Server-streaming requests block until first message is received

[headassbtw]

Bug Report

Version

tonic v0.13.1
tonic-build v0.13.1

Platform

Linux arbiter 6.14.10-zen1-1-zen #1 ZEN SMP PREEMPT_DYNAMIC Wed, 04 Jun 2025 18:52:21 +0000 x86_64 GNU/Linux

Description

Upon requesting a streaming response, the (let's call it) "initial" call blocks until the first message is received, rather than .next() doing the blocking.

My code goes something like this :

let mut response = client.streaming_request(request.clone()).await?.into_inner();
while let Some(obj) = response.next().await { ... }

I would expect .next() to do all the blocking here (bar establishing the connection), but the blockage is split across .streaming_request() and .next(), the former blocking until the first streamed response, and the latter handling all subsequent responses.

[LucioFranco]

The first one waits until it has gotten the initial headers which may also coincide with the first message.