Vendoring goa Services


Code generation makes vendoring a little more complicated as the generation tool also needs to be vendored to guarantee that the generated code stays compatible with other dependencies. As an example here is an extract of what a glide YAML file may look like:

package: github.com/foo/bar
import:
- package: github.com/goadesign/goa
  vcs: git
  version: master
  subpackages:
  - client
  - design
  - design/apidsl
  - dslengine
  - goagen
  - middleware
- package: golang.org/x/tools
  subpackages:
  - go/ast/astutil
- package: gopkg.in/yaml.v2

running glide install installs goagen in the vendor directory so that running:

cd ./vendor/github.com/goadesign/goa/goagen
go build
cd ../../../../../

always produces the same generator tool which can then be used with:

./vendor/github.com/goadesign/goa/goagen/goagen app -d <import path to design package>

Bootstrapping a project using vendoring can be done following these steps (assuming the design is already written):

  1. Generate the initial code with the goagen boostrap command
  2. Run glide create, this produces glide.yaml
  3. Edit glide.yaml and add the entries listed above
  4. Run glide install

You now have a vendor directory that contains the sources for goagen, compile them and use the tool as described above. Don’t forget to recompile the tool after each glide update that updates goa.

Vendoring Clients

Another issue to be aware of is that using a vendored goa causes the code generation tool generated by goagen to also use the vendored goa. This isn’t an issue (and is actually a good thing) until you need to invoke goagen on non-vendored designs. This may happen if you are trying to generate the client of a dependent service for example. In this case the design package of the non-vendored service ends up using the non-vendored goa which means that the design gets initialized in the “wrong” design package.

The symptoms of the problem above is goagen outputting an error message because the design it is trying to use is not initialized (the design.Design variable of the vendored goa design package is nil). The best way to resolve this issue is to vendor the dependent design packages as well (which is probably a good thing to do in the first place).

Code-based generation and vendoring

Another approach to vendoring consists of invoking the generators programmatically instead of via the goagen command line tool.

By writing a small glue package in your repository, your preferred vendoring tool will be able to trace import dependencies and vendor everything for you.

The result is simplified versioning and makes dependencies explicit to the vendoring utility.

For the impatients, here is a concise version of what we’ll see here:

$ mkdir -p $GOPATH/src/github.com/your/pkg/design
$ cd !$
$ # Create your design in the `design` package
$ # Paste the content of `gen/main.go` below to `...github.com/your/pkg/gen/main.go`
$ go run gen/main.go      # generates all the things
$ govendor init           # creates the vendor/ dir
$ govendor add +e         # pull needed packages in

And you’re set. Everyone in your team will be able to deterministically regenerate your code if they tweak the design, without version conflicts.

We do this by creating a small package that invokes goagen’s code generation functions:

cd $GOPATH/src/github.com/your/pkg
mkdir gen

Then put this content into gen/main.go:

package main

import (
	_ "github.com/your/pkg/design"

	"github.com/goadesign/goa/design"
	"github.com/goadesign/goa/goagen/codegen"
	genapp "github.com/goadesign/goa/goagen/gen_app"
	genclient "github.com/goadesign/goa/goagen/gen_client"
	genjs "github.com/goadesign/goa/goagen/gen_js"
	genmain "github.com/goadesign/goa/goagen/gen_main"
	genschema "github.com/goadesign/goa/goagen/gen_schema"
	genswagger "github.com/goadesign/goa/goagen/gen_swagger"
)

func main() {
	codegen.ParseDSL()
	codegen.Run(
		genmain.NewGenerator(
			genmain.API(design.Design),
			genmain.Target("app"),
		),
		genswagger.NewGenerator(
			genswagger.API(design.Design),
		),
		genapp.NewGenerator(
			genapp.API(design.Design),
			genapp.OutDir("app"),
			genapp.Target("app"),
			genapp.NoTest(true),
		),
		genclient.NewGenerator(
			genclient.API(design.Design),
		),
		genschema.NewGenerator(
			genschema.API(design.Design),
		),
		genjs.NewGenerator(
			genjs.API(design.Design),
		),
	)
}

Remove the generators you don’t need from the Run() call.

The code above will cause all the goa code generation packages to be vendored appropriately.

With govendor (you can use whatever vendoring tool you want in a similar way), you can simply do this:

$ govendor init
$ govendor list
 e  github.com/dimfeld/httppath
 e  github.com/goadesign/goa/design
 e  github.com/goadesign/goa/design/apidsl
 e  github.com/goadesign/goa/dslengine
 e  github.com/goadesign/goa/goagen/codegen
 e  github.com/goadesign/goa/goagen/gen_app
 e  github.com/goadesign/goa/goagen/gen_client
 e  github.com/goadesign/goa/goagen/gen_js
 e  github.com/goadesign/goa/goagen/gen_main
 e  github.com/goadesign/goa/goagen/gen_schema
 e  github.com/goadesign/goa/goagen/gen_swagger
 e  github.com/goadesign/goa/goagen/utils
 e  github.com/goadesign/goa/version
 e  github.com/manveru/faker
 e  github.com/satori/go.uuid
 e  github.com/zach-klippenstein/goregen
 e  golang.org/x/tools/go/ast/astutil
 e  gopkg.in/yaml.v2
 l  github.com/your/pkg/design
pl  github.com/your/pkg/gen

and another quick run will vendor all you need to generate your code next time:

$ govendor add +ext
$ wc -l vendor/vendor.json
181 vendor/vendor.json

This gives you control over when to change the code generation packages using your vendoring tool of choice.

Any future runs will deterministically generate the same code, on anyone’s machine, unless you explicitly upgrade goa.

Generate your code

The next step is to actually generate your code based on the design you wrote. Run your gen/main.go this way:

$ cd $GOPATH/src/github.com/your/pkg
$ go run gen/main.go

...
swagger/swagger.json
...
app/contexts.go
...
tool/yourapi-cli/main.go
tool/cli/commands.go
...
client/client.go
...
schema/schema.json
...
js/client.js

While you’re at it, put that line near the top of your/pkg/main.go:

//go:generate go run gen/main.go

Next time, you only need to remember to run go generate. See this article for more info..

Vendoring dependencies of generated code

Once you’ve generated your code once, you’ll see that there are more dependencies:

$ govendor list
$ govendor list
 v  github.com/dimfeld/httppath
 v  github.com/goadesign/goa/design
 v  github.com/goadesign/goa/design/apidsl
 v  github.com/goadesign/goa/dslengine
 v  github.com/goadesign/goa/goagen/codegen
 v  github.com/goadesign/goa/goagen/gen_app
 v  github.com/goadesign/goa/goagen/gen_client
 v  github.com/goadesign/goa/goagen/gen_js
 v  github.com/goadesign/goa/goagen/gen_main
 v  github.com/goadesign/goa/goagen/gen_schema
 v  github.com/goadesign/goa/goagen/gen_swagger
 v  github.com/goadesign/goa/goagen/utils
 v  github.com/goadesign/goa/version
 v  github.com/manveru/faker
 v  github.com/satori/go.uuid
 v  github.com/zach-klippenstein/goregen
 v  golang.org/x/tools/go/ast/astutil
 v  gopkg.in/yaml.v2
 e  github.com/armon/go-metrics
 e  github.com/dimfeld/httppath
 e  github.com/dimfeld/httptreemux
 e  github.com/goadesign/goa
 e  github.com/goadesign/goa/client
 e  github.com/goadesign/goa/middleware
 e  github.com/goadesign/goa/uuid
 e  github.com/inconshreveable/mousetrap
 e  github.com/satori/go.uuid
 e  github.com/spf13/cobra
 e  github.com/spf13/pflag
 e  golang.org/x/net/context
 e  golang.org/x/net/websocket
pl  github.com/your/pkg
 l  github.com/your/pkg/app
 l  github.com/your/pkg/client
 l  github.com/your/pkg/design
pl  github.com/your/pkg/gen
 l  github.com/your/pkg/js
 l  github.com/your/pkg/tool/cli

See how we now have other external dependencies we need to pull in (marked e for external). They include the goadesign/goa package - which holds runtime functions for goa services - to help you write your business logic.

Vendor all of that in with:

$ govendor add +e
$

You’re all good!

Not only are the code generation packages vendored but also goa, its dependencies and your own dependencies.