[DOCKER] A web app that just does Hello World with Go's net / http package
Awakening of Go
With low-layer knowledge, you'll be a self-sufficient engineer! I sent it to myself who enthusiastically learned C language but couldn't find any fun.
Persona
If you want to make a web application, I think Node and Rails are enough at present. For desktop apps, use Electron. Those who want to use Go or something like a terminal application or a system that uses OS functions (Docker and GitHub CLI, which are popular these days, are also made by Go, so if you can use it, you can play it).
Purpose of this article
To decide if you want to learn Go, let's create a simple web app (just display Hello World when you access it).
Development environment
I didn't know if I could trust Go, so I'll do it with Docker to keep the environment clean. If it is interesting, I would like to see the inside with a debugger, so I will build the environment locally.
The directory structure is as follows. Put the go file in the compileFile directory and build it.
compileFile (directory)
Dockerfile
docker-compose.yml
# Dockerfile
FROM golang:latest
RUN mkdir -p /go/src
docker-compose.yml
version: '3'
services:
go:
build: .
ports:
- "8080:8080"
volumes:
- ./compileFile:/go/src
working_dir: /go/src
Go inside the container and check the go command.
Note that you cannot connect 8080 ports unless you specify --service-ports.
Make sure that you can port forward properly with docker ps.
$ docker-compose run --service-ports go /bin/bash
$ docker ps
CONTAINER ID IMAGE COMMAND CREATED STATUS PORTS NAMES
af4f9c066ecd golean_go "/bin/bash" 7 seconds ago Up 2 seconds 0.0.0.0:8080->8080/tcp golean_go_run_a79a836040ab
For now, try typing go to see what commands you can use.
Go is a tool for managing Go source code.
Usage:
go <command> [arguments]
The commands are:
bug start a bug report
build compile packages and dependencies
clean remove object files and cached files
doc show documentation for package or symbol
env print Go environment information
fix update packages to use new APIs
fmt gofmt (reformat) package sources
generate generate Go files by processing source
get add dependencies to current module and install them
install compile and install packages and dependencies
list list packages or modules
mod module maintenance
run compile and run Go program
test test packages
tool run specified go tool
version print Go version
vet report likely mistakes in packages
Use "go help <command>" for more information about a command.
Additional help topics:
buildconstraint build constraints
buildmode build modes
c calling between Go and C
cache build and test caching
environment environment variables
filetype file types
go.mod the go.mod file
gopath GOPATH environment variable
gopath-get legacy GOPATH go get
goproxy module proxy protocol
importpath import path syntax
modules modules, module versions, and more
module-get module-aware go get
module-auth module authentication using go.sum
module-private module configuration for non-public modules
packages package lists and patterns
testflag testing flags
testfunc testing functions
Use "go help <topic>" for more information about that topic.
go build`` go run go fmt is likely to be used in the near future.
Project creation
I wanted to understand Go from a familiar web app. While looking at the sample code, write a program that displays Hello World on the browser.
server/main.go
package main
import "io"
import "net/http"
func mainHandler(w http.ResponseWriter, req *http.Request) {
io.WriteString(w, `Hello World!!!`)
}
func main(){
http.HandleFunc("/main", mainHandler)
http.ListenAndServe(":8080", nil)
}
You can format it with one command, so build it after formatting! By the way, I'm angry if there is a line break position or an unused package, maybe the linter is also working at build time.
When I built it, an executable file with the directory name containing the go file was created.
$ go fmt
$ go build
$ ls
server main.go
$ ./server
When I visited http: // localhost: 8080 / main, I was able to confirm Hello World!
By the way, if you want to run it on Mac, you can compile it for Mac below.
$ GOOS=darwin GOARCH=amd64 go build
net / http package
Let's start from an easy-to-understand place. It seems that you can set up a server with this. It seems that the first argument can specify the port and the second argument can select Handler, and in the case of nil, the default DefaultServeMux is used.
http.ListenAndServe(":8080", nil)
What is DefaultServeMux?
As you read through the documentation, you will find the following:
HandleFunc registers the handler function for the given pattern in the DefaultServeMux.
The documentation for ServeMux explains how patterns are matched.
It says that you can register a handler corresponding to the URL pattern in DefaultServerMux with HandleFunc. Think of it as something routing.
So, the following can be read as executing the processing of mainHandler after accessing / main.
http.HandleFunc("/main", mainHandler)
The io package knows what you're doing, so I'll leave it.
Introduced to Local
You can easily enter with brew.
$ brew install go
$ go version
go version go1.15.3 darwin/amd64
Also include the REPL. It didn't work with gore v0.5.0, so I'm dropping the version.
#You can do this and install it, but you may not need it.
$ export GO111MODULE=on
$ go get github.com/motemen/gore/cmd/[email protected]
$ gore -version
gore 0.4.0 (rev: HEAD/go1.15.3)
If you install it by mistake, you can delete it below.
$ go clean -i github.com/motemen/gore/cmd/gore
By the way, with v0.5.0, the following error message appears.
gore: could not load 'fmt' package: err: exit status 1: stderr: build flag -mod=mod only valid when using modules
Now that the local environment is in place, all you have to do is play.
Summary
I want to use Go for web development! I don't feel like that, but at least I found it more fun than C! I want to make a terminal application or something. For the time being, in order to learn how to use Go, I thought I'd try to make it from a simple web application using a framework or something.
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