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[libmicrohttpd] Problem with HTTP/1.1 chunked packets when connection is

From: Iron Bug at
Subject: [libmicrohttpd] Problem with HTTP/1.1 chunked packets when connection is about to close
Date: Sun, 25 Apr 2021 21:45:58 +0500


I use libmicrohttpd in my project and I found one bug in a very specific 
situation with chunked messages.

The scheme I use is keep-alive connection for transferring some files (chunked 
content, HTTP/1.1 pipelining). When transfer is over, connection is closed by 
client request.

I create responses with MHD_create_response_from_callback and the HTTP header 
"Transfer-Encoding: chunked" is automatically added to packet headers. But when 
the transfer is over and the last file requested, client sends "Connection: 
close". Theoretically, by HTTP standard, the server should process the request 
and then close the socket. And it does so, it sends the chunked data and closes 
the connection. But in the response to the last request it loses the 
"Transfer-Encoding: chunked" header and the client fails to accept the wrong 
formatted HTTP packet. If I manually add "Transfer-Encoding: chunked" to the 
last HTTP response, it works fine. 

I think the problem hides in this code piece:

      file src/microhttpd/connection.c, line 1376, in function 
      if ( (MHD_NO != keepalive_possible (connection)) &&
           (MHD_str_equal_caseless_ (MHD_HTTP_VERSION_1_1,
                                     connection->version) ) )
        if (NULL == have_encoding)
          must_add_chunked_encoding = true;
          connection->have_chunked_upload = true;

The connection is marked as non keep-alive at the moment after "Connection: 
close" and the content is still chunked. But the flag is not set and then the 
error occurs.

Sincerely, Yana A. Kireyonok aka Iron Bug

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