Re: [libmicrohttpd] www-form-urlencoded: dealing with keys with no value

[Christian Grothoff]

Hi Ethan,

I've implemented this now in Git master. Feedback welcome...

Happy hacking!

Christian

On 12/25/19 9:45 AM, Ethan Tuttle wrote:
> Thanks for the response, Chrstian.  I'll take a look at the parsing
> code, but I don't have high confidence I can fix it to your liking
> (and in a secure / performant way).
> 
> Otherwise, I'll stick with my uriparser patch until you get around to it.
> 
> Happy hacking and happy holidays!
> 
> Ethan
> 
> On Tue, Dec 24, 2019 at 6:30 AM Christian Grothoff <address@hidden> wrote:
>>
>> Hi Ethan,
>>
>> I agree that this is a bug, and yes, we should fix it. Thanks for the
>> test case, that is very helpful.
>>
>> I don't know when I can work on it, but worst-case expect a patch by
>> the end of January, if you're lucky and my other bugs go fast (or
>> someone else sends a fix), might of course happen earlier.
>>
>> Happy hacking!
>>
>> Christian
>>
>> On Tue, 2019-12-24 at 04:11 -0800, Ethan Tuttle wrote:
>>> Given post body "a&b=1", how should MHD interpret the data?
>>>
>>> I'm at the end of a long investigation and it's come down to that
>>> question
>>> for post_process_urlencoded() in MHD.
>>>
>>> MHD currently calls back with ("a&b", "1").  The app I'm working
>>> breaks
>>> when it doesn't receive a callback for "b".  The http client in this
>>> case
>>> (that did the urlencoding) is google-http-java-client 1.23.0.
>>>
>>> The client behavior may be questionable, but MHD's behavior doesn't
>>> seem
>>> right either.  Isn't there some principle, "clients should strive for
>>> conformance, servers should strive for forgiveness".
>>>
>>> I've attached a patch to MHD to add a failing test, but without a
>>> fix.  Is
>>> MHD open to changing this behavior, given its maturity?
>>>
>>> Should I post a bug to the bug tracker?
>>>
>>> As for relevant standards, the W3C[1] is not detailed enough to cover
>>> it.
>>> The WhatWG[2] is more specific and allows for empty values and even
>>> empty
>>> keys.  I'd like to callout uriparser[3], another C library I've
>>> patched in
>>> as a work-around.  Uriparser documents their handling of these cases
>>> well:
>>>
>>> * NULL in the value member means there was no '=' in the item text as
>>> with
>>> "?abc&def".
>>> * An empty string in the value member means there was '=' in the item
>>> as
>>> with "?abc=&def".
>>>
>>> [1] https://www.w3.org/TR/html401/interact/forms.html#h-17.13.4.1
>>> [2] https://url.spec.whatwg.org/#urlencoded-parsing
>>> [3] https://uriparser.github.io/doc/api/latest/#querystrings
>>>
>>> commit aa0534af56d135e1b261d127af09c22015c1ff87
>>> Author: Ethan Tuttle <address@hidden>
>>> Date:   Tue Dec 24 03:50:59 2019 -0800
>>>
>>>     urlencoding post-processor: add failing tests for keys without
>>> values
>>>
>>> diff --git a/src/microhttpd/test_postprocessor.c
>>> b/src/microhttpd/test_postprocessor.c
>>> index 75b5ba33..6d5be040 100644
>>> --- a/src/microhttpd/test_postprocessor.c
>>> +++ b/src/microhttpd/test_postprocessor.c
>>> @@ -42,8 +42,18 @@
>>>   * five NULL-entries.
>>>   */
>>>  const char *want[] = {
>>> +#define URL_NOVALUE1_DATA "abc&x=5"
>>> +#define URL_NOVALUE1_START 0
>>> +        "abc", NULL, NULL, NULL, NULL,
>>> +        "x", NULL, NULL, NULL, "5",
>>> +#define URL_NOVALUE1_END (URL_NOVALUE1_START + 10)
>>> +#define URL_NOVALUE2_DATA "abc=&x=5"
>>> +#define URL_NOVALUE2_START URL_NOVALUE1_END
>>> +        "abc", NULL, NULL, NULL, "",
>>> +        "x", NULL, NULL, NULL, "5",
>>> +#define URL_NOVALUE2_END (URL_NOVALUE2_START + 10)
>>>  #define URL_DATA "abc=def&x=5"
>>> -#define URL_START 0
>>> +#define URL_START URL_NOVALUE2_END
>>>    "abc", NULL, NULL, NULL, "def",
>>>    "x", NULL, NULL, NULL, "5",
>>>  #define URL_END (URL_START + 10)
>>> @@ -125,12 +135,14 @@ value_checker (void *cls,
>>>
>>>
>>>  static int
>>> -test_urlencoding (void)
>>> +test_urlencoding_case (unsigned int want_start,
>>> +                       unsigned int want_end,
>>> +                       const char *url_data)
>>>  {
>>>    struct MHD_Connection connection;
>>>    struct MHD_HTTP_Header header;
>>>    struct MHD_PostProcessor *pp;
>>> -  unsigned int want_off = URL_START;
>>> +  unsigned int want_off = want_start;
>>>    size_t i;
>>>    size_t delta;
>>>    size_t size;
>>> @@ -147,19 +159,27 @@ test_urlencoding (void)
>>>    pp = MHD_create_post_processor (&connection,
>>>                                    1024, &value_checker, &want_off);
>>>    i = 0;
>>> -  size = strlen (URL_DATA);
>>> +  size = strlen (url_data);
>>>    while (i < size)
>>>    {
>>>      delta = 1 + MHD_random_ () % (size - i);
>>> -    MHD_post_process (pp, &URL_DATA[i], delta);
>>> +    MHD_post_process (pp, &url_data[i], delta);
>>>      i += delta;
>>>    }
>>>    MHD_destroy_post_processor (pp);
>>> -  if (want_off != URL_END)
>>> +  if (want_off != want_end)
>>>      return 1;
>>>    return 0;
>>>  }
>>>
>>> +static int
>>> +test_urlencoding (void) {
>>> +  unsigned int errorCount = 0;
>>> +  errorCount += test_urlencoding_case(URL_START, URL_END, URL_DATA);
>>> +  errorCount += test_urlencoding_case(URL_NOVALUE1_START,
>>> URL_NOVALUE1_END, URL_NOVALUE1_DATA);
>>> +  errorCount += test_urlencoding_case(URL_NOVALUE2_START,
>>> URL_NOVALUE2_END, URL_NOVALUE2_DATA);
>>> +  return errorCount;
>>> +}
>>>
>>>  static int
>>>  test_multipart_garbage (void)
>>
>>
>