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deps/curl/docs/libcurl/opts/CURLOPT_PROGRESSFUNCTION.md

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+---
+c: Copyright (C) Daniel Stenberg, <daniel.se>, et al.
+SPDX-License-Identifier: curl
+Title: CURLOPT_PROGRESSFUNCTION
+Section: 3
+Source: libcurl
+See-also:
+  - CURLOPT_NOPROGRESS (3)
+  - CURLOPT_VERBOSE (3)
+  - CURLOPT_XFERINFOFUNCTION (3)
+---
+
+# NAME
+
+CURLOPT_PROGRESSFUNCTION - progress meter callback
+
+# SYNOPSIS
+
+~~~c
+#include <curl/curl.h>
+
+int progress_callback(void *clientp,
+                      double dltotal,
+                      double dlnow,
+                      double ultotal,
+                      double ulnow);
+
+CURLcode curl_easy_setopt(CURL *handle, CURLOPT_PROGRESSFUNCTION,
+                          progress_callback);
+~~~
+
+# DESCRIPTION
+
+Pass a pointer to your callback function, which should match the prototype
+shown above.
+
+This option is deprecated and we encourage users to use the
+newer CURLOPT_XFERINFOFUNCTION(3) instead, if you can.
+
+This function gets called by libcurl instead of its internal equivalent with a
+frequent interval. While data is being transferred it is invoked frequently,
+and during slow periods like when nothing is being transferred it can slow
+down to about one call per second.
+
+*clientp* is the pointer set with CURLOPT_PROGRESSDATA(3), it is not
+used by libcurl but is only passed along from the application to the callback.
+
+The callback gets told how much data libcurl is about to transfer and has
+transferred, in number of bytes. *dltotal* is the total number of bytes
+libcurl expects to download in this transfer. *dlnow* is the number of
+bytes downloaded so far. *ultotal* is the total number of bytes libcurl
+expects to upload in this transfer. *ulnow* is the number of bytes
+uploaded so far.
+
+Unknown/unused argument values passed to the callback are be set to zero (like
+if you only download data, the upload size remains 0). Many times the callback
+is called one or more times first, before it knows the data sizes so a program
+must be made to handle that.
+
+If your callback function returns CURL_PROGRESSFUNC_CONTINUE it causes libcurl
+to continue executing the default progress function.
+
+Returning any other non-zero value from this callback makes libcurl abort the
+transfer and return *CURLE_ABORTED_BY_CALLBACK*.
+
+If you transfer data with the multi interface, this function is not called
+during periods of idleness unless you call the appropriate libcurl function
+that performs transfers.
+
+CURLOPT_NOPROGRESS(3) must be set to 0 to make this function actually
+get called.
+
+# DEFAULT
+
+By default, libcurl has an internal progress meter. That is rarely wanted by
+users.
+
+# PROTOCOLS
+
+All
+
+# EXAMPLE
+
+~~~c
+struct progress {
+  char *private;
+  size_t size;
+};
+
+static size_t progress_callback(void *clientp,
+                                double dltotal,
+                                double dlnow,
+                                double ultotal,
+                                double ulnow)
+{
+  struct progress *memory = clientp;
+  printf("private: %p\n", memory->private);
+
+  /* use the values */
+
+  return 0; /* all is good */
+}
+
+int main(void)
+{
+  struct progress data;
+
+  CURL *curl = curl_easy_init();
+  if(curl) {
+    /* pass struct to callback  */
+    curl_easy_setopt(curl, CURLOPT_PROGRESSDATA, &data);
+    curl_easy_setopt(curl, CURLOPT_PROGRESSFUNCTION, progress_callback);
+
+    curl_easy_perform(curl);
+  }
+}
+~~~
+
+# AVAILABILITY
+
+Deprecated since 7.32.0.
+
+# RETURN VALUE
+
+Returns CURLE_OK.