worker/base: allow running without `git` installed

genuinetools/img#195

Signed-off-by: Akihiro Suda <suda.akihiro@lab.ntt.co.jp>

source/git/gitsource.go

@@ -37,17 +37,20 @@ type gitSource struct {
 	locker *locker.Locker
 }
 
+// Supported returns nil if the system supports Git source
+func Supported() error {
+	if err := exec.Command("git", "version").Run(); err != nil {
+		return errors.Wrap(err, "failed to find git binary")
+	}
+	return nil
+}
+
 func NewSource(opt Opt) (source.Source, error) {
 	gs := &gitSource{
 		md:     opt.MetadataStore,
 		cache:  opt.CacheAccessor,
 		locker: locker.New(),
 	}
-
-	if err := exec.Command("git", "version").Run(); err != nil {
-		return nil, errors.Wrap(err, "failed to find git binary")
-	}
-
 	return gs, nil
 }
 

worker/base/worker.go

@@ -46,6 +46,7 @@ import (
 	ocispec "github.com/opencontainers/image-spec/specs-go/v1"
 	specs "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
 	"golang.org/x/sync/errgroup"
 )
 
@@ -118,16 +119,19 @@ func NewWorker(opt WorkerOpt) (*Worker, error) {
 
 	sm.Register(is)
 
-	gs, err := git.NewSource(git.Opt{
-		CacheAccessor: cm,
-		MetadataStore: opt.MetadataStore,
-	})
-	if err != nil {
-		return nil, err
+	if err := git.Supported(); err == nil {
+		gs, err := git.NewSource(git.Opt{
+			CacheAccessor: cm,
+			MetadataStore: opt.MetadataStore,
+		})
+		if err != nil {
+			return nil, err
+		}
+		sm.Register(gs)
+	} else {
+		logrus.Warnf("git source cannot be enabled: %v", err)
 	}
 
-	sm.Register(gs)
-
 	hs, err := http.NewSource(http.Opt{
 		CacheAccessor: cm,
 		MetadataStore: opt.MetadataStore,