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Re: [libmicrohttpd] may libmicrohttpd change the connection pointer

From: Martin Velek
Subject: Re: [libmicrohttpd] may libmicrohttpd change the connection pointer
Date: Thu, 30 Jan 2014 15:15:46 +0100


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


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

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