feat(tvix/store/protos): add Export

Export will traverse a given PathInfo structure, and write the contents
in NAR format to the passed Writer.
It uses directoryLookupFn and blobLookupFn to resolve references.

This is being moved over from nar-bridge. We need to keep the code there
around until we can bump go.mod to storev1 with this merged, but the
tests can already be moved entirely.

Change-Id: Ie0de3077b09344cafa00ff1e2ddb8b52e9e631bc
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9602
Tested-by: BuildkiteCI
Reviewed-by: Brian McGee <brian@bmcgee.ie>
Autosubmit: flokli <flokli@flokli.de>

tvix/store/protos/export_test.go

@@ -0,0 +1,151 @@
+package storev1_test
+
+import (
+	"bytes"
+	"io"
+	"os"
+	"testing"
+
+	castorev1pb "code.tvl.fyi/tvix/castore/protos"
+	storev1pb "code.tvl.fyi/tvix/store/protos"
+	"github.com/stretchr/testify/require"
+	"lukechampine.com/blake3"
+)
+
+func mustDirectoryDigest(d *castorev1pb.Directory) []byte {
+	dgst, err := d.Digest()
+	if err != nil {
+		panic(err)
+	}
+	return dgst
+}
+
+func mustBlobDigest(r io.Reader) []byte {
+	hasher := blake3.New(32, nil)
+	_, err := io.Copy(hasher, r)
+	if err != nil {
+		panic(err)
+	}
+	return hasher.Sum([]byte{})
+}
+
+func TestSymlink(t *testing.T) {
+	pathInfo := &storev1pb.PathInfo{
+
+		Node: &castorev1pb.Node{
+			Node: &castorev1pb.Node_Symlink{
+				Symlink: &castorev1pb.SymlinkNode{
+					Name:   []byte("doesntmatter"),
+					Target: []byte("/nix/store/somewhereelse"),
+				},
+			},
+		},
+	}
+
+	var buf bytes.Buffer
+
+	err := storev1pb.Export(&buf, pathInfo, func([]byte) (*castorev1pb.Directory, error) {
+		panic("no directories expected")
+	}, func([]byte) (io.ReadCloser, error) {
+		panic("no files expected")
+	})
+	require.NoError(t, err, "exporter shouldn't fail")
+
+	f, err := os.Open("testdata/symlink.nar")
+	require.NoError(t, err)
+
+	bytesExpected, err := io.ReadAll(f)
+	if err != nil {
+		panic(err)
+	}
+
+	require.Equal(t, bytesExpected, buf.Bytes(), "expected nar contents to match")
+}
+
+func TestRegular(t *testing.T) {
+	// The blake3 digest of the 0x01 byte.
+	BLAKE3_DIGEST_0X01 := []byte{
+		0x48, 0xfc, 0x72, 0x1f, 0xbb, 0xc1, 0x72, 0xe0, 0x92, 0x5f, 0xa2, 0x7a, 0xf1, 0x67, 0x1d,
+		0xe2, 0x25, 0xba, 0x92, 0x71, 0x34, 0x80, 0x29, 0x98, 0xb1, 0x0a, 0x15, 0x68, 0xa1, 0x88,
+		0x65, 0x2b,
+	}
+
+	pathInfo := &storev1pb.PathInfo{
+		Node: &castorev1pb.Node{
+			Node: &castorev1pb.Node_File{
+				File: &castorev1pb.FileNode{
+					Name:       []byte("doesntmatter"),
+					Digest:     BLAKE3_DIGEST_0X01,
+					Size:       1,
+					Executable: false,
+				},
+			},
+		},
+	}
+
+	var buf bytes.Buffer
+
+	err := storev1pb.Export(&buf, pathInfo, func([]byte) (*castorev1pb.Directory, error) {
+		panic("no directories expected")
+	}, func(blobRef []byte) (io.ReadCloser, error) {
+		if !bytes.Equal(blobRef, BLAKE3_DIGEST_0X01) {
+			panic("unexpected blobref")
+		}
+		return io.NopCloser(bytes.NewBuffer([]byte{0x01})), nil
+	})
+	require.NoError(t, err, "exporter shouldn't fail")
+
+	f, err := os.Open("testdata/onebyteregular.nar")
+	require.NoError(t, err)
+
+	bytesExpected, err := io.ReadAll(f)
+	if err != nil {
+		panic(err)
+	}
+
+	require.Equal(t, bytesExpected, buf.Bytes(), "expected nar contents to match")
+}
+
+func TestEmptyDirectory(t *testing.T) {
+	// construct empty directory node this refers to
+	emptyDirectory := &castorev1pb.Directory{
+		Directories: []*castorev1pb.DirectoryNode{},
+		Files:       []*castorev1pb.FileNode{},
+		Symlinks:    []*castorev1pb.SymlinkNode{},
+	}
+	emptyDirectoryDigest := mustDirectoryDigest(emptyDirectory)
+
+	pathInfo := &storev1pb.PathInfo{
+		Node: &castorev1pb.Node{
+			Node: &castorev1pb.Node_Directory{
+				Directory: &castorev1pb.DirectoryNode{
+					Name:   []byte("doesntmatter"),
+					Digest: emptyDirectoryDigest,
+					Size:   0,
+				},
+			},
+		},
+	}
+
+	var buf bytes.Buffer
+
+	err := storev1pb.Export(&buf, pathInfo, func(directoryRef []byte) (*castorev1pb.Directory, error) {
+		if !bytes.Equal(directoryRef, emptyDirectoryDigest) {
+			panic("unexpected directoryRef")
+		}
+		return emptyDirectory, nil
+	}, func([]byte) (io.ReadCloser, error) {
+		panic("no files expected")
+	})
+	require.NoError(t, err, "exporter shouldn't fail")
+
+	f, err := os.Open("testdata/emptydirectory.nar")
+	require.NoError(t, err)
+
+	bytesExpected, err := io.ReadAll(f)
+	if err != nil {
+		panic(err)
+	}
+
+	require.Equal(t, bytesExpected, buf.Bytes(), "expected nar contents to match")
+}