feat(tvix/store/protos): rename Get to Read, add Stat method r/5528

Stat exposes metadata about a given blob,
such as more granular chunking, baos.
It implicitly allows checking for existence too, as asking this for a
non-existing Blob will return a Status::not_found grpc error.

The previous version returned a Status::not_found error on the Get
request too, but there was no chance to prevent the server from starting
to stream (except sending an immediate cancellation).

Being able to check whether something exists in a BlobStore helps to
prevent from uploading in first place.

The granular chunking bits are an optional optimization - if the
BlobStore implements no more granular chunking, the Stat response can
simply contain a single chunk.

Read returns a stream of BlobChunk, which is just a stream of bytes -
not necessarily using the chunking that's returned in the reply of a
Stat() call. It can be used to read blobs or chunks.

Change-Id: I4b6030ef184ace5484c84ca273b49d710433731d
Reviewed-on: https://cl.tvl.fyi/c/depot/+/7652
Reviewed-by: tazjin <tazjin@tvl.su>
Tested-by: BuildkiteCI

3 files changed, 434 insertions, 88 deletions

diff --git a/tvix/store/protos/rpc_blobstore.pb.go b/tvix/store/protos/rpc_blobstore.pb.go
index 6ea9fb03a5bb..426a2836dfae 100644
--- a/tvix/store/protos/rpc_blobstore.pb.go
+++ b/tvix/store/protos/rpc_blobstore.pb.go
@@ -23,17 +23,28 @@ const (
 	_ = protoimpl.EnforceVersion(protoimpl.MaxVersion - 20)
 )
 
-type GetBlobRequest struct {
+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"`
+	// Whether to include the chunks field
+	IncludeChunks bool `protobuf:"varint,2,opt,name=include_chunks,json=includeChunks,proto3" json:"include_chunks,omitempty"`
+	// Whether to include the inline_bao field, containing an (outboard) bao.
+	// The [bao](https://github.com/oconnor663/bao/blob/master/docs/spec.md)
+	// can be used to validate chunks end up hashing to the same root digest.
+	// These only really matter when only downloading parts of a blob. Some
+	// caution needs to be applied when validating chunks - the bao works with
+	// 1K leaf nodes, which might not align with the chunk sizes - this might
+	// imply a neighboring chunk might need to be (partially) fetched to
+	// validate the hash.
+	IncludeBao bool `protobuf:"varint,3,opt,name=include_bao,json=includeBao,proto3" json:"include_bao,omitempty"`
 }
 
-func (x *GetBlobRequest) Reset() {
-	*x = GetBlobRequest{}
+func (x *StatBlobRequest) Reset() {
+	*x = StatBlobRequest{}
 	if protoimpl.UnsafeEnabled {
 		mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[0]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -41,13 +52,13 @@ func (x *GetBlobRequest) Reset() {
 	}
 }
 
-func (x *GetBlobRequest) String() string {
+func (x *StatBlobRequest) String() string {
 	return protoimpl.X.MessageStringOf(x)
 }
 
-func (*GetBlobRequest) ProtoMessage() {}
+func (*StatBlobRequest) ProtoMessage() {}
 
-func (x *GetBlobRequest) ProtoReflect() protoreflect.Message {
+func (x *StatBlobRequest) ProtoReflect() protoreflect.Message {
 	mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[0]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -59,29 +70,48 @@ func (x *GetBlobRequest) ProtoReflect() protoreflect.Message {
 	return mi.MessageOf(x)
 }
 
-// Deprecated: Use GetBlobRequest.ProtoReflect.Descriptor instead.
-func (*GetBlobRequest) Descriptor() ([]byte, []int) {
+// Deprecated: Use StatBlobRequest.ProtoReflect.Descriptor instead.
+func (*StatBlobRequest) Descriptor() ([]byte, []int) {
 	return file_tvix_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{0}
 }
 
-func (x *GetBlobRequest) GetDigest() []byte {
+func (x *StatBlobRequest) GetDigest() []byte {
 	if x != nil {
 		return x.Digest
 	}
 	return nil
 }
 
-type PutBlobResponse struct {
+func (x *StatBlobRequest) GetIncludeChunks() bool {
+	if x != nil {
+		return x.IncludeChunks
+	}
+	return false
+}
+
+func (x *StatBlobRequest) GetIncludeBao() bool {
+	if x != nil {
+		return x.IncludeBao
+	}
+	return false
+}
+
+// BlobMeta provides more granular chunking information for the requested blob,
+// and baos.
+type BlobMeta 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"`
+	// This provides a list of chunks.
+	// Concatenating their contents would produce a blob with the digest that
+	// was specified in the request.
+	Chunks    []*BlobMeta_ChunkMeta `protobuf:"bytes,1,rep,name=chunks,proto3" json:"chunks,omitempty"`
+	InlineBao []byte                `protobuf:"bytes,2,opt,name=inline_bao,json=inlineBao,proto3" json:"inline_bao,omitempty"`
 }
 
-func (x *PutBlobResponse) Reset() {
-	*x = PutBlobResponse{}
+func (x *BlobMeta) Reset() {
+	*x = BlobMeta{}
 	if protoimpl.UnsafeEnabled {
 		mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[1]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -89,13 +119,13 @@ func (x *PutBlobResponse) Reset() {
 	}
 }
 
-func (x *PutBlobResponse) String() string {
+func (x *BlobMeta) String() string {
 	return protoimpl.X.MessageStringOf(x)
 }
 
-func (*PutBlobResponse) ProtoMessage() {}
+func (*BlobMeta) ProtoMessage() {}
 
-func (x *PutBlobResponse) ProtoReflect() protoreflect.Message {
+func (x *BlobMeta) ProtoReflect() protoreflect.Message {
 	mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[1]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
@@ -107,19 +137,74 @@ func (x *PutBlobResponse) ProtoReflect() protoreflect.Message {
 	return mi.MessageOf(x)
 }
 
-// Deprecated: Use PutBlobResponse.ProtoReflect.Descriptor instead.
-func (*PutBlobResponse) Descriptor() ([]byte, []int) {
+// Deprecated: Use BlobMeta.ProtoReflect.Descriptor instead.
+func (*BlobMeta) Descriptor() ([]byte, []int) {
 	return file_tvix_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{1}
 }
 
-func (x *PutBlobResponse) GetDigest() []byte {
+func (x *BlobMeta) GetChunks() []*BlobMeta_ChunkMeta {
+	if x != nil {
+		return x.Chunks
+	}
+	return nil
+}
+
+func (x *BlobMeta) GetInlineBao() []byte {
+	if x != nil {
+		return x.InlineBao
+	}
+	return nil
+}
+
+type ReadBlobRequest 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 *ReadBlobRequest) Reset() {
+	*x = ReadBlobRequest{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_store_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_store_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_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{2}
+}
+
+func (x *ReadBlobRequest) GetDigest() []byte {
 	if x != nil {
 		return x.Digest
 	}
 	return nil
 }
 
-// This represents a part of a chunk.
+// This represents some bytes of a blob.
 // Blobs are sent in smaller chunks to keep message sizes manageable.
 type BlobChunk struct {
 	state         protoimpl.MessageState
@@ -132,7 +217,7 @@ type BlobChunk struct {
 func (x *BlobChunk) Reset() {
 	*x = BlobChunk{}
 	if protoimpl.UnsafeEnabled {
-		mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[2]
+		mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[3]
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		ms.StoreMessageInfo(mi)
 	}
@@ -145,7 +230,7 @@ func (x *BlobChunk) String() string {
 func (*BlobChunk) ProtoMessage() {}
 
 func (x *BlobChunk) ProtoReflect() protoreflect.Message {
-	mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[2]
+	mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[3]
 	if protoimpl.UnsafeEnabled && x != nil {
 		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
 		if ms.LoadMessageInfo() == nil {
@@ -158,7 +243,7 @@ func (x *BlobChunk) ProtoReflect() protoreflect.Message {
 
 // Deprecated: Use BlobChunk.ProtoReflect.Descriptor instead.
 func (*BlobChunk) Descriptor() ([]byte, []int) {
-	return file_tvix_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{2}
+	return file_tvix_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{3}
 }
 
 func (x *BlobChunk) GetData() []byte {
@@ -168,33 +253,157 @@ func (x *BlobChunk) GetData() []byte {
 	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_store_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_store_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_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{4}
+}
+
+func (x *PutBlobResponse) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+type BlobMeta_ChunkMeta struct {
+	state         protoimpl.MessageState
+	sizeCache     protoimpl.SizeCache
+	unknownFields protoimpl.UnknownFields
+
+	Digest []byte `protobuf:"bytes,1,opt,name=digest,proto3" json:"digest,omitempty"`
+	Size   uint32 `protobuf:"varint,2,opt,name=size,proto3" json:"size,omitempty"`
+}
+
+func (x *BlobMeta_ChunkMeta) Reset() {
+	*x = BlobMeta_ChunkMeta{}
+	if protoimpl.UnsafeEnabled {
+		mi := &file_tvix_store_protos_rpc_blobstore_proto_msgTypes[5]
+		ms := protoimpl.X.MessageStateOf(protoimpl.Pointer(x))
+		ms.StoreMessageInfo(mi)
+	}
+}
+
+func (x *BlobMeta_ChunkMeta) String() string {
+	return protoimpl.X.MessageStringOf(x)
+}
+
+func (*BlobMeta_ChunkMeta) ProtoMessage() {}
+
+func (x *BlobMeta_ChunkMeta) ProtoReflect() protoreflect.Message {
+	mi := &file_tvix_store_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 BlobMeta_ChunkMeta.ProtoReflect.Descriptor instead.
+func (*BlobMeta_ChunkMeta) Descriptor() ([]byte, []int) {
+	return file_tvix_store_protos_rpc_blobstore_proto_rawDescGZIP(), []int{1, 0}
+}
+
+func (x *BlobMeta_ChunkMeta) GetDigest() []byte {
+	if x != nil {
+		return x.Digest
+	}
+	return nil
+}
+
+func (x *BlobMeta_ChunkMeta) GetSize() uint32 {
+	if x != nil {
+		return x.Size
+	}
+	return 0
+}
+
 var File_tvix_store_protos_rpc_blobstore_proto protoreflect.FileDescriptor
 
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+	0x32, 0xd5, 0x01, 0x0a, 0x0b, 0x42, 0x6c, 0x6f, 0x62, 0x53, 0x65, 0x72, 0x76, 0x69, 0x63, 0x65,
+	0x12, 0x3f, 0x0a, 0x04, 0x53, 0x74, 0x61, 0x74, 0x12, 0x1e, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e,
+	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, 0x17, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e,
+	0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f, 0x62, 0x4d, 0x65, 0x74,
+	0x61, 0x12, 0x42, 0x0a, 0x04, 0x52, 0x65, 0x61, 0x64, 0x12, 0x1e, 0x2e, 0x74, 0x76, 0x69, 0x78,
+	0x2e, 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, 0x18, 0x2e, 0x74, 0x76, 0x69, 0x78,
+	0x2e, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f, 0x62, 0x43, 0x68,
+	0x75, 0x6e, 0x6b, 0x30, 0x01, 0x12, 0x41, 0x0a, 0x03, 0x50, 0x75, 0x74, 0x12, 0x18, 0x2e, 0x74,
+	0x76, 0x69, 0x78, 0x2e, 0x73, 0x74, 0x6f, 0x72, 0x65, 0x2e, 0x76, 0x31, 0x2e, 0x42, 0x6c, 0x6f,
+	0x62, 0x43, 0x68, 0x75, 0x6e, 0x6b, 0x1a, 0x1e, 0x2e, 0x74, 0x76, 0x69, 0x78, 0x2e, 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, 0x73, 0x74,
+	0x6f, 0x72, 0x65, 0x2f, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x73, 0x3b, 0x73, 0x74, 0x6f, 0x72, 0x65,
+	0x76, 0x31, 0x62, 0x06, 0x70, 0x72, 0x6f, 0x74, 0x6f, 0x33,
 }
 
 var (
@@ -209,22 +418,28 @@ func file_tvix_store_protos_rpc_blobstore_proto_rawDescGZIP() []byte {
 	return file_tvix_store_protos_rpc_blobstore_proto_rawDescData
 }
 
-var file_tvix_store_protos_rpc_blobstore_proto_msgTypes = make([]protoimpl.MessageInfo, 3)
+var file_tvix_store_protos_rpc_blobstore_proto_msgTypes = make([]protoimpl.MessageInfo, 6)
 var file_tvix_store_protos_rpc_blobstore_proto_goTypes = []interface{}{
-	(*GetBlobRequest)(nil),  // 0: tvix.store.v1.GetBlobRequest
-	(*PutBlobResponse)(nil), // 1: tvix.store.v1.PutBlobResponse
-	(*BlobChunk)(nil),       // 2: tvix.store.v1.BlobChunk
+	(*StatBlobRequest)(nil),    // 0: tvix.store.v1.StatBlobRequest
+	(*BlobMeta)(nil),           // 1: tvix.store.v1.BlobMeta
+	(*ReadBlobRequest)(nil),    // 2: tvix.store.v1.ReadBlobRequest
+	(*BlobChunk)(nil),          // 3: tvix.store.v1.BlobChunk
+	(*PutBlobResponse)(nil),    // 4: tvix.store.v1.PutBlobResponse
+	(*BlobMeta_ChunkMeta)(nil), // 5: tvix.store.v1.BlobMeta.ChunkMeta
 }
 var file_tvix_store_protos_rpc_blobstore_proto_depIdxs = []int32{
-	0, // 0: tvix.store.v1.BlobService.Get:input_type -> tvix.store.v1.GetBlobRequest
-	2, // 1: tvix.store.v1.BlobService.Put:input_type -> tvix.store.v1.BlobChunk
-	2, // 2: tvix.store.v1.BlobService.Get:output_type -> tvix.store.v1.BlobChunk
-	1, // 3: tvix.store.v1.BlobService.Put:output_type -> tvix.store.v1.PutBlobResponse
-	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
+	5, // 0: tvix.store.v1.BlobMeta.chunks:type_name -> tvix.store.v1.BlobMeta.ChunkMeta
+	0, // 1: tvix.store.v1.BlobService.Stat:input_type -> tvix.store.v1.StatBlobRequest
+	2, // 2: tvix.store.v1.BlobService.Read:input_type -> tvix.store.v1.ReadBlobRequest
+	3, // 3: tvix.store.v1.BlobService.Put:input_type -> tvix.store.v1.BlobChunk
+	1, // 4: tvix.store.v1.BlobService.Stat:output_type -> tvix.store.v1.BlobMeta
+	3, // 5: tvix.store.v1.BlobService.Read:output_type -> tvix.store.v1.BlobChunk
+	4, // 6: tvix.store.v1.BlobService.Put:output_type -> tvix.store.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_store_protos_rpc_blobstore_proto_init() }
@@ -234,7 +449,7 @@ func file_tvix_store_protos_rpc_blobstore_proto_init() {
 	}
 	if !protoimpl.UnsafeEnabled {
 		file_tvix_store_protos_rpc_blobstore_proto_msgTypes[0].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*GetBlobRequest); i {
+			switch v := v.(*StatBlobRequest); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -246,7 +461,7 @@ func file_tvix_store_protos_rpc_blobstore_proto_init() {
 			}
 		}
 		file_tvix_store_protos_rpc_blobstore_proto_msgTypes[1].Exporter = func(v interface{}, i int) interface{} {
-			switch v := v.(*PutBlobResponse); i {
+			switch v := v.(*BlobMeta); i {
 			case 0:
 				return &v.state
 			case 1:
@@ -258,6 +473,18 @@ func file_tvix_store_protos_rpc_blobstore_proto_init() {
 			}
 		}
 		file_tvix_store_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_store_protos_rpc_blobstore_proto_msgTypes[3].Exporter = func(v interface{}, i int) interface{} {
 			switch v := v.(*BlobChunk); i {
 			case 0:
 				return &v.state
@@ -269,6 +496,30 @@ func file_tvix_store_protos_rpc_blobstore_proto_init() {
 				return nil
 			}
 		}
+		file_tvix_store_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
+			}
+		}
+		file_tvix_store_protos_rpc_blobstore_proto_msgTypes[5].Exporter = func(v interface{}, i int) interface{} {
+			switch v := v.(*BlobMeta_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{
@@ -276,7 +527,7 @@ func file_tvix_store_protos_rpc_blobstore_proto_init() {
 			GoPackagePath: reflect.TypeOf(x{}).PkgPath(),
 			RawDescriptor: file_tvix_store_protos_rpc_blobstore_proto_rawDesc,
 			NumEnums:      0,
-			NumMessages:   3,
+			NumMessages:   6,
 			NumExtensions: 0,
 			NumServices:   1,
 		},
diff --git a/tvix/store/protos/rpc_blobstore.proto b/tvix/store/protos/rpc_blobstore.proto
index cca195c3d975..e0b700f2d0da 100644
--- a/tvix/store/protos/rpc_blobstore.proto
+++ b/tvix/store/protos/rpc_blobstore.proto
@@ -7,27 +7,67 @@ package tvix.store.v1;
 option go_package = "code.tvl.fyi/tvix/store/protos;storev1";
 
 service BlobService {
-    rpc Get(GetBlobRequest) returns (stream BlobChunk);
+    // Stat exposes metadata about a given blob,
+    // such as more granular chunking, baos.
+    // It implicitly allows checking for existence too, as asking this for a
+    // non-existing Blob will return a Status::not_found grpc error.
+    // If there's no more granular chunking available, the response will simply
+    // contain a single chunk.
+    rpc Stat(StatBlobRequest) returns (BlobMeta);
 
-    rpc Put(stream BlobChunk) returns (PutBlobResponse);
+    // Read returns a stream of BlobChunk, which is just a stream of bytes - not necessarily
+    // using the chunking that's returned in the reply of a Stat() call.
+    rpc Read(ReadBlobRequest) returns (stream BlobChunk);
 
-    // TODO(flokli): We can get fancy here, and add methods to retrieve
-    // [Bao](https://github.com/oconnor663/bao/blob/master/docs/spec.md), and
-    // then support range requests, but that's left for later.
+    // Put uploads a Blob, by reading a stream of bytes.
+    rpc Put(stream BlobChunk) returns (PutBlobResponse);
 }
 
-message GetBlobRequest {
+message StatBlobRequest {
     // The blake3 digest of the blob requested
     bytes digest = 1;
+
+    // Whether to include the chunks field
+    bool include_chunks = 2;
+    // Whether to include the inline_bao field, containing an (outboard) bao.
+    // The [bao](https://github.com/oconnor663/bao/blob/master/docs/spec.md)
+    // can be used to validate chunks end up hashing to the same root digest.
+    // These only really matter when only downloading parts of a blob. Some
+    // caution needs to be applied when validating chunks - the bao works with
+    // 1K leaf nodes, which might not align with the chunk sizes - this might
+    // imply a neighboring chunk might need to be (partially) fetched to
+    // validate the hash.
+    bool include_bao = 3;
 }
 
-message PutBlobResponse {
-    // The blake3 digest of the data that was sent.
+// BlobMeta provides more granular chunking information for the requested blob,
+// and baos.
+message BlobMeta {
+    // This provides a list of chunks.
+    // Concatenating their contents would produce a blob with the digest that
+    // was specified in the request.
+    repeated ChunkMeta chunks = 1;
+
+    message ChunkMeta {
+        bytes digest = 1;
+        uint32 size = 2;
+    }
+
+    bytes inline_bao = 2;
+}
+
+message ReadBlobRequest {
+    // The blake3 digest of the blob requested
     bytes digest = 1;
 }
 
-// This represents a part of a chunk.
+// 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/store/protos/rpc_blobstore_grpc.pb.go b/tvix/store/protos/rpc_blobstore_grpc.pb.go
index f99181cb4d06..f952e78d5a6e 100644
--- a/tvix/store/protos/rpc_blobstore_grpc.pb.go
+++ b/tvix/store/protos/rpc_blobstore_grpc.pb.go
@@ -22,7 +22,17 @@ const _ = grpc.SupportPackageIsVersion7
 //
 // 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 {
-	Get(ctx context.Context, in *GetBlobRequest, opts ...grpc.CallOption) (BlobService_GetClient, error)
+	// Stat exposes metadata about a given blob,
+	// such as more granular chunking, baos.
+	// It implicitly allows checking for existence too, as asking this for a
+	// non-existing Blob will return a Status::not_found grpc error.
+	// If there's no more granular chunking available, the response will simply
+	// contain a single chunk.
+	Stat(ctx context.Context, in *StatBlobRequest, opts ...grpc.CallOption) (*BlobMeta, error)
+	// Read returns a stream of BlobChunk, which is just a stream of bytes - not necessarily
+	// using the chunking that's returned in the reply of a Stat() call.
+	Read(ctx context.Context, in *ReadBlobRequest, opts ...grpc.CallOption) (BlobService_ReadClient, error)
+	// Put uploads a Blob, by reading a stream of bytes.
 	Put(ctx context.Context, opts ...grpc.CallOption) (BlobService_PutClient, error)
 }
 
@@ -34,12 +44,21 @@ func NewBlobServiceClient(cc grpc.ClientConnInterface) BlobServiceClient {
 	return &blobServiceClient{cc}
 }
 
-func (c *blobServiceClient) Get(ctx context.Context, in *GetBlobRequest, opts ...grpc.CallOption) (BlobService_GetClient, error) {
-	stream, err := c.cc.NewStream(ctx, &BlobService_ServiceDesc.Streams[0], "/tvix.store.v1.BlobService/Get", opts...)
+func (c *blobServiceClient) Stat(ctx context.Context, in *StatBlobRequest, opts ...grpc.CallOption) (*BlobMeta, error) {
+	out := new(BlobMeta)
+	err := c.cc.Invoke(ctx, "/tvix.store.v1.BlobService/Stat", in, out, opts...)
 	if err != nil {
 		return nil, err
 	}
-	x := &blobServiceGetClient{stream}
+	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], "/tvix.store.v1.BlobService/Read", opts...)
+	if err != nil {
+		return nil, err
+	}
+	x := &blobServiceReadClient{stream}
 	if err := x.ClientStream.SendMsg(in); err != nil {
 		return nil, err
 	}
@@ -49,16 +68,16 @@ func (c *blobServiceClient) Get(ctx context.Context, in *GetBlobRequest, opts ..
 	return x, nil
 }
 
-type BlobService_GetClient interface {
+type BlobService_ReadClient interface {
 	Recv() (*BlobChunk, error)
 	grpc.ClientStream
 }
 
-type blobServiceGetClient struct {
+type blobServiceReadClient struct {
 	grpc.ClientStream
 }
 
-func (x *blobServiceGetClient) Recv() (*BlobChunk, error) {
+func (x *blobServiceReadClient) Recv() (*BlobChunk, error) {
 	m := new(BlobChunk)
 	if err := x.ClientStream.RecvMsg(m); err != nil {
 		return nil, err
@@ -104,7 +123,17 @@ func (x *blobServicePutClient) CloseAndRecv() (*PutBlobResponse, error) {
 // All implementations must embed UnimplementedBlobServiceServer
 // for forward compatibility
 type BlobServiceServer interface {
-	Get(*GetBlobRequest, BlobService_GetServer) error
+	// Stat exposes metadata about a given blob,
+	// such as more granular chunking, baos.
+	// It implicitly allows checking for existence too, as asking this for a
+	// non-existing Blob will return a Status::not_found grpc error.
+	// If there's no more granular chunking available, the response will simply
+	// contain a single chunk.
+	Stat(context.Context, *StatBlobRequest) (*BlobMeta, error)
+	// Read returns a stream of BlobChunk, which is just a stream of bytes - not necessarily
+	// using the chunking that's returned in the reply of a Stat() call.
+	Read(*ReadBlobRequest, BlobService_ReadServer) error
+	// Put uploads a Blob, by reading a stream of bytes.
 	Put(BlobService_PutServer) error
 	mustEmbedUnimplementedBlobServiceServer()
 }
@@ -113,8 +142,11 @@ type BlobServiceServer interface {
 type UnimplementedBlobServiceServer struct {
 }
 
-func (UnimplementedBlobServiceServer) Get(*GetBlobRequest, BlobService_GetServer) error {
-	return status.Errorf(codes.Unimplemented, "method Get not implemented")
+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")
@@ -132,24 +164,42 @@ func RegisterBlobServiceServer(s grpc.ServiceRegistrar, srv BlobServiceServer) {
 	s.RegisterService(&BlobService_ServiceDesc, srv)
 }
 
-func _BlobService_Get_Handler(srv interface{}, stream grpc.ServerStream) error {
-	m := new(GetBlobRequest)
+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: "/tvix.store.v1.BlobService/Stat",
+	}
+	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).Get(m, &blobServiceGetServer{stream})
+	return srv.(BlobServiceServer).Read(m, &blobServiceReadServer{stream})
 }
 
-type BlobService_GetServer interface {
+type BlobService_ReadServer interface {
 	Send(*BlobChunk) error
 	grpc.ServerStream
 }
 
-type blobServiceGetServer struct {
+type blobServiceReadServer struct {
 	grpc.ServerStream
 }
 
-func (x *blobServiceGetServer) Send(m *BlobChunk) error {
+func (x *blobServiceReadServer) Send(m *BlobChunk) error {
 	return x.ServerStream.SendMsg(m)
 }
 
@@ -185,11 +235,16 @@ func (x *blobServicePutServer) Recv() (*BlobChunk, error) {
 var BlobService_ServiceDesc = grpc.ServiceDesc{
 	ServiceName: "tvix.store.v1.BlobService",
 	HandlerType: (*BlobServiceServer)(nil),
-	Methods:     []grpc.MethodDesc{},
+	Methods: []grpc.MethodDesc{
+		{
+			MethodName: "Stat",
+			Handler:    _BlobService_Stat_Handler,
+		},
+	},
 	Streams: []grpc.StreamDesc{
 		{
-			StreamName:    "Get",
-			Handler:       _BlobService_Get_Handler,
+			StreamName:    "Read",
+			Handler:       _BlobService_Read_Handler,
 			ServerStreams: true,
 		},
 		{