Introduce zed_rpc::proto module containing protobuf stream logic

Co-Authored-By: Nathan Sobo <nathan@zed.dev>

zed-rpc/src/lib.rs

@@ -1 +1,2 @@
 pub mod auth;
+pub mod proto;

zed-rpc/src/proto.rs

@@ -0,0 +1,234 @@
+use futures_io::{AsyncRead, AsyncWrite};
+use futures_lite::{AsyncReadExt, AsyncWriteExt as _};
+use prost::Message;
+use std::io;
+
+include!(concat!(env!("OUT_DIR"), "/zed.messages.rs"));
+
+pub trait Request {
+    type Response;
+}
+
+impl Request for from_client::Auth {
+    type Response = from_server::Ack;
+}
+
+/// A stream of protobuf messages.
+pub struct MessageStream<T> {
+    byte_stream: T,
+    buffer: Vec<u8>,
+}
+
+impl<T> MessageStream<T> {
+    pub fn new(byte_stream: T) -> Self {
+        Self {
+            byte_stream,
+            buffer: Default::default(),
+        }
+    }
+}
+
+impl<T> MessageStream<T>
+where
+    T: AsyncWrite + Unpin,
+{
+    /// Write a given protobuf message to the stream.
+    pub async fn write_message(&mut self, message: &impl Message) -> futures_io::Result<()> {
+        self.buffer.clear();
+        message.encode_length_delimited(&mut self.buffer).unwrap();
+        self.byte_stream.write_all(&self.buffer).await
+    }
+}
+
+impl<T> MessageStream<T>
+where
+    T: AsyncRead + Unpin,
+{
+    /// Read a protobuf message of the given type from the stream.
+    pub async fn read_message<M: Message + Default>(&mut self) -> futures_io::Result<M> {
+        // Ensure the buffer is large enough to hold the maximum delimiter length
+        const MAX_DELIMITER_LEN: usize = 10;
+        self.buffer.clear();
+        self.buffer.resize(MAX_DELIMITER_LEN, 0);
+
+        // Read until a complete length delimiter can be decoded.
+        let mut read_start_offset = 0;
+        let (encoded_len, delimiter_len) = loop {
+            let bytes_read = self
+                .byte_stream
+                .read(&mut self.buffer[read_start_offset..])
+                .await?;
+            read_start_offset += bytes_read;
+
+            let mut buffer = &self.buffer[0..read_start_offset];
+            match prost::decode_length_delimiter(&mut buffer) {
+                Err(_) => {
+                    if read_start_offset >= MAX_DELIMITER_LEN {
+                        return Err(io::Error::new(
+                            io::ErrorKind::InvalidData,
+                            "invalid message length delimiter",
+                        ));
+                    }
+                }
+                Ok(encoded_len) => {
+                    let delimiter_len = read_start_offset - buffer.len();
+                    break (encoded_len, delimiter_len);
+                }
+            }
+        };
+
+        // Read the message itself.
+        self.buffer.resize(delimiter_len + encoded_len, 0);
+        self.byte_stream
+            .read_exact(&mut self.buffer[read_start_offset..])
+            .await?;
+        let message = M::decode(&self.buffer[delimiter_len..])?;
+
+        Ok(message)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use std::{
+        pin::Pin,
+        task::{Context, Poll},
+    };
+
+    #[test]
+    fn test_round_trip_message() {
+        smol::block_on(async {
+            let byte_stream = ChunkedStream {
+                bytes: Vec::new(),
+                read_offset: 0,
+                chunk_size: 3,
+            };
+
+            // In reality there will never be both `FromClient` and `FromServer` messages
+            // sent in the same direction on the same stream.
+            let message1 = FromClient {
+                id: 3,
+                variant: Some(from_client::Variant::Auth(from_client::Auth {
+                    user_id: 5,
+                    access_token: "the-access-token".into(),
+                })),
+            };
+            let message2 = FromServer {
+                request_id: Some(4),
+                variant: Some(from_server::Variant::Ack(from_server::Ack {
+                    error_message: Some(
+                        format!(
+                            "a {}long error message that requires a two-byte length delimiter",
+                            "very ".repeat(60)
+                        )
+                        .into(),
+                    ),
+                })),
+            };
+
+            let mut message_stream = MessageStream::new(byte_stream);
+            message_stream.write_message(&message1).await.unwrap();
+            message_stream.write_message(&message2).await.unwrap();
+            let decoded_message1 = message_stream.read_message::<FromClient>().await.unwrap();
+            let decoded_message2 = message_stream.read_message::<FromServer>().await.unwrap();
+            assert_eq!(decoded_message1, message1);
+            assert_eq!(decoded_message2, message2);
+        });
+    }
+
+    #[test]
+    fn test_read_message_when_length_delimiter_is_not_complete_in_first_read() {
+        smol::block_on(async {
+            let byte_stream = ChunkedStream {
+                bytes: Vec::new(),
+                read_offset: 0,
+                chunk_size: 2,
+            };
+
+            // This message is so long that its length delimiter requires three bytes,
+            // so it won't be delivered in a single read from the chunked byte stream.
+            let message = FromServer {
+                request_id: Some(4),
+                variant: Some(from_server::Variant::Ack(from_server::Ack {
+                    error_message: Some("long ".repeat(256 * 256).into()),
+                })),
+            };
+            assert!(prost::length_delimiter_len(message.encoded_len()) > byte_stream.chunk_size);
+
+            let mut message_stream = MessageStream::new(byte_stream);
+            message_stream.write_message(&message).await.unwrap();
+            let decoded_message = message_stream.read_message::<FromServer>().await.unwrap();
+            assert_eq!(decoded_message, message);
+        });
+    }
+
+    #[test]
+    fn test_protobuf_parse_error() {
+        smol::block_on(async {
+            let byte_stream = ChunkedStream {
+                bytes: Vec::new(),
+                read_offset: 0,
+                chunk_size: 2,
+            };
+
+            let message = FromClient {
+                id: 3,
+                variant: Some(from_client::Variant::Auth(from_client::Auth {
+                    user_id: 5,
+                    access_token: "the-access-token".into(),
+                })),
+            };
+
+            let mut message_stream = MessageStream::new(byte_stream);
+            message_stream.write_message(&message).await.unwrap();
+
+            // Read the wrong type of message from the stream.
+            let result = message_stream.read_message::<FromServer>().await;
+            assert_eq!(result.unwrap_err().kind(), io::ErrorKind::InvalidData);
+        });
+    }
+
+    struct ChunkedStream {
+        bytes: Vec<u8>,
+        read_offset: usize,
+        chunk_size: usize,
+    }
+
+    impl AsyncWrite for ChunkedStream {
+        fn poll_write(
+            mut self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            buf: &[u8],
+        ) -> Poll<io::Result<usize>> {
+            let bytes_written = buf.len().min(self.chunk_size);
+            self.bytes.extend_from_slice(&buf[0..bytes_written]);
+            Poll::Ready(Ok(bytes_written))
+        }
+
+        fn poll_flush(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Poll::Ready(Ok(()))
+        }
+
+        fn poll_close(self: Pin<&mut Self>, _: &mut Context<'_>) -> Poll<io::Result<()>> {
+            Poll::Ready(Ok(()))
+        }
+    }
+
+    impl AsyncRead for ChunkedStream {
+        fn poll_read(
+            mut self: Pin<&mut Self>,
+            _: &mut Context<'_>,
+            buf: &mut [u8],
+        ) -> Poll<io::Result<usize>> {
+            let bytes_read = buf
+                .len()
+                .min(self.chunk_size)
+                .min(self.bytes.len() - self.read_offset);
+            let end_offset = self.read_offset + bytes_read;
+            buf[0..bytes_read].copy_from_slice(&self.bytes[self.read_offset..end_offset]);
+            self.read_offset = end_offset;
+            Poll::Ready(Ok(bytes_read))
+        }
+    }
+}