Go language starts again, go modules' past life, present life and basic use

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2020 In, a developer report within Tencent showed that ,Go Language has become The second largest back-end development language in Tencent , In Tencent, there are a lot of Go Developers are doing business and platform development , The use of a large number of teams and projects also exposed some problems , With Go Modules Appearance , Similar to internal self issued certificates 、 These problems such as safety audit have been gradually solved .

The author is currently in charge of Tencent cloud Go Some problems in the use of programming language , 2021 Responsible for internal management since the beginning of the year goproxy Serve and promote Go Modules Use , These technologies support Tencent cloud 、 WeChat 、 Tencent video 、 Tencent game 、 Tencent music 、 Tencent conference and other star products , And work with the company's internal software source team 、 Worker bee team 、TRPC The team and each CI Close cooperation between the team . In this series of articles , The author will help you begin to learn and understand Go Modules.

Golang Development model evolution

from Go From birth , Users have been using GOPATH This environment variable , With Go The rapid development and growth of language , from GOPATH The compilation dependency problem caused by is also beginning to appear . Finally in the 2019 year , Golang welcome 10 Anniversary ,Google Go The team finally began to focus on this company Golang Ten year environmental variables .

GOPATH Use

Currently in Go There are two development modes in ,GOPATH mode and Go modules mode.

stay Go modules Before ,Go Dependency management in development uses GOPATH Development mode . stay GOPATH In the development mode ,Go Command to use GOPATH Environment variables to achieve the following Several functions ：

1. go install Command to install binary libraries to $GOBIN, The default path is $GOPATH/bin.
2. go install Command to install the compiled package to $GOPATH/pkg/ in , For example example.com/y/z The installation to $GOPATH/pkg/example.com/y/z.a.
3. go get Command to download the source package to $GOPATH/src/ in , For example example.com/y/z Download to $GOPATH/src/example.

Go modules Development history of

GOPATH mode The development model will eventually be eliminated ,Go Official throughout Go Add... To the development ecosystem package version The concept of , And then introduce Go modules Development mode . from GOPATH mode Change the development mode to Go modules It's a long process , It has gone through Several Go The distribution version of ：

• Go 1.11 (2018 year 8 month ) Introduced GO111MODULE environment variable , The default value is auto. If you set this variable GO111MODULE=off, that go The command will always use GOPATH mode Development mode . If you set this variable GO111MODULE=on,go The command will always use Go modules Development mode . If you set this variable GO111MODULE=auto （ Or not set ）,go The command line will decide which mode to use based on the current working directory , If the current directory is $GOPATH/src outside , And exists in the root directory go.mod file , that go The command enables Go module Pattern , Otherwise use GOPATH Development mode . This rule ensures that all in $GOPATH/src Use in auto Value, the original compilation is not affected , And you can also experience the latest... In other directories Go module Development mode .

• Go 1.13 (2019 year 8 month ) Adjust the GO111MODULE=auto In mode pair $GOPATH/src The limitation of , If a code base is in $GOPATH/src in , And there are go.mod Existence of file , go The command enables module Development mode . This allows users to continue to organize their checkout code in an import based hierarchy , However, the module is used to import individual warehouses .

• Go 1.16 (2021 year 2 month ) Will GO111MODULE=on As default , Enabled by default go module Development mode , in other words , By default GOPATH The development mode will be completely shut down . If the user needs to use GOPATH Development patterns can specify environment variables GO111MODULE=auto perhaps GO111MODULE=off.

• Go 1.NN (???) Will be abandoned GO111MODULE Environment variables and GOPATH Development mode , The default is to use completely module Development mode .

GOPATH And Go modules Love wants to kill

For several issues of concern , The author gives the following answers ：

Q1：GOPATH Will variables be removed ？

A： Can't ,GOPATH Variable Will not be removed . Future abandonment GOPATH Development mode does not mean deleting GOPATH environment variable , It will remain , The main functions are as follows ：

• go install Command to install binary to $GOBIN Catalog , Its default location is $GOPATH/bin.
• go get Command cache downloaded modules To $GOMODCACHE Catalog , The default location is $GOPATH/pkg/mod.
• go get Command cache downloaded checksum Data to $GOPATH/pkg/sumdb Catalog .

Q2： I can continue to `GOPATH/src/import/path` Create a code base in ？

A: Sure , Many developers use this file structure to organize their own repositories , You only need to In your own warehouse Add go.mod file .

Q3： If I want to test and modify a dependency library I need , How can I do it ？

A: If you rely on unpublished changes when compiling your project , You can use go.mod Of replace To fulfill your needs .

for instance , If you have already golang.org/x/website and golang.org/x/tools Download to $GOPATH/src/ Under the table of contents , Then you can go to $GOPATH/src/golang.org/x/website/go.mod Add the following instructions to complete the replacement ：

replace golang.org/x/tools => $GOPATH/src/golang.org/x/tools

Of course ,replace Instructions are not perceived GOPATH Of , You can download the code to other directories as well .

from 0 Start using Go Modules

1. Create a new Go module

First create a new directory /home/gopher/hello, Then go to this directory , Then create a new file , hello.go:

package hello

func Hello() string {

return "Hello, world."

}

Then write a corresponding test file hello_test.go:

package hello

import "testing"

func TestHello(t *testing.T) {

want := "Hello, world."

if got := Hello(); got != want {

t.Errorf("Hello() = %q, want %q", got, want)

}

}

Now we have a package, But it's not a module, Because it hasn't been created yet go.mod file . If in /home/gopher/hello Execute... In directory go test, You can see ：

$ go test

go: go.mod file not found in current directory or any parent directory; see 'go help modules'

You can see Go Command line prompt not found go.mod file , You can refer to go help modules. In this case, you can use Go mod init Let's initialize , And then execute Go test：

$ go mod init example.com/hello

go: creating new go.mod: module example.com/hello

go: to add module requirements and sums:

go mod tidy

$go mod tidygo

$ go test

PASS

ok example.com/hello 0.020s

$

In this case ,module The test is done .

And then execute go mod init The command creates a go.mod file :

$ cat go.mod

module example.com/hello

go 1.17

2. to module Add dependency

Go modules The main highlight of is to use code written by others when programming , That is, when you introduce a dependency library, you can have a very good experience . First update hello.go, introduce rsc.io/quote To implement some new functions .

package hello

import "rsc.io/quote"

func Hello() string {

return quote.Hello()

}

then , Test it again ：

$ go test

hello.go:3:8: no required module provides package rsc.io/quote; to add it:

go get rsc.io/quote

$ go get rsc.io/quote

go: downloading rsc.io/quote v1.5.2

go: downloading rsc.io/sampler v1.3.0

go: downloading golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c

go: added golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c

go: added rsc.io/quote v1.5.2

go: added rsc.io/sampler v1.3.0

$ go test

PASS

ok example.com/hello 1.401s

from Go 1.7 Start ,Go modules Start using lazyloading Loading mechanism , The dependent library needs to be updated manually according to the prompt .

Go The order will be based on go.mod To parse and pull the specified dependent version . If in go.mod The specified version... Was not found in , The corresponding command will be prompted to guide the user to add , then Go The command will parse the latest stable version （Latest）, And add to go.mod In file . As you can see in this example , First executed Go test Running requires rsc.io/quote This dependence , But in go.mod Not found in the file , So guide the user to get latest edition , User pass go get rsc.io/quote Got the latest version v1.5.2, And I downloaded two more rsc.io/quote Dependency needed ：rsc.io/sampler and golang.org/x/text. Indirect dependency references are also recorded in go.mod In file , Use indirect Mark with comments .

$ cat go.mod

module example.com/hello

go 1.17

require (

golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c // indirect

rsc.io/quote v1.5.2 // indirect

rsc.io/sampler v1.3.0 // indirect

)

Run... Again go test The command will not repeat the above work , because go.mod It's up to date , And the required dependent packages have been downloaded to the machine （ stay $GOPATH/pkg/mod in ）：

$ go test

PASS

ok example.com/hello 0.020s

Be careful , although Go Command can quickly and easily add new dependencies , but It's not without cost .

As mentioned above , Adding a direct dependency to a project may introduce other indirect dependencies .go list -m all The command can list all dependencies on which the current project depends ：

$ go list -m all

example.com/hello

golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c

rsc.io/quote v1.5.2

rsc.io/sampler v1.3.0

stay go list In the output of , You can see the current module, Also known as main module Will be shown on the first line , Then the others will follow module path Sort . It depends on golang.org/x/text Version number of v0.0.0-20170915032832-14c0d48ead0c Is a pseudo version number , It is Go A version of , Points to a non hit tag Of commit On .

Besides go.mod file ,go The command also maintains a program called go.sum The file of , This file contains the encrypted hash value corresponding to each version .

$ cat go.sum

golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c h1:qgOY6WgZO...

golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c/go.mod h1:Nq...

rsc.io/quote v1.5.2 h1:w5fcysjrx7yqtD/aO+QwRjYZOKnaM9Uh2b40tElTs3...

rsc.io/quote v1.5.2/go.mod h1:LzX7hefJvL54yjefDEDHNONDjII0t9xZLPX...

rsc.io/sampler v1.3.0 h1:7uVkIFmeBqHfdjD+gZwtXXI+RODJ2Wc4O7MPEh/Q...

rsc.io/sampler v1.3.0/go.mod h1:T1hPZKmBbMNahiBKFy5HrXp6adAjACjK9...

Go Command to use go.sum To ensure that the dependency library code downloaded each time is consistent with the first time , So as to ensure that there are no exceptions in the project , therefore go.mod and go.sum Should be uploaded to git In the version control system .

3. Update dependency

From above go list -m all In the output of the command , You can see in the library golang.org/x/text A pseudo version number is used in . First, update this version to the latest stable version ：

$ go get golang.org/x/text

go: downloading golang.org/x/text v0.3.7

go: upgraded golang.org/x/text v0.0.0-20170915032832-14c0d48ead0c => v0.3.7

$ go test

PASS

ok example.com/hello 0.013s

The test can still pass , Then do it again go list -m all:

$ go list -m all

example.com/hello

golang.org/x/text v0.3.7

rsc.io/quote v1.5.2

rsc.io/sampler v1.3.0

$ cat go.mod

module example.com/hello

go 1.17

require (

golang.org/x/text v0.3.7 // indirect

rsc.io/quote v1.5.2 // indirect

rsc.io/sampler v1.3.0 // indirect

)

Conclusion

Go adopt Go modules The dependency management is unified Go Many third parties in the ecology rely on Management , And highly integrated in Go Command line , No need for developers to install and use , Currently under maintenance Go The version already supports Go modules. Haven't switched to Go modules Users of , We strongly recommend that you start using it , Whether it's from the team development experience 、 Performance or safety , Can provide many high-quality features and guarantees .

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