Reuse content buffer in JSONRPC recv for LSP and DAP

Previously `recv` for new messages from the language server or debug
adapter allocated a fresh Vec for each message. Instead we can reuse
the buffer. This resolves TODO comments.

Co-authored-by: Rolo <roloedits@gmail.com>

helix-dap/src/transport.rs

@@ -85,10 +85,11 @@ impl Transport {
     async fn recv_server_message(
         reader: &mut Box<dyn AsyncBufRead + Unpin + Send>,
         buffer: &mut String,
+        content: &mut Vec<u8>,
     ) -> Result<Payload> {
         let mut content_length = None;
         loop {
-            buffer.truncate(0);
+            buffer.clear();
             if reader.read_line(buffer).await? == 0 {
                 return Err(Error::StreamClosed);
             };
@@ -117,17 +118,17 @@ impl Transport {
         }
 
         let content_length = content_length.context("missing content length")?;
-
+        content.resize(content_length, 0);
-        //TODO: reuse vector
+        reader.read_exact(content).await?;
-        let mut content = vec![0; content_length];
+        let msg = std::str::from_utf8(content).context("invalid utf8 from server")?;
-        reader.read_exact(&mut content).await?;
-        let msg = std::str::from_utf8(&content).context("invalid utf8 from server")?;
 
         info!("<- DAP {}", msg);
 
         // try parsing as output (server response) or call (server request)
         let output: serde_json::Result<Payload> = serde_json::from_str(msg);
 
+        content.clear();
+
         Ok(output?)
     }
 
@@ -242,8 +243,15 @@ impl Transport {
         client_tx: UnboundedSender<Payload>,
     ) {
         let mut recv_buffer = String::new();
+        let mut content_buffer = Vec::new();
         loop {
-            match Self::recv_server_message(&mut server_stdout, &mut recv_buffer).await {
+            match Self::recv_server_message(
+                &mut server_stdout,
+                &mut recv_buffer,
+                &mut content_buffer,
+            )
+            .await
+            {
                 Ok(msg) => match transport.process_server_message(&client_tx, msg).await {
                     Ok(_) => (),
                     Err(err) => {

helix-lsp/src/transport.rs

@@ -90,11 +90,12 @@ impl Transport {
     async fn recv_server_message(
         reader: &mut (impl AsyncBufRead + Unpin + Send),
         buffer: &mut String,
+        content: &mut Vec<u8>,
         language_server_name: &str,
     ) -> Result<ServerMessage> {
         let mut content_length = None;
         loop {
-            buffer.truncate(0);
+            buffer.clear();
             if reader.read_line(buffer).await? == 0 {
                 return Err(Error::StreamClosed);
             };
@@ -126,11 +127,9 @@ impl Transport {
         }
 
         let content_length = content_length.context("missing content length")?;
-
+        content.resize(content_length, 0);
-        //TODO: reuse vector
+        reader.read_exact(content).await?;
-        let mut content = vec![0; content_length];
+        let msg = std::str::from_utf8(content).context("invalid utf8 from server")?;
-        reader.read_exact(&mut content).await?;
-        let msg = std::str::from_utf8(&content).context("invalid utf8 from server")?;
 
         info!("{language_server_name} <- {msg}");
 
@@ -255,9 +254,15 @@ impl Transport {
         client_tx: UnboundedSender<(LanguageServerId, jsonrpc::Call)>,
     ) {
         let mut recv_buffer = String::new();
+        let mut content_buffer = Vec::new();
         loop {
-            match Self::recv_server_message(&mut server_stdout, &mut recv_buffer, &transport.name)
+            match Self::recv_server_message(
-                .await
+                &mut server_stdout,
+                &mut recv_buffer,
+                &mut content_buffer,
+                &transport.name,
+            )
+            .await
             {
                 Ok(msg) => {
                     match transport