feat(tvix/castore): extend blobstore protos for verified streaming r/6954

This pdates the proto docstrings a bit, especially w.r.t. verified
streaming.
It also adds send_chunks, send_bao fields to StatBlobRequest (renamed
from BlobMeta)

Change-Id: I590cc8646d86b73bca9f38a9b6d9ea15e4df5cb6
Reviewed-on: https://cl.tvl.fyi/c/depot/+/9951
Tested-by: BuildkiteCI
Reviewed-by: raitobezarius <tvl@lahfa.xyz>

5 files changed, 264 insertions, 91 deletions

diff --git a/tvix/castore-go/rpc_blobstore.pb.go b/tvix/castore-go/rpc_blobstore.pb.go
index 6dbf648a4c10..73bcb91ba931 100644
--- a/tvix/castore-go/rpc_blobstore.pb.go
+++ b/tvix/castore-go/rpc_blobstore.pb.go
@@ -30,6 +30,10 @@ type StatBlobRequest struct {
 
 	// The blake3 digest of the blob requested
 	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3" json:"digest,omitempty"`
+	// Whether the server should reply with a list of more granular chunks.
+	SendChunks bool `protobuf:"varint,2,opt,name=send_chunks,json=sendChunks,proto3" json:"send_chunks,omitempty"`
+	// Whether the server should reply with a bao.
+	SendBao bool `protobuf:"varint,3,opt,name=send_bao,json=sendBao,proto3" json:"send_bao,omitempty"`
 }
 
 func (x *StatBlobRequest) Reset() {
@@ -71,14 +75,36 @@ func (x *StatBlobRequest) GetDigest() []byte {
 	return nil
 }
 
-type BlobMeta struct {
+func (x *StatBlobRequest) GetSendChunks() bool {
+	if x != nil {
+		return x.SendChunks
+	}
+	return false
+}
+
+func (x *StatBlobRequest) GetSendBao() bool {
+	if x != nil {
+		return x.SendBao
+	}
+	return false
+}
+
+type StatBlobResponse struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
 	unknownFields protoimpl.UnknownFields
+
+	// If `send_chunks` was set to true, this MAY contain a list of more
+	// granular chunks, which then may be read individually via the `Read`
+	// method.
+	Chunks []*StatBlobResponse_ChunkMeta `protobuf:"bytes,2,rep,name=chunks,proto3" json:"chunks,omitempty"`
+	// If `send_bao` was set to true, this MAY contain a outboard bao.
+	// The exact format and message types here will still be fleshed out.
+	Bao []byte `protobuf:"bytes,3,opt,name=bao,proto3" json:"bao,omitempty"`
 }
 
-func (x *BlobMeta) Reset() {
-	*x = BlobMeta{}
+func (x *StatBlobResponse) Reset() {
+	*x = StatBlobResponse{}
 	if protoimpl.UnsafeEnabled {
 		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[1]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -86,13 +112,13 @@ func (x *BlobMeta) Reset() {
 	}
 }
 
-func (x *BlobMeta) String() string {
+func (x *StatBlobResponse) String() string {
 	return protoimpl.X.MessageStringOf(x)
 }
 
-func (*BlobMeta) ProtoMessage() {}
+func (*StatBlobResponse) ProtoMessage() {}
 
-func (x *BlobMeta) ProtoReflect() protoreflect.Message {
+func (x *StatBlobResponse) 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))
@@ -104,11 +130,25 @@ func (x *BlobMeta) ProtoReflect() protoreflect.Message {
 	return mi.MessageOf(x)
 }
 
-// Deprecated: Use BlobMeta.ProtoReflect.Descriptor instead.
-func (*BlobMeta) Descriptor() ([]byte, []int) {
+// Deprecated: Use StatBlobResponse.ProtoReflect.Descriptor instead.
+func (*StatBlobResponse) Descriptor() ([]byte, []int) {
 	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{1}
 }
 
+func (x *StatBlobResponse) GetChunks() []*StatBlobResponse_ChunkMeta {
+	if x != nil {
+		return x.Chunks
+	}
+	return nil
+}
+
+func (x *StatBlobResponse) GetBao() []byte {
+	if x != nil {
+		return x.Bao
+	}
+	return nil
+}
+
 type ReadBlobRequest struct {
 	state         protoimpl.MessageState
 	sizeCache     protoimpl.SizeCache
@@ -254,41 +294,112 @@ func (x *PutBlobResponse) GetDigest() []byte {
 	return nil
 }
 
+type StatBlobResponse_ChunkMeta struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	// Digest of that specific chunk
+	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3" json:"digest,omitempty"`
+	// Length of that chunk, in bytes.
+	Size uint64 `protobuf:"varint,2,opt,name=size,proto3" json:"size,omitempty"`
+}
+
+func (x *StatBlobResponse_ChunkMeta) Reset() {
+	*x = StatBlobResponse_ChunkMeta{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[5]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *StatBlobResponse_ChunkMeta) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*StatBlobResponse_ChunkMeta) ProtoMessage() {}
+
+func (x *StatBlobResponse_ChunkMeta) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[5]
+	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 StatBlobResponse_ChunkMeta.ProtoReflect.Descriptor instead.
+func (*StatBlobResponse_ChunkMeta) Descriptor() ([]byte, []int) {
+	return file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP(), []int{1, 0}
+}
+
+func (x *StatBlobResponse_ChunkMeta) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+func (x *StatBlobResponse_ChunkMeta) GetSize() uint64 {
+	if x != nil {
+		return x.Size
+	}
+	return 0
+}
+
 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,
 	0x72, 0x6f, 0x74, 0x6f, 0x73, 0x2f, 0x72, 0x70, 0x63, 0x5f, 0x62, 0x6c, 0x6f, 0x62, 0x73, 0x74,
 	0x6f, 0x72, 0x65, 0x2e, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x12, 0x0f, 0x74, 0x76, 0x69, 0x78, 0x2e,
-	0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x22, 0x29, 0x0a, 0x0f, 0x53, 0x74,
+	0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x22, 0x65, 0x0a, 0x0f, 0x53, 0x74,
 	0x61, 0x74, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x16, 0x0a,
 	0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x18, 0x01, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x06, 0x64,
-	0x69, 0x67, 0x65, 0x73, 0x74, 0x22, 0x0a, 0x0a, 0x08, 0x42, 0x6c, 0x6f, 0x62, 0x4d, 0x65, 0x74,
-	0x61, 0x22, 0x29, 0x0a, 0x0f, 0x52, 0x65, 0x61, 0x64, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65, 0x71,
-	0x75, 0x65, 0x73, 0x74, 0x12, 0x16, 0x0a, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x18, 0x01,
-	0x20, 0x01, 0x28, 0x0c, 0x52, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x22, 0x1f, 0x0a, 0x09,
-	0x42, 0x6c, 0x6f, 0x62, 0x43, 0x68, 0x75, 0x6e, 0x6b, 0x12, 0x12, 0x0a, 0x04, 0x64, 0x61, 0x74,
-	0x61, 0x18, 0x01, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x04, 0x64, 0x61, 0x74, 0x61, 0x22, 0x29, 0x0a,
-	0x0f, 0x50, 0x75, 0x74, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65,
-	0x12, 0x16, 0x0a, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x18, 0x01, 0x20, 0x01, 0x28, 0x0c,
-	0x52, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x32, 0xe1, 0x01, 0x0a, 0x0b, 0x42, 0x6c, 0x6f,
-	0x62, 0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x12, 0x43, 0x0a, 0x04, 0x53, 0x74, 0x61, 0x74,
-	0x12, 0x20, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e,
-	0x76, 0x31, 0x2e, 0x53, 0x74, 0x61, 0x74, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65, 0x71, 0x75, 0x65,
-	0x73, 0x74, 0x1a, 0x19, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72,
-	0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f, 0x62, 0x4d, 0x65, 0x74, 0x61, 0x12, 0x46, 0x0a,
-	0x04, 0x52, 0x65, 0x61, 0x64, 0x12, 0x20, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73,
-	0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x52, 0x65, 0x61, 0x64, 0x42, 0x6c, 0x6f, 0x62,
-	0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x1a, 0x1a, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63,
-	0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f, 0x62, 0x43, 0x68,
-	0x75, 0x6e, 0x6b, 0x30, 0x01, 0x12, 0x45, 0x0a, 0x03, 0x50, 0x75, 0x74, 0x12, 0x1a, 0x2e, 0x74,
-	0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42,
-	0x6c, 0x6f, 0x62, 0x43, 0x68, 0x75, 0x6e, 0x6b, 0x1a, 0x20, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e,
-	0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x50, 0x75, 0x74, 0x42, 0x6c,
-	0x6f, 0x62, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x28, 0x01, 0x42, 0x28, 0x5a, 0x26,
-	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, 0x2d, 0x67, 0x6f, 0x3b, 0x63, 0x61, 0x73,
-	0x74, 0x6f, 0x72, 0x65, 0x76, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
+	0x69, 0x67, 0x65, 0x73, 0x74, 0x12, 0x1f, 0x0a, 0x0b, 0x73, 0x65, 0x6e, 0x64, 0x5f, 0x63, 0x68,
+	0x75, 0x6e, 0x6b, 0x73, 0x18, 0x02, 0x20, 0x01, 0x28, 0x08, 0x52, 0x0a, 0x73, 0x65, 0x6e, 0x64,
+	0x43, 0x68, 0x75, 0x6e, 0x6b, 0x73, 0x12, 0x19, 0x0a, 0x08, 0x73, 0x65, 0x6e, 0x64, 0x5f, 0x62,
+	0x61, 0x6f, 0x18, 0x03, 0x20, 0x01, 0x28, 0x08, 0x52, 0x07, 0x73, 0x65, 0x6e, 0x64, 0x42, 0x61,
+	0x6f, 0x22, 0xa2, 0x01, 0x0a, 0x10, 0x53, 0x74, 0x61, 0x74, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65,
+	0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x12, 0x43, 0x0a, 0x06, 0x63, 0x68, 0x75, 0x6e, 0x6b, 0x73,
+	0x18, 0x02, 0x20, 0x03, 0x28, 0x0b, 0x32, 0x2b, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61,
+	0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x53, 0x74, 0x61, 0x74, 0x42, 0x6c, 0x6f,
+	0x62, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x2e, 0x43, 0x68, 0x75, 0x6e, 0x6b, 0x4d,
+	0x65, 0x74, 0x61, 0x52, 0x06, 0x63, 0x68, 0x75, 0x6e, 0x6b, 0x73, 0x12, 0x10, 0x0a, 0x03, 0x62,
+	0x61, 0x6f, 0x18, 0x03, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x03, 0x62, 0x61, 0x6f, 0x1a, 0x37, 0x0a,
+	0x09, 0x43, 0x68, 0x75, 0x6e, 0x6b, 0x4d, 0x65, 0x74, 0x61, 0x12, 0x16, 0x0a, 0x06, 0x64, 0x69,
+	0x67, 0x65, 0x73, 0x74, 0x18, 0x01, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x06, 0x64, 0x69, 0x67, 0x65,
+	0x73, 0x74, 0x12, 0x12, 0x0a, 0x04, 0x73, 0x69, 0x7a, 0x65, 0x18, 0x02, 0x20, 0x01, 0x28, 0x04,
+	0x52, 0x04, 0x73, 0x69, 0x7a, 0x65, 0x22, 0x29, 0x0a, 0x0f, 0x52, 0x65, 0x61, 0x64, 0x42, 0x6c,
+	0x6f, 0x62, 0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x12, 0x16, 0x0a, 0x06, 0x64, 0x69, 0x67,
+	0x65, 0x73, 0x74, 0x18, 0x01, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73,
+	0x74, 0x22, 0x1f, 0x0a, 0x09, 0x42, 0x6c, 0x6f, 0x62, 0x43, 0x68, 0x75, 0x6e, 0x6b, 0x12, 0x12,
+	0x0a, 0x04, 0x64, 0x61, 0x74, 0x61, 0x18, 0x01, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x04, 0x64, 0x61,
+	0x74, 0x61, 0x22, 0x29, 0x0a, 0x0f, 0x50, 0x75, 0x74, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65, 0x73,
+	0x70, 0x6f, 0x6e, 0x73, 0x65, 0x12, 0x16, 0x0a, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x18,
+	0x01, 0x20, 0x01, 0x28, 0x0c, 0x52, 0x06, 0x64, 0x69, 0x67, 0x65, 0x73, 0x74, 0x32, 0xe9, 0x01,
+	0x0a, 0x0b, 0x42, 0x6c, 0x6f, 0x62, 0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65, 0x12, 0x4b, 0x0a,
+	0x04, 0x53, 0x74, 0x61, 0x74, 0x12, 0x20, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73,
+	0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x53, 0x74, 0x61, 0x74, 0x42, 0x6c, 0x6f, 0x62,
+	0x52, 0x65, 0x71, 0x75, 0x65, 0x73, 0x74, 0x1a, 0x21, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63,
+	0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x53, 0x74, 0x61, 0x74, 0x42, 0x6c,
+	0x6f, 0x62, 0x52, 0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x12, 0x46, 0x0a, 0x04, 0x52, 0x65,
+	0x61, 0x64, 0x12, 0x20, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72,
+	0x65, 0x2e, 0x76, 0x31, 0x2e, 0x52, 0x65, 0x61, 0x64, 0x42, 0x6c, 0x6f, 0x62, 0x52, 0x65, 0x71,
+	0x75, 0x65, 0x73, 0x74, 0x1a, 0x1a, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73, 0x74,
+	0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f, 0x62, 0x43, 0x68, 0x75, 0x6e, 0x6b,
+	0x30, 0x01, 0x12, 0x45, 0x0a, 0x03, 0x50, 0x75, 0x74, 0x12, 0x1a, 0x2e, 0x74, 0x76, 0x69, 0x78,
+	0x2e, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f, 0x62,
+	0x43, 0x68, 0x75, 0x6e, 0x6b, 0x1a, 0x20, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 0x63, 0x61, 0x73,
+	0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x50, 0x75, 0x74, 0x42, 0x6c, 0x6f, 0x62, 0x52,
+	0x65, 0x73, 0x70, 0x6f, 0x6e, 0x73, 0x65, 0x28, 0x01, 0x42, 0x28, 0x5a, 0x26, 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, 0x2d, 0x67, 0x6f, 0x3b, 0x63, 0x61, 0x73, 0x74, 0x6f, 0x72,
+	0x65, 0x76, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -303,26 +414,28 @@ func file_tvix_castore_protos_rpc_blobstore_proto_rawDescGZIP() []byte {
 	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_msgTypes = make([]protoimpl.MessageInfo, 6)
 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
+	(*StatBlobRequest)(nil),            // 0: tvix.castore.v1.StatBlobRequest
+	(*StatBlobResponse)(nil),           // 1: tvix.castore.v1.StatBlobResponse
+	(*ReadBlobRequest)(nil),            // 2: tvix.castore.v1.ReadBlobRequest
+	(*BlobChunk)(nil),                  // 3: tvix.castore.v1.BlobChunk
+	(*PutBlobResponse)(nil),            // 4: tvix.castore.v1.PutBlobResponse
+	(*StatBlobResponse_ChunkMeta)(nil), // 5: tvix.castore.v1.StatBlobResponse.ChunkMeta
 }
 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
+	5, // 0: tvix.castore.v1.StatBlobResponse.chunks:type_name -> tvix.castore.v1.StatBlobResponse.ChunkMeta
+	0, // 1: tvix.castore.v1.BlobService.Stat:input_type -> tvix.castore.v1.StatBlobRequest
+	2, // 2: tvix.castore.v1.BlobService.Read:input_type -> tvix.castore.v1.ReadBlobRequest
+	3, // 3: tvix.castore.v1.BlobService.Put:input_type -> tvix.castore.v1.BlobChunk
+	1, // 4: tvix.castore.v1.BlobService.Stat:output_type -> tvix.castore.v1.StatBlobResponse
+	3, // 5: tvix.castore.v1.BlobService.Read:output_type -> tvix.castore.v1.BlobChunk
+	4, // 6: tvix.castore.v1.BlobService.Put:output_type -> tvix.castore.v1.PutBlobResponse
+	4, // [4:7] is the sub-list for method output_type
+	1, // [1:4] is the sub-list for method input_type
+	1, // [1:1] is the sub-list for extension type_name
+	1, // [1:1] is the sub-list for extension extendee
+	0, // [0:1] is the sub-list for field type_name
 }
 
 func init() { file_tvix_castore_protos_rpc_blobstore_proto_init() }
@@ -344,7 +457,7 @@ func file_tvix_castore_protos_rpc_blobstore_proto_init() {
 			}
 		}
 		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*BlobMeta); i {
+			switch v := v.(*StatBlobResponse); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -391,6 +504,18 @@ func file_tvix_castore_protos_rpc_blobstore_proto_init() {
 				return nil
 			}
 		}
+		file_tvix_castore_protos_rpc_blobstore_proto_msgTypes[5].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*StatBlobResponse_ChunkMeta); 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{
@@ -398,7 +523,7 @@ func file_tvix_castore_protos_rpc_blobstore_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_tvix_castore_protos_rpc_blobstore_proto_rawDesc,
 			NumEnums:      0,
-			NumMessages:   5,
+			NumMessages:   6,
 			NumExtensions: 0,
 			NumServices:   1,
 		},
diff --git a/tvix/castore-go/rpc_blobstore_grpc.pb.go b/tvix/castore-go/rpc_blobstore_grpc.pb.go
index 0876bcc4e95a..e10795bfaf54 100644
--- a/tvix/castore-go/rpc_blobstore_grpc.pb.go
+++ b/tvix/castore-go/rpc_blobstore_grpc.pb.go
@@ -31,21 +31,28 @@ const (
 //
 // 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.
-	//
+	// Stat can be used to check for the existence of a blob, as well as
+	// gathering more data about it, like more granular chunking information
+	// or baos.
+	// Server implementations are not required to provide more granular chunking
+	// information, especially if the digest specified in [StatBlobRequest] is
+	// already a chunk of a blob.
+	Stat(ctx context.Context, in *StatBlobRequest, opts ...grpc.CallOption) (*StatBlobResponse, error)
+	// Read allows reading (all) data of a blob/chunk by the BLAKE3 digest of
+	// its contents.
+	// If the backend communicated more granular chunks in the `Stat` request,
+	// this can also be used to read chunks.
+	// This request returns a stream of BlobChunk, which is just a container for
+	// a stream of bytes.
 	// The server may decide on whatever chunking it may seem fit as a size for
-	// the individual BlobChunk sent in the response stream.
+	// the individual BlobChunk sent in the response stream, this is mostly to
+	// keep individual messages at a manageable size.
 	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.
+	// the stream has no effect on how the server ends up chunking blobs up, if
+	// it does at all.
 	Put(ctx context.Context, opts ...grpc.CallOption) (BlobService_PutClient, error)
 }
 
@@ -57,8 +64,8 @@ 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)
+func (c *blobServiceClient) Stat(ctx context.Context, in *StatBlobRequest, opts ...grpc.CallOption) (*StatBlobResponse, error) {
+	out := new(StatBlobResponse)
 	err := c.cc.Invoke(ctx, BlobService_Stat_FullMethodName, in, out, opts...)
 	if err != nil {
 		return nil, err
@@ -136,21 +143,28 @@ func (x *blobServicePutClient) CloseAndRecv() (*PutBlobResponse, error) {
 // 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.
-	//
+	// Stat can be used to check for the existence of a blob, as well as
+	// gathering more data about it, like more granular chunking information
+	// or baos.
+	// Server implementations are not required to provide more granular chunking
+	// information, especially if the digest specified in [StatBlobRequest] is
+	// already a chunk of a blob.
+	Stat(context.Context, *StatBlobRequest) (*StatBlobResponse, error)
+	// Read allows reading (all) data of a blob/chunk by the BLAKE3 digest of
+	// its contents.
+	// If the backend communicated more granular chunks in the `Stat` request,
+	// this can also be used to read chunks.
+	// This request returns a stream of BlobChunk, which is just a container for
+	// a stream of bytes.
 	// The server may decide on whatever chunking it may seem fit as a size for
-	// the individual BlobChunk sent in the response stream.
+	// the individual BlobChunk sent in the response stream, this is mostly to
+	// keep individual messages at a manageable size.
 	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.
+	// the stream has no effect on how the server ends up chunking blobs up, if
+	// it does at all.
 	Put(BlobService_PutServer) error
 	mustEmbedUnimplementedBlobServiceServer()
 }
@@ -159,7 +173,7 @@ type BlobServiceServer interface {
 type UnimplementedBlobServiceServer struct {
 }
 
-func (UnimplementedBlobServiceServer) Stat(context.Context, *StatBlobRequest) (*BlobMeta, error) {
+func (UnimplementedBlobServiceServer) Stat(context.Context, *StatBlobRequest) (*StatBlobResponse, error) {
 	return nil, status.Errorf(codes.Unimplemented, "method Stat not implemented")
 }
 func (UnimplementedBlobServiceServer) Read(*ReadBlobRequest, BlobService_ReadServer) error {
diff --git a/tvix/castore/protos/rpc_blobstore.proto b/tvix/castore/protos/rpc_blobstore.proto
index 458803fd57cc..93c02d397c44 100644
--- a/tvix/castore/protos/rpc_blobstore.proto
+++ b/tvix/castore/protos/rpc_blobstore.proto
@@ -6,33 +6,66 @@ package tvix.castore.v1;
 
 option go_package = "code.tvl.fyi/tvix/castore-go;castorev1";
 
+// BlobService allows reading (or uploading) content-addressed blobs of data.
+// BLAKE3 is used as a hashing function for the data. Uploading a blob will
+// return the BLAKE3 digest of it, and that's the identifier used to Read/Stat
+// them too.
 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.
-    //
+    // Stat can be used to check for the existence of a blob, as well as
+    // gathering more data about it, like more granular chunking information
+    // or baos.
+    // Server implementations are not required to provide more granular chunking
+    // information, especially if the digest specified in [StatBlobRequest] is
+    // already a chunk of a blob.
+    rpc Stat(StatBlobRequest) returns (StatBlobResponse);
+
+    // Read allows reading (all) data of a blob/chunk by the BLAKE3 digest of
+    // its contents.
+    // If the backend communicated more granular chunks in the `Stat` request,
+    // this can also be used to read chunks.
+    // This request returns a stream of BlobChunk, which is just a container for
+    // a stream of bytes.
     // The server may decide on whatever chunking it may seem fit as a size for
-    // the individual BlobChunk sent in the response stream.
+    // the individual BlobChunk sent in the response stream, this is mostly to
+    // keep individual messages at a manageable size.
     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.
+    // the stream has no effect on how the server ends up chunking blobs up, if
+    // it does at all.
     rpc Put(stream BlobChunk) returns (PutBlobResponse);
 }
 
 message StatBlobRequest {
     // The blake3 digest of the blob requested
     bytes digest = 1;
+
+    // Whether the server should reply with a list of more granular chunks.
+    bool send_chunks = 2;
+
+    // Whether the server should reply with a bao.
+    bool send_bao = 3;
 }
 
-message BlobMeta {
+message StatBlobResponse {
+    // If `send_chunks` was set to true, this MAY contain a list of more
+    // granular chunks, which then may be read individually via the `Read`
+    // method.
+    repeated ChunkMeta chunks = 2;
+
+    message ChunkMeta {
+        // Digest of that specific chunk
+        bytes digest = 1;
+
+        // Length of that chunk, in bytes.
+        uint64 size = 2;
+    }
+
+    // If `send_bao` was set to true, this MAY contain a outboard bao.
+    // The exact format and message types here will still be fleshed out.
+    bytes bao = 3;
 }
 
 message ReadBlobRequest {
diff --git a/tvix/castore/src/blobservice/grpc.rs b/tvix/castore/src/blobservice/grpc.rs
index d0f619fcebcb..8d3bdfa8fa25 100644
--- a/tvix/castore/src/blobservice/grpc.rs
+++ b/tvix/castore/src/blobservice/grpc.rs
@@ -56,6 +56,7 @@ impl BlobService for GRPCBlobService {
         let resp = grpc_client
             .stat(proto::StatBlobRequest {
                 digest: digest.clone().into(),
+                ..Default::default()
             })
             .await;
 
diff --git a/tvix/castore/src/proto/grpc_blobservice_wrapper.rs b/tvix/castore/src/proto/grpc_blobservice_wrapper.rs
index 93db1deef69a..e7092bec1481 100644
--- a/tvix/castore/src/proto/grpc_blobservice_wrapper.rs
+++ b/tvix/castore/src/proto/grpc_blobservice_wrapper.rs
@@ -93,7 +93,7 @@ impl super::blob_service_server::BlobService for GRPCBlobServiceWrapper {
     async fn stat(
         &self,
         request: Request<super::StatBlobRequest>,
-    ) -> Result<Response<super::BlobMeta>, Status> {
+    ) -> Result<Response<super::StatBlobResponse>, Status> {
         let rq = request.into_inner();
         let req_digest = rq
             .digest
@@ -101,7 +101,7 @@ impl super::blob_service_server::BlobService for GRPCBlobServiceWrapper {
             .map_err(|_e| Status::invalid_argument("invalid digest length"))?;
 
         match self.blob_service.has(&req_digest).await {
-            Ok(true) => Ok(Response::new(super::BlobMeta::default())),
+            Ok(true) => Ok(Response::new(super::StatBlobResponse::default())),
             Ok(false) => Err(Status::not_found(format!("blob {} not found", &req_digest))),
             Err(e) => Err(e.into()),
         }