Nous.HTTP.StreamBackend.Req (nous v0.16.4)
View SourceNous.HTTP.StreamBackend implementation backed by Req (Finch
underneath).
Default streaming backend. Drives Req.post/1 with the :into
callback so chunks are pushed into a Task, which forwards them to
the consuming Stream.resource via send/2.
Backpressure
Req's :into callback runs in the spawned Task. Forwarding to the
consumer process is send/2, so a fast producer + slow consumer can
grow the consumer's mailbox.
The producer task watches the consumer's mailbox via
Process.info(parent, :message_queue_len). When the queue length
crosses @backpressure_high_water (default 1_000 chunks) the task
busy-waits in 5ms increments until it drops below
@backpressure_low_water (default 100). This gives Req's :into
callback natural backpressure — the producing socket doesn't read
more bytes while we're waiting — without requiring the consumer to
switch to the Hackney backend.
If the consumer is truly unresponsive (the mailbox stays high for
longer than :backpressure_max_wait_ms), the task emits
{:backpressure_overflow, %{queue_len: n}} and aborts the stream
rather than wedging forever.
Callers whose downstream consumers reliably block per chunk
(LiveView fan-out under load, persistence-on-every-chunk, slow IO)
can still prefer Nous.HTTP.StreamBackend.Hackney, which provides
strict pull-based backpressure via :hackney's {:async, :once}
mode.
TLS verification
Req's defaults handle TLS verification via Mint/Finch (system CAs with peer verification). No additional configuration needed.