core-lightning/lightningd/plugin_hook.c

#include <ccan/io/io.h>
#include <common/memleak.h>
#include <lightningd/jsonrpc.h>
#include <lightningd/plugin_hook.h>
#include <wallet/db.h>

/* Struct containing all the information needed to deserialize and
 * dispatch an eventual plugin_hook response. */
struct plugin_hook_request {
	const struct plugin_hook *hook;
	void *cb_arg;
	struct db *db;
};

static struct plugin_hook *plugin_hook_by_name(const char *name)
{
	static struct plugin_hook **hooks = NULL;
	static size_t num_hooks;
	if (!hooks)
		hooks = autodata_get(hooks, &num_hooks);

	for (size_t i=0; i<num_hooks; i++)
		if (streq(hooks[i]->name, name))
			return hooks[i];
	return NULL;
}

bool plugin_hook_register(struct plugin *plugin, const char *method)
{
	struct plugin_hook *hook = plugin_hook_by_name(method);
	if (!hook) {
		/* No such hook name registered */
		return false;
	} else if (hook->plugin != NULL) {
		/* Another plugin already registered for this name */
		return false;
	}
	hook->plugin = plugin;
	return true;
}

/**
 * Callback to be passed to the jsonrpc_request.
 *
 * Unbundles the arguments, deserializes the response and dispatches
 * it to the hook callback.
 */
static void plugin_hook_callback(const char *buffer, const jsmntok_t *toks,
				 const jsmntok_t *idtok,
				 struct plugin_hook_request *r)
{
	const jsmntok_t *resulttok = json_get_member(buffer, toks, "result");

	if (!resulttok)
		fatal("Plugin for %s returned non-result response %.*s",
		      r->hook->name,
		      toks->end - toks->start, buffer + toks->end);

	db_begin_transaction(r->db);
	r->hook->response_cb(r->cb_arg, buffer, resulttok);
	db_commit_transaction(r->db);
	tal_free(r);
}

void plugin_hook_call_(struct lightningd *ld, const struct plugin_hook *hook,
		       void *payload, void *cb_arg)
{
	struct jsonrpc_request *req;
	struct plugin_hook_request *ph_req;
	if (hook->plugin) {
		/* If we have a plugin that has registered for this
		 * hook, serialize and call it */
		/* FIXME: technically this is a leak, but we don't
		 * currently have a list to store these. We might want
		 * to eventually to inspect in-flight requests. */
		ph_req = notleak(tal(hook->plugin, struct plugin_hook_request));
		/* FIXME: do IO logging for these! */
		req = jsonrpc_request_start(NULL, hook->name, NULL,
					    plugin_hook_callback, ph_req);
		ph_req->hook = hook;
		ph_req->cb_arg = cb_arg;
		ph_req->db = ld->wallet->db;
		hook->serialize_payload(payload, req->stream);
		jsonrpc_request_end(req);
		plugin_request_send(hook->plugin, req);
	} else {
		/* If no plugin has registered for this hook, just
		 * call the callback with a NULL result. Saves us the
		 * roundtrip to the serializer and deserializer. If we
		 * were expecting a default response it should have
		 * been part of the `cb_arg`. */
		hook->response_cb(cb_arg, NULL, NULL);
	}
}

/* We open-code this, because it's just different and special enough to be
 * annoying, and to make it clear that it's totally synchronous. */

/* Special synchronous hook for db */
static struct plugin_hook db_write_hook = { "db_write", NULL, NULL, NULL };
AUTODATA(hooks, &db_write_hook);

static void db_hook_response(const char *buffer, const jsmntok_t *toks,
			     const jsmntok_t *idtok,
			     struct plugin_hook_request *ph_req)
{
	const jsmntok_t *resulttok;
	bool resp;

	resulttok = json_get_member(buffer, toks, "result");
	if (!resulttok)
		fatal("Plugin returned an invalid response to the db_write "
		      "hook: %s", buffer);

	/* We expect result: True.  Anything else we abort. */
	if (!json_to_bool(buffer, resulttok, &resp))
		fatal("Plugin returned an invalid result to the db_write "
		      "hook: %s", buffer);

	/* If it fails, we must not commit to our db. */
	if (!resp)
		fatal("Plugin returned failed db_write: %s.", buffer);

	/* We're done, exit exclusive loop. */
	io_break(ph_req);
}

void plugin_hook_db_sync(struct db *db, const char **changes, const char *final)
{
	const struct plugin_hook *hook = &db_write_hook;
	struct jsonrpc_request *req;
	struct plugin_hook_request *ph_req;
	void *ret;

	if (!hook->plugin)
		return;

	ph_req = notleak(tal(hook->plugin, struct plugin_hook_request));
	/* FIXME: do IO logging for this! */
	req = jsonrpc_request_start(NULL, hook->name, NULL, db_hook_response,
				    ph_req);

	ph_req->hook = hook;
	ph_req->db = db;

	json_array_start(req->stream, "writes");
	for (size_t i = 0; i < tal_count(changes); i++)
		json_add_string(req->stream, NULL, changes[i]);
	if (final)
		json_add_string(req->stream, NULL, final);
	json_array_end(req->stream);
	jsonrpc_request_end(req);

	plugin_request_send(hook->plugin, req);

	/* We can be called on way out of an io_loop, which is already breaking.
	 * That will make this immediately return; save the break value and call
	 * again, then hand it onwards. */
	ret = plugin_exclusive_loop(hook->plugin);
	if (ret != ph_req) {
		void *ret2 = plugin_exclusive_loop(hook->plugin);
		assert(ret2 == ph_req);
		io_break(ret);
	}
}