Embrace Go Modules for Effective Dependency Management

November 19, 2022

A Go module is a collection of Go packages that other Go projects can easily import for development. Starting with Go 1.11, the go command began supporting the use of modules. From Go 1.13 onwards, module mode became the default for all development. I'd like to discuss some important aspects of importing and managing Go modules.

Introduction

The Go packages are stored in a file tree with a go.mod file at its root. Here I take leviliangtw/ths, A lightweight Texas Holdem Server, for example:

module github.com/leviliangtw/ths

go 1.18

require (
	github.com/go-sql-driver/mysql v1.6.0
	github.com/gorilla/context v1.1.1
	github.com/gorilla/sessions v1.2.1
)

require github.com/gorilla/securecookie v1.1.1 // indirect

In the example, there are three important factors in the go.mod file:

Module path: module github.com/leviliangtw/ths
- This is the import path for other projects.
- The path must be formatted like: [git server]/[space]/[repository].
Golang version: go 1.18
- Here you should specify the Golang version of this project.
Dependency requirements: require...
- Other modules needed for a successful build.
- Written as a module path and a specific semantic version.
- Dependency version is of the format like v.x.x.x.

Usages

Here I take the leviliangtw/ths for example again.

First of all, now you are going to manage the modules of the Golang project, and it time to create a new module of itself:

$ go mod init github.com/leviliangtw/Texas-Holdem-Server
go: creating new go.mod: module github.com/leviliangtw/Texas-Holdem-Server
go: to add module requirements and sums:
go mod tidy

When you run or test the project, the go command would automatically looks up the module containing that package and adds it to go.mod, using the latest version. Here you could also use go mod tidy for the same purpose:

$ go mod tidy
go: finding module for package github.com/gorilla/sessions
go: finding module for package github.com/go-sql-driver/mysql
go: finding module for package github.com/gorilla/context
go: found github.com/go-sql-driver/mysql in github.com/go-sql-driver/mysql v1.6.0
go: found github.com/gorilla/context in github.com/gorilla/context v1.1.1
go: found github.com/gorilla/sessions in github.com/gorilla/sessions v1.2.1

Now you check the file go.mod and will get:

$ cat go.mod
module github.com/leviliangtw/ths

go 1.18

require (
    github.com/go-sql-driver/mysql v1.6.0
    github.com/gorilla/context v1.1.1
    github.com/gorilla/sessions v1.2.1
)

require github.com/gorilla/securecookie v1.1.1 // indirect

Then, you also could check its dependencies directly:

$ go list -m all
github.com/leviliangtw/Texas-Holdem-Server
github.com/go-sql-driver/mysql v1.6.0
github.com/gorilla/context v1.1.1
github.com/gorilla/securecookie v1.1.1
github.com/gorilla/sessions v1.2.1

If you would like to use a module of a specified version, you can use go get:

$ go list -m -versions github.com/go-sql-driver/mysql
github.com/go-sql-driver/mysql v1.0.0 v1.0.1 v1.0.2 v1.0.3 v1.1.0 v1.2.0 v1.3.0 v1.4.0 v1.4.1 v1.5.0 v1.6.0

$ go get github.com/go-sql-driver/mysql@v1.5.0
go: downloading github.com/go-sql-driver/mysql v1.5.0
go: downgraded github.com/go-sql-driver/mysql v1.6.0 => v1.5.0

Finally, don't forget that you can cleans up unused dependencies by go mod tidy!

Cheat Sheet

go mod init
- creates a new module and initialize the go.mod file
go run, go build, go test, go mod tidy, etc.
- add needed dependencies to go.mod
go list -m all
- print the current module’s dependencies
go get
- change or add the required version of a dependency
go mod tidy
- remove unused dependencies

Introduction

Usages

Cheat Sheet

References