write.rs

    /// Write a single `Frame` value to the underlying stream.
    ///
    /// The `Frame` value is written to the socket using the various `write_*`
    /// functions provided by `AsyncWrite`. Calling these functions directly on
    /// a `TcpStream` is **not** advised, as this will result in a large number of
    /// syscalls. However, it is fine to call these functions on a *buffered*
    /// write stream. The data will be written to the buffer. Once the buffer is
    /// full, it is flushed to the underlying socket.
    pub async fn write_frame(&mut self, frame: &Frame) -> io::Result<()> {
        // Arrays are encoded by encoding each entry. All other frame types are
        // considered literals. For now, mini-redis is not able to encode
        // recursive frame structures. See below for more details.
        match frame {
            Frame::Array(val) => {
                // Encode the frame type prefix. For an array, it is `*`.
                self.stream.write_u8(b'*').await?;

                // Encode the length of the array.
                self.write_decimal(val.len() as u64).await?;

                // Iterate and encode each entry in the array.
                for entry in &**val {
                    self.write_value(entry).await?;
                }
            }
            // The frame type is a literal. Encode the value directly.
            _ => self.write_value(frame).await?,
        }

        // Ensure the encoded frame is written to the socket. The calls above
        // are to the buffered stream and writes. Calling `flush` writes the
        // remaining contents of the buffer to the socket.
        self.stream.flush().await
    }

    /// Write a frame literal to the stream
    async fn write_value(&mut self, frame: &Frame) -> io::Result<()> {
        match frame {
            Frame::Simple(val) => {
                self.stream.write_u8(b'+').await?;
                self.stream.write_all(val.as_bytes()).await?;
                self.stream.write_all(b"\r\n").await?;
            }
            Frame::Error(val) => {
                self.stream.write_u8(b'-').await?;
                self.stream.write_all(val.as_bytes()).await?;
                self.stream.write_all(b"\r\n").await?;
            }
            Frame::Integer(val) => {
                self.stream.write_u8(b':').await?;
                self.write_decimal(*val).await?;
            }
            Frame::Null => {
                self.stream.write_all(b"$-1\r\n").await?;
            }
            Frame::Bulk(val) => {
                let len = val.len();

                self.stream.write_u8(b'$').await?;
                self.write_decimal(len as u64).await?;
                self.stream.write_all(val).await?;
                self.stream.write_all(b"\r\n").await?;
            }
            // Encoding an `Array` from within a value cannot be done using a
            // recursive strategy. In general, async fns do not support
            // recursion. Mini-redis has not needed to encode nested arrays yet,
            // so for now it is skipped.
            Frame::Array(_val) => unreachable!(),
        }

        Ok(())
    }

    /// Write a decimal frame to the stream
    async fn write_decimal(&mut self, val: u64) -> io::Result<()> {
        use std::io::Write;

        // Convert the value to a string
        let mut buf = [0u8; 20];
        let mut buf = Cursor::new(&mut buf[..]);
        write!(&mut buf, "{}", val)?;

        let pos = buf.position() as usize;
        self.stream.write_all(&buf.get_ref()[..pos]).await?;
        self.stream.write_all(b"\r\n").await?;

        Ok(())
    }