smarthttp: Advertise bundle-uri capability

The first step toward using bundle-URI is making the server advertise it
supports this capability.

Insert uploadpack.advertiseBundleURIs in the git config so the info/refs
response contains the bundle-uri capability.

With this we also introduce the feature flag that allows us to toggle
the use of bundle-URIs.

6 files changed, 158 insertions, 12 deletions

diff --git a/internal/bundleuri/doc.go b/internal/bundleuri/doc.go
new file mode 100644
index 000000000..22a0b4957
--- /dev/null
+++ b/internal/bundleuri/doc.go
@@ -0,0 +1,16 @@
+// Package bundleuri is used to enable the use [Bundle-URI] when the client
+// clones/fetches from the repository.
+//
+// Bundle-URI is a concept in Git that allows the server to send one or more
+// URIs where [git bundles] are available. The client can download such bundles
+// to prepopulate the repository before it starts the object negotiation with
+// the server. This reduces the CPU load on the server, and the amount of
+// traffic that has to travel directly from server to client.
+//
+// This feature piggy-backs onto server-side backups. Refer to the
+// [backup documentation] how to create and store bundles on a cloud provider.
+//
+// [Bundle-URI]: https://git-scm.com/docs/bundle-uri
+// [git bundles]: https://git-scm.com/docs/git-bundle
+// [backup documentation]: https://gitlab.com/gitlab-org/gitaly/-/blob/master/doc/gitaly-backup.md
+package bundleuri
diff --git a/internal/bundleuri/git_config.go b/internal/bundleuri/git_config.go
new file mode 100644
index 000000000..2c6ab5c02
--- /dev/null
+++ b/internal/bundleuri/git_config.go
@@ -0,0 +1,27 @@
+package bundleuri
+
+import (
+	"context"
+
+	"gitlab.com/gitlab-org/gitaly/v16/internal/backup"
+	"gitlab.com/gitlab-org/gitaly/v16/internal/featureflag"
+	"gitlab.com/gitlab-org/gitaly/v16/internal/git"
+	"gitlab.com/gitlab-org/gitaly/v16/internal/gitaly/storage"
+)
+
+// InfoRefsGitConfig return a slice of git.ConfigPairs you can inject into the
+// call to git-upload-pack(1) --advertise-refs, to advertise the use of
+// bundle-URI to the client who clones/fetches from the repository.
+func InfoRefsGitConfig(ctx context.Context) []git.ConfigPair {
+	if featureflag.BundleURI.IsDisabled(ctx) {
+		return []git.ConfigPair{}
+	}
+
+	return []git.ConfigPair{
+		{
+			Key:   "uploadpack.advertiseBundleURIs",
+			Value: "true",
+		},
+	}
+}
+
diff --git a/internal/bundleuri/testhelper_test.go b/internal/bundleuri/testhelper_test.go
new file mode 100644
index 000000000..b2dd3cfea
--- /dev/null
+++ b/internal/bundleuri/testhelper_test.go
@@ -0,0 +1,11 @@
+package bundleuri
+
+import (
+	"testing"
+
+	"gitlab.com/gitlab-org/gitaly/v16/internal/testhelper"
+)
+
+func TestMain(m *testing.M) {
+	testhelper.Run(m)
+}
diff --git a/internal/featureflag/ff_bundle_uri.go b/internal/featureflag/ff_bundle_uri.go
new file mode 100644
index 000000000..c912169dc
--- /dev/null
+++ b/internal/featureflag/ff_bundle_uri.go
@@ -0,0 +1,9 @@
+package featureflag
+
+// BundleURI enables the use of git's bundle URI feature
+var BundleURI = NewFeatureFlag(
+	"bundle_uri",
+	"v16.6.0",
+	"https://gitlab.com/gitlab-org/gitaly/-/issues/5656",
+	false,
+)
diff --git a/internal/gitaly/service/smarthttp/inforefs.go b/internal/gitaly/service/smarthttp/inforefs.go
index 2a01868d7..63be73f0f 100644
--- a/internal/gitaly/service/smarthttp/inforefs.go
+++ b/internal/gitaly/service/smarthttp/inforefs.go
@@ -5,6 +5,7 @@ import (
 	"fmt"
 	"io"
 
+	"gitlab.com/gitlab-org/gitaly/v16/internal/bundleuri"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/git"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/git/pktline"
 	"gitlab.com/gitlab-org/gitaly/v16/internal/log"
@@ -62,11 +63,13 @@ func (s *server) handleInfoRefs(ctx context.Context, service, repoPath string, r
 		cmdOpts = append(cmdOpts, git.WithDisabledHooks())
 	}
 
-	config, err := git.ConvertConfigOptions(req.GitConfigOptions)
+	gitConfig, err := git.ConvertConfigOptions(req.GitConfigOptions)
 	if err != nil {
 		return err
 	}
-	cmdOpts = append(cmdOpts, git.WithConfig(config...))
+	gitConfig = append(gitConfig, bundleuri.InfoRefsGitConfig(ctx)...)
+
+	cmdOpts = append(cmdOpts, git.WithConfig(gitConfig...))
 
 	if _, err := pktline.WriteString(w, fmt.Sprintf("# service=git-%s\n", service)); err != nil {
 		return structerr.NewInternal("pktLine: %w", err)
diff --git a/internal/gitaly/service/smarthttp/inforefs_test.go b/internal/gitaly/service/smarthttp/inforefs_test.go
index ba458bac9..836dfce4a 100644
--- a/internal/gitaly/service/smarthttp/inforefs_test.go
+++ b/internal/gitaly/service/smarthttp/inforefs_test.go
@@ -33,7 +33,10 @@ import (
 func TestInfoRefsUploadPack_successful(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackSuccessful)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackSuccessful)
 }
 
 func testInfoRefsUploadPackSuccessful(t *testing.T, ctx context.Context) {
@@ -63,7 +66,10 @@ func testInfoRefsUploadPackSuccessful(t *testing.T, ctx context.Context) {
 func TestInfoRefsUploadPack_internalRefs(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackInternalRefs)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackInternalRefs)
 }
 
 func testInfoRefsUploadPackInternalRefs(t *testing.T, ctx context.Context) {
@@ -138,7 +144,10 @@ func testInfoRefsUploadPackInternalRefs(t *testing.T, ctx context.Context) {
 func TestInfoRefsUploadPack_validate(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackValidate)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackValidate)
 }
 
 func testInfoRefsUploadPackValidate(t *testing.T, ctx context.Context) {
@@ -176,7 +185,10 @@ func testInfoRefsUploadPackValidate(t *testing.T, ctx context.Context) {
 func TestInfoRefsUploadPack_partialClone(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackPartialClone)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackPartialClone)
 }
 
 func testInfoRefsUploadPackPartialClone(t *testing.T, ctx context.Context) {
@@ -204,7 +216,10 @@ func testInfoRefsUploadPackPartialClone(t *testing.T, ctx context.Context) {
 func TestInfoRefsUploadPack_gitConfigOptions(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackGitConfigOptions)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackGitConfigOptions)
 }
 
 func testInfoRefsUploadPackGitConfigOptions(t *testing.T, ctx context.Context) {
@@ -230,10 +245,45 @@ func testInfoRefsUploadPackGitConfigOptions(t *testing.T, ctx context.Context) {
 	})
 }
 
+func TestInfoRefsUploadPack_bundleURI(t *testing.T) {
+	t.Parallel()
+
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+	).Run(t, testInfoRefsUploadPackBundleURI)
+}
+
+func testInfoRefsUploadPackBundleURI(t *testing.T, ctx context.Context) {
+	t.Parallel()
+
+	ctx = featureflag.OutgoingCtxWithFeatureFlag(ctx, featureflag.BundleURI, true)
+
+	cfg := testcfg.Build(t)
+	cfg.SocketPath = runSmartHTTPServer(t, cfg)
+
+	repo, repoPath := gittest.CreateRepository(t, ctx, cfg)
+
+	gittest.WriteCommit(t, cfg, repoPath, gittest.WithBranch("main"), gittest.WithParents())
+
+	rpcRequest := &gitalypb.InfoRefsRequest{
+		Repository:       repo,
+		GitProtocol:      git.ProtocolV2,
+		GitConfigOptions: []string{"transfer.bundleURI=true"},
+	}
+	response, err := makeInfoRefsUploadPackRequest(t, ctx, cfg.SocketPath, cfg.Auth.Token, rpcRequest)
+	require.NoError(t, err)
+	requireAdvertisedCapabilitiesV2(t, string(response), "git-upload-pack", []string{
+		"bundle-uri",
+	})
+}
+
 func TestInfoRefsUploadPack_gitProtocol(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackGitProtocol)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackGitProtocol)
 }
 
 func testInfoRefsUploadPackGitProtocol(t *testing.T, ctx context.Context) {
@@ -290,7 +340,10 @@ func makeInfoRefsUploadPackRequest(t *testing.T, ctx context.Context, serverSock
 func TestInfoRefsReceivePack_successful(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsReceivePackSuccessful)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsReceivePackSuccessful)
 }
 
 func testInfoRefsReceivePackSuccessful(t *testing.T, ctx context.Context) {
@@ -322,7 +375,10 @@ func TestInfoRefsReceivePack_hiddenRefs(t *testing.T) {
 Object pools are not yet support with WAL. This test is testing with a pooled repository.`)
 
 	t.Parallel()
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsReceivePackHiddenRefs)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsReceivePackHiddenRefs)
 }
 
 func testInfoRefsReceivePackHiddenRefs(t *testing.T, ctx context.Context) {
@@ -352,7 +408,10 @@ func testInfoRefsReceivePackHiddenRefs(t *testing.T, ctx context.Context) {
 func TestInfoRefsReceivePack_validate(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsReceivePackValidate)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsReceivePackValidate)
 }
 
 func testInfoRefsReceivePackValidate(t *testing.T, ctx context.Context) {
@@ -405,6 +464,24 @@ func makeInfoRefsReceivePackRequest(t *testing.T, ctx context.Context, serverSoc
 	return response, err
 }
 
+func requireAdvertisedCapabilitiesV2(t *testing.T, responseBody, expectedService string, expectedCapabilities []string) {
+	t.Helper()
+
+	responseLines := strings.SplitAfter(responseBody, "\n")
+	require.Greater(t, len(responseLines), 2)
+
+	// The first line contains the service announcement
+	require.Equal(t, gittest.Pktlinef(t, "# service=%s\n", expectedService), responseLines[0])
+
+	// The second line contains the protocol version
+	require.Equal(t, "0000"+gittest.Pktlinef(t, "version %d\n", 2), responseLines[1])
+
+	// The third line and following lines contain capabilities
+	for _, expectedCap := range expectedCapabilities {
+		require.Contains(t, responseLines[2:], gittest.Pktlinef(t, "%s\n", expectedCap))
+	}
+}
+
 func requireAdvertisedRefs(t *testing.T, responseBody, expectedService string, expectedRefs []string) {
 	t.Helper()
 
@@ -444,7 +521,10 @@ func (ms *mockStreamer) PutStream(ctx context.Context, repo *gitalypb.Repository
 func TestInfoRefsUploadPack_cache(t *testing.T) {
 	t.Parallel()
 
-	testhelper.NewFeatureSets(featureflag.UploadPackBoundaryBitmapTraversal).Run(t, testInfoRefsUploadPackCache)
+	testhelper.NewFeatureSets(
+		featureflag.UploadPackBoundaryBitmapTraversal,
+		featureflag.BundleURI,
+	).Run(t, testInfoRefsUploadPackCache)
 }
 
 func testInfoRefsUploadPackCache(t *testing.T, ctx context.Context) {