1 files changed, 123 insertions, 0 deletions

diff --git a/xs_webmention.h b/xs_webmention.h
new file mode 100644
index 0000000..8415629
--- /dev/null
+++ b/xs_webmention.h
@@ -0,0 +1,123 @@
+/* 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);
+
+
+#ifdef XS_IMPLEMENTATION
+
+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 (status < 200 || status > 299)
+        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 (status < 200 || status > 299)
+            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 (status < 200 || status > 299)
+            status = -4;
+        else
+            status = 1;
+    }
+    else
+        status = 0;
+
+    return status;
+}
+
+
+#endif /* XS_IMPLEMENTATION */
+
+#endif /* _XS_WEBMENTION_H */