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Win: Add GetHostNameW fallback for win7 using gethostname #150909

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Win: Add GetHostNameW fallback for win7 using gethostname #150909

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12 changes: 12 additions & 0 deletions library/std/src/sys/pal/windows/c.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -227,6 +227,18 @@ compat_fn_with_fallback! {
}
}

#[cfg(target_vendor = "win7")]
compat_fn_with_fallback! {
pub static WS2_32: &CStr = c"ws2_32";

#[cfg(target_vendor = "win7")]
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@hkBst hkBst Jan 11, 2026

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this seems redundant with the outer cfg attr...

pub fn GetHostNameW(name: PWSTR, namelen: i32) -> i32 {
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@PaulDance PaulDance Jan 14, 2026

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I guess it could be nice to link the original issue somewhere around here.

unsafe {
crate::sys::winsock::hostname_fallback(name, namelen)
}
}
}

cfg_select! {
target_vendor = "uwp" => {
windows_targets::link_raw_dylib!("ntdll.dll" "system" fn NtCreateFile(filehandle : *mut HANDLE, desiredaccess : FILE_ACCESS_RIGHTS, objectattributes : *const OBJECT_ATTRIBUTES, iostatusblock : *mut IO_STATUS_BLOCK, allocationsize : *const i64, fileattributes : FILE_FLAGS_AND_ATTRIBUTES, shareaccess : FILE_SHARE_MODE, createdisposition : NTCREATEFILE_CREATE_DISPOSITION, createoptions : NTCREATEFILE_CREATE_OPTIONS, eabuffer : *const core::ffi::c_void, ealength : u32) -> NTSTATUS);
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2 changes: 2 additions & 0 deletions library/std/src/sys/pal/windows/c/bindings.txt
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Expand Up @@ -33,6 +33,7 @@ CONSOLE_MODE
CONSOLE_READCONSOLE_CONTROL
CONTEXT
CopyFileExW
CP_ACP
CP_UTF8
CREATE_ALWAYS
CREATE_BREAKAWAY_FROM_JOB
Expand Down Expand Up @@ -2170,6 +2171,7 @@ GetFileType
GETFINALPATHNAMEBYHANDLE_FLAGS
GetFinalPathNameByHandleW
GetFullPathNameW
gethostname
GetHostNameW
GetLastError
GetModuleFileNameW
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2 changes: 2 additions & 0 deletions library/std/src/sys/pal/windows/c/windows_sys.rs
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Expand Up @@ -130,6 +130,7 @@ windows_targets::link!("ws2_32.dll" "system" fn closesocket(s : SOCKET) -> i32);
windows_targets::link!("ws2_32.dll" "system" fn connect(s : SOCKET, name : *const SOCKADDR, namelen : i32) -> i32);
windows_targets::link!("ws2_32.dll" "system" fn freeaddrinfo(paddrinfo : *const ADDRINFOA));
windows_targets::link!("ws2_32.dll" "system" fn getaddrinfo(pnodename : PCSTR, pservicename : PCSTR, phints : *const ADDRINFOA, ppresult : *mut *mut ADDRINFOA) -> i32);
windows_targets::link!("ws2_32.dll" "system" fn gethostname(name : PSTR, namelen : i32) -> i32);
windows_targets::link!("ws2_32.dll" "system" fn getpeername(s : SOCKET, name : *mut SOCKADDR, namelen : *mut i32) -> i32);
windows_targets::link!("ws2_32.dll" "system" fn getsockname(s : SOCKET, name : *mut SOCKADDR, namelen : *mut i32) -> i32);
windows_targets::link!("ws2_32.dll" "system" fn getsockopt(s : SOCKET, level : i32, optname : i32, optval : PSTR, optlen : *mut i32) -> i32);
Expand Down Expand Up @@ -444,6 +445,7 @@ pub struct CONTEXT_0_0 {
pub type CONTEXT_FLAGS = u32;
pub type COPYFILE_FLAGS = u32;
pub type COPYPROGRESSROUTINE_PROGRESS = u32;
pub const CP_ACP: u32 = 0u32;
pub const CP_UTF8: u32 = 65001u32;
pub const CREATE_ALWAYS: FILE_CREATION_DISPOSITION = 2u32;
pub const CREATE_BREAKAWAY_FROM_JOB: PROCESS_CREATION_FLAGS = 16777216u32;
Expand Down
43 changes: 43 additions & 0 deletions library/std/src/sys/pal/windows/winsock.rs
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Expand Up @@ -78,3 +78,46 @@ where
{
cvt(f())
}

#[cfg(target_vendor = "win7")]
pub unsafe fn hostname_fallback(name: c::PWSTR, namelen: i32) -> i32 {
assert!(namelen >= 1);
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@joboet joboet Jan 12, 2026

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I think this should return SOCKET_ERROR and set the error to WSAEFAULT, just to be safe.


// The documentation of gethostname says that a buffer size of 256 is
// always enough.
let mut buffer = [const { mem::MaybeUninit::<u8>::uninit() }; 256];

// SAFETY: these parameters specify a valid, writable region of memory.
unsafe {
if c::gethostname(buffer.as_mut_ptr().cast(), buffer.len() as i32) == c::SOCKET_ERROR {
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@roblabla roblabla Jan 13, 2026

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It may be worth documenting that we're using this function in the "Underlying system calls" section of library/std/src/net/hostname.rs?

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@tbu- tbu- Jan 13, 2026

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I don't think we document syscalls for the win7 target anywhere(?).

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@Fulgen301 Fulgen301 Jan 13, 2026

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It's technically not a syscall either.

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@ChrisDenton ChrisDenton Jan 13, 2026

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The rust documentation has a habit of using the term "syscall" when it means OS API (technically they're not even syscalls on Linux since we go through libc). But yes, I agree it makes sense to document it. E.g. perhaps similarly to SystemTime.

return c::SOCKET_ERROR;
}
Comment on lines +90 to +94
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@hkBst hkBst Jan 11, 2026

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The safety comment seems to suffice for these lines, but the unsafe block continues. I think it would be better if each unsafe call had its own unsafe block with its own safety comments.


// Subtract one to leave space for the null terminator, as MultiByteToWideChar doesn't terminate the output buffer
// if the number of output characters is equal to the buffer length.
let len = c::MultiByteToWideChar(
c::CP_ACP,
c::MB_ERR_INVALID_CHARS,
buffer.as_mut_ptr().cast(),
-1,
name,
namelen - 1,
);

if len <= 0 {
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@joboet joboet Jan 12, 2026

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MultiByteToWideChar always returns zero on error

Suggested change
if len <= 0 {
if len == 0 {

// GetHostNameW reports WSAEFAULT if the buffer is too small
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@PaulDance PaulDance Jan 14, 2026

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Suggested change
// GetHostNameW reports WSAEFAULT if the buffer is too small
// gethostname reports WSAEFAULT if the buffer is too small

if it indeed still applies here.

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@Fulgen301 Fulgen301 Jan 16, 2026

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That was intentional - if GetHostNameW had a too small buffer, it'd report WSAEFAULT. This provides a fallback implementation, so it matches that error behavior.

if c::GetLastError() == c::ERROR_INSUFFICIENT_BUFFER {
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@joboet joboet Jan 12, 2026

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If the error is not ERROR_INSUFFICIENT_BUFFER, this will not set the socket error variable to indicate a reason for SOCKET_ERROR. I'm not sure what error value is correct, through...

c::SetLastError(c::WSAEFAULT as _);
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@joboet joboet Jan 12, 2026

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This should call WSASetLastError.

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@Fulgen301 Fulgen301 Jan 13, 2026

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Technically unnecessary, as WSASetLastError has been the same as SetLastError for the last decades.

}
return c::SOCKET_ERROR;
}

// Ensure the output is always null terminated.
// If MultiByteToWideChar has already written a null terminator, that null terminator will be included in len
// and this will add a second one, but writing a zero is cheap enough to omit the length comparison.
name.add(len as _).write(0);
}

// Success
0
}
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