fix(http): skip zero length chunks when encoding

src/http/conn.rs

@@ -269,6 +269,10 @@ where I: AsyncRead + AsyncWrite,
                     return Ok(AsyncSink::NotReady(chunk));
                 }
                 if let Some(chunk) = chunk {
+                    if chunk.as_ref().is_empty() {
+                        return Ok(AsyncSink::Ready);
+                    }
+
                     let mut cursor = Cursor::new(chunk);
                     match encoder.encode(&mut self.io, cursor.buf()) {
                         Ok(n) => {

src/http/h1/encode.rs

@@ -63,7 +63,7 @@ impl Encoder {
                 };
 
                 if n == 0 {
-                    return Err(io::Error::new(io::ErrorKind::WouldBlock, "would block"));
+                    return Err(io::Error::new(io::ErrorKind::WriteZero, "write zero"));
                 }
 
                 *remaining -= n as u64;