diff --git a/src/substream/mod.rs b/src/substream/mod.rs
index 5fc1ec3c7..37ba98c05 100644
--- a/src/substream/mod.rs
+++ b/src/substream/mod.rs
@@ -369,7 +369,34 @@ impl Substream {
 
         io.write_all(&payload)
             .await
-            .map_err(|_| Error::SubstreamError(SubstreamError::ConnectionClosed))
+            .map_err(|_| Error::SubstreamError(SubstreamError::ConnectionClosed))?;
+
+        // Flush the stream.
+        io.flush().await.map_err(From::from)
+    }
+
+    /// Send unsigned varint payload to remote peer.
+    async fn send_unsigned_varint_payload<T: AsyncWrite + Unpin>(
+        io: &mut T,
+        bytes: Bytes,
+        max_size: Option<usize>,
+    ) -> crate::Result<()> {
+        if let Some(max_size) = max_size {
+            if bytes.len() > max_size {
+                return Err(Error::IoError(ErrorKind::PermissionDenied));
+            }
+        }
+
+        // Write the length of the frame.
+        let mut buffer = unsigned_varint::encode::usize_buffer();
+        let encoded_len = unsigned_varint::encode::usize(bytes.len(), &mut buffer).len();
+        io.write_all(&buffer[..encoded_len]).await?;
+
+        // Write the frame.
+        io.write_all(bytes.as_ref()).await?;
+
+        // Flush the stream.
+        io.flush().await.map_err(From::from)
     }
 
     /// Send framed data to remote peer.
@@ -386,7 +413,7 @@ impl Substream {
     /// # Panics
     ///
     /// Panics if no codec is provided.
-    pub async fn send_framed(&mut self, mut bytes: Bytes) -> crate::Result<()> {
+    pub async fn send_framed(&mut self, bytes: Bytes) -> crate::Result<()> {
         tracing::trace!(
             target: LOG_TARGET,
             peer = ?self.peer,
@@ -403,48 +430,16 @@ impl Substream {
                 ProtocolCodec::Unspecified => panic!("codec is unspecified"),
                 ProtocolCodec::Identity(payload_size) =>
                     Self::send_identity_payload(substream, payload_size, bytes).await,
-                ProtocolCodec::UnsignedVarint(max_size) => {
-                    check_size!(max_size, bytes.len());
-
-                    let mut buffer = [0u8; 10];
-                    let len = unsigned_varint::encode::usize(bytes.len(), &mut buffer);
-                    let mut offset = 0;
-
-                    while offset < len.len() {
-                        offset += substream.write(&len[offset..]).await?;
-                    }
-
-                    while bytes.has_remaining() {
-                        let nwritten = substream.write(&bytes).await?;
-                        bytes.advance(nwritten);
-                    }
-
-                    substream.flush().await.map_err(From::from)
-                }
+                ProtocolCodec::UnsignedVarint(max_size) =>
+                    Self::send_unsigned_varint_payload(substream, bytes, max_size).await,
             },
             #[cfg(feature = "websocket")]
             SubstreamType::WebSocket(ref mut substream) => match self.codec {
                 ProtocolCodec::Unspecified => panic!("codec is unspecified"),
                 ProtocolCodec::Identity(payload_size) =>
                     Self::send_identity_payload(substream, payload_size, bytes).await,
-                ProtocolCodec::UnsignedVarint(max_size) => {
-                    check_size!(max_size, bytes.len());
-
-                    let mut buffer = [0u8; 10];
-                    let len = unsigned_varint::encode::usize(bytes.len(), &mut buffer);
-                    let mut offset = 0;
-
-                    while offset < len.len() {
-                        offset += substream.write(&len[offset..]).await?;
-                    }
-
-                    while bytes.has_remaining() {
-                        let nwritten = substream.write(&bytes).await?;
-                        bytes.advance(nwritten);
-                    }
-
-                    substream.flush().await.map_err(From::from)
-                }
+                ProtocolCodec::UnsignedVarint(max_size) =>
+                    Self::send_unsigned_varint_payload(substream, bytes, max_size).await,
             },
             #[cfg(feature = "quic")]
             SubstreamType::Quic(ref mut substream) => match self.codec {
@@ -454,7 +449,7 @@ impl Substream {
                 ProtocolCodec::UnsignedVarint(max_size) => {
                     check_size!(max_size, bytes.len());
 
-                    let mut buffer = [0u8; 10];
+                    let mut buffer = unsigned_varint::encode::usize_buffer();
                     let len = unsigned_varint::encode::usize(bytes.len(), &mut buffer);
                     let len = BytesMut::from(len);
 
@@ -466,24 +461,8 @@ impl Substream {
                 ProtocolCodec::Unspecified => panic!("codec is unspecified"),
                 ProtocolCodec::Identity(payload_size) =>
                     Self::send_identity_payload(substream, payload_size, bytes).await,
-                ProtocolCodec::UnsignedVarint(max_size) => {
-                    check_size!(max_size, bytes.len());
-
-                    let mut buffer = [0u8; 10];
-                    let len = unsigned_varint::encode::usize(bytes.len(), &mut buffer);
-                    let mut offset = 0;
-
-                    while offset < len.len() {
-                        offset += substream.write(&len[offset..]).await?;
-                    }
-
-                    while bytes.has_remaining() {
-                        let nwritten = substream.write(&bytes).await?;
-                        bytes.advance(nwritten);
-                    }
-
-                    substream.flush().await.map_err(From::from)
-                }
+                ProtocolCodec::UnsignedVarint(max_size) =>
+                    Self::send_unsigned_varint_payload(substream, bytes, max_size).await,
             },
         }
     }
@@ -722,7 +701,7 @@ impl Sink<Bytes> for Substream {
                 check_size!(max_size, item.len());
 
                 let len = {
-                    let mut buffer = [0u8; 10];
+                    let mut buffer = unsigned_varint::encode::usize_buffer();
                     let len = unsigned_varint::encode::usize(item.len(), &mut buffer);
                     BytesMut::from(len)
                 };