[pbs-devel] [PATCH proxmox v2 1/4] proxmox/tools/websocket: introduce WebSocketError and use it

[Dominik Csapak <d.csapak@proxmox.com>]

this patch introduces a custom WebSocketError, so that we can
detect errors in the websocket protocol and react to it in the
right way

the channel now sends a Result<(OpCode, Box<[u8]>), WebSocketError>
so that we can either react to a control frame, or react to an
errornous data stream (which means sending a close frame
with the appropriate error code)

while at it, change FrameHeader::try_from_bytes to return
Result<Option<FrameHeader>, WebSocketError> instead of a nested
Result with the *guessed* remaining size. This was neither used by
us, nor was it really meaningful, since this can change during the
decode every time new data is read (extensions, mask, payload length, etc.)
so simply returning an Option is enough information for us

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
---
changes from v1:
* fix one instance of Ok(Err) for try_from_bytes that was leftover
* omit the pub const slices and implement to_be_bytes for the ErrorKind
  instead
* (correctly) use extend_from_slice instead of copy_from_slice
* impl std::error::Error instead of From<WebSocketError> for anyhow::Error

 proxmox/src/tools/websocket.rs | 184 ++++++++++++++++++++++++---------
 1 file changed, 133 insertions(+), 51 deletions(-)

diff --git a/proxmox/src/tools/websocket.rs b/proxmox/src/tools/websocket.rs
index fc9a0c5..c6775f0 100644
--- a/proxmox/src/tools/websocket.rs
+++ b/proxmox/src/tools/websocket.rs
@@ -7,7 +7,7 @@
 use std::pin::Pin;
 use std::task::{Context, Poll};
 use std::cmp::min;
-use std::io::{self, ErrorKind};
+use std::io;
 use std::future::Future;
 
 use futures::select;
@@ -29,9 +29,65 @@ use hyper::header::{
 use futures::future::FutureExt;
 use futures::ready;
 
-use crate::io_format_err;
+use crate::sys::error::io_err_other;
 use crate::tools::byte_buffer::ByteBuffer;
 
+// see RFC6455 section 7.4.1
+#[derive(Debug, Clone, Copy)]
+#[repr(u16)]
+pub enum WebSocketErrorKind {
+    Normal = 1000,
+    ProtocolError = 1002,
+    InvalidData = 1003,
+    Other = 1008,
+    Unexpected = 1011,
+}
+
+impl WebSocketErrorKind {
+    #[inline]
+    pub fn to_be_bytes(self) -> [u8; 2] {
+        (self as u16).to_be_bytes()
+    }
+}
+
+impl std::fmt::Display for WebSocketErrorKind {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        write!(f, "{}", *self as u16)
+    }
+}
+
+#[derive(Debug, Clone)]
+pub struct WebSocketError{
+    kind: WebSocketErrorKind,
+    message: String,
+}
+
+impl WebSocketError {
+    pub fn new(kind: WebSocketErrorKind, message: &str) -> Self {
+        Self{
+            kind,
+            message: message.to_string()
+        }
+    }
+
+    pub fn generate_frame_payload(&self) -> Vec<u8> {
+        let msglen = self.message.len().min(125);
+        let code = self.kind.to_be_bytes();
+        let mut data = Vec::with_capacity(msglen + 2);
+        data.extend_from_slice(&code);
+        data.extend_from_slice(&self.message.as_bytes()[..msglen]);
+        data
+    }
+}
+
+impl std::fmt::Display for WebSocketError {
+    fn fmt(&self, f: &mut std::fmt::Formatter) -> Result<(), std::fmt::Error> {
+        write!(f, "{} (Code: {})", self.message, self.kind)
+    }
+}
+
+impl std::error::Error for WebSocketError {}
+
 #[repr(u8)]
 #[derive(Debug, PartialEq, PartialOrd, Copy, Clone)]
 /// Represents an OpCode of a websocket frame
@@ -293,25 +349,23 @@ impl FrameHeader {
     /// Tries to parse a FrameHeader from bytes.
     ///
     /// When there are not enough bytes to completely parse the header,
-    /// returns Ok(Err(size)) where size determines how many bytes
-    /// are missing to parse further (this amount can change when more
-    /// information is available)
+    /// returns Ok(None)
     ///
     /// Example:
     /// ```
     /// # use proxmox::tools::websocket::*;
     /// # use std::io;
-    /// # fn main() -> io::Result<()> {
+    /// # fn main() -> Result<(), WebSocketError> {
     /// let frame = create_frame(None, &[0,1,2,3], OpCode::Ping)?;
     /// let header = FrameHeader::try_from_bytes(&frame[..1])?;
     /// match header {
-    ///     Ok(_) => unreachable!(),
-    ///     Err(x) => assert_eq!(x, 1),
+    ///     Some(_) => unreachable!(),
+    ///     None => {},
     /// }
     /// let header = FrameHeader::try_from_bytes(&frame[..2])?;
     /// match header {
-    ///     Err(x) => unreachable!(),
-    ///     Ok(header) => assert_eq!(header, FrameHeader{
+    ///     None => unreachable!(),
+    ///     Some(header) => assert_eq!(header, FrameHeader{
     ///         fin: true,
     ///         mask: None,
     ///         frametype: OpCode::Ping,
@@ -322,19 +376,19 @@ impl FrameHeader {
     /// # Ok(())
     /// # }
     /// ```
-    pub fn try_from_bytes(data: &[u8]) -> io::Result<Result<FrameHeader, usize>> {
+    pub fn try_from_bytes(data: &[u8]) -> Result<Option<FrameHeader>, WebSocketError> {
         let len = data.len();
         if len < 2 {
-            return Ok(Err(2 - len));
+            return Ok(None);
         }
 
         let data = data;
 
         // we do not support extensions
         if data[0] & 0b01110000 > 0 {
-            return Err(io::Error::new(
-                ErrorKind::InvalidData,
-                "Extensions not supported",
+            return Err(WebSocketError::new(
+                    WebSocketErrorKind::ProtocolError,
+                    "Extensions not supported",
             ));
         }
 
@@ -347,14 +401,17 @@ impl FrameHeader {
             9 => OpCode::Ping,
             10 => OpCode::Pong,
             other => {
-                return Err(io::Error::new(ErrorKind::InvalidData, format!("Unknown OpCode {}", other)));
+                return Err(WebSocketError::new(
+                        WebSocketErrorKind::ProtocolError,
+                        &format!("Unknown OpCode {}", other),
+                ));
             }
         };
 
         if !fin && frametype.is_control() {
-            return Err(io::Error::new(
-                ErrorKind::InvalidData,
-                "Control frames cannot be fragmented",
+            return Err(WebSocketError::new(
+                    WebSocketErrorKind::ProtocolError,
+                    "Control frames cannot be fragmented",
             ));
         }
 
@@ -368,14 +425,14 @@ impl FrameHeader {
         let mut payload_len: usize = (data[1] & 0b01111111).into();
         if payload_len == 126 {
             if len < 4 {
-                return Ok(Err(4 - len));
+                return Ok(None);
             }
             payload_len = u16::from_be_bytes([data[2], data[3]]) as usize;
             mask_offset += 2;
             payload_offset += 2;
         } else if payload_len == 127 {
             if len < 10 {
-                return Ok(Err(10 - len));
+                return Ok(None);
             }
             payload_len = u64::from_be_bytes([
                 data[2], data[3], data[4], data[5], data[6], data[7], data[8], data[9],
@@ -385,16 +442,16 @@ impl FrameHeader {
         }
 
         if payload_len > 125 && frametype.is_control() {
-            return Err(io::Error::new(
-                ErrorKind::InvalidData,
-                "Control frames cannot carry more than 125 bytes of data",
+            return Err(WebSocketError::new(
+                    WebSocketErrorKind::ProtocolError,
+                    "Control frames cannot carry more than 125 bytes of data",
             ));
         }
 
         let mask = match mask_bit {
             true => {
                 if len < mask_offset + 4 {
-                    return Ok(Err(mask_offset + 4 - len));
+                    return Ok(None);
                 }
                 let mut mask = [0u8; 4];
                 mask.copy_from_slice(&data[mask_offset as usize..payload_offset as usize]);
@@ -403,7 +460,7 @@ impl FrameHeader {
             false => None,
         };
 
-        Ok(Ok(FrameHeader {
+        Ok(Some(FrameHeader {
             fin,
             mask,
             frametype,
@@ -413,6 +470,8 @@ impl FrameHeader {
     }
 }
 
+type WebSocketReadResult = Result<(OpCode, Box<[u8]>), WebSocketError>;
+
 /// Wraps a reader that implements AsyncRead and implements it itself.
 ///
 /// On read, reads the underlying reader and tries to decode the frames and
@@ -422,7 +481,7 @@ impl FrameHeader {
 /// Has an internal Buffer for storing incomplete headers.
 pub struct WebSocketReader<R: AsyncRead> {
     reader: Option<R>,
-    sender: mpsc::UnboundedSender<(OpCode, Box<[u8]>)>,
+    sender: mpsc::UnboundedSender<WebSocketReadResult>,
     read_buffer: Option<ByteBuffer>,
     header: Option<FrameHeader>,
     state: ReaderState<R>,
@@ -431,11 +490,11 @@ pub struct WebSocketReader<R: AsyncRead> {
 impl<R: AsyncReadExt> WebSocketReader<R> {
     /// Creates a new WebSocketReader with the given CallBack for control frames
     /// and a default buffer size of 4096.
-    pub fn new(reader: R, sender: mpsc::UnboundedSender<(OpCode, Box<[u8]>)>) -> WebSocketReader<R> {
+    pub fn new(reader: R, sender: mpsc::UnboundedSender<WebSocketReadResult>) -> WebSocketReader<R> {
         Self::with_capacity(reader, 4096, sender)
     }
 
-    pub fn with_capacity(reader: R, capacity: usize, sender: mpsc::UnboundedSender<(OpCode, Box<[u8]>)>) -> WebSocketReader<R> {
+    pub fn with_capacity(reader: R, capacity: usize, sender: mpsc::UnboundedSender<WebSocketReadResult>) -> WebSocketReader<R> {
         WebSocketReader {
             reader: Some(reader),
             sender,
@@ -512,13 +571,19 @@ impl<R: AsyncReadExt + Unpin + Send + 'static> AsyncRead for WebSocketReader<R>
                     let mut header = match this.header.take() {
                         Some(header) => header,
                         None => {
-                            let header = match FrameHeader::try_from_bytes(&read_buffer[..])? {
-                                Ok(header) => header,
-                                Err(_) => {
+                            let header = match FrameHeader::try_from_bytes(&read_buffer[..]) {
+                                Ok(Some(header)) => header,
+                                Ok(None) => {
                                     this.state = ReaderState::NoData;
                                     this.read_buffer = Some(read_buffer);
                                     continue;
-                                }
+                                },
+                                Err(err) => {
+                                    if let Err(err) = this.sender.send(Err(err.clone())) {
+                                        return Poll::Ready(Err(io_err_other(err)));
+                                    }
+                                    return Poll::Ready(Err(io_err_other(err)));
+                                },
                             };
 
                             read_buffer.consume(header.header_len as usize);
@@ -531,7 +596,7 @@ impl<R: AsyncReadExt + Unpin + Send + 'static> AsyncRead for WebSocketReader<R>
 
                             let mut data = read_buffer.remove_data(header.payload_len);
                             mask_bytes(header.mask, &mut data);
-                            if let Err(err) = this.sender.send((header.frametype, data)) {
+                            if let Err(err) = this.sender.send(Ok((header.frametype, data))) {
                                 eprintln!("error sending control frame: {}", err);
                             }
 
@@ -639,10 +704,37 @@ impl WebSocket {
         Ok((Self { text }, response))
     }
 
+    async fn handle_channel_message<W>(
+        result: WebSocketReadResult,
+        writer: &mut WebSocketWriter<W>
+    ) -> Result<OpCode, Error>
+    where
+        W: AsyncWrite + Unpin + Send,
+    {
+        match result {
+            Ok((OpCode::Ping, msg)) => {
+                writer.send_control_frame(None, OpCode::Pong, &msg).await?;
+                Ok(OpCode::Pong)
+            }
+            Ok((OpCode::Close, msg)) => {
+                writer.send_control_frame(None, OpCode::Close, &msg).await?;
+                Ok(OpCode::Close)
+            }
+            Ok((opcode, _)) => {
+                // ignore other frames
+                Ok(opcode)
+            },
+            Err(err) => {
+                writer.send_control_frame(None, OpCode::Close, &err.generate_frame_payload()).await?;
+                Err(Error::from(err))
+            }
+        }
+    }
+
     async fn copy_to_websocket<R, W>(
         mut reader: &mut R,
-        writer: &mut WebSocketWriter<W>,
-        receiver: &mut mpsc::UnboundedReceiver<(OpCode, Box<[u8]>)>) -> Result<bool, Error>
+        mut writer: &mut WebSocketWriter<W>,
+        receiver: &mut mpsc::UnboundedReceiver<WebSocketReadResult>) -> Result<bool, Error>
     where
         R: AsyncRead + Unpin + Send,
         W: AsyncWrite + Unpin + Send,
@@ -654,20 +746,10 @@ impl WebSocket {
                 let bytes = select!{
                     res = buf.read_from_async(&mut reader).fuse() => res?,
                     res = receiver.recv().fuse() => {
-                        let (opcode, msg) = res.ok_or(format_err!("control channel closed"))?;
-                        match opcode {
-                            OpCode::Ping => {
-                                writer.send_control_frame(None, OpCode::Pong, &msg).await?;
-                                continue;
-                            }
-                            OpCode::Close => {
-                                writer.send_control_frame(None, OpCode::Close, &msg).await?;
-                                return Ok(true);
-                            }
-                            _ => {
-                                // ignore other frames
-                                continue;
-                            }
+                        let res = res.ok_or_else(|| format_err!("control channel closed"))?;
+                        match Self::handle_channel_message(res, &mut writer).await? {
+                            OpCode::Close => return Ok(true),
+                            _ => { continue; },
                         }
                     }
                 };
@@ -720,7 +802,7 @@ impl WebSocket {
             res = term_future.fuse() => match res {
                 Ok(sent_close) if !sent_close => {
                     // status code 1000 => 0x03E8
-                    wswriter.send_control_frame(None, OpCode::Close, &[0x03, 0xE8]).await?;
+                    wswriter.send_control_frame(None, OpCode::Close, &WebSocketErrorKind::Normal.to_be_bytes()).await?;
                     Ok(())
                 }
                 Ok(_) => Ok(()),
-- 
2.20.1