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.\" generated by cd2nroff 0.1 from CURLOPT_HSTSWRITEFUNCTION.md
.TH CURLOPT_HSTSWRITEFUNCTION 3 "2025-06-27" libcurl
.SH NAME
CURLOPT_HSTSWRITEFUNCTION \- write callback for HSTS hosts
.SH SYNOPSIS
.nf
#include <curl/curl.h>
struct curl_hstsentry {
char *name;
size_t namelen;
unsigned int includeSubDomains:1;
char expire[18]; /* YYYYMMDD HH:MM:SS [null-terminated] */
};
struct curl_index {
size_t index; /* the provided entry's "index" or count */
size_t total; /* total number of entries to save */
};
CURLSTScode hstswrite(CURL *easy, struct curl_hstsentry *sts,
struct curl_index *count, void *clientp);
CURLcode curl_easy_setopt(CURL *handle, CURLOPT_HSTSWRITEFUNCTION, hstswrite);
.fi
.SH DESCRIPTION
Pass a pointer to your callback function, as the prototype shows above.
This callback function gets called by libcurl repeatedly to allow the
application to store the in\-memory HSTS cache when libcurl is about to discard
it.
Set the \fIclientp\fP argument with the \fICURLOPT_HSTSWRITEDATA(3)\fP option
or it is NULL.
When the callback is invoked, the \fIsts\fP pointer points to a populated
struct: Read the hostname to \(aqname\(aq (it is \fInamelen\fP bytes long and null
terminated. The \fIincludeSubDomains\fP field is non\-zero if the entry matches
subdomains. The \fIexpire\fP string is a date stamp null\-terminated string
using the syntax YYYYMMDD HH:MM:SS.
The callback should return \fICURLSTS_OK\fP if it succeeded and is prepared to
be called again (for another host) or \fICURLSTS_DONE\fP if there is nothing
more to do. It can also return \fICURLSTS_FAIL\fP to signal error.
This option does not enable HSTS, you need to use \fICURLOPT_HSTS_CTRL(3)\fP to
do that.
.SH DEFAULT
NULL \- no callback.
.SH PROTOCOLS
This functionality affects http only
.SH EXAMPLE
.nf
struct priv {
void *custom;
};
static CURLSTScode hswr_cb(CURL *easy, struct curl_hstsentry *sts,
struct curl_index *count, void *clientp)
{
/* save the passed in HSTS data somewhere */
return CURLSTS_OK;
}
int main(void)
{
CURL *curl = curl_easy_init();
if(curl) {
struct priv my_stuff;
CURLcode res;
/* set HSTS read callback */
curl_easy_setopt(curl, CURLOPT_HSTSWRITEFUNCTION, hswr_cb);
/* pass in suitable argument to the callback */
curl_easy_setopt(curl, CURLOPT_HSTSWRITEDATA, &my_stuff);
res = curl_easy_perform(curl);
}
}
.fi
.SH AVAILABILITY
Added in curl 7.74.0
.SH RETURN VALUE
This returns CURLE_OK.
.SH SEE ALSO
.BR CURLOPT_HSTS (3),
.BR CURLOPT_HSTSWRITEDATA (3),
.BR CURLOPT_HSTSWRITEFUNCTION (3),
.BR CURLOPT_HSTS_CTRL (3)