From a94c3257b1720fa395474df9cdbf32b322ea62fc Mon Sep 17 00:00:00 2001
From: "Jeong, YunWon" <jeong@youknowone.org>
Date: Mon, 3 Aug 2026 19:17:13 +0900
Subject: [PATCH] socket: accept a filesystem-encoded hostname in sethostname
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`socket.sethostname` took `PyUtf8StrRef`, so it rejected `bytes` outright and
refused a `str` carrying a surrogate escape. `socketmodule.c
socket_sethostname` accepts a bytes object directly, falls back to
`PyUnicode_FSConverter` for anything else, and hands the syscall the resulting
buffer and its length — the name is never required to be UTF-8.

Take `FsPath`, the converter `if_nametoindex` in this same module already uses,
and pass its bytes down. `host_env::socket::sethostname` correspondingly takes
`&[u8]` and builds the `OsStr` from them; `nix::unistd::sethostname` accepts
`AsRef<OsStr>` and passes pointer and length to the syscall, so nothing on the
path needs a NUL terminator or valid UTF-8.

`Lib/test/test_socket.py test_sethostname` covers this: it calls
`socket.sethostname(b'bar')` and asserts the hostname changed. The test is
skipped unless run as root, which is why the gap went unnoticed.

Assisted-by: Claude
---
 crates/host_env/src/socket.rs | 10 ++++++++--
 crates/stdlib/src/socket.rs   |  4 ++--
 2 files changed, 10 insertions(+), 4 deletions(-)

diff --git a/crates/host_env/src/socket.rs b/crates/host_env/src/socket.rs
index af4af2717cd..542031e6fa8 100644
--- a/crates/host_env/src/socket.rs
+++ b/crates/host_env/src/socket.rs
@@ -44,9 +44,15 @@ pub use libc::{AF_ALG, AF_CAN};
 #[cfg(target_os = "linux")]
 pub use libc::{sockaddr_alg, sockaddr_can};
 
+/// Set the system's hostname from its filesystem-encoded bytes.
+///
+/// `socketmodule.c socket_sethostname` reads the argument as a buffer and
+/// passes `buf.buf`/`buf.len` straight to the syscall, so a name is not
+/// required to be UTF-8; taking `&[u8]` keeps that true here as well.
 #[cfg(all(unix, not(target_os = "redox")))]
-pub fn sethostname(hostname: &str) -> io::Result<()> {
-    nix::unistd::sethostname(hostname).map_err(io::Error::from)
+pub fn sethostname(hostname: &[u8]) -> io::Result<()> {
+    use std::os::unix::ffi::OsStrExt;
+    nix::unistd::sethostname(std::ffi::OsStr::from_bytes(hostname)).map_err(io::Error::from)
 }
 
 #[cfg(unix)]
diff --git a/crates/stdlib/src/socket.rs b/crates/stdlib/src/socket.rs
index 968399ca782..e4f7a491658 100644
--- a/crates/stdlib/src/socket.rs
+++ b/crates/stdlib/src/socket.rs
@@ -2325,8 +2325,8 @@ mod _socket {
 
     #[cfg(all(unix, not(any(target_os = "redox", target_os = "android"))))]
     #[pyfunction]
-    fn sethostname(hostname: PyUtf8StrRef) -> std::io::Result<()> {
-        host_socket::sethostname(hostname.as_str())
+    fn sethostname(hostname: FsPath) -> std::io::Result<()> {
+        host_socket::sethostname(hostname.as_bytes())
     }
 
     #[pyfunction]