push/go/trigger/trigger.go

package trigger

import (
	"fmt"
	"math/rand"
	"time"

	compute "google.golang.org/api/compute/v1"
)

// ByMetadata triggers a pulld instance to look for new packages by writing a
// value to the 'pushrev' instance metadata, which pulld waits for changes on
// that metadata instance value by doing a hanging GET.
//
// 'revValue' is a unique value to write to the 'pushrev' key, which should
// be the full identifier of the package that was updated.
func ByMetadata(comp *compute.Service, project, revValue, serverName, zone string) error {
	// Add a little randomness to the revValue so it's always unique
	// and this forces pulld to check for new packages.
	r := rand.New(rand.NewSource(time.Now().UnixNano()))
	revValue = fmt.Sprintf("%s %d", revValue, r.Int63())

	inst, err := comp.Instances.Get(project, zone, serverName).Do()
	if err != nil {
		return fmt.Errorf("Could not find metadata fingerprint address: %s", err)
	}
	found := false
	for _, it := range inst.Metadata.Items {
		if it.Key == "pushrev" {
			it.Value = &revValue
			found = true
		}
	}
	if !found {
		inst.Metadata.Items = append(inst.Metadata.Items,
			&compute.MetadataItems{
				Key:   "pushrev",
				Value: &revValue,
			})
	}
	op, err := comp.Instances.SetMetadata(project, zone, serverName, inst.Metadata).Do()
	if err != nil || op.HTTPStatusCode != 200 {
		return fmt.Errorf("Failed to set pushrev for server instance %q: %s", serverName, err)
	}
	return nil
}