main: return different exit code when an input is not found

This commit makes skopeo return a different exit code when an
input is not found. The use case is `osbuild` which uses skopeo
to inspect images and it would be nice to differenciate between
an image that is not found and general skopeo errors (or errors
like network issues etc).

I picked exit code (2) for not found because it is also the value
of ENOENT but that is arbitrary and I'm happy to switch to any
other value (we could do `44` as `404` :-) - happy about ideas).

Man page and a test are added.

Signed-off-by: Michael Vogt <[email protected]>

cmd/skopeo/main.go

@@ -129,6 +129,10 @@ func main() {
 	}
 	rootCmd, _ := createApp()
 	if err := rootCmd.Execute(); err != nil {
+		if isNotFoundImageError(err) {
+			logrus.StandardLogger().Log(logrus.FatalLevel, err)
+			logrus.Exit(2)
+		}
 		logrus.Fatal(err)
 	}
 }

cmd/skopeo/proxy.go

@@ -73,13 +73,10 @@ import (
 
 	"github.com/containers/image/v5/image"
 	"github.com/containers/image/v5/manifest"
-	ocilayout "github.com/containers/image/v5/oci/layout"
 	"github.com/containers/image/v5/pkg/blobinfocache"
 	"github.com/containers/image/v5/transports"
 	"github.com/containers/image/v5/transports/alltransports"
 	"github.com/containers/image/v5/types"
-	dockerdistributionerrcode "github.com/docker/distribution/registry/api/errcode"
-	dockerdistributionapi "github.com/docker/distribution/registry/api/v2"
 	"github.com/opencontainers/go-digest"
 	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
@@ -219,25 +216,6 @@ func (h *proxyHandler) OpenImage(args []any) (replyBuf, error) {
 	return h.openImageImpl(args, false)
 }
 
-// isDockerManifestUnknownError is a copy of code from containers/image,
-// please update there first.
-func isDockerManifestUnknownError(err error) bool {
-	var ec dockerdistributionerrcode.ErrorCoder
-	if !errors.As(err, &ec) {
-		return false
-	}
-	return ec.ErrorCode() == dockerdistributionapi.ErrorCodeManifestUnknown
-}
-
-// isNotFoundImageError heuristically attempts to determine whether an error
-// is saying the remote source couldn't find the image (as opposed to an
-// authentication error, an I/O error etc.)
-// TODO drive this into containers/image properly
-func isNotFoundImageError(err error) bool {
-	return isDockerManifestUnknownError(err) ||
-		errors.Is(err, ocilayout.ImageNotFoundError{})
-}
-
 func (h *proxyHandler) openImageImpl(args []any, allowNotFound bool) (retReplyBuf replyBuf, retErr error) {
 	h.lock.Lock()
 	defer h.lock.Unlock()

cmd/skopeo/utils.go

@@ -12,9 +12,13 @@ import (
 	"github.com/containers/common/pkg/retry"
 	"github.com/containers/image/v5/directory"
 	"github.com/containers/image/v5/manifest"
+	ocilayout "github.com/containers/image/v5/oci/layout"
 	"github.com/containers/image/v5/pkg/compression"
+	"github.com/containers/image/v5/storage"
 	"github.com/containers/image/v5/transports/alltransports"
 	"github.com/containers/image/v5/types"
+	dockerdistributionerrcode "github.com/docker/distribution/registry/api/errcode"
+	dockerdistributionapi "github.com/docker/distribution/registry/api/v2"
 	imgspecv1 "github.com/opencontainers/image-spec/specs-go/v1"
 	"github.com/sirupsen/logrus"
 	"github.com/spf13/cobra"
@@ -406,3 +410,23 @@ func promptForPassphrase(privateKeyFile string, stdin, stdout *os.File) (string,
 	fmt.Fprintf(stdout, "\n")
 	return string(passphrase), nil
 }
+
+// isNotFoundImageError heuristically attempts to determine whether an error
+// is saying the remote source couldn't find the image (as opposed to an
+// authentication error, an I/O error etc.)
+// TODO drive this into containers/image properly
+func isNotFoundImageError(err error) bool {
+	return isDockerManifestUnknownError(err) ||
+		errors.Is(err, storage.ErrNoSuchImage) ||
+		errors.Is(err, ocilayout.ImageNotFoundError{})
+}
+
+// isDockerManifestUnknownError is a copy of code from containers/image,
+// please update there first.
+func isDockerManifestUnknownError(err error) bool {
+	var ec dockerdistributionerrcode.ErrorCoder
+	if !errors.As(err, &ec) {
+		return false
+	}
+	return ec.ErrorCode() == dockerdistributionapi.ErrorCodeManifestUnknown
+}

docs/skopeo.1.md

@@ -114,6 +114,15 @@ Print the version number
 | [skopeo-standalone-verify(1)](skopeo-standalone-verify.1.md)| Verify an image signature.                                   |
 | [skopeo-sync(1)](skopeo-sync.1.md)| Synchronize images between registry repositories and local directories.                |
 
+## EXIT STATUS
+`skopeo` exists with status 0 on success, non-zero on error.
+
+Details about the exist statuses:
+
+**1** Generic error, details can be found in the error message.
+
+**2** The input image cannot be found. Note that this is best effort and for remote registries the status often cannot be reliably reported.
+
 ## FILES
   **/etc/containers/policy.json**
   Default trust policy file, if **--policy** is not specified.

systemtest/010-inspect.bats

@@ -129,4 +129,11 @@ END_EXPECT
     expect_output --from="$repo_tags" "" "inspect --no-tags was expected to return empty RepoTags[]"
 }
 
+@test "inspect: image unknown" {
+    # non existing image
+    run_skopeo 2 inspect containers-storage:non-existing-tag
+    expect_output --substring "identifier is not an image" \
+		  "skopeo inspect containers-storage:010101010101"
+}
+
 # vim: filetype=sh

systemtest/040-local-registry-auth.bats

@@ -40,7 +40,7 @@ function setup() {
     expect_output --substring "authentication required"
 
     # Correct creds, but no such image
-    run_skopeo 1 inspect --tls-verify=false --creds=$testuser:$testpassword \
+    run_skopeo 2 inspect --tls-verify=false --creds=$testuser:$testpassword \
                docker://localhost:5000/nonesuch
     expect_output --substring "manifest unknown"
 

systemtest/060-delete.bats

@@ -24,7 +24,7 @@ function setup() {
     run_skopeo delete --tls-verify=false $localimg
 
     # make sure image is removed from registry
-    expected_rc=1
+    expected_rc=2
     run_skopeo $expected_rc inspect --tls-verify=false $localimg
 }