Re: [libmicrohttpd] may libmicrohttpd change the connection pointer

[Martin Velek]

Hi,

Thank You, it helps a lot. You have described exactly what I am planning to do.

Best
Martin

On Thu, Jan 30, 2014 at 2:42 PM, Christian Grothoff <address@hidden> wrote:
> On 01/30/2014 01:15 PM, Martin Velek wrote:
>> Hello,
>>
>> do not you know, can I rely on "constant" struct MHD_Connection
>> *connection pointer passed to (*MHD_AccessHandlerCallback)? The
>> constant is meant as not varying during a single connection. It is
>> quite difficult to explain for me so let me outline the example :)
>>
>> The problem:
>> I need to access URI parameters in the response callback.
>>
>> The solution:
>> The function (*MHD_AccessHandlerCallback) creates a response from
>> callback by passing (*MHD_ContentReaderCallback) to the function
>> MHD_create_response_from_callback. The pointer to struct
>> MHD_Connection * is stored in the crc_cls (extra argument to crc).
>>
>> In the (*MHD_ContentReaderCallback) callback, the void *cls is casted
>> to struct MHD_Connection * and call MHD_get_connection_values to get
>> values.
>>
>> The problem appears when the libmicrohttpd somehow reallocates the
>> connection pointer internally during the next call of
>> (*MHD_AccessHandlerCallback) or (*MHD_ContentReaderCallback). I
>> remind, I think only one connection => *con_cls != NULL previusly set
>> to something different from NULL.
>>
>> The story above can be also summarized to this question:
>> How can I access the connection information from the response callback?
>
> You can safely pass the connection as the closure to your response
> callback (or pass some other struct that you defined that has a pointer
> to the connection in it), but in those cases you must not share the
> 'response' object with multiple connections (which you are otherwise
> free to do).
>
> I hope this helps!
>
> Happy hacking!
>
> -Christian