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Fix #1778: Double mdns recv_buffer to 4096 bytes (#1779)

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Also add warn if parsing of a packet fails, so problems with for example packet
sizes can more easily be detected.

Reasoning:

The previous 2048 bytes is already larger than the recommend size by
[rfc6762](https://tools.ietf.org/html/rfc6762#page-46), which recommends
a packet size that fits within the interface MTU.

Nevertheless the rfc also states, that if more data needs to be
transmitted one should rely on IP fragments, which would only pose
problems when interfacing with devices not understanding IP fragments.
The standard also imposes a strict upper limit of 9000 bytes.

Therefore raising `recv_buffer` to 4096 seems sensible, given that we
already exceed the recommend size and given that we are not restricting
the size when sending in any way. Meaning the implementation already
sends packets larger than recommended, just can't handle them on
reception.
This commit is contained in:
Robert Klotzner 2020-10-05 10:03:21 +02:00 committed by GitHub
parent 8cec457b5e
commit fe30849eec
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GPG Key ID: 4AEE18F83AFDEB23
1 changed files with 10 additions and 3 deletions
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13
protocols/mdns/src/service.rs
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@ -23,6 +23,7 @@ use dns_parser::{Packet, RData};
use either::Either::{Left, Right};
use futures::{future, prelude::*};
use libp2p_core::{multiaddr::{Multiaddr, Protocol}, PeerId};
use log::warn;
use std::{convert::TryFrom as _, fmt, io, net::Ipv4Addr, net::SocketAddr, str, time::{Duration, Instant}};
use wasm_timer::Interval;
use lazy_static::lazy_static;
@ -122,7 +123,12 @@ pub struct $service_name {
/// regularly to recover from errors. Otherwise we could simply use an `Option<Interval>`.
silent: bool,
/// Buffer used for receiving data from the main socket.
recv_buffer: [u8; 2048],
/// RFC6762 discourages packets larger than the interface MTU, but allows sizes of up to 9000
/// bytes, if it can be ensured that all participating devices can handle such large packets.
/// For computers with several interfaces and IP addresses responses can easily reach sizes in
/// the range of 3000 bytes, so 4096 seems sensible for now. For more information see
/// [rfc6762](https://tools.ietf.org/html/rfc6762#page-46).
recv_buffer: [u8; 4096],
/// Buffers pending to send on the main socket.
send_buffers: Vec<Vec<u8>>,
/// Buffers pending to send on the query socket.
@ -173,7 +179,7 @@ impl $service_name {
query_socket,
query_interval: Interval::new_at(Instant::now(), Duration::from_secs(20)),
silent,
recv_buffer: [0; 2048],
recv_buffer: [0; 4096],
send_buffers: Vec::new(),
query_send_buffers: Vec::new(),
})
@ -346,7 +352,8 @@ impl MdnsPacket {
return Some(resp);
}
}
Err(_) => {
Err(err) => {
warn!("Parsing mdns packet failed: {:?}", err);
return None;
}
}