From a863d82c7954d1c231d623309d69ba75160c5ef8 Mon Sep 17 00:00:00 2001
From: Hailey Somerville <hailey@hailey.lol>
Date: Fri, 18 Aug 2023 19:12:35 +1000
Subject: [PATCH] set expedited forwarding on broadcast packets

---
 Cargo.lock  | 10 ++++++++++
 Cargo.toml  |  2 +-
 src/main.rs |  8 ++++++++
 3 files changed, 19 insertions(+), 1 deletion(-)

diff --git a/Cargo.lock b/Cargo.lock
index 492b197..a21d653 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -436,6 +436,15 @@ version = "2.5.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "2dffe52ecf27772e601905b7522cb4ef790d2cc203488bbd0e2fe85fcb74566d"
 
+[[package]]
+name = "memoffset"
+version = "0.7.1"
+source = "registry+https://github.com/rust-lang/crates.io-index"
+checksum = "5de893c32cde5f383baa4c04c5d6dbdd735cfd4a794b0debdb2bb1b421da5ff4"
+dependencies = [
+ "autocfg",
+]
+
 [[package]]
 name = "minimal-lexical"
 version = "0.2.1"
@@ -491,6 +500,7 @@ dependencies = [
  "bitflags",
  "cfg-if",
  "libc",
+ "memoffset",
  "static_assertions",
 ]
 
diff --git a/Cargo.toml b/Cargo.toml
index a3a4ac2..1f16d4f 100644
--- a/Cargo.toml
+++ b/Cargo.toml
@@ -9,7 +9,7 @@ edition = "2021"
 bytemuck = { version = "1.13.1", features = ["derive"] }
 cpal = "0.15.2"
 derive_more = "0.99.17"
-nix = { version = "0.26.2", features = ["time"], default-features = false }
+nix = { version = "0.26.2", features = ["time", "socket", "net"], default-features = false }
 static_assertions = "1.1.0"
 structopt = "0.3.26"
 termcolor = "1.2.0"
diff --git a/src/main.rs b/src/main.rs
index 8907fc7..0361e75 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -5,6 +5,7 @@ mod status;
 mod resample;
 
 use std::net::{UdpSocket, Ipv4Addr, SocketAddrV4};
+use std::os::fd::AsRawFd;
 use std::process::ExitCode;
 use std::sync::{Mutex, Arc};
 use std::time::Duration;
@@ -12,6 +13,7 @@ use std::time::Duration;
 use bytemuck::Zeroable;
 use cpal::traits::{DeviceTrait, HostTrait, StreamTrait};
 use cpal::{OutputCallbackInfo, StreamConfig, InputCallbackInfo, BufferSize, SupportedBufferSize};
+use nix::sys::socket::sockopt::IpTos;
 use structopt::StructOpt;
 
 use protocol::{TimestampMicros, AudioPacket, PacketBuffer, TimePacket, MAX_PACKET_SIZE, TimePacketPadding};
@@ -93,6 +95,12 @@ fn run_stream(opt: StreamOpt) -> Result<(), RunError> {
     socket.join_multicast_v4(&opt.group, bind.ip())
         .map_err(RunError::JoinMulticast)?;
 
+    const IPTOS_DSCP_EF: i32 = 0xb8;
+    if let Err(e) = nix::sys::socket::setsockopt(socket.as_raw_fd(), IpTos, &IPTOS_DSCP_EF) {
+        eprintln!("warning: failed to set IPTOS_DSCP_EF (expedited forwarding) on broadcast socket: {e:?}");
+    }
+
+
     // we don't need it:
     let _ = socket.set_multicast_loop_v4(false);