// SPDX-License-Identifier: MIT
// Copyright © 2022 The Tvix Authors
syntax = "proto3";

package tvix.store.v1;

option go_package = "code.tvl.fyi/tvix/store/protos;storev1";

service BlobService {
    // 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);

    // 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.
    //
    // It specifically is NOT necessarily using chunk sizes communicated in a
    // previous Stat request.
    //
    // It's up to the specific store to decide on whether it allows Read on a
    // Blob at all, or only on smaller chunks communicated in a Stat() call
    // first.
    //
    // Clients are enouraged to Stat() first, and then only read the individual
    // chunks they don't have yet.
    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;

    // 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;
}

// 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 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;
}