docs: private byte[] readBody(Map<String, List<String>> headers, WebSocketInputStream input)
      {
          // Get the value of "Content-Length" header.
          int length = getContentLength(headers);
  
          if (length <= 0)
          {
              // Response body is not available.
              return null;
          }
  
          try
          {
              // Allocate a byte array of the content length.
              byte[] body = new byte[length];
  
              // Read the response body into the byte array.
              input.readBytes(body, length);
  
              // Return the content of the response body.
              return body;
          }
          catch (Throwable t)
          {
              // Response body is not available.
              return null;
          }
      }