feat: add ancillary data (control message) helpers for sendmsg/recvmsg #645
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,202 @@ | ||
| use std::fmt; | ||
| use std::mem; | ||
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| /// Returns the space required in a control message buffer for a single message | ||
| /// with `data_len` bytes of ancillary data. | ||
| /// | ||
| /// Returns `None` if `data_len` does not fit in `libc::c_uint`. | ||
| /// | ||
| /// Corresponds to `CMSG_SPACE(3)`. | ||
| pub fn cmsg_space(data_len: usize) -> Option<usize> { | ||
| let len = libc::c_uint::try_from(data_len).ok()?; | ||
| // SAFETY: pure arithmetic. | ||
| usize::try_from(unsafe { libc::CMSG_SPACE(len) }).ok() | ||
| } | ||
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| /// A control message parsed from a `recvmsg(2)` control buffer. | ||
| /// | ||
| /// Returned by [`ControlMessages`]. | ||
| pub struct ControlMessage<'a> { | ||
| cmsg_level: i32, | ||
| cmsg_type: i32, | ||
| data: &'a [u8], | ||
| } | ||
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| impl<'a> ControlMessage<'a> { | ||
| /// Corresponds to `cmsg_level` in `cmsghdr`. | ||
| pub fn cmsg_level(&self) -> i32 { | ||
| self.cmsg_level | ||
| } | ||
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| /// Corresponds to `cmsg_type` in `cmsghdr`. | ||
| pub fn cmsg_type(&self) -> i32 { | ||
| self.cmsg_type | ||
| } | ||
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| /// The ancillary data payload. | ||
| /// | ||
| /// Corresponds to the data portion following the `cmsghdr`. | ||
| pub fn data(&self) -> &'a [u8] { | ||
| self.data | ||
| } | ||
| } | ||
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| impl<'a> fmt::Debug for ControlMessage<'a> { | ||
| fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| "ControlMessage".fmt(fmt) | ||
| } | ||
| } | ||
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| /// Iterator over control messages in a `recvmsg(2)` control buffer. | ||
| /// | ||
| /// See [`crate::MsgHdrMut::with_control`] and [`crate::MsgHdrMut::control_len`]. | ||
| pub struct ControlMessages<'a> { | ||
| buf: &'a [u8], | ||
| offset: usize, | ||
| } | ||
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| impl<'a> ControlMessages<'a> { | ||
| /// Create a new `ControlMessages` from the filled control buffer. | ||
| /// | ||
| /// Pass `&raw_buf[..msg.control_len()]` where `raw_buf` is the slice | ||
| /// passed to [`crate::MsgHdrMut::with_control`] before calling `recvmsg(2)`. | ||
| pub fn new(buf: &'a [u8]) -> Self { | ||
| Self { buf, offset: 0 } | ||
| } | ||
| } | ||
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| impl<'a> Iterator for ControlMessages<'a> { | ||
| type Item = ControlMessage<'a>; | ||
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| #[allow(clippy::useless_conversion)] | ||
| fn next(&mut self) -> Option<Self::Item> { | ||
| let hdr_size = mem::size_of::<libc::cmsghdr>(); | ||
| // SAFETY: pure arithmetic; gives CMSG_ALIGN(sizeof(cmsghdr)). | ||
| let data_offset: usize = | ||
| usize::try_from(unsafe { libc::CMSG_LEN(0) }).unwrap_or(usize::MAX); | ||
|
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| if self.offset + hdr_size > self.buf.len() { | ||
| return None; | ||
| } | ||
|
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| // SAFETY: range is within `buf`; read_unaligned handles any alignment. | ||
| let cmsg: libc::cmsghdr = unsafe { | ||
| std::ptr::read_unaligned(self.buf.as_ptr().add(self.offset) as *const libc::cmsghdr) | ||
| }; | ||
|
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| let total_len = usize::try_from(cmsg.cmsg_len).unwrap_or(0); | ||
| if total_len < data_offset { | ||
| return None; | ||
| } | ||
| let data_len = total_len - data_offset; | ||
|
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| let data_abs_start = self.offset + data_offset; | ||
| let data_abs_end = data_abs_start.saturating_add(data_len); | ||
| if data_abs_end > self.buf.len() { | ||
| return None; | ||
| } | ||
|
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| let item = ControlMessage { | ||
| cmsg_level: cmsg.cmsg_level, | ||
| cmsg_type: cmsg.cmsg_type, | ||
| data: &self.buf[data_abs_start..data_abs_end], | ||
| }; | ||
|
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| // SAFETY: pure arithmetic; CMSG_SPACE(data_len) == CMSG_ALIGN(total_len). | ||
| let advance = match libc::c_uint::try_from(data_len) { | ||
| Ok(dl) => usize::try_from(unsafe { libc::CMSG_SPACE(dl) }).unwrap_or(usize::MAX), | ||
| Err(_) => return None, | ||
| }; | ||
| self.offset = self.offset.saturating_add(advance); | ||
|
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| Some(item) | ||
| } | ||
| } | ||
|
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| impl<'a> fmt::Debug for ControlMessages<'a> { | ||
| fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| "ControlMessages".fmt(fmt) | ||
| } | ||
| } | ||
|
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| /// Builds a control message buffer for use with `sendmsg(2)`. | ||
| /// | ||
| /// See [`crate::MsgHdr::with_control`] and [`cmsg_space`]. | ||
| pub struct ControlMessageEncoder<'a> { | ||
| buf: &'a mut [u8], | ||
| len: usize, | ||
| } | ||
|
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| impl<'a> ControlMessageEncoder<'a> { | ||
| /// Create a new `ControlMessageEncoder` backed by `buf`. | ||
| /// | ||
| /// Zeroes `buf` on creation to ensure padding bytes are clean. | ||
| /// Allocate `buf` with the sum of [`cmsg_space`] for each intended message. | ||
| pub fn new(buf: &'a mut [u8]) -> Self { | ||
| buf.fill(0); | ||
| Self { buf, len: 0 } | ||
| } | ||
|
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| /// Append a control message carrying `data`. | ||
| /// | ||
| /// Returns `Err` if `data` exceeds `c_uint::MAX` or the buffer is too small. | ||
| pub fn push(&mut self, cmsg_level: i32, cmsg_type: i32, data: &[u8]) -> std::io::Result<()> { | ||
| let data_len_uint = libc::c_uint::try_from(data.len()).map_err(|_| { | ||
| std::io::Error::new( | ||
| std::io::ErrorKind::InvalidInput, | ||
| "ancillary data payload too large (exceeds c_uint::MAX)", | ||
| ) | ||
| })?; | ||
| // SAFETY: pure arithmetic. | ||
| let space: usize = | ||
| usize::try_from(unsafe { libc::CMSG_SPACE(data_len_uint) }).unwrap_or(usize::MAX); | ||
| if self.len + space > self.buf.len() { | ||
| return Err(std::io::Error::new( | ||
| std::io::ErrorKind::InvalidInput, | ||
| "control message buffer too small", | ||
| )); | ||
| } | ||
| // SAFETY: pure arithmetic. | ||
| let cmsg_len = unsafe { libc::CMSG_LEN(data_len_uint) }; | ||
| unsafe { | ||
| // SAFETY: offset is within buf; write_unaligned handles alignment 1. | ||
| // Use zeroed() + field assignment to handle platform-specific padding | ||
| // (e.g. musl adds __pad1); buf is pre-zeroed but the write must be | ||
| // self-contained for correctness. | ||
| let cmsg_ptr = self.buf.as_mut_ptr().add(self.len) as *mut libc::cmsghdr; | ||
| let mut hdr: libc::cmsghdr = mem::zeroed(); | ||
| hdr.cmsg_len = cmsg_len as _; | ||
| hdr.cmsg_level = cmsg_level; | ||
| hdr.cmsg_type = cmsg_type; | ||
| std::ptr::write_unaligned(cmsg_ptr, hdr); | ||
| // SAFETY: CMSG_DATA gives the correct offset past alignment padding. | ||
| let data_ptr = libc::CMSG_DATA(cmsg_ptr); | ||
| std::ptr::copy_nonoverlapping(data.as_ptr(), data_ptr, data.len()); | ||
| } | ||
| self.len += space; | ||
| Ok(()) | ||
| } | ||
|
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| /// Returns the encoded bytes. | ||
| /// | ||
| /// Corresponds to the slice to pass to [`crate::MsgHdr::with_control`]. | ||
| pub fn as_bytes(&self) -> &[u8] { | ||
| &self.buf[..self.len] | ||
| } | ||
|
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| /// Returns the number of bytes written. | ||
| pub fn len(&self) -> usize { | ||
| self.len | ||
| } | ||
|
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| /// Returns `true` if no control messages have been pushed. | ||
| pub fn is_empty(&self) -> bool { | ||
| self.len == 0 | ||
| } | ||
| } | ||
|
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| impl<'a> fmt::Debug for ControlMessageEncoder<'a> { | ||
| fn fmt(&self, fmt: &mut fmt::Formatter<'_>) -> fmt::Result { | ||
| "ControlMessageEncoder".fmt(fmt) | ||
| } | ||
| } |
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Can you drop the CI changes from this pr? Let's focus this pr on one thing.