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CURLOPT_DEBUGFUNCTION(3)   Library Functions Manual   CURLOPT_DEBUGFUNCTION(3)

NAME
       CURLOPT_DEBUGFUNCTION - debug callback

SYNOPSIS
       #include	<curl/curl.h>

       typedef enum {
	 CURLINFO_TEXT = 0,
	 CURLINFO_HEADER_IN,	/* 1 */
	 CURLINFO_HEADER_OUT,	/* 2 */
	 CURLINFO_DATA_IN,	/* 3 */
	 CURLINFO_DATA_OUT,	/* 4 */
	 CURLINFO_SSL_DATA_IN,	/* 5 */
	 CURLINFO_SSL_DATA_OUT,	/* 6 */
	 CURLINFO_END
       } curl_infotype;

       int debug_callback(CURL *handle,
			  curl_infotype	type,
			  char *data,
			  size_t size,
			  void *clientp);

       CURLcode	curl_easy_setopt(CURL *handle, CURLOPT_DEBUGFUNCTION,
				 debug_callback);

DESCRIPTION
       Pass a pointer to your callback function, which should match the	proto-
       type shown above.

       CURLOPT_DEBUGFUNCTION(3)	replaces the standard debug function used when
       CURLOPT_VERBOSE(3)  is in effect. This callback receives	debug informa-
       tion, as	specified in the type argument.	This function must  return  0.
       The  data  pointed  to  by  the	char  *	passed to this function	is not
       null-terminated,	but is exactly of the size as told by the  size	 argu-
       ment.

       WARNING	this  callback may receive sensitive contents from headers and
       data, including information sent	as CURLINFO_TEXT.

       The clientp argument is the pointer set with CURLOPT_DEBUGDATA(3).

       Available curl_infotype values:

       CURLINFO_TEXT
	      The data is informational	text.

       CURLINFO_HEADER_IN
	      The data is header (or header-like) data received	from the peer.

       CURLINFO_HEADER_OUT
	      The data is header (or header-like) data sent to the peer.

       CURLINFO_DATA_IN
	      The data is the unprocessed  protocol  data  received  from  the
	      peer.  Even if the data is encoded or compressed,	it is not pro-
	      vided decoded nor	decompressed to	this callback. If you need the
	      data in decoded and decompressed	form,  use  CURLOPT_WRITEFUNC-
	      TION(3).

       CURLINFO_DATA_OUT
	      The data is protocol data	sent to	the peer.

       CURLINFO_SSL_DATA_OUT
	      The data is SSL/TLS (binary) data	sent to	the peer.

       CURLINFO_SSL_DATA_IN
	      The data is SSL/TLS (binary) data	received from the peer.

       WARNING:	This callback may be called with the curl handle set to	an in-
       ternal handle. (Added in	8.4.0)

       If  you need to distinguish your	curl handle from internal handles then
       set CURLOPT_PRIVATE(3) on your handle.

DEFAULT
       NULL

PROTOCOLS
       This functionality affects all supported	protocols

EXAMPLE
       static
       void dump(const char *text,
		 FILE *stream, unsigned	char *ptr, size_t size)
       {
	 size_t	i;
	 size_t	c;
	 unsigned int width = 0x10;

	 fprintf(stream, "%s, %10.10ld bytes (0x%8.8lx)\n",
		 text, (long)size, (long)size);

	 for(i = 0; i <	size; i	+= width) {
	   fprintf(stream, "%4.4lx: ", (long)i);

	   /* show hex to the left */
	   for(c = 0; c	< width; c++) {
	     if(i + c <	size)
	       fprintf(stream, "%02x ",	ptr[i +	c]);
	     else
	       fputs("	 ", stream);
	   }

	   /* show data	on the right */
	   for(c = 0; (c < width) && (i	+ c < size); c++) {
	     char x = (ptr[i + c] >= 0x20 && ptr[i + c]	< 0x80)	? ptr[i	+ c] : '.';
	     fputc(x, stream);
	   }

	   fputc('\n', stream);	/* newline */
	 }
       }

       static
       int my_trace(CURL *handle, curl_infotype	type,
		    char *data,	size_t size,
		    void *clientp)
       {
	 const char *text;
	 (void)handle; /* prevent compiler warning */
	 (void)clientp;

	 switch(type) {
	 case CURLINFO_TEXT:
	   fputs("== Info: ", stderr);
	   fwrite(data,	size, 1, stderr);
	 default: /* in	case a new one is introduced to	shock us */
	   return 0;

	 case CURLINFO_HEADER_OUT:
	   text	= "=> Send header";
	   break;
	 case CURLINFO_DATA_OUT:
	   text	= "=> Send data";
	   break;
	 case CURLINFO_SSL_DATA_OUT:
	   text	= "=> Send SSL data";
	   break;
	 case CURLINFO_HEADER_IN:
	   text	= "<= Recv header";
	   break;
	 case CURLINFO_DATA_IN:
	   text	= "<= Recv data";
	   break;
	 case CURLINFO_SSL_DATA_IN:
	   text	= "<= Recv SSL data";
	   break;
	 }

	 dump(text, stderr, (unsigned char *)data, size);
	 return	0;
       }

       int main(void)
       {
	 CURL *curl;
	 CURLcode res;

	 curl =	curl_easy_init();
	 if(curl) {
	   curl_easy_setopt(curl, CURLOPT_DEBUGFUNCTION, my_trace);

	   /* the DEBUGFUNCTION	has no effect until we enable VERBOSE */
	   curl_easy_setopt(curl, CURLOPT_VERBOSE, 1L);

	   /* example.com is redirected, so we tell libcurl to follow redirection */
	   curl_easy_setopt(curl, CURLOPT_FOLLOWLOCATION, 1L);

	   curl_easy_setopt(curl, CURLOPT_URL, "https://example.com/");
	   res = curl_easy_perform(curl);
	   /* Check for	errors */
	   if(res != CURLE_OK)
	     fprintf(stderr, "curl_easy_perform() failed: %s\n",
		     curl_easy_strerror(res));

	   /* always cleanup */
	   curl_easy_cleanup(curl);
	 }
	 return	0;
       }

AVAILABILITY
       Added in	curl 7.9.6

RETURN VALUE
       curl_easy_setopt(3) returns a CURLcode indicating success or error.

       CURLE_OK	(0) means everything was OK, non-zero means an error occurred,
       see libcurl-errors(3).

SEE ALSO
       CURLINFO_CONN_ID(3),  CURLINFO_XFER_ID(3),  CURLOPT_DEBUGDATA(3),  CUR-
       LOPT_VERBOSE(3),	curl_global_trace(3)

libcurl				  2025-06-03	      CURLOPT_DEBUGFUNCTION(3)

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