enable gcr and heroku plugins

cmd/drone-docker-gcr/main.go

@@ -0,0 +1,50 @@
+package main
+
+import (
+	"encoding/base64"
+	"os"
+	"os/exec"
+	"path"
+	"strings"
+)
+
+func main() {
+	var (
+		username = "_json_key"
+		password = os.Getenv("GCR_TOKEN")
+		registry = os.Getenv("PLUGIN_REGISTRY")
+		repo     = os.Getenv("PLUGIN_REPO")
+	)
+
+	// decode the token if base64 encoded
+	decoded, err := base64.StdEncoding.DecodeString(password)
+	if err == nil {
+		password = string(decoded)
+	}
+
+	// default registry value
+	if registry == "" {
+		registry = "gcr.io"
+	}
+
+	// must use the fully qualified repo name. If the
+	// repo name does not have the registry prefix we
+	// should prepend.
+	if !strings.HasPrefix(repo, registry) {
+		repo = path.Join(registry, repo)
+		os.Setenv("PLUGIN_REPO", repo)
+	}
+
+	os.Setenv("PLUGIN_REGISTRY", registry)
+	os.Setenv("DOCKER_USERNAME", username)
+	os.Setenv("DOCKER_PASSWORD", password)
+
+	// invoke the base docker plugin binary
+	cmd := exec.Command("drone-docker")
+	cmd.Stdout = os.Stdout
+	cmd.Stderr = os.Stderr
+	err = cmd.Run()
+	if err != nil {
+		os.Exit(1)
+	}
+}