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smoltcp-rs / smoltcp

a smol tcp/ip stack
BSD Zero Clause License
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Difference between a ListenEndpoint with addr == None and addr == Some(Ipv4Address::UNSPECIFIED) #981

Closed kbleeke closed 2 months ago

kbleeke commented 3 months ago

I've run into a problem where UDP sockets created with bind(8080) [port is arbitrary] and bind(Ipv4Addr::UNSPECIFIED, 8080) behave differently.

The first behaves as expected: it accepts packet from any source IP and sends packets with the local IP address in the source field.

The second, however, seems (to me unexpectedly) take Ipv4Addr::UNSPECIFIED literally and does not accepts packets from any address. It also sends packet with 0.0.0.0 as the source address instead of substituting the correct IP. I was able to receive packets from the broadcast address, presumably it also accepts packet with 0.0.0.0 as the source address.

I am not using smoltcp directly but embassy_net but the relvant code here seems to be in smoltcp.

Dirbaio commented 3 months ago

This is intended behavior, smoltcp represents some IP as Some, and no IP as None. Some(0.0.0.0) means exactly that, the 0.0.0.0 IP (which is invalid).

using Some/None is idiomatic Rust, using the zero value in-band to signal "no value" is not, it's a C thing.

kbleeke commented 2 months ago

Ok, thanks. Nothing to be done here, then