wayland_backend/rs/
wire.rs

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1//! Types and routines used to manipulate arguments from the wire format
2
3use std::collections::VecDeque;
4use std::ffi::CStr;
5use std::os::unix::io::{BorrowedFd, OwnedFd, RawFd};
6
7use crate::protocol::{Argument, ArgumentType, Message};
8
9use smallvec::SmallVec;
10
11/// Error generated when trying to serialize a message into buffers
12#[derive(Debug)]
13pub enum MessageWriteError {
14    /// The buffer is too small to hold the message contents
15    BufferTooSmall,
16    /// The message contains a FD that could not be dup-ed
17    DupFdFailed(std::io::Error),
18}
19
20impl std::error::Error for MessageWriteError {}
21
22impl std::fmt::Display for MessageWriteError {
23    #[cfg_attr(coverage, coverage(off))]
24    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
25        match self {
26            Self::BufferTooSmall => {
27                f.write_str("The provided buffer is too small to hold message content.")
28            }
29            Self::DupFdFailed(e) => {
30                write!(
31                    f,
32                    "The message contains a file descriptor that could not be dup()-ed ({}).",
33                    e
34                )
35            }
36        }
37    }
38}
39
40/// Error generated when trying to deserialize a message from buffers
41#[derive(Debug, Clone)]
42pub enum MessageParseError {
43    /// The message references a FD but the buffer FD is empty
44    MissingFD,
45    /// More data is needed to deserialize the message
46    MissingData,
47    /// The message is malformed and cannot be parsed
48    Malformed,
49}
50
51impl std::error::Error for MessageParseError {}
52
53impl std::fmt::Display for MessageParseError {
54    #[cfg_attr(coverage, coverage(off))]
55    fn fmt(&self, f: &mut ::std::fmt::Formatter) -> Result<(), ::std::fmt::Error> {
56        match *self {
57            Self::MissingFD => {
58                f.write_str("The message references a FD but the buffer FD is empty.")
59            }
60            Self::MissingData => f.write_str("More data is needed to deserialize the message"),
61            Self::Malformed => f.write_str("The message is malformed and cannot be parsed"),
62        }
63    }
64}
65
66/// Serialize the contents of this message into provided buffers
67///
68/// Returns the number of elements written in each buffer
69///
70/// Any serialized Fd will be `dup()`-ed in the process
71pub fn write_to_buffers(
72    msg: &Message<u32, RawFd>,
73    payload: &mut [u8],
74    fds: &mut Vec<OwnedFd>,
75) -> Result<usize, MessageWriteError> {
76    let orig_payload_len = payload.len();
77    // Helper function to write a u32 or a RawFd to its buffer
78    fn write_buf(u: u32, payload: &mut [u8]) -> Result<&mut [u8], MessageWriteError> {
79        if payload.len() >= 4 {
80            let (head, tail) = payload.split_at_mut(4);
81            head.copy_from_slice(&u.to_ne_bytes());
82            Ok(tail)
83        } else {
84            Err(MessageWriteError::BufferTooSmall)
85        }
86    }
87
88    // Helper function to write byte arrays in payload
89    fn write_array_to_payload<'a>(
90        array: &[u8],
91        payload: &'a mut [u8],
92    ) -> Result<&'a mut [u8], MessageWriteError> {
93        // size header
94        let payload = write_buf(array.len() as u32, payload)?;
95
96        // Handle padding
97        let len = next_multiple_of(array.len(), 4);
98
99        if payload.len() < len {
100            return Err(MessageWriteError::BufferTooSmall);
101        }
102
103        let (buffer_slice, rest) = payload.split_at_mut(len);
104        buffer_slice[..array.len()].copy_from_slice(array);
105        Ok(rest)
106    }
107
108    let free_size = payload.len();
109    if free_size < 2 * 4 {
110        return Err(MessageWriteError::BufferTooSmall);
111    }
112
113    let (header, mut payload) = payload.split_at_mut(2 * 4);
114
115    // write the contents in the buffer
116    for arg in &msg.args {
117        payload = match *arg {
118            Argument::Int(i) => write_buf(i as u32, payload)?,
119            Argument::Uint(u) => write_buf(u, payload)?,
120            Argument::Fixed(f) => write_buf(f as u32, payload)?,
121            Argument::Str(Some(ref s)) => write_array_to_payload(s.as_bytes_with_nul(), payload)?,
122            Argument::Str(None) => write_array_to_payload(&[], payload)?,
123            Argument::Object(o) => write_buf(o, payload)?,
124            Argument::NewId(n) => write_buf(n, payload)?,
125            Argument::Array(ref a) => write_array_to_payload(a, payload)?,
126            Argument::Fd(fd) => {
127                let dup_fd = unsafe { BorrowedFd::borrow_raw(fd) }
128                    .try_clone_to_owned()
129                    .map_err(MessageWriteError::DupFdFailed)?;
130                fds.push(dup_fd);
131                payload
132            }
133        };
134    }
135
136    let wrote_size = free_size - payload.len();
137    header[..4].copy_from_slice(&msg.sender_id.to_ne_bytes());
138    header[4..]
139        .copy_from_slice(&(((wrote_size as u32) << 16) | u32::from(msg.opcode)).to_ne_bytes());
140    Ok(orig_payload_len - payload.len())
141}
142
143/// Attempts to parse a single wayland message with the given signature.
144///
145/// If the buffers contains several messages, only the first one will be parsed,
146/// and the unused tail of the buffers is returned. If a single message was present,
147/// the returned slices should thus be empty.
148///
149/// Errors if the message is malformed.
150#[allow(clippy::type_complexity)]
151pub fn parse_message<'a>(
152    raw: &'a [u8],
153    signature: &[ArgumentType],
154    fds: &mut VecDeque<OwnedFd>,
155) -> Result<(Message<u32, OwnedFd>, &'a [u8]), MessageParseError> {
156    // helper function to read arrays
157    fn read_array_from_payload(
158        array_len: usize,
159        payload: &[u8],
160    ) -> Result<(&[u8], &[u8]), MessageParseError> {
161        let len = next_multiple_of(array_len, 4);
162        if len > payload.len() {
163            return Err(MessageParseError::MissingData);
164        }
165        Ok((&payload[..array_len], &payload[len..]))
166    }
167
168    if raw.len() < 2 * 4 {
169        return Err(MessageParseError::MissingData);
170    }
171
172    let sender_id = u32::from_ne_bytes([raw[0], raw[1], raw[2], raw[3]]);
173    let word_2 = u32::from_ne_bytes([raw[4], raw[5], raw[6], raw[7]]);
174    let opcode = (word_2 & 0x0000_FFFF) as u16;
175    let len = (word_2 >> 16) as usize;
176
177    if len < 2 * 4 {
178        return Err(MessageParseError::Malformed);
179    } else if len > raw.len() {
180        return Err(MessageParseError::MissingData);
181    }
182
183    let fd_len = signature.iter().filter(|x| matches!(x, ArgumentType::Fd)).count();
184    if fd_len > fds.len() {
185        return Err(MessageParseError::MissingFD);
186    }
187
188    let (mut payload, rest) = raw.split_at(len);
189    payload = &payload[2 * 4..];
190
191    let arguments = signature
192        .iter()
193        .map(|argtype| {
194            if let ArgumentType::Fd = *argtype {
195                // don't consume input but fd
196                if let Some(front) = fds.pop_front() {
197                    Ok(Argument::Fd(front))
198                } else {
199                    Err(MessageParseError::MissingFD)
200                }
201            } else if payload.len() >= 4 {
202                let (front, mut tail) = payload.split_at(4);
203                let front = u32::from_ne_bytes(front.try_into().unwrap());
204                let arg = match *argtype {
205                    ArgumentType::Int => Ok(Argument::Int(front as i32)),
206                    ArgumentType::Uint => Ok(Argument::Uint(front)),
207                    ArgumentType::Fixed => Ok(Argument::Fixed(front as i32)),
208                    ArgumentType::Str(_) => {
209                        read_array_from_payload(front as usize, tail).and_then(|(v, rest)| {
210                            tail = rest;
211                            if !v.is_empty() {
212                                match CStr::from_bytes_with_nul(v) {
213                                    Ok(s) => Ok(Argument::Str(Some(Box::new(s.into())))),
214                                    Err(_) => Err(MessageParseError::Malformed),
215                                }
216                            } else {
217                                Ok(Argument::Str(None))
218                            }
219                        })
220                    }
221                    ArgumentType::Object(_) => Ok(Argument::Object(front)),
222                    ArgumentType::NewId => Ok(Argument::NewId(front)),
223                    ArgumentType::Array => {
224                        read_array_from_payload(front as usize, tail).map(|(v, rest)| {
225                            tail = rest;
226                            Argument::Array(Box::new(v.into()))
227                        })
228                    }
229                    ArgumentType::Fd => unreachable!(),
230                };
231                payload = tail;
232                arg
233            } else {
234                Err(MessageParseError::MissingData)
235            }
236        })
237        .collect::<Result<SmallVec<_>, MessageParseError>>()?;
238
239    let msg = Message { sender_id, opcode, args: arguments };
240    Ok((msg, rest))
241}
242
243// Stabalized in Rust 1.73
244fn next_multiple_of(lhs: usize, rhs: usize) -> usize {
245    match lhs % rhs {
246        0 => lhs,
247        r => lhs + (rhs - r),
248    }
249}
250
251#[cfg(test)]
252mod tests {
253    use super::*;
254    use crate::protocol::AllowNull;
255    use smallvec::smallvec;
256    use std::{ffi::CString, os::unix::io::IntoRawFd};
257
258    #[test]
259    fn into_from_raw_cycle() {
260        let mut bytes_buffer = vec![0; 1024];
261        let mut fd_buffer = Vec::new();
262
263        let msg = Message {
264            sender_id: 42,
265            opcode: 7,
266            args: smallvec![
267                Argument::Uint(3),
268                Argument::Fixed(-89),
269                Argument::Str(Some(Box::new(CString::new(&b"I like trains!"[..]).unwrap()))),
270                Argument::Array(vec![1, 2, 3, 4, 5, 6, 7, 8, 9].into()),
271                Argument::Object(88),
272                Argument::NewId(56),
273                Argument::Int(-25),
274            ],
275        };
276        // write the message to the buffers
277        write_to_buffers(&msg, &mut bytes_buffer[..], &mut fd_buffer).unwrap();
278        // read them back
279        let mut fd_buffer = VecDeque::from(fd_buffer);
280        let (rebuilt, _) = parse_message(
281            &bytes_buffer[..],
282            &[
283                ArgumentType::Uint,
284                ArgumentType::Fixed,
285                ArgumentType::Str(AllowNull::No),
286                ArgumentType::Array,
287                ArgumentType::Object(AllowNull::No),
288                ArgumentType::NewId,
289                ArgumentType::Int,
290            ],
291            &mut fd_buffer,
292        )
293        .unwrap();
294        assert_eq!(rebuilt.map_fd(IntoRawFd::into_raw_fd), msg);
295    }
296}
wayland_backend/rs/wire.rs

wayland_backend/rs/
wire.rs
