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Allow the dev server socket to be reused immediately #4709

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Apr 26, 2023
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Allow the dev server socket to be reused immediately #4709

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Allow dev server socket to be reused immediately
alexkirsz Apr 26, 2023
a393b56
disable reuseaddr on windows
sokra Apr 26, 2023
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4 changes: 4 additions & 0 deletions crates/turbopack-dev-server/src/lib.rs
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Expand Up @@ -107,6 +107,10 @@ impl DevServer {
// real TCP listener, see if it bound, and get its bound address.
let socket = Socket::new(Domain::for_address(addr), Type::STREAM, Some(Protocol::TCP))
.context("unable to create socket")?;
// Allow the socket to be reused immediately after closing. This ensures that
// the dev server can be restarted on the same address without a buffer time for
// the OS to release the socket.
let _ = socket.set_reuse_address(true);
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This will also allow binding to the same port twice, no?

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pretty sure this will break our find_port function
https://github.com/vercel/next.js/blob/3bdaed01ba9e1a86a16fd243e5bdb5e4894ed5aa/packages/next-swc/crates/next-dev/src/lib.rs#L173-L173

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That's SO_REUSEPORT.

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This indicates that futher calls to bind may allow reuse of local addresses. For IPv4 sockets this means that a socket may bind even when there's a socket already listening on this port

from the rustdoc

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https://learn.microsoft.com/en-us/windows/win32/winsock/using-so-reuseaddr-and-so-exclusiveaddruse#using-so_reuseaddr

also windows docs

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and it also says linux now matches this behavior

I'm fine with merging this for macOS/Linux only, but we might have to update the port finding code, we've already had a bunch of bug reports because of it not reporting ports in use correctly / not finding a new port as expected in the past and this might make it worse

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this may very well break find_port on macos and linux

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I'll test find_port on macOS with and without this option.

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find_port still works properly with this option on macOS. However, as you said, binding to different local addresses no longer produces an error.

One way to fix this would be to replace find_port to run lsof/other OS-specific commands to check if a port is in use instead of trying to bind to that port.

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This seems to match the old behavior from before #4565: https://github.com/rust-lang/rust/blob/9c044d77a334609513f3b615e0763a40cc02424d/library/std/src/sys_common/net.rs#L399-L407

if matches!(addr, SocketAddr::V6(_)) {
// When possible bind to v4 and v6, otherwise ignore the error
let _ = socket.set_only_v6(false);
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