docs/libcurl/opts/CURLOPT_DEBUGFUNCTION.3

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.TH CURLOPT_DEBUGFUNCTION 3 "November 04, 2020" "libcurl 7.78.0" "curl_easy_setopt options"

.SH NAME
CURLOPT_DEBUGFUNCTION \- debug callback
.SH SYNOPSIS
.nf
#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 *userptr);

CURLcode curl_easy_setopt(CURL *handle, CURLOPT_DEBUGFUNCTION,
                          debug_callback);
.SH DESCRIPTION
Pass a pointer to your callback function, which should match the prototype
shown above.

\fICURLOPT_DEBUGFUNCTION(3)\fP replaces the standard debug function used when
\fICURLOPT_VERBOSE(3)\fP is in effect. This callback receives debug
information, as specified in the \fItype\fP argument. This function must
return 0. The \fIdata\fP pointed to by the char * passed to this function WILL
NOT be null-terminated, but will be exactly of the \fIsize\fP as told by the
\fIsize\fP argument.

The \fIuserptr\fP argument is the pointer set with \fICURLOPT_DEBUGDATA(3)\fP.

Available curl_infotype values:
.IP CURLINFO_TEXT
The data is informational text.
.IP CURLINFO_HEADER_IN
The data is header (or header-like) data received from the peer.
.IP CURLINFO_HEADER_OUT
The data is header (or header-like) data sent to the peer.
.IP CURLINFO_DATA_IN
The data is protocol data received from the peer.
.IP CURLINFO_DATA_OUT
The data is protocol data sent to the peer.
.IP CURLINFO_SSL_DATA_OUT
The data is SSL/TLS (binary) data sent to the peer.
.IP CURLINFO_SSL_DATA_IN
The data is SSL/TLS (binary) data received from the peer.
.SH DEFAULT
NULL
.SH PROTOCOLS
All
.SH EXAMPLE
.nf
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 *userp)
{
  const char *text;
  (void)handle; /* prevent compiler warning */
  (void)userp;

  switch (type) {
  case CURLINFO_TEXT:
    fprintf(stderr, "== Info: %s", data);
  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;
}
.fi
.SH AVAILABILITY
Always
.SH RETURN VALUE
Returns CURLE_OK
.SH "SEE ALSO"
.BR CURLOPT_VERBOSE "(3), " CURLOPT_DEBUGDATA "(3), "