wayland_commons/wire.rs
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//! Types and routines used to manipulate arguments from the wire format
use std::ffi::{CStr, CString};
use std::os::unix::io::RawFd;
use std::ptr;
use nix::{Error as NixError, Result as NixResult};
use smallvec::SmallVec;
// The value of 4 is chosen for the following reasons:
// - almost all messages have 4 arguments or less
// - there are some potentially spammy events that have 3/4 arguments (wl_touch.move has 4 for example)
//
// This brings the size of Message to 11*usize (instead of 4*usize with a regular vec), but eliminates
// almost all allocations that may occur during the processing of messages, both client-side and server-side.
const INLINE_ARGS: usize = 4;
/// Wire metadata of a given message
#[derive(Copy, Clone, Debug)]
pub struct MessageDesc {
/// Name of this message
pub name: &'static str,
/// Signature of the message
pub signature: &'static [ArgumentType],
/// Minimum required version of the interface
pub since: u32,
/// Whether this message is a destructor
pub destructor: bool,
}
/// Enum of possible argument types as recognized by the wire
#[derive(Copy, Clone, PartialEq, Debug)]
pub enum ArgumentType {
/// i32
Int,
/// u32
Uint,
/// fixed point, 1/256 precision
Fixed,
/// CString
Str,
/// id of a wayland object
Object,
/// id of a newly created wayland object
NewId,
/// Vec<u8>
Array,
/// RawFd
Fd,
}
/// Enum of possible argument as recognized by the wire, including values
#[derive(Clone, PartialEq, Debug)]
#[allow(clippy::box_collection)]
pub enum Argument {
/// i32
Int(i32),
/// u32
Uint(u32),
/// fixed point, 1/256 precision
Fixed(i32),
/// CString
///
/// The value is boxed to reduce the stack size of Argument. The performance
/// impact is negligible as `string` arguments are pretty rare in the protocol.
Str(Box<CString>),
/// id of a wayland object
Object(u32),
/// id of a newly created wayland object
NewId(u32),
/// Vec<u8>
///
/// The value is boxed to reduce the stack size of Argument. The performance
/// impact is negligible as `array` arguments are pretty rare in the protocol.
Array(Box<Vec<u8>>),
/// RawFd
Fd(RawFd),
}
impl Argument {
/// Retrieve the type of a given argument instance
pub fn get_type(&self) -> ArgumentType {
match *self {
Argument::Int(_) => ArgumentType::Int,
Argument::Uint(_) => ArgumentType::Uint,
Argument::Fixed(_) => ArgumentType::Fixed,
Argument::Str(_) => ArgumentType::Str,
Argument::Object(_) => ArgumentType::Object,
Argument::NewId(_) => ArgumentType::NewId,
Argument::Array(_) => ArgumentType::Array,
Argument::Fd(_) => ArgumentType::Fd,
}
}
}
impl std::fmt::Display for Argument {
fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
match self {
Argument::Int(value) => write!(f, "{}", value),
Argument::Uint(value) => write!(f, "{}", value),
Argument::Fixed(value) => write!(f, "{}", value),
Argument::Str(value) => write!(f, "{:?}", value),
Argument::Object(value) => write!(f, "{}", value),
Argument::NewId(value) => write!(f, "{}", value),
Argument::Array(value) => write!(f, "{:?}", value),
Argument::Fd(value) => write!(f, "{}", value),
}
}
}
/// A wire message
#[derive(Debug, Clone, PartialEq)]
pub struct Message {
/// ID of the object sending this message
pub sender_id: u32,
/// Opcode of the message
pub opcode: u16,
/// Arguments of the message
pub args: SmallVec<[Argument; INLINE_ARGS]>,
}
/// Error generated when trying to serialize a message into buffers
#[derive(Debug, Clone)]
pub enum MessageWriteError {
/// The buffer is too small to hold the message contents
BufferTooSmall,
/// The message contains a FD that could not be dup-ed
DupFdFailed(::nix::Error),
}
impl std::error::Error for MessageWriteError {}
impl std::fmt::Display for MessageWriteError {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
match *self {
MessageWriteError::BufferTooSmall => {
f.write_str("The provided buffer is too small to hold message content.")
}
MessageWriteError::DupFdFailed(_) => {
f.write_str("The message contains a file descriptor that could not be dup()-ed.")
}
}
}
}
/// Error generated when trying to deserialize a message from buffers
#[derive(Debug, Clone)]
pub enum MessageParseError {
/// The message references a FD but the buffer FD is empty
MissingFD,
/// More data is needed to deserialize the message
MissingData,
/// The message is malformed and cannot be parsed
Malformed,
}
impl std::error::Error for MessageParseError {}
impl std::fmt::Display for MessageParseError {
fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
match *self {
MessageParseError::MissingFD => {
f.write_str("The message references a FD but the buffer FD is empty.")
}
MessageParseError::MissingData => {
f.write_str("More data is needed to deserialize the message")
}
MessageParseError::Malformed => {
f.write_str("The message is malformed and cannot be parsed")
}
}
}
}
impl Message {
/// Serialize the contents of this message into provided buffers
///
/// Returns the number of elements written in each buffer
///
/// Any serialized Fd will be `dup()`-ed in the process
pub fn write_to_buffers(
&self,
payload: &mut [u32],
mut fds: &mut [RawFd],
) -> Result<(usize, usize), MessageWriteError> {
let orig_payload_len = payload.len();
let orig_fds_len = fds.len();
// Helper function to write a u32 or a RawFd to its buffer
fn write_buf<T>(u: T, payload: &mut [T]) -> Result<&mut [T], MessageWriteError> {
if let Some((head, tail)) = payload.split_first_mut() {
*head = u;
Ok(tail)
} else {
Err(MessageWriteError::BufferTooSmall)
}
}
// Helper function to write byte arrays in payload
fn write_array_to_payload<'a>(
array: &[u8],
payload: &'a mut [u32],
) -> Result<&'a mut [u32], MessageWriteError> {
let array_len = array.len();
let word_len = array_len / 4 + if array_len % 4 != 0 { 1 } else { 0 };
// need enough space to store the whole array with padding and a size header
if payload.len() < 1 + word_len {
return Err(MessageWriteError::BufferTooSmall);
}
// size header
payload[0] = array_len as u32;
let (buffer_slice, rest) = payload[1..].split_at_mut(word_len);
unsafe {
ptr::copy(array.as_ptr(), buffer_slice.as_mut_ptr() as *mut u8, array_len);
}
Ok(rest)
}
let free_size = payload.len();
if free_size < 2 {
return Err(MessageWriteError::BufferTooSmall);
}
let (header, mut payload) = payload.split_at_mut(2);
// we store all fds we dup-ed in this, which will auto-close
// them on drop, if any of the `?` early-returns
let mut pending_fds = FdStore::new();
// write the contents in the buffer
for arg in &self.args {
// Just to make the borrow checker happy
let old_payload = payload;
match *arg {
Argument::Int(i) => payload = write_buf(i as u32, old_payload)?,
Argument::Uint(u) => payload = write_buf(u, old_payload)?,
Argument::Fixed(f) => payload = write_buf(f as u32, old_payload)?,
Argument::Str(ref s) => {
payload = write_array_to_payload(s.as_bytes_with_nul(), old_payload)?;
}
Argument::Object(o) => payload = write_buf(o, old_payload)?,
Argument::NewId(n) => payload = write_buf(n, old_payload)?,
Argument::Array(ref a) => {
payload = write_array_to_payload(a, old_payload)?;
}
Argument::Fd(fd) => {
let old_fds = fds;
let dup_fd = dup_fd_cloexec(fd).map_err(MessageWriteError::DupFdFailed)?;
pending_fds.push(dup_fd);
fds = write_buf(dup_fd, old_fds)?;
payload = old_payload;
}
}
}
// we reached here, all writing was successful
// no FD needs to be closed
pending_fds.clear();
let wrote_size = (free_size - payload.len()) * 4;
header[0] = self.sender_id;
header[1] = ((wrote_size as u32) << 16) | u32::from(self.opcode);
Ok((orig_payload_len - payload.len(), orig_fds_len - fds.len()))
}
/// Attempts to parse a single wayland message with the given signature.
///
/// If the buffers contains several messages, only the first one will be parsed,
/// and the unused tail of the buffers is returned. If a single message was present,
/// the returned slices should thus be empty.
///
/// Errors if the message is malformed.
pub fn from_raw<'a, 'b>(
raw: &'a [u32],
signature: &[ArgumentType],
fds: &'b [RawFd],
) -> Result<(Message, &'a [u32], &'b [RawFd]), MessageParseError> {
// helper function to read arrays
fn read_array_from_payload(
array_len: usize,
payload: &[u32],
) -> Result<(&[u8], &[u32]), MessageParseError> {
let word_len = array_len / 4 + if array_len % 4 != 0 { 1 } else { 0 };
if word_len > payload.len() {
return Err(MessageParseError::MissingData);
}
let (array_contents, rest) = payload.split_at(word_len);
let array = unsafe {
::std::slice::from_raw_parts(array_contents.as_ptr() as *const u8, array_len)
};
Ok((array, rest))
}
if raw.len() < 2 {
return Err(MessageParseError::MissingData);
}
let sender_id = raw[0];
let word_2 = raw[1];
let opcode = (word_2 & 0x0000_FFFF) as u16;
let len = (word_2 >> 16) as usize / 4;
if len < 2 || len > raw.len() {
return Err(MessageParseError::Malformed);
}
let (mut payload, rest) = raw.split_at(len);
payload = &payload[2..];
let mut fds = fds;
let arguments = signature
.iter()
.map(|argtype| {
if let ArgumentType::Fd = *argtype {
// don't consume input but fd
if let Some((&front, tail)) = fds.split_first() {
fds = tail;
Ok(Argument::Fd(front))
} else {
Err(MessageParseError::MissingFD)
}
} else if let Some((&front, mut tail)) = payload.split_first() {
let arg = match *argtype {
ArgumentType::Int => Ok(Argument::Int(front as i32)),
ArgumentType::Uint => Ok(Argument::Uint(front)),
ArgumentType::Fixed => Ok(Argument::Fixed(front as i32)),
ArgumentType::Str => read_array_from_payload(front as usize, tail)
.and_then(|(v, rest)| {
tail = rest;
match CStr::from_bytes_with_nul(v) {
Ok(s) => Ok(Argument::Str(Box::new(s.into()))),
Err(_) => Err(MessageParseError::Malformed),
}
}),
ArgumentType::Object => Ok(Argument::Object(front)),
ArgumentType::NewId => Ok(Argument::NewId(front)),
ArgumentType::Array => {
read_array_from_payload(front as usize, tail).map(|(v, rest)| {
tail = rest;
Argument::Array(Box::new(v.into()))
})
}
ArgumentType::Fd => unreachable!(),
};
payload = tail;
arg
} else {
Err(MessageParseError::MissingData)
}
})
.collect::<Result<SmallVec<_>, MessageParseError>>()?;
let msg = Message { sender_id, opcode, args: arguments };
Ok((msg, rest, fds))
}
}
/// Duplicate a `RawFd` and set the CLOEXEC flag on the copy
pub fn dup_fd_cloexec(fd: RawFd) -> NixResult<RawFd> {
use nix::fcntl;
match fcntl::fcntl(fd, fcntl::FcntlArg::F_DUPFD_CLOEXEC(0)) {
Ok(newfd) => Ok(newfd),
Err(NixError::EINVAL) => {
// F_DUPFD_CLOEXEC is not recognized, kernel too old, fallback
// to setting CLOEXEC manually
let newfd = fcntl::fcntl(fd, fcntl::FcntlArg::F_DUPFD(0))?;
let flags = fcntl::fcntl(newfd, fcntl::FcntlArg::F_GETFD);
let result = flags
.map(|f| fcntl::FdFlag::from_bits(f).unwrap() | fcntl::FdFlag::FD_CLOEXEC)
.and_then(|f| fcntl::fcntl(newfd, fcntl::FcntlArg::F_SETFD(f)));
match result {
Ok(_) => {
// setting the O_CLOEXEC worked
Ok(newfd)
}
Err(e) => {
// something went wrong in F_GETFD or F_SETFD
let _ = ::nix::unistd::close(newfd);
Err(e)
}
}
}
Err(e) => Err(e),
}
}
/*
* utility struct that closes every FD it contains on drop
*/
struct FdStore {
fds: Vec<RawFd>,
}
impl FdStore {
fn new() -> FdStore {
FdStore { fds: Vec::new() }
}
fn push(&mut self, fd: RawFd) {
self.fds.push(fd);
}
fn clear(&mut self) {
self.fds.clear();
}
}
impl Drop for FdStore {
fn drop(&mut self) {
use nix::unistd::close;
for fd in self.fds.drain(..) {
// not much can be done if we can't close that anyway...
let _ = close(fd);
}
}
}
#[cfg(test)]
mod tests {
use super::*;
use smallvec::smallvec;
#[test]
fn into_from_raw_cycle() {
let mut bytes_buffer = vec![0; 1024];
let mut fd_buffer = vec![0; 10];
let msg = Message {
sender_id: 42,
opcode: 7,
args: smallvec![
Argument::Uint(3),
Argument::Fixed(-89),
Argument::Str(Box::new(CString::new(&b"I like trains!"[..]).unwrap())),
Argument::Array(vec![1, 2, 3, 4, 5, 6, 7, 8, 9].into()),
Argument::Object(88),
Argument::NewId(56),
Argument::Int(-25),
],
};
// write the message to the buffers
msg.write_to_buffers(&mut bytes_buffer[..], &mut fd_buffer[..]).unwrap();
// read them back
let (rebuilt, _, _) = Message::from_raw(
&bytes_buffer[..],
&[
ArgumentType::Uint,
ArgumentType::Fixed,
ArgumentType::Str,
ArgumentType::Array,
ArgumentType::Object,
ArgumentType::NewId,
ArgumentType::Int,
],
&fd_buffer[..],
)
.unwrap();
assert_eq!(rebuilt, msg);
}
}