Decouple redis dependency from blob descriptor cache

Ensure that clients can use the blob descriptor cache provider without needing
the redis package.

Signed-off-by: Stephen J Day <stephen.day@docker.com>

docs/storage/cache/suite.go

@@ -0,0 +1,141 @@
+package cache
+
+import (
+	"testing"
+
+	"github.com/docker/distribution"
+	"github.com/docker/distribution/context"
+	"github.com/docker/distribution/digest"
+)
+
+// CheckBlobDescriptorCache takes a cache implementation through a common set
+// of operations. If adding new tests, please add them here so new
+// implementations get the benefit. This should be used for unit tests.
+func CheckBlobDescriptorCache(t *testing.T, provider BlobDescriptorCacheProvider) {
+	ctx := context.Background()
+
+	checkBlobDescriptorCacheEmptyRepository(t, ctx, provider)
+	checkBlobDescriptorCacheSetAndRead(t, ctx, provider)
+}
+
+func checkBlobDescriptorCacheEmptyRepository(t *testing.T, ctx context.Context, provider BlobDescriptorCacheProvider) {
+	if _, err := provider.Stat(ctx, "sha384:abc"); err != distribution.ErrBlobUnknown {
+		t.Fatalf("expected unknown blob error with empty store: %v", err)
+	}
+
+	cache, err := provider.RepositoryScoped("")
+	if err == nil {
+		t.Fatalf("expected an error when asking for invalid repo")
+	}
+
+	cache, err = provider.RepositoryScoped("foo/bar")
+	if err != nil {
+		t.Fatalf("unexpected error getting repository: %v", err)
+	}
+
+	if err := cache.SetDescriptor(ctx, "", distribution.Descriptor{
+		Digest:    "sha384:abc",
+		Length:    10,
+		MediaType: "application/octet-stream"}); err != digest.ErrDigestInvalidFormat {
+		t.Fatalf("expected error with invalid digest: %v", err)
+	}
+
+	if err := cache.SetDescriptor(ctx, "sha384:abc", distribution.Descriptor{
+		Digest:    "",
+		Length:    10,
+		MediaType: "application/octet-stream"}); err == nil {
+		t.Fatalf("expected error setting value on invalid descriptor")
+	}
+
+	if _, err := cache.Stat(ctx, ""); err != digest.ErrDigestInvalidFormat {
+		t.Fatalf("expected error checking for cache item with empty digest: %v", err)
+	}
+
+	if _, err := cache.Stat(ctx, "sha384:abc"); err != distribution.ErrBlobUnknown {
+		t.Fatalf("expected unknown blob error with empty repo: %v", err)
+	}
+}
+
+func checkBlobDescriptorCacheSetAndRead(t *testing.T, ctx context.Context, provider BlobDescriptorCacheProvider) {
+	localDigest := digest.Digest("sha384:abc")
+	expected := distribution.Descriptor{
+		Digest:    "sha256:abc",
+		Length:    10,
+		MediaType: "application/octet-stream"}
+
+	cache, err := provider.RepositoryScoped("foo/bar")
+	if err != nil {
+		t.Fatalf("unexpected error getting scoped cache: %v", err)
+	}
+
+	if err := cache.SetDescriptor(ctx, localDigest, expected); err != nil {
+		t.Fatalf("error setting descriptor: %v", err)
+	}
+
+	desc, err := cache.Stat(ctx, localDigest)
+	if err != nil {
+		t.Fatalf("unexpected error statting fake2:abc: %v", err)
+	}
+
+	if expected != desc {
+		t.Fatalf("unexpected descriptor: %#v != %#v", expected, desc)
+	}
+
+	// also check that we set the canonical key ("fake:abc")
+	desc, err = cache.Stat(ctx, localDigest)
+	if err != nil {
+		t.Fatalf("descriptor not returned for canonical key: %v", err)
+	}
+
+	if expected != desc {
+		t.Fatalf("unexpected descriptor: %#v != %#v", expected, desc)
+	}
+
+	// ensure that global gets extra descriptor mapping
+	desc, err = provider.Stat(ctx, localDigest)
+	if err != nil {
+		t.Fatalf("expected blob unknown in global cache: %v, %v", err, desc)
+	}
+
+	if desc != expected {
+		t.Fatalf("unexpected descriptor: %#v != %#v", expected, desc)
+	}
+
+	// get at it through canonical descriptor
+	desc, err = provider.Stat(ctx, expected.Digest)
+	if err != nil {
+		t.Fatalf("unexpected error checking glboal descriptor: %v", err)
+	}
+
+	if desc != expected {
+		t.Fatalf("unexpected descriptor: %#v != %#v", expected, desc)
+	}
+
+	// now, we set the repo local mediatype to something else and ensure it
+	// doesn't get changed in the provider cache.
+	expected.MediaType = "application/json"
+
+	if err := cache.SetDescriptor(ctx, localDigest, expected); err != nil {
+		t.Fatalf("unexpected error setting descriptor: %v", err)
+	}
+
+	desc, err = cache.Stat(ctx, localDigest)
+	if err != nil {
+		t.Fatalf("unexpected error getting descriptor: %v", err)
+	}
+
+	if desc != expected {
+		t.Fatalf("unexpected descriptor: %#v != %#v", desc, expected)
+	}
+
+	desc, err = provider.Stat(ctx, localDigest)
+	if err != nil {
+		t.Fatalf("unexpected error getting global descriptor: %v", err)
+	}
+
+	expected.MediaType = "application/octet-stream" // expect original mediatype in global
+
+	if desc != expected {
+		t.Fatalf("unexpected descriptor: %#v != %#v", desc, expected)
+	}
+}