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Re: [libmicrohttpd] 0.9.67 regression

From: Tim Rühsen
Subject: Re: [libmicrohttpd] 0.9.67 regression
Date: Sat, 26 Oct 2019 18:07:16 +0200
User-agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.9.0

Hi Christian,

I am just staring at minimal_example_empty.c and wonder what should
happen when I call the executable !? Anyways, I can't easily fill it
with content that works as a reproducer.

It seems to occur only with HTTPS, HTTP definitely works as expected.

To reproduce:
git clone
cd wget2
make -j$(nproc)
make -j$(nproc) check -C tests TESTS=test--https-enforce-soft2

It doesn't come back immediately... so open up a second terminal and
  tail -f tests/test--https-enforce-soft2.log

You will see the GET request from wget2 and then waiting 10s without
seeing the response. With MHD <= 0.9.66 you'll immediately get the response.

The MHD server code is in tests/libtest.c.
wget_test_start_server() starts the servers, one for HTTPS and another
one for HTTP (which is likely not relevant here).

The HTTPS server is started around L733 with
        httpsdaemon = MHD_start_daemon(MHD_USE_SELECT_INTERNALLY | MHD_USE_TLS
#if MHD_VERSION >= 0x00096302
        port_num, _check_to_accept, (void *) (ptrdiff_t) SERVER_MODE,
&_answer_to_connection, NULL,
        MHD_OPTION_HTTPS_MEM_KEY, key_pem,
        MHD_OPTION_HTTPS_MEM_CERT, cert_pem,
        MHD_OPTION_CONNECTION_MEMORY_LIMIT, (size_t) 1*1024*1024,

The test executes wget2 sends a request to the HTTPS server (as you can
see in the .log file of the test):

26.172501.240 GnuTLS init
26.172501.253 Certificates loaded: 128
26.172501.253 GnuTLS init done
26.172501.253 TLS False Start requested
26.172501.253 ALPN offering h2
26.172501.253 ALPN offering http/1.1
WARNING: The certificate's (stapled) OCSP status has not been sent
26.172501.267 TLS False Start: off
26.172501.267 GnuTLS: Get ALPN: The requested data were not available.
26.172501.267 Handshake completed
26.172501.267 established connection localhost
26.172501.267 # sent 233 bytes:
GET /robots.txt HTTP/1.1
Host: localhost
Accept-Encoding: gzip, deflate, bzip2, xz, lzma, br, zstd, lzip
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8
User-Agent: wget2/1.99.2
Connection: keep-alive

26.172501.267 [0] action=2 pending=1 host=0x5606a570abf0
26.172501.267 ### req 0x7f331c2e9380 pending requests = 1
###### here the client is waiting for the response for max 10s

Hopefully, the above information gives you a chance to track the issue down.

Regards, Tim

On 24.10.19 18:01, Christian Grothoff wrote:
> Hi Tim,
> Your one-liner just fixes the FTBFS and is itself correct.
> The commit just before that broke everything is the one activating ng0's
> big GSoC work which significantly changes the transmission logic (and
> was thus prepared by many, many other patches before).
> I do of course have a hunch as to where the issue might be (0 bytes body
> means no send() for the body, after all. So that might prevent proper
> uncorking, and that might trigger in a test suite that expects low
> latency. But then again, your report says "no reply at all", not just
> +200 ms. So strange.
> Anyway, I would really appreciate being able to reproduce this one. You
> could also point me to the wget code, I'd dig there myself, but it would
> likely take a bit longer in that case ;-).
> Happy hacking!
> Christian
> On 10/24/19 4:07 PM, Tim Rühsen wrote:
>> Hi Christian,
>> thanks for the test file - I'll try to copy our code into it.
>> Meanwhile I bisected the git commits...
>> The last functioning is
>> 02a9ae28d64498266869b49b042905946df7ce66 "synt"
>> The next one is not buildable here
>> 379da4ce093bdc957b53b563aa1ae0c7c37c19ac " define a check
>> And this is the commit that broke our test suite
>> 8ce24c2ae433fdf1ec125211d3622f3c27b56797 "_len -> _size"
>> It's just a one-liner... I hope this helps :-)
>> Regards, Tim
>> On 10/24/19 12:48 PM, Christian Grothoff wrote:
>>> Hi Tim,
>>> I cannot reproduce this. We do test for empty body in test_get.c, and
>>> that test passes. I also wrote (and now pushed to master) a
>>> minimal_example_empty.c, using both the 200 and 204 status codes. It
>>> works for me on loopback as well as over the network, using both curl
>>> and wget as clients.
>>> Maybe your issue is about a specific threading mode or something else
>>> you are doing?  Please modify the minimal_example_empty.c to emulate the
>>> situation that is causing the issue.
>>> Thanks!
>>> Christian
>>> On 10/23/19 3:39 PM, Tim Rühsen wrote:
>>>> Hi,
>>>> with 0.9.67 some tests for Wget2 fail which were fine with 0.9.66. This
>>>> is still reproducible with latest master.
>>>> As it seems, a response with an empty body doesn't send a response any 
>>>> more.
>>>> That means
>>>>   response = MHD_create_response_from_buffer(0, (void *) "",
>>>> doesn't work, while
>>>>   response = MHD_create_response_from_buffer(1, (void *) "x",
>>>> still generates a response.
>>>> I tested this with MHD_HTTP_BAD_REQUEST, MHD_HTTP_OK and
>>>> MHD_HTTP_NOT_FOUND used for MHD_queue_response().
>>>> Regards, Tim

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