Go modules WARSAW, MAY 22 2019 Oleg Kovalov Allegro Twitter: oleg_kovalov Github: cristaloleg 

Me - Gopher for ~4 years - Open-source contributor - Engineer at allegro.pl core team Twitter: @oleg_kovalov Github: @cristaloleg 

Long story short Image credit: ©Istockphoto/JamesBrey time 

- GOPATH Pre-modules era (2012-2018) 

- GOPATH - godep - gopkg.in - glide Pre-modules era (2012-2018) 

- GOPATH - godep - gopkg.in - glide - vendor dir Pre-modules era (2012-2018) 

- GOPATH - godep - gopkg.in - glide - vendor dir - dep Pre-modules era (2012-2018) 

- GOPATH - godep - gopkg.in - glide - vendor dir - dep - ... Pre-modules era (2012-2018) 

Go modules 

- Modules Go modules 

- Modules - Semantic versioning Go modules 

- Modules - Semantic versioning - Import compatibility rule Go modules 

- Modules - Semantic versioning - Import compatibility rule - go.mod Go modules 

- A module is a collection of Go packages that are versioned as a single unit What is a module? 

- A module is a collection of Go packages that are versioned as a single unit - (often) a single version-control repository is a single module What is a module? 

What is a module? - A module is a tree/directory of Go source files with a go.mod file in the root directory 

What is a module? - A module is a tree/directory of Go source files with a go.mod file in the root directory - Can live outside of a GOPATH 

Semantic versioning (http://semver.org) 

If an old and a new package have the same import path, the new package must be backwards-compatible with the old package. Import compatibility rule 

GO111MODULE=auto go build ./… GO111MODULE 

GO111MODULE=auto go build ./… - Inside GOPATH defaults to old 1.10 behavior (ignoring modules) GO111MODULE 

GO111MODULE GO111MODULE=auto go build ./… - Inside GOPATH defaults to old 1.10 behavior (ignoring modules) - Outside GOPATH while inside a file tree with a go.mod = defaults to modules behavior 

- auto(default) - on - off GO111MODULE 

GO111MODULE - auto(default) - on - off $ export GO111MODULE=on $ go build ./... 

Changes to go get 

# same (@latest is default for 'go get') $ go get github.com/gorilla/mux@latest Changes to go get 

# same (@latest is default for 'go get') $ go get github.com/gorilla/mux@latest # records v1.6.2 $ go get github.com/gorilla/[email protected] Changes to go get 

# same (@latest is default for 'go get') $ go get github.com/gorilla/mux@latest # records v1.6.2 $ go get github.com/gorilla/[email protected] # records v1.6.2 $ go get github.com/gorilla/mux@e3702bed2 Changes to go get 

# same (@latest is default for 'go get') $ go get github.com/gorilla/mux@latest # records v1.6.2 $ go get github.com/gorilla/[email protected] # records v1.6.2 $ go get github.com/gorilla/mux@e3702bed2 # records v0.0.0-20180517173623-c85619274f5d $ go get github.com/gorilla/mux@c856192 Changes to go get 

# same (@latest is default for 'go get') $ go get github.com/gorilla/mux@latest # records v1.6.2 $ go get github.com/gorilla/[email protected] # records v1.6.2 $ go get github.com/gorilla/mux@e3702bed2 # records v0.0.0-20180517173623-c85619274f5d $ go get github.com/gorilla/mux@c856192 # records current meaning of master $ go get github.com/gorilla/mux@master Changes to go get 

$ mkdir /mygo/hello $ cd /mygo/hello $ go mod init github.com/golang/hello go: creating new go.mod: module github.com/golang/hello $ ls go.mod $ cat go.mod module github.com/golang/hello Let’s start 

$ git clone https://github.com/go-gitea/gitea Cloning into gitea... $ cd gitea Convert to modules 

$ git clone https://github.com/go-gitea/gitea Cloning into gitea... $ cd gitea $ go mod init go: creating new go.mod: module github.com/go-gitea/gitea go: copying requirements from Gopkg.lock Convert to modules 

$ git clone https://github.com/go-gitea/gitea Cloning into gitea... $ cd gitea $ go mod init go: creating new go.mod: module github.com/go-gitea/gitea go: copying requirements from Gopkg.lock $ go mod tidy go: extracting github.com/PuerkitoBio/goquery v1.5.0 go: extracting github.com/blevesearch/bleve v0.7.0 go: finding github.com/go-macaron/session/redis latest go: finding github.com/google/pprof v0.0.0-20181206194817-3ea8567a2e57 go: finding golang.org/x/lint v0.0.0-20190301231843-5614ed5bae6f go: finding github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b go: finding golang.org/x/lint v0.0.0-20190227174305-5b3e6a55c961 go: finding golang.org/x/time v0.0.0-20181108054448-85acf8d2951c go: downloading github.com/facebookgo/grace v0.0.0-20180706040059-75cf19382434 Convert to modules 

How to read go.mod 

module github.com/hashicorp/consul ... How to read go.mod 

module github.com/hashicorp/consul go 1.12 ... How to read go.mod 

module github.com/hashicorp/consul go 1.12 require ( github.com/NYTimes/gziphandler v1.0.1 ... How to read go.mod 

module github.com/hashicorp/consul go 1.12 require ( github.com/NYTimes/gziphandler v1.0.1 github.com/DataDog/datadog-go v0.0.0-20160329135253-cc2f4770f4d6 // indirect ... How to read go.mod 

module github.com/hashicorp/consul go 1.12 require ( github.com/NYTimes/gziphandler v1.0.1 github.com/DataDog/datadog-go v0.0.0-20160329135253-cc2f4770f4d6 // indirect ... How to read go.mod 

module github.com/hashicorp/consul go 1.12 require ( github.com/NYTimes/gziphandler v1.0.1 github.com/DataDog/datadog-go v0.0.0-20160329135253-cc2f4770f4d6 // indirect github.com/go-redis/redis v6.15.2+incompatible ... ) ... How to read go.mod 

How to read go.mod module github.com/hashicorp/consul go 1.12 require ( github.com/NYTimes/gziphandler v1.0.1 github.com/DataDog/datadog-go v0.0.0-20160329135253-cc2f4770f4d6 // indirect github.com/go-redis/redis v6.15.2+incompatible ... ) replace github.com/hashicorp/consul/api => ./api replace github.com/hashicorp/consul/sdk => ./sdk ... 

How to read go.mod module github.com/hashicorp/consul go 1.12 require ( github.com/NYTimes/gziphandler v1.0.1 github.com/DataDog/datadog-go v0.0.0-20160329135253-cc2f4770f4d6 // indirect github.com/go-redis/redis v6.15.2+incompatible ... ) replace github.com/hashicorp/consul/api => ./api replace github.com/hashicorp/consul/sdk => ./sdk exclude github.com/not-a-hacker/supergeil v1270.0.1 

How to read go.sum 

How to read go.sum 

cloud.google.com/go v0.26.0 h1:e0WKqKTd5BnrG8aKH3J3h+QvEIQtSUcf2n5UZ5ZgLtQ= cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw= How to read go.sum 

cloud.google.com/go v0.26.0 h1:e0WKqKTd5BnrG8aKH3J3h+QvEIQtSUcf2n5UZ5ZgLtQ= cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw= github.com/Azure/azure-sdk-for-go v16.0.0+incompatible h1:gr1qKY/Ll72VjFTZmaBwRK1yQHAxCnV25ekOKroc9ws= github.com/Azure/azure-sdk-for-go v16.0.0+incompatible/go.mod h1:9XXNKU+eRnpl9moKnB4QOLf1HestfXbmab5FXxiDBjc= How to read go.sum 

cloud.google.com/go v0.26.0 h1:e0WKqKTd5BnrG8aKH3J3h+QvEIQtSUcf2n5UZ5ZgLtQ= cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw= github.com/Azure/azure-sdk-for-go v16.0.0+incompatible h1:gr1qKY/Ll72VjFTZmaBwRK1yQHAxCnV25ekOKroc9ws= github.com/Azure/azure-sdk-for-go v16.0.0+incompatible/go.mod h1:9XXNKU+eRnpl9moKnB4QOLf1HestfXbmab5FXxiDBjc= // you might want to use go mod verify How to read go.sum 

Usage: go mod [arguments] The commands are: download download modules to local cache edit edit go.mod from tools or scripts fix make go.mod semantically consistent graph print module requirement graph init initialize new module in current directory tidy add missing and remove unused modules vendor make vendored copy of dependencies verify verify dependencies have expected content why explain why packages or modules are needed go mod commands 

# go and get a repo $ go get github.com/go-gitea/gitea $ cd ~/go/src/github.com/go-gitea/gitea go mod why 

# go and get a repo $ go get github.com/go-gitea/gitea $ cd ~/go/src/github.com/go-gitea/gitea # set a env var and check why do we use this dependency $ export GO111MODULE=on go mod why 

# go and get a repo $ go get github.com/go-gitea/gitea $ cd ~/go/src/github.com/go-gitea/gitea # set a env var and check why do we use this dependency $ export GO111MODULE=on $ go mod why github.com/RoaringBitmap/roaring # github.com/RoaringBitmap/roaring code.gitea.io/gitea/modules/indexer github.com/blevesearch/bleve github.com/blevesearch/bleve/index/scorch github.com/RoaringBitmap/roaring go mod why 

FROM golang ENV GO111MODULE=on Dockerfile 

FROM golang ENV GO111MODULE=on WORKDIR /app COPY go.mod . COPY go.sum . Dockerfile 

FROM golang ENV GO111MODULE=on WORKDIR /app COPY go.mod . COPY go.sum . RUN go mod download COPY . . Dockerfile 

Dockerfile FROM golang ENV GO111MODULE=on WORKDIR /app COPY go.mod . COPY go.sum . RUN go mod download COPY . . RUN CGO_ENABLED=0 GOOS=linux go build -a -o app.exec ./... EXPOSE 8000 ENTRYPOINT ["./app.exec"] 

Use local changes 

Use local changes - Сhange in go.mod manually 

Use local changes - Сhange in go.mod manually - go mod edit -replace ‘foo.com/bar=../bar’ 

Use local changes - Сhange in go.mod manually - go mod edit -replace ‘foo.com/bar=../bar’ - or use awesome gohack tool by Roger Peppe 

# install $ go get github.com/rogpeppe/gohack gohack by Roger Peppe 

# install $ go get github.com/rogpeppe/gohack $ gohack get example.com/foo/bar # will clone repo into $HOME/gohack/example.com/foo/bar # will add: replace example.com/foo/bar /home/rog/gohack/example.com/foo/bar gohack by Roger Peppe 

# install $ go get github.com/rogpeppe/gohack $ gohack get example.com/foo/bar # will clone repo into $HOME/gohack/example.com/foo/bar # will add: replace example.com/foo/bar /home/rog/gohack/example.com/foo/bar $ cat go.mod replace example.com/foo/bar => /home/rog/gohack/example.com/foo/bar gohack by Roger Peppe 

gohack by Roger Peppe # install $ go get github.com/rogpeppe/gohack $ gohack get example.com/foo/bar # will clone repo into $HOME/gohack/example.com/foo/bar # will add: replace example.com/foo/bar /home/rog/gohack/example.com/foo/bar $ cat go.mod replace example.com/foo/bar => /home/rog/gohack/example.com/foo/bar # to remove specific replace: $ gohack undo example.com/foo/bar # to remove all replaces: $ gohack undo 

Go Proxy 

Go Proxy https://proxy.golang.org https://github.com/gomods/athens - export GOPROXY=my.proxy.com - go get github.com/foo/bar 

Future 

- Enabled by default Future 

- Enabled by default - More robust ecosystem Future 

- Enabled by default - More robust ecosystem - More secure Future 

- Enabled by default - More robust ecosystem - More secure - More tools understand modules Future 

- Enabled by default - More robust ecosystem - More secure - More tools understand modules - No vendor (perhaps?) Future 

- Enabled by default - More robust ecosystem - More secure - More tools understand modules - No vendor (perhaps?) - Less “but it works on my machine!” Future 

Why package management is hard? 

That’s all folks Thank you Questions? Twitter: @oleg_kovalov Github: @cristaloleg