how to manually fail a client streaming?

[glorv]

Currently, client stream receives a request with type impl tonic::IntoStreamingRequest<Message=...>, it seems not expose a interface to manually fail this streaming. A real world user case is to use client streaming to send a file, each message represent a chunk of this file. It is possible that the source of file may meet error, e.g, read from a disk file meet IO errors, thus we may want to manually terminate the streaming with a fail status so the server side can know that this is not s successful call.

I saw the internal pat of the client streaming will also transfer this stream to Stream<Item=<Result<Message, tonic::Status>>> at:

tonic/tonic/src/codec/encode.rs

Lines 38 to 54 in d312dcc

	pub(crate) fn encode_client<T, U>(
	encoder: T,
	source: U,
	compression_encoding: Option<CompressionEncoding>,
	max_message_size: Option<usize>,
	) -> EncodeBody<impl Stream<Item = Result<Bytes, Status>>>
	where
	T: Encoder<Error = Status>,
	U: Stream<Item = T::Item>,
	{
	let stream = EncodedBytes::new(
	encoder,
	source.fuse().map(Ok),
	compression_encoding,
	SingleMessageCompressionOverride::default(),
	max_message_size,
	);

thus, it is better to expose the Result to the input type? Why not directly the request type as impl tonic::IntoStreamingRequest<Message=Result<ReqType, tonic::Status>>?