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

[Christian Grothoff]

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)