feat(tvix/store/protos): implement Size() and Digest() for Directory r/5508

This adds Size() and Digest() functions for the golang version.

Change-Id: If71445a9bb26100bb4076ac4f5c96945b33919f9
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7325
Tested-by: BuildkiteCI
Reviewed-by: tazjin <tazjin@tvl.su>

4 files changed, 251 insertions, 0 deletions

diff --git a/tvix/store/protos/castore.go b/tvix/store/protos/castore.go
new file mode 100644
index 000000000000..38419b40da99
--- /dev/null
+++ b/tvix/store/protos/castore.go
@@ -0,0 +1,39 @@
+package storev1
+
+import (
+	"fmt"
+
+	"google.golang.org/protobuf/proto"
+	"lukechampine.com/blake3"
+)
+
+// The size of a directory is calculated by summing up the numbers of
+// `directories`, `files` and `symlinks`, and for each directory, its size
+// field.
+func (d *Directory) Size() uint32 {
+	var size uint32
+	size = uint32(len(d.Files) + len(d.Symlinks))
+	for _, d := range d.Directories {
+		size += 1 + d.Size
+	}
+	return size
+}
+
+func (d *Directory) Digest() ([]byte, error) {
+	b, err := proto.MarshalOptions{
+		Deterministic: true,
+	}.Marshal(d)
+
+	if err != nil {
+		return nil, fmt.Errorf("error while marshalling directory: %w", err)
+	}
+
+	h := blake3.New(32, nil)
+
+	_, err = h.Write(b)
+	if err != nil {
+		return nil, fmt.Errorf("error writing to hasher: %w", err)
+	}
+
+	return h.Sum(nil), nil
+}
diff --git a/tvix/store/protos/castore_test.go b/tvix/store/protos/castore_test.go
new file mode 100644
index 000000000000..cac73f29c7f0
--- /dev/null
+++ b/tvix/store/protos/castore_test.go
@@ -0,0 +1,100 @@
+package storev1_test
+
+import (
+	"testing"
+
+	storev1pb "code.tvl.fyi/tvix/store/protos"
+	"github.com/stretchr/testify/assert"
+)
+
+var (
+	dummyDigest = []byte{
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00, 0x00,
+		0x00, 0x00, 0x00, 0x00,
+	}
+)
+
+func TestDirectorySize(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		d := storev1pb.Directory{
+			Directories: []*storev1pb.DirectoryNode{},
+			Files:       []*storev1pb.FileNode{},
+			Symlinks:    []*storev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(0), d.Size())
+	})
+
+	t.Run("containing single empty directory", func(t *testing.T) {
+		d := storev1pb.Directory{
+			Directories: []*storev1pb.DirectoryNode{{
+				Name:   "foo",
+				Digest: dummyDigest,
+				Size:   0,
+			}},
+			Files:    []*storev1pb.FileNode{},
+			Symlinks: []*storev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(1), d.Size())
+	})
+
+	t.Run("containing single non-empty directory", func(t *testing.T) {
+		d := storev1pb.Directory{
+			Directories: []*storev1pb.DirectoryNode{{
+				Name:   "foo",
+				Digest: dummyDigest,
+				Size:   4,
+			}},
+			Files:    []*storev1pb.FileNode{},
+			Symlinks: []*storev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(5), d.Size())
+	})
+
+	t.Run("containing single file", func(t *testing.T) {
+		d := storev1pb.Directory{
+			Directories: []*storev1pb.DirectoryNode{},
+			Files: []*storev1pb.FileNode{{
+				Name:       "foo",
+				Digest:     dummyDigest,
+				Size:       42,
+				Executable: false,
+			}},
+			Symlinks: []*storev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(1), d.Size())
+	})
+
+	t.Run("containing single symlink", func(t *testing.T) {
+		d := storev1pb.Directory{
+			Directories: []*storev1pb.DirectoryNode{},
+			Files:       []*storev1pb.FileNode{},
+			Symlinks: []*storev1pb.SymlinkNode{{
+				Name:   "foo",
+				Target: "bar",
+			}},
+		}
+
+		assert.Equal(t, uint32(1), d.Size())
+	})
+
+}
+func TestDirectoryDigest(t *testing.T) {
+	d := storev1pb.Directory{
+		Directories: []*storev1pb.DirectoryNode{},
+		Files:       []*storev1pb.FileNode{},
+		Symlinks:    []*storev1pb.SymlinkNode{},
+	}
+
+	dgst, err := d.Digest()
+	assert.NoError(t, err, "calling Digest() on a directory shouldn't error")
+	assert.Equal(t, []byte{
+		0xaf, 0x13, 0x49, 0xb9, 0xf5, 0xf9, 0xa1, 0xa6, 0xa0, 0x40, 0x4d, 0xea, 0x36, 0xdc,
+		0xc9, 0x49, 0x9b, 0xcb, 0x25, 0xc9, 0xad, 0xc1, 0x12, 0xb7, 0xcc, 0x9a, 0x93, 0xca,
+		0xe4, 0x1f, 0x32, 0x62,
+	}, dgst)
+}
diff --git a/tvix/store/protos/go.mod b/tvix/store/protos/go.mod
index 6653f1a375d7..8a21555eaad5 100644
--- a/tvix/store/protos/go.mod
+++ b/tvix/store/protos/go.mod
@@ -1,3 +1,19 @@
 module code.tvl.fyi/tvix/store/protos
 
 go 1.19
+
+require (
+	github.com/davecgh/go-spew v1.1.1 // indirect
+	github.com/golang/protobuf v1.5.2 // indirect
+	github.com/klauspost/cpuid/v2 v2.0.9 // indirect
+	github.com/pmezard/go-difflib v1.0.0 // indirect
+	github.com/stretchr/testify v1.8.1 // indirect
+	golang.org/x/net v0.0.0-20220722155237-a158d28d115b // indirect
+	golang.org/x/sys v0.0.0-20220722155257-8c9f86f7a55f // indirect
+	golang.org/x/text v0.4.0 // indirect
+	google.golang.org/genproto v0.0.0-20200526211855-cb27e3aa2013 // indirect
+	google.golang.org/grpc v1.51.0 // indirect
+	google.golang.org/protobuf v1.28.1 // indirect
+	gopkg.in/yaml.v3 v3.0.1 // indirect
+	lukechampine.com/blake3 v1.1.7 // indirect
+)
diff --git a/tvix/store/protos/go.sum b/tvix/store/protos/go.sum
new file mode 100644
index 000000000000..7a603cdb120d
--- /dev/null
+++ b/tvix/store/protos/go.sum
@@ -0,0 +1,96 @@
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