Fix blocking when reading into empty buffer

CHANGELOG.md

@@ -7,6 +7,10 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## Unreleased
 
+## 0.16.3 - ?
+
+- Don't block when reading into an empty buffer
+
 ## 0.16.2 - 2023-11-02
 
 - Re-add `impl_trait_projections` to support older nightly rustc versions

src/asynch.rs

@@ -163,6 +163,9 @@ where
 
     /// Read and decrypt data filling the provided slice.
     pub async fn read(&mut self, buf: &mut [u8]) -> Result<usize, TlsError> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
         let mut buffer = self.read_buffered().await?;
 
         let len = buffer.pop_into(buf);
@@ -460,6 +463,9 @@ where
     State: SplitState,
 {
     async fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
         let mut buffer = self.read_buffered().await?;
 
         let len = buffer.pop_into(buf);

src/blocking.rs

@@ -156,6 +156,9 @@ where
 
     /// Read and decrypt data filling the provided slice.
     pub fn read(&mut self, buf: &mut [u8]) -> Result<usize, TlsError> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
         let mut buffer = self.read_buffered()?;
 
         let len = buffer.pop_into(buf);
@@ -450,6 +453,9 @@ where
     State: SplitState,
 {
     fn read(&mut self, buf: &mut [u8]) -> Result<usize, Self::Error> {
+        if buf.is_empty() {
+            return Ok(0);
+        }
         let mut buffer = self.read_buffered()?;
 
         let len = buffer.pop_into(buf);

tests/client_test.rs

@@ -140,6 +140,11 @@ async fn test_ping() {
     assert_eq!(b"ping", &rx_buf[..sz]);
     log::info!("Read {} bytes: {:?}", sz, &rx_buf[..sz]);
 
+    // Test that embedded-tls doesn't block if the buffer is empty.
+    let mut rx_buf = [0; 0];
+    let sz = tls.read(&mut rx_buf).await.expect("error reading data");
+    assert_eq!(sz, 0);
+
     tls.close()
         .await
         .map_err(|(_, e)| e)
@@ -304,6 +309,11 @@ fn test_blocking_ping() {
     assert_eq!(b"ping", &rx_buf[..sz]);
     log::info!("Read {} bytes: {:?}", sz, &rx_buf[..sz]);
 
+    // Test that embedded-tls doesn't block if the buffer is empty.
+    let mut rx_buf = [0; 0];
+    let sz = tls.read(&mut rx_buf).expect("error reading data");
+    assert_eq!(sz, 0);
+
     tls.close()
         .map_err(|(_, e)| e)
         .expect("error closing session");