refactor(tvix): move castore into tvix-castore crate r/6629

This splits the pure content-addressed layers from tvix-store into a
`castore` crate, and only leaves PathInfo related things, as well as the
CLI entrypoint in the tvix-store crate.

Notable changes:
 - `fixtures` and `utils` had to be moved out of the `test` cfg, so they
   can be imported from tvix-store.
 - Some ad-hoc fixtures in the test were moved to proper fixtures in the
   same step.
 - The protos are now created by a (more static) recipe in the protos/
   directory.

The (now two) golang targets are commented out, as it's not possible to
update them properly in the same CL. This will be done by a followup CL
once this is merged (and whitby deployed)

Bug: https://b.tvl.fyi/issues/301

Change-Id: I8d675d4bf1fb697eb7d479747c1b1e3635718107
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9370
Reviewed-by: tazjin <tazjin@tvl.su>
Reviewed-by: flokli <flokli@flokli.de>
Autosubmit: flokli <flokli@flokli.de>
Tested-by: BuildkiteCI
Reviewed-by: Connor Brewster <cbrewster@hey.com>

13 files changed, 2522 insertions, 0 deletions

diff --git a/tvix/castore/protos/LICENSE b/tvix/castore/protos/LICENSE
new file mode 100644
index 000000000000..2034ada6fd9a
--- /dev/null
+++ b/tvix/castore/protos/LICENSE
@@ -0,0 +1,21 @@
+Copyright © The Tvix Authors
+
+Permission is hereby granted, free of charge, to any person obtaining
+a copy of this software and associated documentation files (the
+“Software”), to deal in the Software without restriction, including
+without limitation the rights to use, copy, modify, merge, publish,
+distribute, sublicense, and/or sell copies of the Software, and to
+permit persons to whom the Software is furnished to do so, subject to
+the following conditions:
+
+The above copyright notice and this permission notice shall be
+included in all copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED “AS IS”, WITHOUT WARRANTY OF ANY KIND,
+EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
+MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
+IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
+CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
+TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
+SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
+
diff --git a/tvix/castore/protos/castore.go b/tvix/castore/protos/castore.go
new file mode 100644
index 000000000000..102ba4bff75d
--- /dev/null
+++ b/tvix/castore/protos/castore.go
@@ -0,0 +1,164 @@
+package castorev1
+
+import (
+	"bytes"
+	"encoding/base64"
+	"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
+}
+
+// isValidName checks a name for validity.
+// We disallow slashes, null bytes, '.', '..' and the empty string.
+// Depending on the context, a *Node message with an empty string as name is
+// allowed, but they don't occur inside a Directory message.
+func isValidName(n []byte) bool {
+	if len(n) == 0 || bytes.Equal(n, []byte("..")) || bytes.Equal(n, []byte{'.'}) || bytes.Contains(n, []byte{'\x00'}) || bytes.Contains(n, []byte{'/'}) {
+		return false
+	}
+	return true
+}
+
+// Validate thecks the Directory message for invalid data, such as:
+// - violations of name restrictions
+// - invalid digest lengths
+// - not properly sorted lists
+// - duplicate names in the three lists
+func (d *Directory) Validate() error {
+	// seenNames contains all seen names so far.
+	// We populate this to ensure node names are unique across all three lists.
+	seenNames := make(map[string]interface{})
+
+	// We also track the last seen name in each of the three lists,
+	// to ensure nodes are sorted by their names.
+	var lastDirectoryName, lastFileName, lastSymlinkName []byte
+
+	// helper function to only insert in sorted order.
+	// used with the three lists above.
+	// Note this consumes a *pointer to* a string,  as it mutates it.
+	insertIfGt := func(lastName *[]byte, name []byte) error {
+		// update if it's greater than the previous name
+		if bytes.Compare(name, *lastName) == 1 {
+			*lastName = name
+			return nil
+		} else {
+			return fmt.Errorf("%v is not in sorted order", name)
+		}
+	}
+
+	// insertOnce inserts into seenNames if the key doesn't exist yet.
+	insertOnce := func(name []byte) error {
+		encoded := base64.StdEncoding.EncodeToString(name)
+		if _, found := seenNames[encoded]; found {
+			return fmt.Errorf("duplicate name: %v", string(name))
+		}
+		seenNames[encoded] = nil
+		return nil
+	}
+
+	// Loop over all Directories, Files and Symlinks individually.
+	// Check the name for validity, check a potential digest for length,
+	// then check for sorting in the current list, and uniqueness across all three lists.
+	for _, directoryNode := range d.Directories {
+		directoryName := directoryNode.GetName()
+
+		// check name for validity
+		if !isValidName(directoryName) {
+			return fmt.Errorf("invalid name for DirectoryNode: %v", directoryName)
+		}
+
+		// check digest to be 32 bytes
+		digestLen := len(directoryNode.GetDigest())
+		if digestLen != 32 {
+			return fmt.Errorf("invalid digest length for DirectoryNode: %d", digestLen)
+		}
+
+		// ensure names are sorted
+		if err := insertIfGt(&lastDirectoryName, directoryName); err != nil {
+			return err
+		}
+
+		// add to seenNames
+		if err := insertOnce(directoryName); err != nil {
+			return err
+		}
+
+	}
+
+	for _, fileNode := range d.Files {
+		fileName := fileNode.GetName()
+
+		// check name for validity
+		if !isValidName(fileName) {
+			return fmt.Errorf("invalid name for FileNode: %v", fileName)
+		}
+
+		// check digest to be 32 bytes
+		digestLen := len(fileNode.GetDigest())
+		if digestLen != 32 {
+			return fmt.Errorf("invalid digest length for FileNode: %d", digestLen)
+		}
+
+		// ensure names are sorted
+		if err := insertIfGt(&lastFileName, fileName); err != nil {
+			return err
+		}
+
+		// add to seenNames
+		if err := insertOnce(fileName); err != nil {
+			return err
+		}
+	}
+
+	for _, symlinkNode := range d.Symlinks {
+		symlinkName := symlinkNode.GetName()
+
+		// check name for validity
+		if !isValidName(symlinkName) {
+			return fmt.Errorf("invalid name for SymlinkNode: %v", symlinkName)
+		}
+
+		// ensure names are sorted
+		if err := insertIfGt(&lastSymlinkName, symlinkName); err != nil {
+			return err
+		}
+
+		// add to seenNames
+		if err := insertOnce(symlinkName); err != nil {
+			return err
+		}
+	}
+
+	return nil
+}
diff --git a/tvix/castore/protos/castore.pb.go b/tvix/castore/protos/castore.pb.go
new file mode 100644
index 000000000000..5323d6c923a8
--- /dev/null
+++ b/tvix/castore/protos/castore.pb.go
@@ -0,0 +1,580 @@
+// SPDX-FileCopyrightText: edef <edef@unfathomable.blue>
+// SPDX-License-Identifier: OSL-3.0 OR MIT OR Apache-2.0
+
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.31.0
+// 	protoc        (unknown)
+// source: tvix/castore/protos/castore.proto
+
+package castorev1
+
+import (
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+// A Directory can contain Directory, File or Symlink nodes.
+// Each of these nodes have a name attribute, which is the basename in that directory
+// and node type specific attributes.
+// The name attribute:
+//   - MUST not contain slashes or null bytes
+//   - MUST not be '.' or '..'
+//   - MUST be unique across all three lists
+//
+// Elements in each list need to be lexicographically ordered by the name
+// attribute.
+type Directory struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Directories []*DirectoryNode `protobuf:"bytes,1,rep,name=directories,proto3" json:"directories,omitempty"`
+	Files       []*FileNode      `protobuf:"bytes,2,rep,name=files,proto3" json:"files,omitempty"`
+	Symlinks    []*SymlinkNode   `protobuf:"bytes,3,rep,name=symlinks,proto3" json:"symlinks,omitempty"`
+}
+
+func (x *Directory) Reset() {
+	*x = Directory{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_castore_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *Directory) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Directory) ProtoMessage() {}
+
+func (x *Directory) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_castore_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Directory.ProtoReflect.Descriptor instead.
+func (*Directory) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_castore_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *Directory) GetDirectories() []*DirectoryNode {
+	if x != nil {
+		return x.Directories
+	}
+	return nil
+}
+
+func (x *Directory) GetFiles() []*FileNode {
+	if x != nil {
+		return x.Files
+	}
+	return nil
+}
+
+func (x *Directory) GetSymlinks() []*SymlinkNode {
+	if x != nil {
+		return x.Symlinks
+	}
+	return nil
+}
+
+// A DirectoryNode represents a directory in a Directory.
+type DirectoryNode struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The (base)name of the directory
+	Name []byte `protobuf:"bytes,1,opt,name=name,proto3" json:"name,omitempty"`
+	// The blake3 hash of a Directory message, serialized in protobuf canonical form.
+	Digest []byte `protobuf:"bytes,2,opt,name=digest,proto3" json:"digest,omitempty"`
+	// Number of child elements in the Directory referred to by `digest`.
+	// Calculated by summing up the numbers of `directories`, `files` and
+	// `symlinks`, and for each directory, its size field. Used for inode
+	// number calculation.
+	// This field is precisely as verifiable as any other Merkle tree edge.
+	// Resolve `digest`, and you can compute it incrementally. Resolve the
+	// entire tree, and you can fully compute it from scratch.
+	// A credulous implementation won't reject an excessive size, but this is
+	// harmless: you'll have some ordinals without nodes. Undersizing is
+	// obvious and easy to reject: you won't have an ordinal for some nodes.
+	Size uint32 `protobuf:"varint,3,opt,name=size,proto3" json:"size,omitempty"`
+}
+
+func (x *DirectoryNode) Reset() {
+	*x = DirectoryNode{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_castore_proto_msgTypes[1]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *DirectoryNode) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*DirectoryNode) ProtoMessage() {}
+
+func (x *DirectoryNode) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_castore_proto_msgTypes[1]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use DirectoryNode.ProtoReflect.Descriptor instead.
+func (*DirectoryNode) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_castore_proto_rawDescGZIP(), []int{1}
+}
+
+func (x *DirectoryNode) GetName() []byte {
+	if x != nil {
+		return x.Name
+	}
+	return nil
+}
+
+func (x *DirectoryNode) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+func (x *DirectoryNode) GetSize() uint32 {
+	if x != nil {
+		return x.Size
+	}
+	return 0
+}
+
+// A FileNode represents a regular or executable file in a Directory.
+type FileNode struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The (base)name of the file
+	Name []byte `protobuf:"bytes,1,opt,name=name,proto3" json:"name,omitempty"`
+	// The blake3 digest of the file contents
+	Digest []byte `protobuf:"bytes,2,opt,name=digest,proto3" json:"digest,omitempty"`
+	// The file content size
+	Size uint32 `protobuf:"varint,3,opt,name=size,proto3" json:"size,omitempty"`
+	// Whether the file is executable
+	Executable bool `protobuf:"varint,4,opt,name=executable,proto3" json:"executable,omitempty"`
+}
+
+func (x *FileNode) Reset() {
+	*x = FileNode{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_castore_proto_msgTypes[2]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *FileNode) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*FileNode) ProtoMessage() {}
+
+func (x *FileNode) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_castore_proto_msgTypes[2]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use FileNode.ProtoReflect.Descriptor instead.
+func (*FileNode) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_castore_proto_rawDescGZIP(), []int{2}
+}
+
+func (x *FileNode) GetName() []byte {
+	if x != nil {
+		return x.Name
+	}
+	return nil
+}
+
+func (x *FileNode) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+func (x *FileNode) GetSize() uint32 {
+	if x != nil {
+		return x.Size
+	}
+	return 0
+}
+
+func (x *FileNode) GetExecutable() bool {
+	if x != nil {
+		return x.Executable
+	}
+	return false
+}
+
+// A SymlinkNode represents a symbolic link in a Directory.
+type SymlinkNode struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The (base)name of the symlink
+	Name []byte `protobuf:"bytes,1,opt,name=name,proto3" json:"name,omitempty"`
+	// The target of the symlink.
+	Target []byte `protobuf:"bytes,2,opt,name=target,proto3" json:"target,omitempty"`
+}
+
+func (x *SymlinkNode) Reset() {
+	*x = SymlinkNode{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_castore_proto_msgTypes[3]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *SymlinkNode) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*SymlinkNode) ProtoMessage() {}
+
+func (x *SymlinkNode) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_castore_proto_msgTypes[3]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use SymlinkNode.ProtoReflect.Descriptor instead.
+func (*SymlinkNode) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_castore_proto_rawDescGZIP(), []int{3}
+}
+
+func (x *SymlinkNode) GetName() []byte {
+	if x != nil {
+		return x.Name
+	}
+	return nil
+}
+
+func (x *SymlinkNode) GetTarget() []byte {
+	if x != nil {
+		return x.Target
+	}
+	return nil
+}
+
+// A Node is either a DirectoryNode, FileNode or SymlinkNode.
+type Node struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Types that are assignable to Node:
+	//
+	//	*Node_Directory
+	//	*Node_File
+	//	*Node_Symlink
+	Node isNode_Node `protobuf_oneof:"node"`
+}
+
+func (x *Node) Reset() {
+	*x = Node{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_castore_proto_msgTypes[4]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *Node) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*Node) ProtoMessage() {}
+
+func (x *Node) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_castore_proto_msgTypes[4]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use Node.ProtoReflect.Descriptor instead.
+func (*Node) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_castore_proto_rawDescGZIP(), []int{4}
+}
+
+func (m *Node) GetNode() isNode_Node {
+	if m != nil {
+		return m.Node
+	}
+	return nil
+}
+
+func (x *Node) GetDirectory() *DirectoryNode {
+	if x, ok := x.GetNode().(*Node_Directory); ok {
+		return x.Directory
+	}
+	return nil
+}
+
+func (x *Node) GetFile() *FileNode {
+	if x, ok := x.GetNode().(*Node_File); ok {
+		return x.File
+	}
+	return nil
+}
+
+func (x *Node) GetSymlink() *SymlinkNode {
+	if x, ok := x.GetNode().(*Node_Symlink); ok {
+		return x.Symlink
+	}
+	return nil
+}
+
+type isNode_Node interface {
+	isNode_Node()
+}
+
+type Node_Directory struct {
+	Directory *DirectoryNode `protobuf:"bytes,1,opt,name=directory,proto3,oneof"`
+}
+
+type Node_File struct {
+	File *FileNode `protobuf:"bytes,2,opt,name=file,proto3,oneof"`
+}
+
+type Node_Symlink struct {
+	Symlink *SymlinkNode `protobuf:"bytes,3,opt,name=symlink,proto3,oneof"`
+}
+
+func (*Node_Directory) isNode_Node() {}
+
+func (*Node_File) isNode_Node() {}
+
+func (*Node_Symlink) isNode_Node() {}
+
+var File_tvix_castore_protos_castore_proto protoreflect.FileDescriptor
+
+var file_tvix_castore_protos_castore_proto_rawDesc = []byte{
+	0x0a, 0x21, 0x74, 0x76, 0x69, 0x78, 0x2f, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2f, 0x70,
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+	0x65, 0x12, 0x38, 0x0a, 0x07, 0x73, 0x79, 0x6d, 0x6c, 0x69, 0x6e, 0x6b, 0x18, 0x03, 0x20, 0x01,
+	0x28, 0x0b, 0x32, 0x1c, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72,
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+	0x48, 0x00, 0x52, 0x07, 0x73, 0x79, 0x6d, 0x6c, 0x69, 0x6e, 0x6b, 0x42, 0x06, 0x0a, 0x04, 0x6e,
+	0x6f, 0x64, 0x65, 0x42, 0x2c, 0x5a, 0x2a, 0x63, 0x6f, 0x64, 0x65, 0x2e, 0x74, 0x76, 0x6c, 0x2e,
+	0x66, 0x79, 0x69, 0x2f, 0x74, 0x76, 0x69, 0x78, 0x2f, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65,
+	0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x73, 0x3b, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x76,
+	0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+}
+
+var (
+	file_tvix_castore_protos_castore_proto_rawDescOnce sync.Once
+	file_tvix_castore_protos_castore_proto_rawDescData = file_tvix_castore_protos_castore_proto_rawDesc
+)
+
+func file_tvix_castore_protos_castore_proto_rawDescGZIP() []byte {
+	file_tvix_castore_protos_castore_proto_rawDescOnce.Do(func() {
+		file_tvix_castore_protos_castore_proto_rawDescData = protoimpl.X.CompressGZIP(file_tvix_castore_protos_castore_proto_rawDescData)
+	})
+	return file_tvix_castore_protos_castore_proto_rawDescData
+}
+
+var file_tvix_castore_protos_castore_proto_msgTypes = make([]protoimpl.MessageInfo, 5)
+var file_tvix_castore_protos_castore_proto_goTypes = []interface{}{
+	(*Directory)(nil),     // 0: tvix.castore.v1.Directory
+	(*DirectoryNode)(nil), // 1: tvix.castore.v1.DirectoryNode
+	(*FileNode)(nil),      // 2: tvix.castore.v1.FileNode
+	(*SymlinkNode)(nil),   // 3: tvix.castore.v1.SymlinkNode
+	(*Node)(nil),          // 4: tvix.castore.v1.Node
+}
+var file_tvix_castore_protos_castore_proto_depIdxs = []int32{
+	1, // 0: tvix.castore.v1.Directory.directories:type_name -> tvix.castore.v1.DirectoryNode
+	2, // 1: tvix.castore.v1.Directory.files:type_name -> tvix.castore.v1.FileNode
+	3, // 2: tvix.castore.v1.Directory.symlinks:type_name -> tvix.castore.v1.SymlinkNode
+	1, // 3: tvix.castore.v1.Node.directory:type_name -> tvix.castore.v1.DirectoryNode
+	2, // 4: tvix.castore.v1.Node.file:type_name -> tvix.castore.v1.FileNode
+	3, // 5: tvix.castore.v1.Node.symlink:type_name -> tvix.castore.v1.SymlinkNode
+	6, // [6:6] is the sub-list for method output_type
+	6, // [6:6] is the sub-list for method input_type
+	6, // [6:6] is the sub-list for extension type_name
+	6, // [6:6] is the sub-list for extension extendee
+	0, // [0:6] is the sub-list for field type_name
+}
+
+func init() { file_tvix_castore_protos_castore_proto_init() }
+func file_tvix_castore_protos_castore_proto_init() {
+	if File_tvix_castore_protos_castore_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_tvix_castore_protos_castore_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*Directory); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_castore_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*DirectoryNode); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_castore_proto_msgTypes[2].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*FileNode); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_castore_proto_msgTypes[3].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*SymlinkNode); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_castore_proto_msgTypes[4].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*Node); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	file_tvix_castore_protos_castore_proto_msgTypes[4].OneofWrappers = []interface{}{
+		(*Node_Directory)(nil),
+		(*Node_File)(nil),
+		(*Node_Symlink)(nil),
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_tvix_castore_protos_castore_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   5,
+			NumExtensions: 0,
+			NumServices:   0,
+		},
+		GoTypes:           file_tvix_castore_protos_castore_proto_goTypes,
+		DependencyIndexes: file_tvix_castore_protos_castore_proto_depIdxs,
+		MessageInfos:      file_tvix_castore_protos_castore_proto_msgTypes,
+	}.Build()
+	File_tvix_castore_protos_castore_proto = out.File
+	file_tvix_castore_protos_castore_proto_rawDesc = nil
+	file_tvix_castore_protos_castore_proto_goTypes = nil
+	file_tvix_castore_protos_castore_proto_depIdxs = nil
+}
diff --git a/tvix/castore/protos/castore.proto b/tvix/castore/protos/castore.proto
new file mode 100644
index 000000000000..d99df43857ac
--- /dev/null
+++ b/tvix/castore/protos/castore.proto
@@ -0,0 +1,72 @@
+// SPDX-FileCopyrightText: edef <edef@unfathomable.blue>
+// SPDX-License-Identifier: OSL-3.0 OR MIT OR Apache-2.0
+
+syntax = "proto3";
+
+package tvix.castore.v1;
+
+option go_package = "code.tvl.fyi/tvix/castore/protos;castorev1";
+
+// A Directory can contain Directory, File or Symlink nodes.
+// Each of these nodes have a name attribute, which is the basename in that directory
+// and node type specific attributes.
+// The name attribute:
+//  - MUST not contain slashes or null bytes
+//  - MUST not be '.' or '..'
+//  - MUST be unique across all three lists
+// Elements in each list need to be lexicographically ordered by the name
+// attribute.
+message Directory {
+    repeated DirectoryNode directories = 1;
+    repeated FileNode files = 2;
+    repeated SymlinkNode symlinks = 3;
+}
+
+// A DirectoryNode represents a directory in a Directory.
+message DirectoryNode {
+    // The (base)name of the directory
+    bytes name = 1;
+    // The blake3 hash of a Directory message, serialized in protobuf canonical form.
+    bytes digest = 2;
+    // Number of child elements in the Directory referred to by `digest`.
+    // Calculated by summing up the numbers of `directories`, `files` and
+    // `symlinks`, and for each directory, its size field. Used for inode
+    // number calculation.
+    // This field is precisely as verifiable as any other Merkle tree edge.
+    // Resolve `digest`, and you can compute it incrementally. Resolve the
+    // entire tree, and you can fully compute it from scratch.
+    // A credulous implementation won't reject an excessive size, but this is
+    // harmless: you'll have some ordinals without nodes. Undersizing is
+    // obvious and easy to reject: you won't have an ordinal for some nodes.
+    uint32 size = 3;
+}
+
+// A FileNode represents a regular or executable file in a Directory.
+message FileNode {
+    // The (base)name of the file
+    bytes name = 1;
+    // The blake3 digest of the file contents
+    bytes digest = 2;
+    // The file content size
+    uint32 size = 3;
+    // Whether the file is executable
+    bool executable = 4;
+}
+
+// A SymlinkNode represents a symbolic link in a Directory.
+message SymlinkNode {
+    // The (base)name of the symlink
+    bytes name = 1;
+    // The target of the symlink.
+    bytes target = 2;
+}
+
+// A Node is either a DirectoryNode, FileNode or SymlinkNode.
+message Node {
+    oneof node {
+        DirectoryNode directory = 1;
+        FileNode file = 2;
+        SymlinkNode symlink = 3;
+    }
+}
+
diff --git a/tvix/castore/protos/castore_test.go b/tvix/castore/protos/castore_test.go
new file mode 100644
index 000000000000..958d399d76cc
--- /dev/null
+++ b/tvix/castore/protos/castore_test.go
@@ -0,0 +1,271 @@
+package castorev1_test
+
+import (
+	"testing"
+
+	castorev1pb "code.tvl.fyi/tvix/castore/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 := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{},
+			Files:       []*castorev1pb.FileNode{},
+			Symlinks:    []*castorev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(0), d.Size())
+	})
+
+	t.Run("containing single empty directory", func(t *testing.T) {
+		d := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{{
+				Name:   []byte([]byte("foo")),
+				Digest: dummyDigest,
+				Size:   0,
+			}},
+			Files:    []*castorev1pb.FileNode{},
+			Symlinks: []*castorev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(1), d.Size())
+	})
+
+	t.Run("containing single non-empty directory", func(t *testing.T) {
+		d := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{{
+				Name:   []byte("foo"),
+				Digest: dummyDigest,
+				Size:   4,
+			}},
+			Files:    []*castorev1pb.FileNode{},
+			Symlinks: []*castorev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(5), d.Size())
+	})
+
+	t.Run("containing single file", func(t *testing.T) {
+		d := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{},
+			Files: []*castorev1pb.FileNode{{
+				Name:       []byte("foo"),
+				Digest:     dummyDigest,
+				Size:       42,
+				Executable: false,
+			}},
+			Symlinks: []*castorev1pb.SymlinkNode{},
+		}
+
+		assert.Equal(t, uint32(1), d.Size())
+	})
+
+	t.Run("containing single symlink", func(t *testing.T) {
+		d := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{},
+			Files:       []*castorev1pb.FileNode{},
+			Symlinks: []*castorev1pb.SymlinkNode{{
+				Name:   []byte("foo"),
+				Target: []byte("bar"),
+			}},
+		}
+
+		assert.Equal(t, uint32(1), d.Size())
+	})
+
+}
+func TestDirectoryDigest(t *testing.T) {
+	d := castorev1pb.Directory{
+		Directories: []*castorev1pb.DirectoryNode{},
+		Files:       []*castorev1pb.FileNode{},
+		Symlinks:    []*castorev1pb.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)
+}
+
+func TestDirectoryValidate(t *testing.T) {
+	t.Run("empty", func(t *testing.T) {
+		d := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{},
+			Files:       []*castorev1pb.FileNode{},
+			Symlinks:    []*castorev1pb.SymlinkNode{},
+		}
+
+		assert.NoError(t, d.Validate())
+	})
+
+	t.Run("invalid names", func(t *testing.T) {
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{{
+					Name:   []byte{},
+					Digest: dummyDigest,
+					Size:   42,
+				}},
+				Files:    []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{},
+			}
+
+			assert.ErrorContains(t, d.Validate(), "invalid name")
+		}
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{{
+					Name:   []byte("."),
+					Digest: dummyDigest,
+					Size:   42,
+				}},
+				Files:    []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{},
+			}
+
+			assert.ErrorContains(t, d.Validate(), "invalid name")
+		}
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{},
+				Files: []*castorev1pb.FileNode{{
+					Name:       []byte(".."),
+					Digest:     dummyDigest,
+					Size:       42,
+					Executable: false,
+				}},
+				Symlinks: []*castorev1pb.SymlinkNode{},
+			}
+
+			assert.ErrorContains(t, d.Validate(), "invalid name")
+		}
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{},
+				Files:       []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{{
+					Name:   []byte("\x00"),
+					Target: []byte("foo"),
+				}},
+			}
+
+			assert.ErrorContains(t, d.Validate(), "invalid name")
+		}
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{},
+				Files:       []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{{
+					Name:   []byte("foo/bar"),
+					Target: []byte("foo"),
+				}},
+			}
+
+			assert.ErrorContains(t, d.Validate(), "invalid name")
+		}
+	})
+
+	t.Run("invalid digest", func(t *testing.T) {
+		d := castorev1pb.Directory{
+			Directories: []*castorev1pb.DirectoryNode{{
+				Name:   []byte("foo"),
+				Digest: nil,
+				Size:   42,
+			}},
+			Files:    []*castorev1pb.FileNode{},
+			Symlinks: []*castorev1pb.SymlinkNode{},
+		}
+
+		assert.ErrorContains(t, d.Validate(), "invalid digest length")
+	})
+
+	t.Run("sorting", func(t *testing.T) {
+		// "b" comes before "a", bad.
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{{
+					Name:   []byte("b"),
+					Digest: dummyDigest,
+					Size:   42,
+				}, {
+					Name:   []byte("a"),
+					Digest: dummyDigest,
+					Size:   42,
+				}},
+				Files:    []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{},
+			}
+			assert.ErrorContains(t, d.Validate(), "is not in sorted order")
+		}
+
+		// "a" exists twice, bad.
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{{
+					Name:   []byte("a"),
+					Digest: dummyDigest,
+					Size:   42,
+				}},
+				Files: []*castorev1pb.FileNode{{
+					Name:       []byte("a"),
+					Digest:     dummyDigest,
+					Size:       42,
+					Executable: false,
+				}},
+				Symlinks: []*castorev1pb.SymlinkNode{},
+			}
+			assert.ErrorContains(t, d.Validate(), "duplicate name")
+		}
+
+		// "a" comes before "b", all good.
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{{
+					Name:   []byte("a"),
+					Digest: dummyDigest,
+					Size:   42,
+				}, {
+					Name:   []byte("b"),
+					Digest: dummyDigest,
+					Size:   42,
+				}},
+				Files:    []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{},
+			}
+			assert.NoError(t, d.Validate(), "shouldn't error")
+		}
+
+		// [b, c] and [a] are both properly sorted.
+		{
+			d := castorev1pb.Directory{
+				Directories: []*castorev1pb.DirectoryNode{{
+					Name:   []byte("b"),
+					Digest: dummyDigest,
+					Size:   42,
+				}, {
+					Name:   []byte("c"),
+					Digest: dummyDigest,
+					Size:   42,
+				}},
+				Files: []*castorev1pb.FileNode{},
+				Symlinks: []*castorev1pb.SymlinkNode{{
+					Name:   []byte("a"),
+					Target: []byte("foo"),
+				}},
+			}
+			assert.NoError(t, d.Validate(), "shouldn't error")
+		}
+	})
+}
diff --git a/tvix/castore/protos/go.mod b/tvix/castore/protos/go.mod
new file mode 100644
index 000000000000..35219aba5c1b
--- /dev/null
+++ b/tvix/castore/protos/go.mod
@@ -0,0 +1,19 @@
+module code.tvl.fyi/tvix/castore/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/castore/protos/go.sum b/tvix/castore/protos/go.sum
new file mode 100644
index 000000000000..7a603cdb120d
--- /dev/null
+++ b/tvix/castore/protos/go.sum
@@ -0,0 +1,96 @@
+cloud.google.com/go v0.26.0/go.mod h1:aQUYkXzVsufM+DwF1aE+0xfcU+56JwCaLick0ClmMTw=
+github.com/BurntSushi/toml v0.3.1/go.mod h1:xHWCNGjB5oqiDr8zfno3MHue2Ht5sIBksp03qcyfWMU=
+github.com/census-instrumentation/opencensus-proto v0.2.1/go.mod h1:f6KPmirojxKA12rnyqOA5BBL4O983OfeGPqjHWSTneU=
+github.com/client9/misspell v0.3.4/go.mod h1:qj6jICC3Q7zFZvVWo7KLAzC3yx5G7kyvSDkc90ppPyw=
+github.com/davecgh/go-spew v1.1.0/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/davecgh/go-spew v1.1.1 h1:vj9j/u1bqnvCEfJOwUhtlOARqs3+rkHYY13jYWTU97c=
+github.com/davecgh/go-spew v1.1.1/go.mod h1:J7Y8YcW2NihsgmVo/mv3lAwl/skON4iLHjSsI+c5H38=
+github.com/envoyproxy/go-control-plane v0.9.1-0.20191026205805-5f8ba28d4473/go.mod h1:YTl/9mNaCwkRvm6d1a2C3ymFceY/DCBVvsKhRF0iEA4=
+github.com/envoyproxy/protoc-gen-validate v0.1.0/go.mod h1:iSmxcyjqTsJpI2R4NaDN7+kN2VEUnK/pcBlmesArF7c=
+github.com/golang/glog v0.0.0-20160126235308-23def4e6c14b/go.mod h1:SBH7ygxi8pfUlaOkMMuAQtPIUF8ecWP5IEl/CR7VP2Q=
+github.com/golang/mock v1.1.1/go.mod h1:oTYuIxOrZwtPieC+H1uAHpcLFnEyAGVDL/k47Jfbm0A=
+github.com/golang/protobuf v1.2.0/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.3.2/go.mod h1:6lQm79b+lXiMfvg/cZm0SGofjICqVBUtrP5yJMmIC1U=
+github.com/golang/protobuf v1.4.0-rc.1/go.mod h1:ceaxUfeHdC40wWswd/P6IGgMaK3YpKi5j83Wpe3EHw8=
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+honnef.co/go/tools v0.0.0-20190523083050-ea95bdfd59fc/go.mod h1:rf3lG4BRIbNafJWhAfAdb/ePZxsR/4RtNHQocxwk9r4=
+lukechampine.com/blake3 v1.1.7 h1:GgRMhmdsuK8+ii6UZFDL8Nb+VyMwadAgcJyfYHxG6n0=
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diff --git a/tvix/castore/protos/rpc_blobstore.pb.go b/tvix/castore/protos/rpc_blobstore.pb.go
new file mode 100644
index 000000000000..1afc82674451
--- /dev/null
+++ b/tvix/castore/protos/rpc_blobstore.pb.go
@@ -0,0 +1,414 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.31.0
+// 	protoc        (unknown)
+// source: tvix/castore/protos/rpc_blobstore.proto
+
+package castorev1
+
+import (
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+type StatBlobRequest struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The blake3 digest of the blob requested
+	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3" json:"digest,omitempty"`
+}
+
+func (x *StatBlobRequest) Reset() {
+	*x = StatBlobRequest{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *StatBlobRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*StatBlobRequest) ProtoMessage() {}
+
+func (x *StatBlobRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use StatBlobRequest.ProtoReflect.Descriptor instead.
+func (*StatBlobRequest) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{0}
+}
+
+func (x *StatBlobRequest) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+type BlobMeta struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+}
+
+func (x *BlobMeta) Reset() {
+	*x = BlobMeta{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[1]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *BlobMeta) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*BlobMeta) ProtoMessage() {}
+
+func (x *BlobMeta) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[1]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use BlobMeta.ProtoReflect.Descriptor instead.
+func (*BlobMeta) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{1}
+}
+
+type ReadBlobRequest struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The blake3 digest of the blob or chunk requested
+	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3" json:"digest,omitempty"`
+}
+
+func (x *ReadBlobRequest) Reset() {
+	*x = ReadBlobRequest{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[2]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *ReadBlobRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*ReadBlobRequest) ProtoMessage() {}
+
+func (x *ReadBlobRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[2]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use ReadBlobRequest.ProtoReflect.Descriptor instead.
+func (*ReadBlobRequest) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{2}
+}
+
+func (x *ReadBlobRequest) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+// This represents some bytes of a blob.
+// Blobs are sent in smaller chunks to keep message sizes manageable.
+type BlobChunk struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Data []byte `protobuf:"bytes,1,opt,name=data,proto3" json:"data,omitempty"`
+}
+
+func (x *BlobChunk) Reset() {
+	*x = BlobChunk{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[3]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *BlobChunk) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*BlobChunk) ProtoMessage() {}
+
+func (x *BlobChunk) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[3]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use BlobChunk.ProtoReflect.Descriptor instead.
+func (*BlobChunk) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{3}
+}
+
+func (x *BlobChunk) GetData() []byte {
+	if x != nil {
+		return x.Data
+	}
+	return nil
+}
+
+type PutBlobResponse struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// The blake3 digest of the data that was sent.
+	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3" json:"digest,omitempty"`
+}
+
+func (x *PutBlobResponse) Reset() {
+	*x = PutBlobResponse{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[4]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *PutBlobResponse) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*PutBlobResponse) ProtoMessage() {}
+
+func (x *PutBlobResponse) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[4]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use PutBlobResponse.ProtoReflect.Descriptor instead.
+func (*PutBlobResponse) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{4}
+}
+
+func (x *PutBlobResponse) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+var File_tvix_castore_protos_rpc_blobstore_proto protoreflect.FileDescriptor
+
+var file_tvix_castore_protos_rpc_blobstore_proto_rawDesc = []byte{
+	0x0a, 0x27, 0x74, 0x76, 0x69, 0x78, 0x2f, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2f, 0x70,
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+	0x63, 0x6f, 0x64, 0x65, 0x2e, 0x74, 0x76, 0x6c, 0x2e, 0x66, 0x79, 0x69, 0x2f, 0x74, 0x76, 0x69,
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+	0x3b, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x76, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74,
+	0x6f, 0x33,
+}
+
+var (
+	file_tvix_castore_protos_rpc_blobstore_proto_rawDescOnce sync.Once
+	file_tvix_castore_protos_rpc_blobstore_proto_rawDescData = file_tvix_castore_protos_rpc_blobstore_proto_rawDesc
+)
+
+func file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP() []byte {
+	file_tvix_castore_protos_rpc_blobstore_proto_rawDescOnce.Do(func() {
+		file_tvix_castore_protos_rpc_blobstore_proto_rawDescData = protoimpl.X.CompressGZIP(file_tvix_castore_protos_rpc_blobstore_proto_rawDescData)
+	})
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescData
+}
+
+var file_tvix_castore_protos_rpc_blobstore_proto_msgTypes = make([]protoimpl.MessageInfo, 5)
+var file_tvix_castore_protos_rpc_blobstore_proto_goTypes = []interface{}{
+	(*StatBlobRequest)(nil), // 0: tvix.castore.v1.StatBlobRequest
+	(*BlobMeta)(nil),        // 1: tvix.castore.v1.BlobMeta
+	(*ReadBlobRequest)(nil), // 2: tvix.castore.v1.ReadBlobRequest
+	(*BlobChunk)(nil),       // 3: tvix.castore.v1.BlobChunk
+	(*PutBlobResponse)(nil), // 4: tvix.castore.v1.PutBlobResponse
+}
+var file_tvix_castore_protos_rpc_blobstore_proto_depIdxs = []int32{
+	0, // 0: tvix.castore.v1.BlobService.Stat:input_type -> tvix.castore.v1.StatBlobRequest
+	2, // 1: tvix.castore.v1.BlobService.Read:input_type -> tvix.castore.v1.ReadBlobRequest
+	3, // 2: tvix.castore.v1.BlobService.Put:input_type -> tvix.castore.v1.BlobChunk
+	1, // 3: tvix.castore.v1.BlobService.Stat:output_type -> tvix.castore.v1.BlobMeta
+	3, // 4: tvix.castore.v1.BlobService.Read:output_type -> tvix.castore.v1.BlobChunk
+	4, // 5: tvix.castore.v1.BlobService.Put:output_type -> tvix.castore.v1.PutBlobResponse
+	3, // [3:6] is the sub-list for method output_type
+	0, // [0:3] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_tvix_castore_protos_rpc_blobstore_proto_init() }
+func file_tvix_castore_protos_rpc_blobstore_proto_init() {
+	if File_tvix_castore_protos_rpc_blobstore_proto != nil {
+		return
+	}
+	if !protoimpl.UnsafeEnabled {
+		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*StatBlobRequest); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*BlobMeta); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[2].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*ReadBlobRequest); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[3].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*BlobChunk); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[4].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*PutBlobResponse); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_tvix_castore_protos_rpc_blobstore_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   5,
+			NumExtensions: 0,
+			NumServices:   1,
+		},
+		GoTypes:           file_tvix_castore_protos_rpc_blobstore_proto_goTypes,
+		DependencyIndexes: file_tvix_castore_protos_rpc_blobstore_proto_depIdxs,
+		MessageInfos:      file_tvix_castore_protos_rpc_blobstore_proto_msgTypes,
+	}.Build()
+	File_tvix_castore_protos_rpc_blobstore_proto = out.File
+	file_tvix_castore_protos_rpc_blobstore_proto_rawDesc = nil
+	file_tvix_castore_protos_rpc_blobstore_proto_goTypes = nil
+	file_tvix_castore_protos_rpc_blobstore_proto_depIdxs = nil
+}
diff --git a/tvix/castore/protos/rpc_blobstore.proto b/tvix/castore/protos/rpc_blobstore.proto
new file mode 100644
index 000000000000..6ee9a80f0afc
--- /dev/null
+++ b/tvix/castore/protos/rpc_blobstore.proto
@@ -0,0 +1,52 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+syntax = "proto3";
+
+package tvix.castore.v1;
+
+option go_package = "code.tvl.fyi/tvix/castore/protos;castorev1";
+
+service BlobService {
+    // In the future, Stat will expose more metadata about a given blob,
+    // such as more granular chunking, baos.
+    // For now, it's only used to check for the existence of a blob, as asking
+    // this for a non-existing Blob will return a Status::not_found gRPC error.
+    rpc Stat(StatBlobRequest) returns (BlobMeta);
+
+    // Read returns a stream of BlobChunk, which is just a stream of bytes with
+    // the digest specified in ReadBlobRequest.
+    //
+    // The server may decide on whatever chunking it may seem fit as a size for
+    // the individual BlobChunk sent in the response stream.
+    rpc Read(ReadBlobRequest) returns (stream BlobChunk);
+
+    // Put uploads a Blob, by reading a stream of bytes.
+    //
+    // The way the data is chunked up in individual BlobChunk messages sent in
+    // the stream has no effect on how the server ends up chunking blobs up.
+    rpc Put(stream BlobChunk) returns (PutBlobResponse);
+}
+
+message StatBlobRequest {
+    // The blake3 digest of the blob requested
+    bytes digest = 1;
+}
+
+message BlobMeta {
+}
+
+message ReadBlobRequest {
+    // The blake3 digest of the blob or chunk requested
+    bytes digest = 1;
+}
+
+// This represents some bytes of a blob.
+// Blobs are sent in smaller chunks to keep message sizes manageable.
+message BlobChunk {
+    bytes data = 1;
+}
+
+message PutBlobResponse {
+    // The blake3 digest of the data that was sent.
+    bytes digest = 1;
+}
diff --git a/tvix/castore/protos/rpc_blobstore_grpc.pb.go b/tvix/castore/protos/rpc_blobstore_grpc.pb.go
new file mode 100644
index 000000000000..0876bcc4e95a
--- /dev/null
+++ b/tvix/castore/protos/rpc_blobstore_grpc.pb.go
@@ -0,0 +1,274 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+
+// Code generated by protoc-gen-go-grpc. DO NOT EDIT.
+// versions:
+// - protoc-gen-go-grpc v1.3.0
+// - protoc             (unknown)
+// source: tvix/castore/protos/rpc_blobstore.proto
+
+package castorev1
+
+import (
+	context "context"
+	grpc "google.golang.org/grpc"
+	codes "google.golang.org/grpc/codes"
+	status "google.golang.org/grpc/status"
+)
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+// Requires gRPC-Go v1.32.0 or later.
+const _ = grpc.SupportPackageIsVersion7
+
+const (
+	BlobService_Stat_FullMethodName = "/tvix.castore.v1.BlobService/Stat"
+	BlobService_Read_FullMethodName = "/tvix.castore.v1.BlobService/Read"
+	BlobService_Put_FullMethodName  = "/tvix.castore.v1.BlobService/Put"
+)
+
+// BlobServiceClient is the client API for BlobService service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://pkg.go.dev/google.golang.org/grpc/?tab=doc#ClientConn.NewStream.
+type BlobServiceClient interface {
+	// In the future, Stat will expose more metadata about a given blob,
+	// such as more granular chunking, baos.
+	// For now, it's only used to check for the existence of a blob, as asking
+	// this for a non-existing Blob will return a Status::not_found gRPC error.
+	Stat(ctx context.Context, in *StatBlobRequest, opts ...grpc.CallOption) (*BlobMeta, error)
+	// Read returns a stream of BlobChunk, which is just a stream of bytes with
+	// the digest specified in ReadBlobRequest.
+	//
+	// The server may decide on whatever chunking it may seem fit as a size for
+	// the individual BlobChunk sent in the response stream.
+	Read(ctx context.Context, in *ReadBlobRequest, opts ...grpc.CallOption) (BlobService_ReadClient, error)
+	// Put uploads a Blob, by reading a stream of bytes.
+	//
+	// The way the data is chunked up in individual BlobChunk messages sent in
+	// the stream has no effect on how the server ends up chunking blobs up.
+	Put(ctx context.Context, opts ...grpc.CallOption) (BlobService_PutClient, error)
+}
+
+type blobServiceClient struct {
+	cc grpc.ClientConnInterface
+}
+
+func NewBlobServiceClient(cc grpc.ClientConnInterface) BlobServiceClient {
+	return &blobServiceClient{cc}
+}
+
+func (c *blobServiceClient) Stat(ctx context.Context, in *StatBlobRequest, opts ...grpc.CallOption) (*BlobMeta, error) {
+	out := new(BlobMeta)
+	err := c.cc.Invoke(ctx, BlobService_Stat_FullMethodName, in, out, opts...)
+	if err != nil {
+		return nil, err
+	}
+	return out, nil
+}
+
+func (c *blobServiceClient) Read(ctx context.Context, in *ReadBlobRequest, opts ...grpc.CallOption) (BlobService_ReadClient, error) {
+	stream, err := c.cc.NewStream(ctx, &BlobService_ServiceDesc.Streams[0], BlobService_Read_FullMethodName, opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &blobServiceReadClient{stream}
+	if err := x.ClientStream.SendMsg(in); err != nil {
+		return nil, err
+	}
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	return x, nil
+}
+
+type BlobService_ReadClient interface {
+	Recv() (*BlobChunk, error)
+	grpc.ClientStream
+}
+
+type blobServiceReadClient struct {
+	grpc.ClientStream
+}
+
+func (x *blobServiceReadClient) Recv() (*BlobChunk, error) {
+	m := new(BlobChunk)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+func (c *blobServiceClient) Put(ctx context.Context, opts ...grpc.CallOption) (BlobService_PutClient, error) {
+	stream, err := c.cc.NewStream(ctx, &BlobService_ServiceDesc.Streams[1], BlobService_Put_FullMethodName, opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &blobServicePutClient{stream}
+	return x, nil
+}
+
+type BlobService_PutClient interface {
+	Send(*BlobChunk) error
+	CloseAndRecv() (*PutBlobResponse, error)
+	grpc.ClientStream
+}
+
+type blobServicePutClient struct {
+	grpc.ClientStream
+}
+
+func (x *blobServicePutClient) Send(m *BlobChunk) error {
+	return x.ClientStream.SendMsg(m)
+}
+
+func (x *blobServicePutClient) CloseAndRecv() (*PutBlobResponse, error) {
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	m := new(PutBlobResponse)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// BlobServiceServer is the server API for BlobService service.
+// All implementations must embed UnimplementedBlobServiceServer
+// for forward compatibility
+type BlobServiceServer interface {
+	// In the future, Stat will expose more metadata about a given blob,
+	// such as more granular chunking, baos.
+	// For now, it's only used to check for the existence of a blob, as asking
+	// this for a non-existing Blob will return a Status::not_found gRPC error.
+	Stat(context.Context, *StatBlobRequest) (*BlobMeta, error)
+	// Read returns a stream of BlobChunk, which is just a stream of bytes with
+	// the digest specified in ReadBlobRequest.
+	//
+	// The server may decide on whatever chunking it may seem fit as a size for
+	// the individual BlobChunk sent in the response stream.
+	Read(*ReadBlobRequest, BlobService_ReadServer) error
+	// Put uploads a Blob, by reading a stream of bytes.
+	//
+	// The way the data is chunked up in individual BlobChunk messages sent in
+	// the stream has no effect on how the server ends up chunking blobs up.
+	Put(BlobService_PutServer) error
+	mustEmbedUnimplementedBlobServiceServer()
+}
+
+// UnimplementedBlobServiceServer must be embedded to have forward compatible implementations.
+type UnimplementedBlobServiceServer struct {
+}
+
+func (UnimplementedBlobServiceServer) Stat(context.Context, *StatBlobRequest) (*BlobMeta, error) {
+	return nil, status.Errorf(codes.Unimplemented, "method Stat not implemented")
+}
+func (UnimplementedBlobServiceServer) Read(*ReadBlobRequest, BlobService_ReadServer) error {
+	return status.Errorf(codes.Unimplemented, "method Read not implemented")
+}
+func (UnimplementedBlobServiceServer) Put(BlobService_PutServer) error {
+	return status.Errorf(codes.Unimplemented, "method Put not implemented")
+}
+func (UnimplementedBlobServiceServer) mustEmbedUnimplementedBlobServiceServer() {}
+
+// UnsafeBlobServiceServer may be embedded to opt out of forward compatibility for this service.
+// Use of this interface is not recommended, as added methods to BlobServiceServer will
+// result in compilation errors.
+type UnsafeBlobServiceServer interface {
+	mustEmbedUnimplementedBlobServiceServer()
+}
+
+func RegisterBlobServiceServer(s grpc.ServiceRegistrar, srv BlobServiceServer) {
+	s.RegisterService(&BlobService_ServiceDesc, srv)
+}
+
+func _BlobService_Stat_Handler(srv interface{}, ctx context.Context, dec func(interface{}) error, interceptor grpc.UnaryServerInterceptor) (interface{}, error) {
+	in := new(StatBlobRequest)
+	if err := dec(in); err != nil {
+		return nil, err
+	}
+	if interceptor == nil {
+		return srv.(BlobServiceServer).Stat(ctx, in)
+	}
+	info := &grpc.UnaryServerInfo{
+		Server:     srv,
+		FullMethod: BlobService_Stat_FullMethodName,
+	}
+	handler := func(ctx context.Context, req interface{}) (interface{}, error) {
+		return srv.(BlobServiceServer).Stat(ctx, req.(*StatBlobRequest))
+	}
+	return interceptor(ctx, in, info, handler)
+}
+
+func _BlobService_Read_Handler(srv interface{}, stream grpc.ServerStream) error {
+	m := new(ReadBlobRequest)
+	if err := stream.RecvMsg(m); err != nil {
+		return err
+	}
+	return srv.(BlobServiceServer).Read(m, &blobServiceReadServer{stream})
+}
+
+type BlobService_ReadServer interface {
+	Send(*BlobChunk) error
+	grpc.ServerStream
+}
+
+type blobServiceReadServer struct {
+	grpc.ServerStream
+}
+
+func (x *blobServiceReadServer) Send(m *BlobChunk) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func _BlobService_Put_Handler(srv interface{}, stream grpc.ServerStream) error {
+	return srv.(BlobServiceServer).Put(&blobServicePutServer{stream})
+}
+
+type BlobService_PutServer interface {
+	SendAndClose(*PutBlobResponse) error
+	Recv() (*BlobChunk, error)
+	grpc.ServerStream
+}
+
+type blobServicePutServer struct {
+	grpc.ServerStream
+}
+
+func (x *blobServicePutServer) SendAndClose(m *PutBlobResponse) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func (x *blobServicePutServer) Recv() (*BlobChunk, error) {
+	m := new(BlobChunk)
+	if err := x.ServerStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// BlobService_ServiceDesc is the grpc.ServiceDesc for BlobService service.
+// It's only intended for direct use with grpc.RegisterService,
+// and not to be introspected or modified (even as a copy)
+var BlobService_ServiceDesc = grpc.ServiceDesc{
+	ServiceName: "tvix.castore.v1.BlobService",
+	HandlerType: (*BlobServiceServer)(nil),
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "Stat",
+			Handler:    _BlobService_Stat_Handler,
+		},
+	},
+	Streams: []grpc.StreamDesc{
+		{
+			StreamName:    "Read",
+			Handler:       _BlobService_Read_Handler,
+			ServerStreams: true,
+		},
+		{
+			StreamName:    "Put",
+			Handler:       _BlobService_Put_Handler,
+			ClientStreams: true,
+		},
+	},
+	Metadata: "tvix/castore/protos/rpc_blobstore.proto",
+}
diff --git a/tvix/castore/protos/rpc_directory.pb.go b/tvix/castore/protos/rpc_directory.pb.go
new file mode 100644
index 000000000000..f658c6b60cc0
--- /dev/null
+++ b/tvix/castore/protos/rpc_directory.pb.go
@@ -0,0 +1,273 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+
+// Code generated by protoc-gen-go. DO NOT EDIT.
+// versions:
+// 	protoc-gen-go v1.31.0
+// 	protoc        (unknown)
+// source: tvix/castore/protos/rpc_directory.proto
+
+package castorev1
+
+import (
+	protoreflect "google.golang.org/protobuf/reflect/protoreflect"
+	protoimpl "google.golang.org/protobuf/runtime/protoimpl"
+	reflect "reflect"
+	sync "sync"
+)
+
+const (
+	// Verify that this generated code is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(20 - protoimpl.MinVersion)
+	// Verify that runtime/protoimpl is sufficiently up-to-date.
+	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
+)
+
+type GetDirectoryRequest struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Types that are assignable to ByWhat:
+	//
+	//	*GetDirectoryRequest_Digest
+	ByWhat isGetDirectoryRequest_ByWhat `protobuf_oneof:"by_what"`
+	// If set to true, recursively resolve all child Directory messages.
+	// Directory messages SHOULD be streamed in a recursive breadth-first walk,
+	// but other orders are also fine, as long as Directory messages are only
+	// sent after they are referred to from previously sent Directory messages.
+	Recursive bool `protobuf:"varint,2,opt,name=recursive,proto3" json:"recursive,omitempty"`
+}
+
+func (x *GetDirectoryRequest) Reset() {
+	*x = GetDirectoryRequest{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_directory_proto_msgTypes[0]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *GetDirectoryRequest) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*GetDirectoryRequest) ProtoMessage() {}
+
+func (x *GetDirectoryRequest) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_directory_proto_msgTypes[0]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use GetDirectoryRequest.ProtoReflect.Descriptor instead.
+func (*GetDirectoryRequest) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_directory_proto_rawDescGZIP(), []int{0}
+}
+
+func (m *GetDirectoryRequest) GetByWhat() isGetDirectoryRequest_ByWhat {
+	if m != nil {
+		return m.ByWhat
+	}
+	return nil
+}
+
+func (x *GetDirectoryRequest) GetDigest() []byte {
+	if x, ok := x.GetByWhat().(*GetDirectoryRequest_Digest); ok {
+		return x.Digest
+	}
+	return nil
+}
+
+func (x *GetDirectoryRequest) GetRecursive() bool {
+	if x != nil {
+		return x.Recursive
+	}
+	return false
+}
+
+type isGetDirectoryRequest_ByWhat interface {
+	isGetDirectoryRequest_ByWhat()
+}
+
+type GetDirectoryRequest_Digest struct {
+	// The blake3 hash of the (root) Directory message, serialized in
+	// protobuf canonical form.
+	// Keep in mind this can be a subtree of another root.
+	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3,oneof"`
+}
+
+func (*GetDirectoryRequest_Digest) isGetDirectoryRequest_ByWhat() {}
+
+type PutDirectoryResponse struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	RootDigest []byte `protobuf:"bytes,1,opt,name=root_digest,json=rootDigest,proto3" json:"root_digest,omitempty"`
+}
+
+func (x *PutDirectoryResponse) Reset() {
+	*x = PutDirectoryResponse{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_directory_proto_msgTypes[1]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *PutDirectoryResponse) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*PutDirectoryResponse) ProtoMessage() {}
+
+func (x *PutDirectoryResponse) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_directory_proto_msgTypes[1]
+	if protoimpl.UnsafeEnabled && x != nil {
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		if ms.LoadMessageInfo() == nil {
+			ms.StoreMessageInfo(mi)
+		}
+		return ms
+	}
+	return mi.MessageOf(x)
+}
+
+// Deprecated: Use PutDirectoryResponse.ProtoReflect.Descriptor instead.
+func (*PutDirectoryResponse) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_directory_proto_rawDescGZIP(), []int{1}
+}
+
+func (x *PutDirectoryResponse) GetRootDigest() []byte {
+	if x != nil {
+		return x.RootDigest
+	}
+	return nil
+}
+
+var File_tvix_castore_protos_rpc_directory_proto protoreflect.FileDescriptor
+
+var file_tvix_castore_protos_rpc_directory_proto_rawDesc = []byte{
+	0x0a, 0x27, 0x74, 0x76, 0x69, 0x78, 0x2f, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2f, 0x70,
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+	0x72, 0x65, 0x63, 0x74, 0x6f, 0x72, 0x79, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x12,
+	0x1f, 0x0a, 0x0b, 0x72, 0x6f, 0x6f, 0x74, 0x5f, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x18, 0x01,
+	0x20, 0x01, 0x28, 0x0c, 0x52, 0x0a, 0x72, 0x6f, 0x6f, 0x74, 0x44, 0x69, 0x67, 0x65, 0x73, 0x74,
+	0x32, 0xa9, 0x01, 0x0a, 0x10, 0x44, 0x69, 0x72, 0x65, 0x63, 0x74, 0x6f, 0x72, 0x79, 0x53, 0x65,
+	0x72, 0x76, 0x69, 0x63, 0x65, 0x12, 0x49, 0x0a, 0x03, 0x47, 0x65, 0x74, 0x12, 0x24, 0x2e, 0x74,
+	0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x47,
+	0x65, 0x74, 0x44, 0x69, 0x72, 0x65, 0x63, 0x74, 0x6f, 0x72, 0x79, 0x52, 0x65, 0x71, 0x75, 0x65,
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+	0x65, 0x2e, 0x76, 0x31, 0x2e, 0x44, 0x69, 0x72, 0x65, 0x63, 0x74, 0x6f, 0x72, 0x79, 0x30, 0x01,
+	0x12, 0x4a, 0x0a, 0x03, 0x50, 0x75, 0x74, 0x12, 0x1a, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63,
+	0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x44, 0x69, 0x72, 0x65, 0x63, 0x74,
+	0x6f, 0x72, 0x79, 0x1a, 0x25, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f,
+	0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x50, 0x75, 0x74, 0x44, 0x69, 0x72, 0x65, 0x63, 0x74, 0x6f,
+	0x72, 0x79, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x28, 0x01, 0x42, 0x2c, 0x5a, 0x2a,
+	0x63, 0x6f, 0x64, 0x65, 0x2e, 0x74, 0x76, 0x6c, 0x2e, 0x66, 0x79, 0x69, 0x2f, 0x74, 0x76, 0x69,
+	0x78, 0x2f, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x73,
+	0x3b, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x76, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74,
+	0x6f, 0x33,
+}
+
+var (
+	file_tvix_castore_protos_rpc_directory_proto_rawDescOnce sync.Once
+	file_tvix_castore_protos_rpc_directory_proto_rawDescData = file_tvix_castore_protos_rpc_directory_proto_rawDesc
+)
+
+func file_tvix_castore_protos_rpc_directory_proto_rawDescGZIP() []byte {
+	file_tvix_castore_protos_rpc_directory_proto_rawDescOnce.Do(func() {
+		file_tvix_castore_protos_rpc_directory_proto_rawDescData = protoimpl.X.CompressGZIP(file_tvix_castore_protos_rpc_directory_proto_rawDescData)
+	})
+	return file_tvix_castore_protos_rpc_directory_proto_rawDescData
+}
+
+var file_tvix_castore_protos_rpc_directory_proto_msgTypes = make([]protoimpl.MessageInfo, 2)
+var file_tvix_castore_protos_rpc_directory_proto_goTypes = []interface{}{
+	(*GetDirectoryRequest)(nil),  // 0: tvix.castore.v1.GetDirectoryRequest
+	(*PutDirectoryResponse)(nil), // 1: tvix.castore.v1.PutDirectoryResponse
+	(*Directory)(nil),            // 2: tvix.castore.v1.Directory
+}
+var file_tvix_castore_protos_rpc_directory_proto_depIdxs = []int32{
+	0, // 0: tvix.castore.v1.DirectoryService.Get:input_type -> tvix.castore.v1.GetDirectoryRequest
+	2, // 1: tvix.castore.v1.DirectoryService.Put:input_type -> tvix.castore.v1.Directory
+	2, // 2: tvix.castore.v1.DirectoryService.Get:output_type -> tvix.castore.v1.Directory
+	1, // 3: tvix.castore.v1.DirectoryService.Put:output_type -> tvix.castore.v1.PutDirectoryResponse
+	2, // [2:4] is the sub-list for method output_type
+	0, // [0:2] is the sub-list for method input_type
+	0, // [0:0] is the sub-list for extension type_name
+	0, // [0:0] is the sub-list for extension extendee
+	0, // [0:0] is the sub-list for field type_name
+}
+
+func init() { file_tvix_castore_protos_rpc_directory_proto_init() }
+func file_tvix_castore_protos_rpc_directory_proto_init() {
+	if File_tvix_castore_protos_rpc_directory_proto != nil {
+		return
+	}
+	file_tvix_castore_protos_castore_proto_init()
+	if !protoimpl.UnsafeEnabled {
+		file_tvix_castore_protos_rpc_directory_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*GetDirectoryRequest); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+		file_tvix_castore_protos_rpc_directory_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*PutDirectoryResponse); i {
+			case 0:
+				return &v.state
+			case 1:
+				return &v.sizeCache
+			case 2:
+				return &v.unknownFields
+			default:
+				return nil
+			}
+		}
+	}
+	file_tvix_castore_protos_rpc_directory_proto_msgTypes[0].OneofWrappers = []interface{}{
+		(*GetDirectoryRequest_Digest)(nil),
+	}
+	type x struct{}
+	out := protoimpl.TypeBuilder{
+		File: protoimpl.DescBuilder{
+			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
+			RawDescriptor: file_tvix_castore_protos_rpc_directory_proto_rawDesc,
+			NumEnums:      0,
+			NumMessages:   2,
+			NumExtensions: 0,
+			NumServices:   1,
+		},
+		GoTypes:           file_tvix_castore_protos_rpc_directory_proto_goTypes,
+		DependencyIndexes: file_tvix_castore_protos_rpc_directory_proto_depIdxs,
+		MessageInfos:      file_tvix_castore_protos_rpc_directory_proto_msgTypes,
+	}.Build()
+	File_tvix_castore_protos_rpc_directory_proto = out.File
+	file_tvix_castore_protos_rpc_directory_proto_rawDesc = nil
+	file_tvix_castore_protos_rpc_directory_proto_goTypes = nil
+	file_tvix_castore_protos_rpc_directory_proto_depIdxs = nil
+}
diff --git a/tvix/castore/protos/rpc_directory.proto b/tvix/castore/protos/rpc_directory.proto
new file mode 100644
index 000000000000..8d4c22828547
--- /dev/null
+++ b/tvix/castore/protos/rpc_directory.proto
@@ -0,0 +1,48 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+syntax = "proto3";
+
+package tvix.castore.v1;
+
+import "tvix/castore/protos/castore.proto";
+
+option go_package = "code.tvl.fyi/tvix/castore/protos;castorev1";
+
+service DirectoryService {
+  // Get retrieves a stream of Directory messages, by using the lookup
+  // parameters in GetDirectoryRequest.
+  // Keep in mind multiple DirectoryNodes in different parts of the graph might
+  // have the same digest if they have the same underlying contents,
+  // so sending subsequent ones can be omitted.
+  rpc Get(GetDirectoryRequest) returns (stream Directory);
+
+  // Put uploads a graph of Directory messages.
+  // Individual Directory messages need to be send in an order walking up
+  // from the leaves to the root - a Directory message can only refer to
+  // Directory messages previously sent in the same stream.
+  // Keep in mind multiple DirectoryNodes in different parts of the graph might
+  // have the same digest if they have the same underlying contents,
+  // so sending subsequent ones can be omitted.
+  // We might add a separate method, allowing to send partial graphs at a later
+  // time, if requiring to send the full graph turns out to be a problem.
+  rpc Put(stream Directory) returns (PutDirectoryResponse);
+}
+
+message GetDirectoryRequest {
+  oneof by_what {
+      // The blake3 hash of the (root) Directory message, serialized in
+      // protobuf canonical form.
+      // Keep in mind this can be a subtree of another root.
+      bytes digest = 1;
+  }
+
+  // If set to true, recursively resolve all child Directory messages.
+  // Directory messages SHOULD be streamed in a recursive breadth-first walk,
+  // but other orders are also fine, as long as Directory messages are only
+  // sent after they are referred to from previously sent Directory messages.
+  bool recursive = 2;
+}
+
+message PutDirectoryResponse {
+  bytes root_digest = 1;
+}
diff --git a/tvix/castore/protos/rpc_directory_grpc.pb.go b/tvix/castore/protos/rpc_directory_grpc.pb.go
new file mode 100644
index 000000000000..f19e457d867b
--- /dev/null
+++ b/tvix/castore/protos/rpc_directory_grpc.pb.go
@@ -0,0 +1,238 @@
+// SPDX-License-Identifier: MIT
+// Copyright © 2022 The Tvix Authors
+
+// Code generated by protoc-gen-go-grpc. DO NOT EDIT.
+// versions:
+// - protoc-gen-go-grpc v1.3.0
+// - protoc             (unknown)
+// source: tvix/castore/protos/rpc_directory.proto
+
+package castorev1
+
+import (
+	context "context"
+	grpc "google.golang.org/grpc"
+	codes "google.golang.org/grpc/codes"
+	status "google.golang.org/grpc/status"
+)
+
+// This is a compile-time assertion to ensure that this generated file
+// is compatible with the grpc package it is being compiled against.
+// Requires gRPC-Go v1.32.0 or later.
+const _ = grpc.SupportPackageIsVersion7
+
+const (
+	DirectoryService_Get_FullMethodName = "/tvix.castore.v1.DirectoryService/Get"
+	DirectoryService_Put_FullMethodName = "/tvix.castore.v1.DirectoryService/Put"
+)
+
+// DirectoryServiceClient is the client API for DirectoryService service.
+//
+// For semantics around ctx use and closing/ending streaming RPCs, please refer to https://pkg.go.dev/google.golang.org/grpc/?tab=doc#ClientConn.NewStream.
+type DirectoryServiceClient interface {
+	// Get retrieves a stream of Directory messages, by using the lookup
+	// parameters in GetDirectoryRequest.
+	// Keep in mind multiple DirectoryNodes in different parts of the graph might
+	// have the same digest if they have the same underlying contents,
+	// so sending subsequent ones can be omitted.
+	Get(ctx context.Context, in *GetDirectoryRequest, opts ...grpc.CallOption) (DirectoryService_GetClient, error)
+	// Put uploads a graph of Directory messages.
+	// Individual Directory messages need to be send in an order walking up
+	// from the leaves to the root - a Directory message can only refer to
+	// Directory messages previously sent in the same stream.
+	// Keep in mind multiple DirectoryNodes in different parts of the graph might
+	// have the same digest if they have the same underlying contents,
+	// so sending subsequent ones can be omitted.
+	// We might add a separate method, allowing to send partial graphs at a later
+	// time, if requiring to send the full graph turns out to be a problem.
+	Put(ctx context.Context, opts ...grpc.CallOption) (DirectoryService_PutClient, error)
+}
+
+type directoryServiceClient struct {
+	cc grpc.ClientConnInterface
+}
+
+func NewDirectoryServiceClient(cc grpc.ClientConnInterface) DirectoryServiceClient {
+	return &directoryServiceClient{cc}
+}
+
+func (c *directoryServiceClient) Get(ctx context.Context, in *GetDirectoryRequest, opts ...grpc.CallOption) (DirectoryService_GetClient, error) {
+	stream, err := c.cc.NewStream(ctx, &DirectoryService_ServiceDesc.Streams[0], DirectoryService_Get_FullMethodName, opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &directoryServiceGetClient{stream}
+	if err := x.ClientStream.SendMsg(in); err != nil {
+		return nil, err
+	}
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	return x, nil
+}
+
+type DirectoryService_GetClient interface {
+	Recv() (*Directory, error)
+	grpc.ClientStream
+}
+
+type directoryServiceGetClient struct {
+	grpc.ClientStream
+}
+
+func (x *directoryServiceGetClient) Recv() (*Directory, error) {
+	m := new(Directory)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+func (c *directoryServiceClient) Put(ctx context.Context, opts ...grpc.CallOption) (DirectoryService_PutClient, error) {
+	stream, err := c.cc.NewStream(ctx, &DirectoryService_ServiceDesc.Streams[1], DirectoryService_Put_FullMethodName, opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &directoryServicePutClient{stream}
+	return x, nil
+}
+
+type DirectoryService_PutClient interface {
+	Send(*Directory) error
+	CloseAndRecv() (*PutDirectoryResponse, error)
+	grpc.ClientStream
+}
+
+type directoryServicePutClient struct {
+	grpc.ClientStream
+}
+
+func (x *directoryServicePutClient) Send(m *Directory) error {
+	return x.ClientStream.SendMsg(m)
+}
+
+func (x *directoryServicePutClient) CloseAndRecv() (*PutDirectoryResponse, error) {
+	if err := x.ClientStream.CloseSend(); err != nil {
+		return nil, err
+	}
+	m := new(PutDirectoryResponse)
+	if err := x.ClientStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// DirectoryServiceServer is the server API for DirectoryService service.
+// All implementations must embed UnimplementedDirectoryServiceServer
+// for forward compatibility
+type DirectoryServiceServer interface {
+	// Get retrieves a stream of Directory messages, by using the lookup
+	// parameters in GetDirectoryRequest.
+	// Keep in mind multiple DirectoryNodes in different parts of the graph might
+	// have the same digest if they have the same underlying contents,
+	// so sending subsequent ones can be omitted.
+	Get(*GetDirectoryRequest, DirectoryService_GetServer) error
+	// Put uploads a graph of Directory messages.
+	// Individual Directory messages need to be send in an order walking up
+	// from the leaves to the root - a Directory message can only refer to
+	// Directory messages previously sent in the same stream.
+	// Keep in mind multiple DirectoryNodes in different parts of the graph might
+	// have the same digest if they have the same underlying contents,
+	// so sending subsequent ones can be omitted.
+	// We might add a separate method, allowing to send partial graphs at a later
+	// time, if requiring to send the full graph turns out to be a problem.
+	Put(DirectoryService_PutServer) error
+	mustEmbedUnimplementedDirectoryServiceServer()
+}
+
+// UnimplementedDirectoryServiceServer must be embedded to have forward compatible implementations.
+type UnimplementedDirectoryServiceServer struct {
+}
+
+func (UnimplementedDirectoryServiceServer) Get(*GetDirectoryRequest, DirectoryService_GetServer) error {
+	return status.Errorf(codes.Unimplemented, "method Get not implemented")
+}
+func (UnimplementedDirectoryServiceServer) Put(DirectoryService_PutServer) error {
+	return status.Errorf(codes.Unimplemented, "method Put not implemented")
+}
+func (UnimplementedDirectoryServiceServer) mustEmbedUnimplementedDirectoryServiceServer() {}
+
+// UnsafeDirectoryServiceServer may be embedded to opt out of forward compatibility for this service.
+// Use of this interface is not recommended, as added methods to DirectoryServiceServer will
+// result in compilation errors.
+type UnsafeDirectoryServiceServer interface {
+	mustEmbedUnimplementedDirectoryServiceServer()
+}
+
+func RegisterDirectoryServiceServer(s grpc.ServiceRegistrar, srv DirectoryServiceServer) {
+	s.RegisterService(&DirectoryService_ServiceDesc, srv)
+}
+
+func _DirectoryService_Get_Handler(srv interface{}, stream grpc.ServerStream) error {
+	m := new(GetDirectoryRequest)
+	if err := stream.RecvMsg(m); err != nil {
+		return err
+	}
+	return srv.(DirectoryServiceServer).Get(m, &directoryServiceGetServer{stream})
+}
+
+type DirectoryService_GetServer interface {
+	Send(*Directory) error
+	grpc.ServerStream
+}
+
+type directoryServiceGetServer struct {
+	grpc.ServerStream
+}
+
+func (x *directoryServiceGetServer) Send(m *Directory) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func _DirectoryService_Put_Handler(srv interface{}, stream grpc.ServerStream) error {
+	return srv.(DirectoryServiceServer).Put(&directoryServicePutServer{stream})
+}
+
+type DirectoryService_PutServer interface {
+	SendAndClose(*PutDirectoryResponse) error
+	Recv() (*Directory, error)
+	grpc.ServerStream
+}
+
+type directoryServicePutServer struct {
+	grpc.ServerStream
+}
+
+func (x *directoryServicePutServer) SendAndClose(m *PutDirectoryResponse) error {
+	return x.ServerStream.SendMsg(m)
+}
+
+func (x *directoryServicePutServer) Recv() (*Directory, error) {
+	m := new(Directory)
+	if err := x.ServerStream.RecvMsg(m); err != nil {
+		return nil, err
+	}
+	return m, nil
+}
+
+// DirectoryService_ServiceDesc is the grpc.ServiceDesc for DirectoryService service.
+// It's only intended for direct use with grpc.RegisterService,
+// and not to be introspected or modified (even as a copy)
+var DirectoryService_ServiceDesc = grpc.ServiceDesc{
+	ServiceName: "tvix.castore.v1.DirectoryService",
+	HandlerType: (*DirectoryServiceServer)(nil),
+	Methods:     []grpc.MethodDesc{},
+	Streams: []grpc.StreamDesc{
+		{
+			StreamName:    "Get",
+			Handler:       _DirectoryService_Get_Handler,
+			ServerStreams: true,
+		},
+		{
+			StreamName:    "Put",
+			Handler:       _DirectoryService_Put_Handler,
+			ClientStreams: true,
+		},
+	},
+	Metadata: "tvix/castore/protos/rpc_directory.proto",
+}