Update src/AsyncWebSocket.cpp

Co-authored-by: Copilot <175728472+Copilot@users.noreply.github.com>

Author: mathieucarbou

src/AsyncWebSocket.cpp

@@ -540,21 +540,27 @@ void AsyncWebSocketClient::_onData(void *pbuf, size_t plen) {
     }
 
     if (_pinfo.masked > 0 && _pinfo.masked < 5) {
-      // Handle fragmented mask data - Safari may split the 4-byte mask across multiple packets
-      int mask_bytes_read = _pinfo.masked - 1;
-      while (mask_bytes_read < 4) {
-        if (plen == 0) {
-          // wait for more data
-          _pinfo.masked = mask_bytes_read + 1;
-          _pstate = 1;
-          return;
+      // Handle Safari edge case: close frame with plen 0, mask bit set, but no mask bytes
+      if (_pinfo.len == 0 && plen == 0) {
+        // Malformed frame (Safari bug): treat as unmasked for compatibility
+        _pinfo.masked = 0;
+      } else {
+        // Handle fragmented mask data - Safari may split the 4-byte mask across multiple packets
+        int mask_bytes_read = _pinfo.masked - 1;
+        while (mask_bytes_read < 4) {
+          if (plen == 0) {
+            // wait for more data
+            _pinfo.masked = mask_bytes_read + 1;
+            _pstate = 1;
+            return;
+          }
+          _pinfo.mask[mask_bytes_read] = data[0];
+          data += 1;
+          plen -= 1;
+          mask_bytes_read++;
         }
-        _pinfo.mask[mask_bytes_read] = data[0];
-        data += 1;
-        plen -= 1;
-        mask_bytes_read++;
+        _pinfo.masked = 1;  // restore boolean semantics: mask fully read
       }
-      _pinfo.masked = 1;  // restore boolean semantics: mask fully read
     }
 
     const size_t datalen = std::min((size_t)(_pinfo.len - _pinfo.index), plen);