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/* copyright (c) 2025 grunfink et al. / MIT license */
#ifndef _XS_WEBMENTION_H
#define _XS_WEBMENTION_H
int xs_webmention_send(const char *source, const char *target, const char *user_agent);
int xs_webmention_hook(const char *source, const char *target, const char *user_agent);
#ifdef XS_IMPLEMENTATION
#include "xs_http.h"
int xs_webmention_send(const char *source, const char *target, const char *user_agent)
/* sends a Webmention to target.
Returns: < 0, error; 0, no Webmention endpoint; > 0, Webmention sent */
{
int status = 0;
xs *endpoint = NULL;
xs *ua = xs_fmt("%s (Webmention)", user_agent ? user_agent : "xs_webmention");
xs *headers = xs_dict_new();
headers = xs_dict_set(headers, "accept", "text/html");
headers = xs_dict_set(headers, "user-agent", ua);
xs *h_req = NULL;
int p_size = 0;
/* try first a HEAD, to see if there is a Webmention Link header */
h_req = xs_http_request("HEAD", target, headers, NULL, 0, &status, NULL, &p_size, 0);
/* return immediate failures */
if (!xs_http_valid_status(status))
return -1;
const char *link = xs_dict_get(h_req, "link");
if (xs_is_string(link) && xs_regex_match(link, "rel *= *(\"|')?webmention")) {
/* endpoint is between < and > */
xs *r = xs_regex_select_n(link, "<[^>]+>", 1);
if (xs_list_len(r) == 1) {
endpoint = xs_dup(xs_list_get(r, 0));
endpoint = xs_strip_chars_i(endpoint, "<>");
}
}
if (endpoint == NULL) {
/* no Link header; get the content */
xs *g_req = NULL;
xs *payload = NULL;
g_req = xs_http_request("GET", target, headers, NULL, 0, &status, &payload, &p_size, 0);
if (!xs_http_valid_status(status))
return -1;
const char *ctype = xs_dict_get(g_req, "content-type");
/* not HTML? no point in looking inside */
if (!xs_is_string(ctype) || xs_str_in(ctype, "text/html") == -1)
return -2;
if (!xs_is_string(payload))
return -3;
xs *links = xs_regex_select(payload, "<(a +|link +)[^>]+>");
const char *link;
xs_list_foreach(links, link) {
if (xs_regex_match(link, "rel *= *(\"|')?webmention")) {
/* found; extract the href */
xs *r = xs_regex_select_n(link, "href *= *(\"|')?[^\"]+(\"|')", 1);
if (xs_list_len(r) == 1) {
xs *l = xs_split_n(xs_list_get(r, 0), "=", 1);
if (xs_list_len(l) == 2) {
endpoint = xs_dup(xs_list_get(l, 1));
endpoint = xs_strip_chars_i(endpoint, " \"'");
break;
}
}
}
}
}
/* is it a relative endpoint? */
if (xs_is_string(endpoint)) {
if (!xs_startswith(endpoint, "https://") && !xs_startswith(endpoint, "http://")) {
xs *l = xs_split(target, "/");
if (xs_list_len(l) < 3)
endpoint = xs_free(endpoint);
else {
xs *s = xs_fmt("%s/" "/%s", xs_list_get(l, 0), xs_list_get(l, 2));
endpoint = xs_str_wrap_i(s, endpoint, NULL);
}
}
}
if (xs_is_string(endpoint)) {
/* got it! */
headers = xs_dict_set(headers, "content-type", "application/x-www-form-urlencoded");
xs *body = xs_fmt("source=%s&target=%s", source, target);
xs *rsp = xs_http_request("POST", endpoint, headers, body, strlen(body), &status, NULL, 0, 0);
if (!xs_http_valid_status(status))
status = -4;
else
status = 1;
}
else
status = 0;
return status;
}
int xs_webmention_hook(const char *source, const char *target, const char *user_agent)
/* a Webmention has been received for a target that is ours; check if the source
really contains a link to our target */
{
int status = 0;
xs *ua = xs_fmt("%s (Webmention)", user_agent ? user_agent : "xs_webmention");
xs *headers = xs_dict_new();
headers = xs_dict_set(headers, "accept", "text/html");
headers = xs_dict_set(headers, "user-agent", ua);
xs *g_req = NULL;
xs *payload = NULL;
int p_size = 0;
g_req = xs_http_request("GET", source, headers, NULL, 0, &status, &payload, &p_size, 0);
if (!xs_http_valid_status(status))
return -1;
if (!xs_is_string(payload))
return -2;
/* note: a "rogue" webmention can include a link to our target in commented-out HTML code */
xs *links = xs_regex_select(payload, "<(a +|link +)[^>]+>");
const char *link;
status = 0;
xs_list_foreach(links, link) {
/* if the link contains our target, it's valid */
if (xs_str_in(link, target) != -1) {
status = 1;
break;
}
}
return status;
}
#endif /* XS_IMPLEMENTATION */
#endif /* _XS_WEBMENTION_H */
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