Replace custom blob gRPC API with ByteStream

client/proto/bytestream.proto

Index: client/proto/bytestream.proto
diff --git a/client/proto/bytestream.proto b/client/proto/bytestream.proto
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+// Copyright 2016 Google Inc.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+syntax = "proto3";
+
+package google.bytestream;
+
+// #### Introduction
+//
+// The Byte Stream API enables a client to read and write a stream of bytes to
+// and from a resource. Resources have names, and these names are supplied in
+// the API calls below to identify the resource that is being read from or
+// written to.
+//
+// All implementations of the Byte Stream API export the interface defined here:
+//
+// * `Read()`: Reads the contents of a resource.
+//
+// * `Write()`: Writes the contents of a resource. The client can call `Write()`
+//   multiple times with the same resource and can check the status of the write
+//   by calling `QueryWriteStatus()`.
+//
+// #### Service parameters and metadata
+//
+// The ByteStream API provides no direct way to access/modify any metadata
+// associated with the resource.
+//
+// #### Errors
+//
+// The errors returned by the service are in the Google canonical error space.
+service ByteStream {
+  // `Read()` is used to retrieve the contents of a resource as a sequence
+  // of bytes. The bytes are returned in a sequence of responses, and the
+  // responses are delivered as the results of a server-side streaming RPC.
+  rpc Read(ReadRequest) returns (stream ReadResponse);
+
+  // `Write()` is used to send the contents of a resource as a sequence of
+  // bytes. The bytes are sent in a sequence of request protos of a client-side
+  // streaming RPC.
+  //
+  // A `Write()` action is resumable. If there is an error or the connection is
+  // broken during the `Write()`, the client should check the status of the
+  // `Write()` by calling `QueryWriteStatus()` and continue writing from the
+  // returned `committed_size`. This may be less than the amount of data the
+  // client previously sent.
+  //
+  // Calling `Write()` on a resource name that was previously written and
+  // finalized could cause an error, depending on whether the underlying service
+  // allows over-writing of previously written resources.
+  //
+  // When the client closes the request channel, the service will respond with
+  // a `WriteResponse`. The service will not view the resource as `complete`
+  // until the client has sent a `WriteRequest` with `finish_write` set to
+  // `true`. Sending any requests on a stream after sending a request with
+  // `finish_write` set to `true` will cause an error. The client **should**
+  // check the `WriteResponse` it receives to determine how much data the
+  // service was able to commit and whether the service views the resource as
+  // `complete` or not.
+  rpc Write(stream WriteRequest) returns (WriteResponse);
+
+  // `QueryWriteStatus()` is used to find the `committed_size` for a resource
+  // that is being written, which can then be used as the `write_offset` for
+  // the next `Write()` call.
+  //
+  // If the resource does not exist (i.e., the resource has been deleted, or the
+  // first `Write()` has not yet reached the service), this method returns the
+  // error `NOT_FOUND`.
+  //
+  // The client **may** call `QueryWriteStatus()` at any time to determine how
+  // much data has been processed for this resource. This is useful if the
+  // client is buffering data and needs to know which data can be safely
+  // evicted. For any sequence of `QueryWriteStatus()` calls for a given
+  // resource name, the sequence of returned `committed_size` values will be
+  // non-decreasing.
+  rpc QueryWriteStatus(QueryWriteStatusRequest) returns (QueryWriteStatusResponse);
+}
+
+// Request object for ByteStream.Read.
+message ReadRequest {
+  // The name of the resource to read.
+  string resource_name = 1;
+
+  // The offset for the first byte to return in the read, relative to the start
+  // of the resource.
+  //
+  // A `read_offset` that is negative or greater than the size of the resource
+  // will cause an `OUT_OF_RANGE` error.
+  int64 read_offset = 2;
+
+  // The maximum number of `data` bytes the server is allowed to return in the
+  // sum of all `ReadResponse` messages. A `read_limit` of zero indicates that
+  // there is no limit, and a negative `read_limit` will cause an error.
+  //
+  // If the stream returns fewer bytes than allowed by the `read_limit` and no
+  // error occurred, the stream includes all data from the `read_offset` to the
+  // end of the resource.
+  int64 read_limit = 3;
+}
+
+// Response object for ByteStream.Read.
+message ReadResponse {
+  // A portion of the data for the resource. The service **may** leave `data`
+  // empty for any given `ReadResponse`. This enables the service to inform the
+  // client that the request is still live while it is running an operation to
+  // generate more data.
+  bytes data = 10;
+}
+
+// Request object for ByteStream.Write.
+message WriteRequest {
+  // The name of the resource to write. This **must** be set on the first
+  // `WriteRequest` of each `Write()` action. If it is set on subsequent calls,
+  // it **must** match the value of the first request.
+  string resource_name = 1;
+
+  // The offset from the beginning of the resource at which the data should be
+  // written. It is required on all `WriteRequest`s.
+  //
+  // In the first `WriteRequest` of a `Write()` action, it indicates
+  // the initial offset for the `Write()` call. The value **must** be equal to
+  // the `committed_size` that a call to `QueryWriteStatus()` would return.
+  //
+  // On subsequent calls, this value **must** be set and **must** be equal to
+  // the sum of the first `write_offset` and the sizes of all `data` bundles
+  // sent previously on this stream.
+  //
+  // An incorrect value will cause an error.
+  int64 write_offset = 2;
+
+  // If `true`, this indicates that the write is complete. Sending any
+  // `WriteRequest`s subsequent to one in which `finish_write` is `true` will
+  // cause an error.
+  bool finish_write = 3;
+
+  // A portion of the data for the resource. The client **may** leave `data`
+  // empty for any given `WriteRequest`. This enables the client to inform the
+  // service that the request is still live while it is running an operation to
+  // generate more data.
+  bytes data = 10;
+}
+
+// Response object for ByteStream.Write.
+message WriteResponse {
+  // The number of bytes that have been processed for the given resource.
+  int64 committed_size = 1;
+}
+
+// Request object for ByteStream.QueryWriteStatus.
+message QueryWriteStatusRequest {
+  // The name of the resource whose write status is being requested.
+  string resource_name = 1;
+}
+
+// Response object for ByteStream.QueryWriteStatus.
+message QueryWriteStatusResponse {
+  // The number of bytes that have been processed for the given resource.
+  int64 committed_size = 1;
+
+  // `complete` is `true` only if the client has sent a `WriteRequest` with
+  // `finish_write` set to true, and the server has processed that request.
+  bool complete = 2;
+}