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Re: [libmicrohttpd] Strange char 0x7f added after last POST notification

From: Imóveis Nacionais
Subject: Re: [libmicrohttpd] Strange char 0x7f added after last POST notification
Date: Mon, 13 Apr 2020 10:27:41 +0100

But I am just handling arrived data when *upload_data_size > 0. Here is the code:

else if(strcmp(method, "POST") == 0)
        ST_PER_THREAD_DATA* pstThreadData = *ptr;
        if( pstThreadData == NULL)
            ST_PER_THREAD_DATA * cThreadData = (ST_PER_THREAD_DATA*) malloc(sizeof(ST_PER_THREAD_DATA));
            cThreadData->nThreadID = nThID;

            *ptr = cThreadData;
            return MHD_YES;  

        if(*upload_data_size > 0)
            printf("Before strcpy (%s) (%s) (%d)\n",pstThreadData->strData,upload_data,*upload_data_size);
            printf("After strcpy (%s) (%s) (%d)\n",pstThreadData->strData,upload_data,*upload_data_size);

            *upload_data_size = 0;
            return MHD_YES;

            //After strcpy ({"key98"}) ({"key98"}) (9)
            //END OF POST DATA GATHERING            
            printf("In the end of post we have (%s) (%d) \n",pstThreadData->strData, strlen(pstThreadData->strData));
            //In the end of post we have ({"key98"}) (10)

Please, is there anything wrong with the (testing) code?

Thank you

On Mon, Apr 13, 2020 at 10:00 AM Christian Grothoff <address@hidden> wrote:
On 4/13/20 2:11 AM, Imóveis Nacionais wrote:
> Then when in the "*upload_data_size = 0" situation, using a printf
> sometimes I can see that the thread context data has the 0x7f char appended
> and of course the strlen now is one char extra. This happens between the
> last post call with *upload_data_size > 0 and *upload_data_size = 0.
> Does this char has any meaning in the libmicrohttpd context?
> Why is this char being added?

You're seeing undefined behavior. When '*upload_data_size' is zero, you
are not allowed to look into '*upload_data'. It is NEVER warranted to be
a 0-terminated char* in the first place, and right now you're just
reading data out of bounds.  Do not rely on getting 0x7f or anything
meaningful, in fact, expect reading more than '*upload_data_size' bytes
from '*upload_data' to be deadly.

Happy hacking!


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