My implementation of ircv3/ircv3-ideas#108

##  `+draft/rated`
This lets users who post media mark their posts as "Not safe for work" to some degree, allowing other users to choose whether or not they want to see this post.

files/rated.c

@@ -0,0 +1,85 @@
+/*
+  Licence: GPLv3 or later
+  Copyright Ⓒ 2023 Valerie Pond
+  draft/rated
+
+*/
+/*** <<<MODULE MANAGER START>>>
+module
+{
+		documentation "https://github.com/ValwareIRC/valware-unrealircd-mods/blob/main/rated/README.md";
+		troubleshooting "In case of problems, documentation or e-mail me at [email protected]";
+		min-unrealircd-version "6.*";
+		max-unrealircd-version "6.*";
+		post-install-text {
+				"The module is installed. Now all you need to do is add a loadmodule line:";
+				"loadmodule \"third/rated\";";
+				"The module does not need any other configuration.";
+		}
+}
+*** <<<MODULE MANAGER END>>>
+*/
+
+
+#include "unrealircd.h"
+#define MTAG_RATED "+draft/rated" // can be changed at a later date
+
+ModuleHeader MOD_HEADER = {
+	"third/rated",
+	"1.0",
+	"+draft/rated",
+	"Valware",
+	"unrealircd-6",
+};
+
+int rated_mtag_is_ok(Client *client, const char *name, const char *value);
+void mtag_add_rated(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature);
+
+MOD_INIT()
+{
+	MessageTagHandlerInfo mtag;
+
+	MARK_AS_GLOBAL_MODULE(modinfo);
+
+	memset(&mtag, 0, sizeof(mtag));
+	mtag.is_ok = rated_mtag_is_ok;
+	mtag.flags = MTAG_HANDLER_FLAGS_NO_CAP_NEEDED;
+	mtag.name = MTAG_RATED;
+	MessageTagHandlerAdd(modinfo->handle, &mtag);
+
+	HookAddVoid(modinfo->handle, HOOKTYPE_NEW_MESSAGE, 0, mtag_add_rated);
+
+	return MOD_SUCCESS;
+}
+
+MOD_LOAD()
+{
+	return MOD_SUCCESS;
+}
+
+MOD_UNLOAD()
+{
+	return MOD_SUCCESS;
+}
+
+int rated_mtag_is_ok(Client *client, const char *name, const char *value)
+{
+	if (strlen(value) && strlen(value) >= 100) // allow null values but cap long values to 100 chars.
+        return 0;
+	return 1;
+}
+
+void mtag_add_rated(Client *client, MessageTag *recv_mtags, MessageTag **mtag_list, const char *signature)
+{
+	MessageTag *m;
+
+	if (IsUser(client))
+	{
+		m = find_mtag(recv_mtags, MTAG_RATED);
+		if (m)
+		{
+			m = duplicate_mtag(m);
+			AddListItem(m, *mtag_list);
+		}
+	}
+}