A client/server helper wrapper for endpoints in Go.

go/src/infra/gae/epclient/epclient.go

Index: go/src/infra/gae/epclient/epclient.go
diff --git a/go/src/infra/gae/epclient/epclient.go b/go/src/infra/gae/epclient/epclient.go
new file mode 100644
index 0000000000000000000000000000000000000000..6c55da03931fe97d593d80edc92c67861424b79e
--- /dev/null
+++ b/go/src/infra/gae/epclient/epclient.go
@@ -0,0 +1,206 @@
+// Copyright 2015 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// The following comment allows `go generate` to correctly generate clients
+// for all endpoints services located in the "infra/gae/epservice" package.
+//go:generate goapp run epclient.go
+
+// EPClient will auto-generate endpoints clients from Google Cloud Endpoint
+// service definitions. The tool assumes that:
+//   * all go endpoint service definitions occur in a package which has
+//     a public method `RegisterEndpointsService(*endpoints.Server) error`, and
+//     that calling this method will register the endpoints service with the
+//     provided server or return an error.
+//   * goapp exists in PATH (and understands all the import paths in the
+//     defined services)
+//   * google-api-go-generator exists in PATH.

[dnj, 2015/06/08 16:43:18]

Could you "enforce" this by adding it as a Go dependency here? If this package
becomes go-gettable, it would be useful to have the API generator be pulled in
as a dependency.

[iannucci, 2015/06/09 00:01:54]

It's a 'main' package, so I can't add it as an import dependency.

+package main
+
+import (
+	"bytes"
+	"encoding/json"
+	"flag"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"path/filepath"
+	"strings"
+	"text/template"
+	"time"
+
+	"infra/libs/jsutil"
+)
+
+var (
+	servicePackagesBase = flag.String("pkgs", "infra/gae/epservice",
+		"The base Go package to walk to find service definitions.")
+	outDir = flag.String("outdir", ".",
+		"The directory to generate the client libraries in.")
+	runOnly = flag.Bool("run", false,
+		"If set to true, will run the server and wait, without generating any clients.")
+	clearDatastore = flag.Bool("clear_datastore", false,
+		"If set to true, will clear the datastore when in 'run' mode.")
+)
+
+var serviceScript = `
+package main

[dnj, 2015/06/08 16:43:18]

Add "generated" comment, info, timestamp.

[iannucci, 2015/06/09 00:01:54]

Done.

+
+import (
+	"fmt"
+
+{{range $idx, $pkg := .Pkgs}}
+	pkg{{$idx}} "{{$pkg.Imp}}"{{end}}
+
+	"github.com/GoogleCloudPlatform/go-endpoints/endpoints"
+)
+
+func init() {
+	var err error
+	server := endpoints.NewServer("")
+
+	{{range $idx, $pkg := .Pkgs }}
+	err = pkg{{$idx}}.RegisterEndpointsService(server)
+	if err != nil {
+		panic(fmt.Errorf("Error while registering service {{$pkg}}: %s", err))
+	}
+	{{end}}
+
+	server.HandleHTTP(nil)
+}
+`
+
+const appYaml = `
+application: epclient-tmp-app

[dnj, 2015/06/08 16:43:18]

Add "generated" comment, info, timestamp.

[iannucci, 2015/06/09 00:01:54]

Done.

+version: nope
+runtime: go
+api_version: go1
+
+handlers:
+- url: /.*
+  script: _go_app
+`
+
+var temp = template.Must(template.New("service").Parse(serviceScript))
+
+// Pkg holds the import and real filesystem paths of an endpoint service
+// package. It's exported merely for reflection purposes, since it's used
+// by text/template.
+type Pkg struct {
+	Imp string
+	Pth string
+}
+
+func boom(err error) {
+	if err != nil {
+		panic(err)
+	}
+}
+
+func getPkgs() []Pkg {
+	cmd := exec.Command("goapp", "list", "-json", filepath.Join(*servicePackagesBase, "..."))
+	d, err := cmd.Output()
+	boom(err)
+
+	d = []byte("[" + strings.Replace(string(d), "}\n{", "},{", -1) + "]")
+
+	js := interface{}(nil)
+	boom(json.Unmarshal(d, &js))
+
+	ret := []Pkg{}
+
+	for _, m := range js.([]interface{}) {
+		ret = append(ret, Pkg{
+			jsutil.Get(m, "ImportPath").(string),
+			jsutil.Get(m, "Dir").(string),
+		})
+	}
+
+	return ret
+}
+
+func writeFiles(dir string, pkgs []Pkg) {
+	buf := &bytes.Buffer{}
+	if err := temp.Execute(buf, struct{ Pkgs []Pkg }{pkgs}); err != nil {
+		panic(err)
+	}
+
+	if err := ioutil.WriteFile(filepath.Join(dir, "app.go"), buf.Bytes(), 0666); err != nil {
+		panic(err)
+	}
+
+	if err := ioutil.WriteFile(filepath.Join(dir, "app.yaml"), []byte(appYaml), 0666); err != nil {
+		panic(err)
+	}
+}
+
+func parseFlags() {
+	err := error(nil)

[dnj, 2015/06/08 16:43:17]

I generally prefer "var err error" *shrug* Up to you of course.

[iannucci, 2015/06/09 00:01:53]

me too... I was getting bikeshedding elsewhere on this. changed to the other
thing.

+	flag.Parse()
+	if *outDir == "" {
+		if *outDir, err = os.Getwd(); err != nil {
+			panic(err)
+		}
+	}
+	if *outDir, err = filepath.Abs(*outDir); err != nil {
+		panic(err)
+	}
+}
+
+func startServer(dir string) (func(), func()) {
+	args := []string{"serve"}
+	if *clearDatastore {
+		args = append(args, "-clear_datastore")
+	}
+	args = append(args, dir)
+	server := exec.Command("goapp", args...)
+	server.Stdout = os.Stdout
+	server.Stderr = os.Stderr
+	if err := server.Start(); err != nil {
+		panic(err)
+	}
+	time.Sleep(time.Second) // yeah yeah, sue me.

[dnj, 2015/06/08 16:43:18]

Since you know the discovery service URL, you could just ping it here until it
succeeds.

[iannucci, 2015/06/09 00:01:54]

Done.

+	fmt.Println("Discovery service up")
+
+	wait := func() { server.Wait() }
+	stop := func() {
+		server.Process.Signal(os.Interrupt)
+		wait()
+	}
+	return stop, wait
+}
+
+func generate() {
+	gencmd := exec.Command("google-api-go-generator", "-discoveryurl", "http://localhost:8080/_ah/api/discovery/v1/apis", "-gendir", *outDir, "-cache=false")
+	gencmd.Stdout = os.Stdout
+	gencmd.Stderr = os.Stderr
+	if err := gencmd.Run(); err != nil {
+		panic(err)
+	}
+}
+
+func main() {
+	parseFlags()
+

[dnj, 2015/06/08 16:43:18]

Test that "google-api-go-generator" and "goapp" are on PATH first.

[iannucci, 2015/06/09 00:01:53]

Done.

+	pkgs := getPkgs()
+
+	dir, err := ioutil.TempDir("", "epclient_gen")
+	if err != nil {
+		panic(err)
+	}
+	defer os.RemoveAll(dir)
+
+	writeFiles(dir, pkgs)
+
+	stop, wait := startServer(dir)
+	defer stop()
+
+	if *runOnly {
+		wait()
+	} else {
+		generate()
+	}
+
+	// inject DoWithRetries methods.
+}