniBudha, Solutions Architect, Amazon Web Services, whom I am deeply indebted to. I also thank Ashwin Baskaran, Senior Director, Citrix, who encouraged and pushed me forward in all possible ways. Thank you! I cannot name everyone here; the list is so big. However, I sincerely thank all my friends who always wished success for this book. About the Reviewer Anshul Joshi is a data scientist with experience in recommendation systems, predictive modeling, neural networks, and high-performance computing. His research interests encompass deep learning, artificial intelligence, and computational physics. Most of the time, he can be found exploring GitHub or trying anything new he can get his hands on. His blog can be found at https:/​/​anshuljoshi.​com/.​ www.PacktPub.com For support files and downloads related to your book, please visit www.PacktPub.com. Did you know that Packt offers eBook versions of every book published, with PDF and ePub files available? 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Table of Contents Preface 1 Chapter 1: Getting Started with REST API Development 7 Types of web services 8 REST API 9 Characteristics of REST services 10 REST verbs and status codes 11 GET 13 POST, PUT, and PATCH 14 DELETE and OPTIONS 15 Cross-Origin Resource Sharing (CORS) 16 Types of status codes 17 2xx family (successful) 18 3xx family (redirection) 18 4xx family (client error) 18 5xx family (server error) 19 Rise of REST API with Single Page Applications 19 Old and new ways of data flow in SPA 20 Why Go for REST API development? 22 Setting up the project and running the development server 22 Demystifying GOPATH 23 Building our first service – finding the Roman numeral 25 Breaking down the code 29 Live reloading the application with supervisord and Gulp 30 Monitoring your Go web server with supervisord 30 Installing supervisord 30 Using Gulp for creating auto code compiling and server reloading 32 Understanding the gulpfile 34 Summary 35 Chapter 2: Handling Routing for Our REST Services 36 Getting the code 37 Understanding Go's net/http package 37 Running the code 38 ServeMux, a basic router in Go 38 Running the code 40 Adding multiple handlers using ServeMux 40 Table of Contents Running the code 41 Introducing httprouter, a lightweight HTTP router 42 Installation 42 Program explanation 44 Building the simple static file server in minutes 46 Introducing Gorilla Mux, a powerful HTTP router 47 Installation 48 Fundamentals of Gorilla Mux 48 Reverse mapping URL 50 Custom paths 50 Path Prefix 51 Strict Slash 51 Encoded paths 52 Query-based matching 52 Host-based matching 53 SQL injections in URLs and ways to avoid them 55 Creating a basic API layout for URL shortening services 56 Summary 57 Chapter 3: Working with Middleware and RPC 58 Getting the code 58 What is middleware? 59 Creating a basic middleware 60 Multiple middleware and chaining 63 Painless middleware chaining with Alice 69 Using Gorilla's Handlers middleware for Logging 70 What is RPC? 72 Creating an RPC server 73 Creating an RPC client 74 JSON RPC using Gorilla RPC 76 Summary 79 Chapter 4: Simplifying RESTful Services with Popular Go Frameworks 80 Getting the code 80 go-restful, a framework for REST API creation 81 CRUD operations and SQLite3 basics 83 Building a Metro Rail API with go-restful 85 Design specification 86 Creating database models 86 Building RESTful APIs with the Gin framework 96 Building a RESTful API with Revel.go 102 [ ii ] Table of Contents Summary 107 Chapter 5: Working with MongoDB and Go to Create REST APIs 109 Getting the code 109 Introduction to MongoDB 110 Installing MongoDB and using the shell 110 Working with the Mongo shell 112 Introducing mgo, a MongoDB driver for Go 117 RESTful API with Gorilla Mux and MongoDB 120 Boosting the querying performance with indexing 125 Designing an e-commerce data document model 128 Summary 131 Chapter 6: Working with Protocol Buffers and GRPC 132 Getting the code 132 Introduction to protocol buffers 133 Protocol buffer language 134 Scalar values 135 Enumerations and repeated fields 136 Compiling a protocol buffer with protoc 138 Introduction to GRPC 144 Bidirectional streaming with GRPC 151 Summary 156 Chapter 7: Working with PostgreSQL, JSON, and Go 158 Getting the code 158 Installing the PostgreSQL database 159 Adding users and databases in PostgreSQL 160 pq, a pure PostgreSQL database driver for Go 162 Implementing a URL shortening service using Postgres and pq 165 Defining the Base62 algorithm 165 Exploring the JSON store in PostgreSQL 172 GORM, a powerful ORM for Go 172 Implementing the e-commerce REST API 174 Summary 180 Chapter 8: Building a REST API Client in Go and Unit Testing 181 Getting the code 182 Plan for building a REST API client 182 Basics for