kike: implement connection limit

Somehow I'm not sure whether this thing is useful in any sense.

src/kike.c

@@ -37,7 +37,7 @@ static struct config_item g_config_table[] =
 	{ "ssl_cert",        NULL,              "Server SSL certificate (PEM)"   },
 	{ "ssl_key",         NULL,              "Server SSL private key (PEM)"   },
 
-	{ "max_connections", NULL,              "Maximum client connections"     },
+	{ "max_connections", "0",               "Global connection limit"        },
 	{ "ping_interval",   "180",             "Interval between PING's (sec)"  },
 	{ NULL,              NULL,              NULL                             }
 };
@@ -365,6 +365,7 @@ struct server_context
 	int listen_fd;                      ///< Listening socket FD
 	struct client *clients;             ///< Clients
 	SSL_CTX *ssl_ctx;                   ///< SSL context
+	unsigned n_clients;                 ///< Current number of connections
 
 	struct str_map users;               ///< Maps nicknames to clients
 	struct str_map channels;            ///< Maps channel names to data
@@ -377,6 +378,7 @@ struct server_context
 	struct str_map config;              ///< Server configuration
 	char *server_name;                  ///< Our server name
 	unsigned ping_interval;             ///< Ping interval in seconds
+	unsigned max_connections;           ///< Max. connections allowed or 0
 	struct str_vector motd;             ///< MOTD (none if empty)
 	nl_catd catalog;                    ///< Message catalog for server msgs
 };
@@ -384,14 +386,10 @@ struct server_context
 static void
 server_context_init (struct server_context *self)
 {
-	str_map_init (&self->config);
-	self->config.free = free;
-	load_config_defaults (&self->config, g_config_table);
-
 	self->listen_fd = -1;
 	self->clients = NULL;
+	self->n_clients = 0;
 
-	self->server_name = NULL;
 	str_map_init (&self->users);
 	self->users.key_xfrm = irc_strxfrm;
 	// TODO: set channel_free() as the free function?
@@ -404,6 +402,13 @@ server_context_init (struct server_context *self)
 	self->quitting = false;
 	self->polling = false;
 
+	str_map_init (&self->config);
+	self->config.free = free;
+	load_config_defaults (&self->config, g_config_table);
+
+	self->server_name = NULL;
+	self->ping_interval = 0;
+	self->max_connections = 0;
 	str_vector_init (&self->motd);
 	self->catalog = (nl_catd) -1;
 }
@@ -476,6 +481,7 @@ client_kill (struct client *c, const char *reason)
 	c->socket_fd = -1;
 	client_free (c);
 	LIST_UNLINK (ctx->clients, c);
+	ctx->n_clients--;
 	free (c);
 }
 
@@ -1239,8 +1245,6 @@ on_irc_client_available (const struct pollfd *pfd, void *user_data)
 	(void) pfd;
 	struct server_context *ctx = user_data;
 
-	// TODO: stop accepting new connections when `max_connections' is reached
-
 	while (true)
 	{
 		// XXX: `struct sockaddr_storage' is not the most portable thing
@@ -1252,9 +1256,8 @@ on_irc_client_available (const struct pollfd *pfd, void *user_data)
 		{
 			if (errno == EAGAIN)
 				break;
-			if (errno == EINTR)
+			if (errno == EINTR
-				continue;
+			 || errno == ECONNABORTED)
-			if (errno == ECONNABORTED)
 				continue;
 
 			// TODO: handle resource exhaustion (EMFILE, ENFILE) specially
@@ -1263,6 +1266,14 @@ on_irc_client_available (const struct pollfd *pfd, void *user_data)
 			exit_fatal ("%s: %s", "accept", strerror (errno));
 		}
 
+		if (ctx->max_connections != 0
+		 && ctx->n_clients >= ctx->max_connections)
+		{
+			print_debug ("connection limit reached, refusing connection");
+			close (fd);
+			continue;
+		}
+
 		char host[NI_MAXHOST] = "unknown", port[NI_MAXSERV] = "unknown";
 		int err = getnameinfo ((struct sockaddr *) &peer, peer_len,
 			host, sizeof host, port, sizeof port, NI_NUMERICSERV);
@@ -1276,6 +1287,7 @@ on_irc_client_available (const struct pollfd *pfd, void *user_data)
 		c->socket_fd = fd;
 		c->hostname = xstrdup (host);
 		LIST_PREPEND (ctx->clients, c);
+		ctx->n_clients++;
 
 		set_blocking (fd, false);
 		poller_set (&ctx->poller, fd, POLLIN,
@@ -1434,16 +1446,19 @@ static bool
 irc_parse_config (struct server_context *ctx, struct error **e)
 {
 	unsigned long ul;
+#define PARSE_UNSIGNED(name, min, max)                                         \
+	const char *name = str_map_find (&ctx->config, #name);                     \
+	hard_assert (name != NULL);                                                \
+	if (!xstrtoul (&ul, name, 10) || ul > max || ul < min)                     \
+	{                                                                          \
+		error_set (e, "invalid configuration value for `%s': %s",              \
+			#name, "the number is invalid or out of range");                   \
+		return false;                                                          \
+	}                                                                          \
+	ctx->name = ul
 
-	const char *ping_interval = str_map_find (&ctx->config, "ping_interval");
+	PARSE_UNSIGNED (ping_interval,   1, UINT_MAX);
-	hard_assert (ping_interval != NULL);  // We have a default value for this
+	PARSE_UNSIGNED (max_connections, 0, UINT_MAX);
-	if (!xstrtoul (&ul, ping_interval, 10) || ul > UINT_MAX)
-	{
-		error_set (e, "invalid configuration value for `%s': %s",
-			"ping_interval", "the number is invalid or out of range");
-		return false;
-	}
-	ctx->ping_interval = ul;
 	return true;
 }