plume: add cosa2stream

Part of implementing openshift/os#477

I don't think for RHCOS (at least initially) we will go
through the whole "release.json" middle ground, so let's
add a command to directly turn 1 or more cosa build(s) into a stream
JSON.

Because the "cosa build" -> "release" bits are in Python,
we semi-hackily fork it off as a subprocess.  But, it works.

mantle/cmd/plume/cosa2stream.go

@@ -0,0 +1,88 @@
+// Copyright Red Hat, Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package main
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"os/exec"
+	"time"
+
+	"github.com/coreos/stream-metadata-go/release"
+	"github.com/coreos/stream-metadata-go/stream"
+	"github.com/spf13/cobra"
+)
+
+var (
+	cmdCosaBuildToStream = &cobra.Command{
+		Use:   "cosa2stream [options]",
+		Short: "Generate stream JSON from a coreos-assembler build",
+		RunE:  runCosaBuildToStream,
+
+		SilenceUsage: true,
+	}
+
+	streamBaseURL string
+	streamName    string
+)
+
+func init() {
+	cmdCosaBuildToStream.Flags().StringVar(&streamBaseURL, "url", "", "Base URL for build")
+	cmdCosaBuildToStream.Flags().StringVar(&streamName, "name", "", "Stream name")
+	cmdCosaBuildToStream.MarkFlagRequired("name")
+	root.AddCommand(cmdCosaBuildToStream)
+}
+
+func runCosaBuildToStream(cmd *cobra.Command, args []string) error {
+	releaseTmpf, err := ioutil.TempFile("", "release")
+	if err != nil {
+		return err
+	}
+	childArgs := []string{"generate-release-meta", "--name=" + streamName, "--output=" + releaseTmpf.Name()}
+	if streamBaseURL != "" {
+		childArgs = append(childArgs, "--stream-baseurl="+streamBaseURL)
+	}
+	childArgs = append(childArgs, args...)
+	c := exec.Command("cosa", childArgs...)
+	c.Stderr = os.Stderr
+	if err := c.Run(); err != nil {
+		return err
+	}
+
+	var rel release.Release
+	buf, err := ioutil.ReadAll(releaseTmpf)
+	if err != nil {
+		return err
+	}
+	if err := json.Unmarshal(buf, &rel); err != nil {
+		return err
+	}
+
+	// Generate output stream from release
+	outStream := stream.Stream{
+		Stream:        streamName,
+		Metadata:      stream.Metadata{LastModified: time.Now().UTC().Format(time.RFC3339)},
+		Architectures: rel.ToStreamArchitectures(),
+	}
+
+	// Serialize to JSON
+	encoder := json.NewEncoder(os.Stdout)
+	if err := encoder.Encode(&outStream); err != nil {
+		return fmt.Errorf("Error while encoding: %v", err)
+	}
+	return nil
+}