pub const SEND_WINDOW: u64 = 10_000_000;Expand description
Aggregate unacknowledged outbound stream data per connection, in bytes.
The mirror image of CONNECTION_RECEIVE_WINDOW, and the only bound on what
this process buffers for a client that has stopped reading. 10 MB over the
~90 ms path RTT is about 889 Mbps against a measured peak of 177 Mbps, so it
is nowhere near a throughput constraint.
Set to exactly what quinn already defaults to, so it changes not a byte on the
wire today. It is pinned rather than inherited because upstream derives that
default from STREAM_RWND, a private constant inside quinn’s
TransportConfig::default with no stability guarantee, while the arithmetic
above is quoted against it. Dependabot proposes cargo bumps weekly; a patch
release that moved that constant would leave the documented numbers quietly
false. Setting the value here makes them true by construction instead of by
inheritance.
Note the asymmetry it leaves: 16 MiB of inbound credit granted against a
10 MB outbound cap, on a proxy whose traffic is mostly outbound. That is an
accepted decision, not an oversight — lifting the outbound cap to match would
add roughly 1.6 GiB of theoretical worst case across max_connections (256 by
default) in exchange for throughput we cannot measure a need for.