optimize by merging 3 unbuffered reads on IPC message header into one

This reduces the number of system calls done for reading an
incoming IPC message from 4 to 2 and improves latency

async/src/common.rs

@@ -6,16 +6,15 @@ use swayipc_types::{Error::InvalidMagic, Fallible, MAGIC};
 pub(super) async fn receive_from_stream(
     stream: &mut Async<UnixStream>,
 ) -> Fallible<(u32, Vec<u8>)> {
-    let mut magic_data = [0_u8; 6];
-    stream.read_exact(&mut magic_data).await?;
+    let mut header_buf = [0_u8; 14];
+    stream.read_exact(&mut header_buf).await?;
+    let magic_data: [u8; 6] = header_buf[..6].try_into().unwrap();
     if magic_data != MAGIC {
         return Err(InvalidMagic(magic_data));
     }
-    let mut payload_len_buf = [0_u8; 4];
-    stream.read_exact(&mut payload_len_buf).await?;
+    let payload_len_buf: [u8; 4] = header_buf[6..10].try_into().unwrap();
     let payload_len = u32::from_ne_bytes(payload_len_buf);
-    let mut reply_type_buf = [0_u8; 4];
-    stream.read_exact(&mut reply_type_buf).await?;
+    let reply_type_buf: [u8; 4] = header_buf[10..14].try_into().unwrap();
     let reply_type = u32::from_ne_bytes(reply_type_buf);
     let mut reply_payload = vec![0_u8; payload_len as usize];
     stream.read_exact(&mut reply_payload).await?;

blocking/src/common.rs

@@ -3,16 +3,15 @@ use std::os::unix::net::UnixStream;
 use swayipc_types::{Error::InvalidMagic, Fallible, MAGIC};
 
 pub(super) fn receive_from_stream(stream: &mut UnixStream) -> Fallible<(u32, Vec<u8>)> {
-    let mut magic_data = [0_u8; 6];
-    stream.read_exact(&mut magic_data)?;
+    let mut header_buf = [0_u8; 14];
+    stream.read_exact(&mut header_buf)?;
+    let magic_data: [u8; 6] = header_buf[..6].try_into().unwrap();
     if magic_data != MAGIC {
         return Err(InvalidMagic(magic_data));
     }
-    let mut payload_len_buf = [0_u8; 4];
-    stream.read_exact(&mut payload_len_buf)?;
+    let payload_len_buf: [u8; 4] = header_buf[6..10].try_into().unwrap();
     let payload_len = u32::from_ne_bytes(payload_len_buf);
-    let mut reply_type_buf = [0_u8; 4];
-    stream.read_exact(&mut reply_type_buf)?;
+    let reply_type_buf: [u8; 4] = header_buf[10..14].try_into().unwrap();
     let reply_type = u32::from_ne_bytes(reply_type_buf);
     let mut reply_payload = vec![0_u8; payload_len as usize];
     stream.read_exact(&mut reply_payload)?;