How do I import a specific version of a package us

Question

coming from a Node environment I used to install a specific version of a vendor lib into the project folder (node_modules) by telling npm to install that version of that lib from the package.json or even directly from the console, like so:

$ npm install express@4.0.0

Then I used to import that version of that package in my project just with:

var express = require('express');

Now, I want to do the same thing with go. How can I do that? Is it possible to install a specific version of a package? If so, using a centralized $GOPATH, how can I import one version instead of another?

I would do something like this:

$ go get github.com/wilk/uuid@0.0.1
$ go get github.com/wilk/uuid@0.0.2

But then, how can I make a difference during the import?

Answer 1

The approach I've found workable is git's submodule system. Using that you can submodule in a given version of the code and upgrading/downgrading is explicit and recorded - never haphazard.

The folder structure I've taken with this is:

+ myproject
++ src
+++ myproject
+++ github.com
++++ submoduled_project of some kind.

Answer 2

go get is the Go package manager. It works in a completely decentralized way and how package discovery still possible without a central package hosting repository.

Besides locating and downloading packages, the other big role of a package manager is handling multiple versions of the same package. Go takes the most minimal and pragmatic approach of any package manager. There is no such thing as multiple versions of a Go package.

go get always pulls from the HEAD of the default branch in the repository. Always. This has two important implications:

1. As a package author, you must adhere to the stable HEAD philosophy. Your default branch must always be the stable, released version of your package. You must do work in feature branches and only merge when ready to release.

2. New major versions of your package must have their own repository. Put simply, each major version of your package (following semantic versioning) would have its own repository and thus its own import path.

   e.g. github.com/jpoehls/gophermail-v1 and github.com/jpoehls/gophermail-v2.

As someone building an application in Go, the above philosophy really doesn't have a downside. Every import path is a stable API. There are no version numbers to worry about. Awesome!

For more details : http://zduck.com/2014/go-and-package-versioning/

Answer 3

Really surprised nobody has mentioned gopkg.in.

gopkg.in is a service that provides a wrapper (redirect) that lets you express versions as repo urls, without actually creating repos. eg gopkg.in/yaml.v1 vs gopkg.in/yaml.v2, even though they both live at https://github.com/go-yaml/yaml

• gopkg.in/yaml.v1 redirects to https://github.com/go-yaml/yaml/tree/v1
• gopkg.in/yaml.v2 redirects to https://github.com/go-yaml/yaml/tree/v2

This isn't perfect if the author is not following proper versioning practices (by incrementing the version number when breaking backwards compatibility), but it does work with branches and tags.

Answer 4

You can set version by offical dep

dep ensure --add github.com/gorilla/websocket@1.2.0

Update 18-11-23: From Go 1.11 mod is official experiment. Please see @krish answer.

Answer 5

You can use git checkout to get an specific version and build your program using this version.

Example:

export GOPATH=~/
go get github.com/whateveruser/whateverrepo
cd ~/src/github.com/whateveruser/whateverrepo
git tag -l
# supose tag v0.0.2 is correct version
git checkout tags/v0.0.2
go run whateverpackage/main.go

Answer 6

dep is the official experiment for dependency management for Go language. It requires Go 1.8 or newer to compile.

To start managing dependencies using dep, run the following command from your project's root directory:

dep init

After execution two files will be generated: Gopkg.toml ("manifest"), Gopkg.lock and necessary packages will be downloaded into vendor directory.

Let's assume that you have the project which uses github.com/gorilla/websocket package. dep will generate following files:

Gopkg.toml

# Gopkg.toml example
#
# Refer to https://github.com/golang/dep/blob/master/docs/Gopkg.toml.md
# for detailed Gopkg.toml documentation.
#
# required = ["github.com/user/thing/cmd/thing"]
# ignored = ["github.com/user/project/pkgX", "bitbucket.org/user/project/pkgA/pkgY"]
#
# [[constraint]]
#   name = "github.com/user/project"
#   version = "1.0.0"
#
# [[constraint]]
#   name = "github.com/user/project2"
#   branch = "dev"
#   source = "github.com/myfork/project2"
#
# [[override]]
#  name = "github.com/x/y"
#  version = "2.4.0"


[[constraint]]
  name = "github.com/gorilla/websocket"
  version = "1.2.0"

Gopkg.lock

# This file is autogenerated, do not edit; changes may be undone by the next 'dep ensure'.


[[projects]]
  name = "github.com/gorilla/websocket"
  packages = ["."]
  revision = "ea4d1f681babbce9545c9c5f3d5194a789c89f5b"
  version = "v1.2.0"

[solve-meta]
  analyzer-name = "dep"
  analyzer-version = 1
  inputs-digest = "941e8dbe52e16e8a7dff4068b7ba53ae69a5748b29fbf2bcb5df3a063ac52261"
  solver-name = "gps-cdcl"
  solver-version = 1

There are commands which help you to update/delete/etc packages, please find more info on official github repo of dep (dependency management tool for Go).