From nil to Gopher - Speaker Deck

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From nil to Gopher GopherLX Marco Talento 24/10/2018

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WHY GO?

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https://pbs.twimg.com/media/B79paXxIcAAu0CN.jpg

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Why GO? ● Compiled static language ● Simple (25 keywords) and performant ● GO routines and concurrency model ● Great Tooling (testing, benchmarking, profiling) ● Cross compilation and easy to deploy (single binary) ● Awesome community (gophers.slack.com)

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Learning GO https://bit.ly/2pOQT8J

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Learning GO ● I started Learning GO in 2017 ● A Tour of GO (https://tour.golang.org) ● Books (The GO programming Language) ● Videos and Courses: JustForFunc, GopherCon, Ardan Labs, Todd Macleod ● Looking at Open Source Projects (Upsin, Apex, InfluxDB, HashiCorp, etc...)

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Let's build something https://golang.org/doc/gopher/pencil/

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Requirements ● Building something useful ● Try to use most of the go features ● Good DX (Developer experience) ● Testing and Quality

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IMGART

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IMGART ● HTTP service for image manipulation ● Configurable profiles ● Image Caching ● Source Code: https://github.com/Talento90/imgart

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Example GET /api/v1/images?imgSrc=https://bit.ly/2JFW2HO &filters=[{"id":"overlay","parameters":{"position":[25,75],"url":"https://goo.gl/UBrXeo"}},{"i d":"overlay","parameters":{"position":[22,-35],"url":"https://goo.gl/aEkkDh"}}, {"id":"crop","parameters":{"rectangle":[0,0,202,150]}}] &profile=my-custom-profile ++ + + =

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Where do I start?

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Question and Decisions ● How should I organize my application? ● Error Handling? ● How to Debug? ● How to maintain code quality? ● Should I care about cancellation?

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How to structure GO applications?

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Structure Application ● Flat packages (everything in the root level) ● Organize packages by components (models, controllers, repositories) ● Clean Architecture (Entities, Use Cases, Adapters) ● Hexagonal Architecture (Domain, Application, Infrastructure) ● How do you structure your GO apps - Kat Zien talk at GopherCon 2018

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Structure Application ● Group packages by domain ● Dependencies Inwards ● No circular dependencies ● Isolate external dependencies

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Code Structure ● /root folder - configuration, Dockerfiles, CI/CD ○ makefile - scripts for debug, run tests, build ● /cmd - Main applications (api/main.go, cli/main.go) ● /mock - Mocks for external dependencies ● /httpapi - HTTP service ● /imgart - Core Domain (entities, interfaces) ● /effect, image, profile - Domain Logic ● /repository - Repository implementations (redis, mongo)

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Error Handling https://bit.ly/2d0qz5C

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Errors ● Error is a bug in a program that causes unexpected behaviour ● Good errors must give helpful information for programmers ● Errors should be divided: ○ Application Error e.g. Error establishing a database connection ○ User Error e.g. An internal error has occurred. Please contact support

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Errors in GO https://golang.org/src/errors/errors.go

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Application Errors ● Errors should have an internal type (e.g. permissions, conflict) ● Readable message with a clear context (e.g. Profile id: 123 does not exist) ● The original error (Debug purposes)

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Example: Handle Errors to Status Codes

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Debugging with package fmt fmt.Printf("debug: %s", value)

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Delve ● Debugger for GO ● Installation using go get ○ go get -u github.com/derekparker/delve/cmd/dlv ● Run dlv command ○ dlv debug github.com/talento90/imgart/cmd/imgartapi ○ dlv test github.com/talento90/imgart/image ● Open Source: https://github.com/derekparker/delve

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Testing and Quality Tools

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Testing Package ● Package testing provides support for automated testing of Go packages ○ go test -v -race ./... ● Package that provides support for HTTP testing: net/http/httptest ● Find code using the following pattern: ○ func TestXxx(*testing.T) ● Supports Benchmarking tests ○ func BenchmarkXxx(*testing.B)

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Table testing https://github.com/golang/go/wiki/TableDrivenTests

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Quality Tools ● go vet - Examines code and reports suspicious constructs ● golint - Linter for Go source code ● gocyclo - Calculates cyclomatic complexities ● megacheck - Static Code Analyser ● More tools: https://staticcheck.io, https://goreportcard.com

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Why cancellation matters?

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Request Lifecycle Request Lifecycle Download Image Input Process Image Response User Cancel Request

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context.Context https://golang.org/pkg/context/

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context.Context Errors

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ctx.Context Example

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HTTP Requests (Download Image)

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Demo (Let's deal with cancellation)

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Summary

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https://twitter.com/rakyll/status/869762601642799104

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Recap ● GO has a rich standard library ● Organize application by domain ● Errors must be programmer friendly ● ctx.Context Package ○ WithValue must store request scoped values (e.g: CorrelationId) ○ Provides cancellation

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Thank you You can find me at: ● [email protected] ● https://twitter.com/Talento90 ● https://github.com/Talento90

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Questions?