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                     23: .TH CURLOPT_IOCTLFUNCTION 3 "March 23, 2020" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_IOCTLFUNCTION \- callback for I/O operations
                     27: .SH SYNOPSIS
                     28: .nf
                     29: #include <curl/curl.h>
                     30: 
                     31: typedef enum {
                     32:   CURLIOE_OK,            /* I/O operation successful */
                     33:   CURLIOE_UNKNOWNCMD,    /* command was unknown to callback */
                     34:   CURLIOE_FAILRESTART,   /* failed to restart the read */
                     35:   CURLIOE_LAST           /* never use */
                     36: } curlioerr;
                     37: 
                     38: typedef enum  {
                     39:   CURLIOCMD_NOP,         /* no operation */
                     40:   CURLIOCMD_RESTARTREAD, /* restart the read stream from start */
                     41:   CURLIOCMD_LAST         /* never use */
                     42: } curliocmd;
                     43: 
                     44: curlioerr ioctl_callback(CURL *handle, int cmd, void *clientp);
                     45: 
                     46: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_IOCTLFUNCTION, ioctl_callback);
                     47: .SH DESCRIPTION
                     48: Pass a pointer to your callback function, which should match the prototype
                     49: shown above.
                     50: 
                     51: This callback function gets called by libcurl when something special
                     52: I/O-related needs to be done that the library can't do by itself. For now,
                     53: rewinding the read data stream is the only action it can request. The
                     54: rewinding of the read data stream may be necessary when doing an HTTP PUT or
                     55: POST with a multi-pass authentication method.
                     56: 
                     57: The callback MUST return \fICURLIOE_UNKNOWNCMD\fP if the input \fIcmd\fP is
                     58: not \fICURLIOCMD_RESTARTREAD\fP.
                     59: 
                     60: The \fIclientp\fP argument to the callback is set with the
                     61: \fICURLOPT_IOCTLDATA(3)\fP option.
                     62: 
                     63: This option is deprecated! Do not use it. Use \fICURLOPT_SEEKFUNCTION(3)\fP
                     64: instead to provide seeking! If \fICURLOPT_SEEKFUNCTION(3)\fP is set, this
                     65: parameter will be ignored when seeking.
                     66: .SH DEFAULT
                     67: By default, this parameter is set to NULL. Not used.
                     68: .SH PROTOCOLS
                     69: Used with HTTP
                     70: .SH EXAMPLE
                     71: .nf
                     72: static curlioerr ioctl_callback(CURL *handle, int cmd, void *clientp)
                     73: {
                     74:   struct data *io = (struct data *)clientp;
                     75:   if(cmd == CURLIOCMD_RESTARTREAD) {
                     76:     lseek(fd, 0, SEEK_SET);
                     77:     current_offset = 0;
                     78:     return CURLIOE_OK;
                     79:   }
                     80:   return CURLIOE_UNKNOWNCMD;
                     81: }
                     82: {
                     83:   struct data ioctl_data;
                     84:   curl_easy_setopt(curl, CURLOPT_IOCTLFUNCTION, ioctl_callback);
                     85:   curl_easy_setopt(curl, CURLOPT_IOCTLDATA, &ioctl_data);
                     86: }
                     87: .fi
                     88: .SH AVAILABILITY
                     89: Added in 7.12.3
                     90: .SH RETURN VALUE
                     91: Returns CURLE_OK if the option is supported, and CURLE_UNKNOWN_OPTION if not.
                     92: .SH "SEE ALSO"
                     93: .BR CURLOPT_IOCTLDATA "(3), " CURLOPT_SEEKFUNCTION "(3), "