Support multiple `Sec-WebSocket-Extensions` request headers

src/handshake/server.rs

@@ -246,14 +246,16 @@ impl<S: Read + Write, C: Callback> HandshakeRole for ServerHandshake<S, C> {
 
                 let mut response = create_response(&result)?;
                 if let Some(compression) = &self.config.and_then(|c| c.compression) {
-                    if let Some(extensions) = result
+                    for extensions in result
                         .headers()
-                        .get("Sec-WebSocket-Extensions")
-                        .and_then(|v| v.to_str().ok())
+                        .get_all("Sec-WebSocket-Extensions")
+                        .iter()
+                        .filter_map(|h| h.to_str().ok())
                     {
                         if let Some((agreed, pmce)) = compression.negotiation_response(extensions) {
                             self.pmce = Some(pmce);
                             response.headers_mut().insert("Sec-WebSocket-Extensions", agreed);
+                            break;
                         }
                     }
                 }