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                     23: .TH CURLOPT_PROGRESSFUNCTION 3 "March 23, 2020" "libcurl 7.70.0" "curl_easy_setopt options"
                     24: 
                     25: .SH NAME
                     26: CURLOPT_PROGRESSFUNCTION \- callback to progress meter function
                     27: .SH SYNOPSIS
                     28: #include <curl/curl.h>
                     29: 
                     30: int progress_callback(void *clientp,
                     31:                       double dltotal,
                     32:                       double dlnow,
                     33:                       double ultotal,
                     34:                       double ulnow);
                     35: 
                     36: CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROGRESSFUNCTION, progress_callback);
                     37: .SH DESCRIPTION
                     38: Pass a pointer to your callback function, which should match the prototype
                     39: shown above.
                     40: 
                     41: We encourage users to use the newer \fICURLOPT_XFERINFOFUNCTION(3)\fP instead,
                     42: if you can.
                     43: 
                     44: This function gets called by libcurl instead of its internal equivalent with a
                     45: frequent interval. While data is being transferred it will be called very
                     46: frequently, and during slow periods like when nothing is being transferred it
                     47: can slow down to about one call per second.
                     48: 
                     49: \fIclientp\fP is the pointer set with \fICURLOPT_PROGRESSDATA(3)\fP, it is not
                     50: used by libcurl but is only passed along from the application to the callback.
                     51: 
                     52: The callback gets told how much data libcurl will transfer and has
                     53: transferred, in number of bytes. \fIdltotal\fP is the total number of bytes
                     54: libcurl expects to download in this transfer. \fIdlnow\fP is the number of
                     55: bytes downloaded so far. \fIultotal\fP is the total number of bytes libcurl
                     56: expects to upload in this transfer. \fIulnow\fP is the number of bytes
                     57: uploaded so far.
                     58: 
                     59: Unknown/unused argument values passed to the callback will be set to zero
                     60: (like if you only download data, the upload size will remain 0). Many times
                     61: the callback will be called one or more times first, before it knows the data
                     62: sizes so a program must be made to handle that.
                     63: 
                     64: If your callback function returns CURL_PROGRESSFUNC_CONTINUE it will cause
                     65: libcurl to continue executing the default progress function.
                     66: 
                     67: Returning any other non-zero value from this callback will cause libcurl to
                     68: abort the transfer and return \fICURLE_ABORTED_BY_CALLBACK\fP.
                     69: 
                     70: If you transfer data with the multi interface, this function will not be
                     71: called during periods of idleness unless you call the appropriate libcurl
                     72: function that performs transfers.
                     73: 
                     74: \fICURLOPT_NOPROGRESS(3)\fP must be set to 0 to make this function actually
                     75: get called.
                     76: .SH DEFAULT
                     77: By default, libcurl has an internal progress meter. That's rarely wanted by
                     78: users.
                     79: .SH PROTOCOLS
                     80: All
                     81: .SH EXAMPLE
                     82: https://curl.haxx.se/libcurl/c/progressfunc.html
                     83: .SH AVAILABILITY
                     84: Always
                     85: .SH RETURN VALUE
                     86: Returns CURLE_OK.
                     87: .SH "SEE ALSO"
                     88: .BR CURLOPT_VERBOSE "(3), " CURLOPT_NOPROGRESS "(3), "