xK/zyklonb.c

/*
 * zyklonb.c: the experimental IRC bot
 *
 * Copyright (c) 2014 - 2020, Přemysl Eric Janouch <p@janouch.name>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "config.h"
#define PROGRAM_NAME "ZyklonB"

#include "common.c"

// --- Configuration (application-specific) ------------------------------------

static struct simple_config_item g_config_table[] =
{
	{ "nickname",        "ZyklonB",         "IRC nickname"                   },
	{ "username",        "bot",             "IRC user name"                  },
	{ "realname",        "ZyklonB IRC bot", "IRC real name/e-mail"           },

	{ "irc_host",        NULL,              "Address of the IRC server"      },
	{ "irc_port",        "6667",            "Port of the IRC server"         },
	{ "tls",             "off",             "Whether to use TLS"             },
	{ "tls_cert",        NULL,              "Client TLS certificate (PEM)"   },
	{ "tls_verify",      "on",              "Whether to verify certificates" },
	{ "tls_ca_file",     NULL,              "OpenSSL CA bundle file"         },
	{ "tls_ca_path",     NULL,              "OpenSSL CA bundle path"         },
	{ "autojoin",        NULL,              "Channels to join on start"      },
	{ "reconnect",       "on",              "Whether to reconnect on error"  },
	{ "reconnect_delay", "5",               "Time between reconnecting"      },

	{ "socks_host",      NULL,              "Address of a SOCKS 4a/5 proxy"  },
	{ "socks_port",      "1080",            "SOCKS port number"              },
	{ "socks_username",  NULL,              "SOCKS auth. username"           },
	{ "socks_password",  NULL,              "SOCKS auth. password"           },

	{ "prefix",          ":",               "The prefix for bot commands"    },
	{ "admin",           NULL,              "Host mask for administrators"   },
	{ "plugins",         NULL,              "The plugins to load on startup" },
	{ "plugin_dir",      NULL,              "Plugin search path override"    },
	{ "recover",         "on",              "Whether to re-launch on crash"  },

	{ NULL,              NULL,              NULL                             }
};

// --- Application data --------------------------------------------------------

struct plugin
{
	LIST_HEADER (struct plugin)
	struct bot_context *ctx;            ///< Parent context

	char *name;                         ///< Plugin identifier
	pid_t pid;                          ///< PID of the plugin process

	bool is_zombie;                     ///< Whether the child is a zombie
	bool initialized;                   ///< Ready to exchange IRC messages
	struct str queued_output;           ///< Output queued up until initialized

	// Since we're doing non-blocking I/O, we need to queue up data so that
	// we don't stall on plugins unnecessarily.

	int read_fd;                        ///< The read end of the comm. pipe
	int write_fd;                       ///< The write end of the comm. pipe

	struct poller_fd read_event;        ///< Read FD event
	struct poller_fd write_event;       ///< Write FD event

	struct str read_buffer;             ///< Unprocessed input
	struct str write_buffer;            ///< Output yet to be sent out
};

static struct plugin *
plugin_new (void)
{
	struct plugin *self = xcalloc (1, sizeof *self);
	self->pid = -1;
	self->queued_output = str_make ();

	self->read_fd = -1;
	self->read_buffer = str_make ();
	self->write_fd = -1;
	self->write_buffer = str_make ();
	return self;
}

static void
plugin_destroy (struct plugin *self)
{
	soft_assert (self->pid == -1);
	free (self->name);

	str_free (&self->read_buffer);
	if (!soft_assert (self->read_fd == -1))
		xclose (self->read_fd);

	str_free (&self->write_buffer);
	if (!soft_assert (self->write_fd == -1))
		xclose (self->write_fd);

	if (!self->initialized)
		str_free (&self->queued_output);

	free (self);
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

struct bot_context
{
	struct str_map config;              ///< User configuration
	regex_t *admin_re;                  ///< Regex to match our administrator
	bool reconnect;                     ///< Whether to reconnect on conn. fail.
	unsigned long reconnect_delay;      ///< Reconnect delay in seconds

	int irc_fd;                         ///< Socket FD of the server
	struct str read_buffer;             ///< Input yet to be processed
	struct poller_fd irc_event;         ///< IRC FD event
	bool irc_registered;                ///< Whether we may send messages now

	struct poller_fd signal_event;      ///< Signal FD event
	struct poller_timer ping_tmr;       ///< We should send a ping
	struct poller_timer timeout_tmr;    ///< Connection seems to be dead
	struct poller_timer reconnect_tmr;  ///< We should reconnect now

	SSL_CTX *ssl_ctx;                   ///< SSL context
	SSL *ssl;                           ///< SSL connection

	struct plugin *plugins;             ///< Linked list of plugins
	struct str_map plugins_by_name;     ///< Indexes @em plugins by their name

	struct poller poller;               ///< Manages polled descriptors
	bool quitting;                      ///< User requested quitting
	bool polling;                       ///< The event loop is running
};

static void on_irc_ping_timeout (void *user_data);
static void on_irc_timeout (void *user_data);
static void on_irc_reconnect_timeout (void *user_data);

static void
bot_context_init (struct bot_context *self)
{
	self->config = str_map_make (free);
	simple_config_load_defaults (&self->config, g_config_table);
	self->admin_re = NULL;

	self->irc_fd = -1;
	self->read_buffer = str_make ();
	self->irc_registered = false;

	self->ssl = NULL;
	self->ssl_ctx = NULL;

	self->plugins = NULL;
	self->plugins_by_name = str_map_make (NULL);

	poller_init (&self->poller);
	self->quitting = false;
	self->polling = false;

	self->timeout_tmr = poller_timer_make (&self->poller);
	self->timeout_tmr.dispatcher = on_irc_timeout;
	self->timeout_tmr.user_data = self;

	self->ping_tmr = poller_timer_make (&self->poller);
	self->ping_tmr.dispatcher = on_irc_ping_timeout;
	self->ping_tmr.user_data = self;

	self->reconnect_tmr = poller_timer_make (&self->poller);
	self->reconnect_tmr.dispatcher = on_irc_reconnect_timeout;
	self->reconnect_tmr.user_data = self;
}

static void
bot_context_free (struct bot_context *self)
{
	str_map_free (&self->config);
	if (self->admin_re)
		regex_free (self->admin_re);
	str_free (&self->read_buffer);

	// TODO: terminate the plugins properly before this is called
	LIST_FOR_EACH (struct plugin, link, self->plugins)
		plugin_destroy (link);

	if (self->irc_fd != -1)
	{
		poller_fd_reset (&self->irc_event);
		xclose (self->irc_fd);
	}
	if (self->ssl)
		SSL_free (self->ssl);
	if (self->ssl_ctx)
		SSL_CTX_free (self->ssl_ctx);

	str_map_free (&self->plugins_by_name);
	poller_free (&self->poller);
}

static void
irc_shutdown (struct bot_context *ctx)
{
	// TODO: set a timer after which we cut the connection?
	// Generally non-critical
	if (ctx->ssl)
		soft_assert (SSL_shutdown (ctx->ssl) != -1);
	else
		soft_assert (shutdown (ctx->irc_fd, SHUT_WR) == 0);
}

static void
try_finish_quit (struct bot_context *ctx)
{
	if (ctx->quitting && ctx->irc_fd == -1 && !ctx->plugins)
		ctx->polling = false;
}

static bool plugin_zombify (struct plugin *);

static void
initiate_quit (struct bot_context *ctx)
{
	// Initiate bringing down of the two things that block our shutdown:
	// a/ the IRC socket, b/ our child processes:

	for (struct plugin *plugin = ctx->plugins;
		plugin; plugin = plugin->next)
		plugin_zombify (plugin);
	if (ctx->irc_fd != -1)
		irc_shutdown (ctx);

	ctx->quitting = true;
	try_finish_quit (ctx);
}

static bool irc_send (struct bot_context *ctx,
	const char *format, ...) ATTRIBUTE_PRINTF (2, 3);

static bool
irc_send (struct bot_context *ctx, const char *format, ...)
{
	va_list ap;

	if (g_debug_mode)
	{
		fputs ("[IRC] <== \"", stderr);
		va_start (ap, format);
		vfprintf (stderr, format, ap);
		va_end (ap);
		fputs ("\"\n", stderr);
	}

	if (!soft_assert (ctx->irc_fd != -1))
		return false;

	va_start (ap, format);
	struct str str = str_make ();
	str_append_vprintf (&str, format, ap);
	str_append (&str, "\r\n");
	va_end (ap);

	bool result = true;
	if (ctx->ssl)
	{
		// TODO: call SSL_get_error() to detect if a clean shutdown has occured
		ERR_clear_error ();
		if (SSL_write (ctx->ssl, str.str, str.len) != (int) str.len)
		{
			print_debug ("%s: %s: %s", __func__, "SSL_write",
				xerr_describe_error ());
			result = false;
		}
	}
	else if (write (ctx->irc_fd, str.str, str.len) != (ssize_t) str.len)
	{
		print_debug ("%s: %s: %s", __func__, "write", strerror (errno));
		result = false;
	}

	str_free (&str);
	return result;
}

static bool
irc_get_boolean_from_config
	(struct bot_context *ctx, const char *name, bool *value, struct error **e)
{
	const char *str = str_map_find (&ctx->config, name);
	hard_assert (str != NULL);

	if (set_boolean_if_valid (value, str))
		return true;

	return error_set (e, "invalid configuration value for `%s'", name);
}

static bool
irc_initialize_ca_set (SSL_CTX *ssl_ctx, const char *file, const char *path,
	struct error **e)
{
	ERR_clear_error ();

	if (file || path)
	{
		if (SSL_CTX_load_verify_locations (ssl_ctx, file, path))
			return true;

		return error_set (e, "%s: %s",
			"failed to set locations for the CA certificate bundle",
			xerr_describe_error ());
	}

	if (!SSL_CTX_set_default_verify_paths (ssl_ctx))
		return error_set (e, "%s: %s",
			"couldn't load the default CA certificate bundle",
			xerr_describe_error ());
	return true;
}

static bool
irc_initialize_ca (struct bot_context *ctx, struct error **e)
{
	const char *ca_file = str_map_find (&ctx->config, "tls_ca_file");
	const char *ca_path = str_map_find (&ctx->config, "tls_ca_path");

	char *full_file = ca_file
		? resolve_filename (ca_file, resolve_relative_config_filename) : NULL;
	char *full_path = ca_path
		? resolve_filename (ca_path, resolve_relative_config_filename) : NULL;

	bool ok = false;
	if      (ca_file && !full_file)
		error_set (e, "couldn't find the CA bundle file");
	else if (ca_path && !full_path)
		error_set (e, "couldn't find the CA bundle path");
	else
		ok = irc_initialize_ca_set (ctx->ssl_ctx, full_file, full_path, e);

	free (full_file);
	free (full_path);
	return ok;
}

static bool
irc_initialize_ssl_ctx (struct bot_context *ctx, struct error **e)
{
	// Disable deprecated protocols (see RFC 7568)
	SSL_CTX_set_options (ctx->ssl_ctx, SSL_OP_NO_SSLv2 | SSL_OP_NO_SSLv3);

	bool verify;
	if (!irc_get_boolean_from_config (ctx, "tls_verify", &verify, e))
		return false;
	SSL_CTX_set_verify (ctx->ssl_ctx,
		verify ? SSL_VERIFY_PEER : SSL_VERIFY_NONE, NULL);

	struct error *error = NULL;
	if (!irc_initialize_ca (ctx, &error))
	{
		if (verify)
		{
			error_propagate (e, error);
			return false;
		}

		// Only inform the user if we're not actually verifying
		print_warning ("%s", error->message);
		error_free (error);
	}
	return true;
}

static bool
irc_initialize_tls (struct bot_context *ctx, struct error **e)
{
	const char *error_info = NULL;
	ctx->ssl_ctx = SSL_CTX_new (SSLv23_client_method ());
	if (!ctx->ssl_ctx)
		goto error_ssl_1;
	if (!irc_initialize_ssl_ctx (ctx, e))
		goto error_ssl_2;

	ctx->ssl = SSL_new (ctx->ssl_ctx);
	if (!ctx->ssl)
		goto error_ssl_2;

	const char *tls_cert = str_map_find (&ctx->config, "tls_cert");
	if (tls_cert)
	{
		char *path = resolve_filename
			(tls_cert, resolve_relative_config_filename);
		if (!path)
			print_error ("%s: %s", "cannot open file", tls_cert);
		// XXX: perhaps we should read the file ourselves for better messages
		else if (!SSL_use_certificate_file (ctx->ssl, path, SSL_FILETYPE_PEM)
			|| !SSL_use_PrivateKey_file (ctx->ssl, path, SSL_FILETYPE_PEM))
			print_error ("%s: %s", "setting the TLS client certificate failed",
				xerr_describe_error ());
		free (path);
	}

	SSL_set_connect_state (ctx->ssl);
	if (!SSL_set_fd (ctx->ssl, ctx->irc_fd))
		goto error_ssl_3;
	// Avoid SSL_write() returning SSL_ERROR_WANT_READ
	SSL_set_mode (ctx->ssl, SSL_MODE_AUTO_RETRY);

	switch (xssl_get_error (ctx->ssl, SSL_connect (ctx->ssl), &error_info))
	{
	case SSL_ERROR_NONE:
		return true;
	case SSL_ERROR_ZERO_RETURN:
		error_info = "server closed the connection";
	default:
		break;
	}

error_ssl_3:
	SSL_free (ctx->ssl);
	ctx->ssl = NULL;
error_ssl_2:
	SSL_CTX_free (ctx->ssl_ctx);
	ctx->ssl_ctx = NULL;
error_ssl_1:
	if (!error_info)
		error_info = xerr_describe_error ();
	return error_set (e, "%s: %s", "could not initialize TLS", error_info);
}

static bool
irc_establish_connection (struct bot_context *ctx,
	const char *host, const char *port, struct error **e)
{
	struct addrinfo gai_hints, *gai_result, *gai_iter;
	memset (&gai_hints, 0, sizeof gai_hints);
	gai_hints.ai_socktype = SOCK_STREAM;

	int err = getaddrinfo (host, port, &gai_hints, &gai_result);
	if (err)
		return error_set (e, "%s: %s: %s", "connection failed",
			"getaddrinfo", gai_strerror (err));

	int sockfd;
	for (gai_iter = gai_result; gai_iter; gai_iter = gai_iter->ai_next)
	{
		sockfd = socket (gai_iter->ai_family,
			gai_iter->ai_socktype, gai_iter->ai_protocol);
		if (sockfd == -1)
			continue;
		set_cloexec (sockfd);

		int yes = 1;
		soft_assert (setsockopt (sockfd, SOL_SOCKET, SO_KEEPALIVE,
			&yes, sizeof yes) != -1);

		const char *real_host = host;

		// Let's try to resolve the address back into a real hostname;
		// we don't really need this, so we can let it quietly fail
		char buf[NI_MAXHOST];
		err = getnameinfo (gai_iter->ai_addr, gai_iter->ai_addrlen,
			buf, sizeof buf, NULL, 0, 0);
		if (err)
			print_debug ("%s: %s", "getnameinfo", gai_strerror (err));
		else
			real_host = buf;

		// XXX: we shouldn't mix these statuses with `struct error'; choose 1!
		char *address = format_host_port_pair (real_host, port);
		print_status ("connecting to %s...", address);
		free (address);

		if (!connect (sockfd, gai_iter->ai_addr, gai_iter->ai_addrlen))
			break;

		xclose (sockfd);
	}

	freeaddrinfo (gai_result);

	if (!gai_iter)
		return error_set (e, "connection failed");

	ctx->irc_fd = sockfd;
	return true;
}

// --- Signals -----------------------------------------------------------------

static int g_signal_pipe[2];            ///< A pipe used to signal... signals

static struct strv
	g_original_argv,                    ///< Original program arguments
	g_recovery_env;                     ///< Environment for re-exec recovery

/// Program termination has been requested by a signal
static volatile sig_atomic_t g_termination_requested;

/// Points to startup reason location within `g_recovery_environment'
static char **g_startup_reason_location;
/// The environment variable used to pass the startup reason when re-executing
static const char g_startup_reason_str[] = "STARTUP_REASON";

static void
sigchld_handler (int signum)
{
	(void) signum;

	int original_errno = errno;
	// Just so that the read end of the pipe wakes up the poller.
	// NOTE: Linux has signalfd() and eventfd(), and the BSD's have kqueue.
	//   All of them are better than this approach, although platform-specific.
	if (write (g_signal_pipe[1], "c", 1) == -1)
		soft_assert (errno == EAGAIN);
	errno = original_errno;
}

static void
sigterm_handler (int signum)
{
	(void) signum;

	g_termination_requested = true;

	int original_errno = errno;
	if (write (g_signal_pipe[1], "t", 1) == -1)
		soft_assert (errno == EAGAIN);
	errno = original_errno;
}

static void
setup_signal_handlers (void)
{
	if (pipe (g_signal_pipe) == -1)
		exit_fatal ("%s: %s", "pipe", strerror (errno));

	set_cloexec (g_signal_pipe[0]);
	set_cloexec (g_signal_pipe[1]);

	// So that the pipe cannot overflow; it would make write() block within
	// the signal handler, which is something we really don't want to happen.
	// The same holds true for read().
	set_blocking (g_signal_pipe[0], false);
	set_blocking (g_signal_pipe[1], false);

	struct sigaction sa;
	sa.sa_flags = SA_RESTART;
	sa.sa_handler = sigchld_handler;
	sigemptyset (&sa.sa_mask);

	if (sigaction (SIGCHLD, &sa, NULL) == -1)
		exit_fatal ("sigaction: %s", strerror (errno));

	signal (SIGPIPE, SIG_IGN);

	sa.sa_handler = sigterm_handler;
	if (sigaction (SIGINT, &sa, NULL) == -1
	 || sigaction (SIGTERM, &sa, NULL) == -1)
		exit_fatal ("sigaction: %s", strerror (errno));
}

static void
translate_signal_info (int no, const char **name, int code, const char **reason)
{
	if (code == SI_USER)         *reason = "signal sent by kill()";
	if (code == SI_QUEUE)        *reason = "signal sent by sigqueue()";

	switch (no)
	{
	case SIGILL:
		*name = "SIGILL";
		if (code == ILL_ILLOPC)  *reason = "illegal opcode";
		if (code == ILL_ILLOPN)  *reason = "illegal operand";
		if (code == ILL_ILLADR)  *reason = "illegal addressing mode";
		if (code == ILL_ILLTRP)  *reason = "illegal trap";
		if (code == ILL_PRVOPC)  *reason = "privileged opcode";
		if (code == ILL_PRVREG)  *reason = "privileged register";
		if (code == ILL_COPROC)  *reason = "coprocessor error";
		if (code == ILL_BADSTK)  *reason = "internal stack error";
		break;
	case SIGFPE:
		*name = "SIGFPE";
		if (code == FPE_INTDIV)  *reason = "integer divide by zero";
		if (code == FPE_INTOVF)  *reason = "integer overflow";
		if (code == FPE_FLTDIV)  *reason = "floating-point divide by zero";
		if (code == FPE_FLTOVF)  *reason = "floating-point overflow";
		if (code == FPE_FLTUND)  *reason = "floating-point underflow";
		if (code == FPE_FLTRES)  *reason = "floating-point inexact result";
		if (code == FPE_FLTINV)  *reason = "invalid floating-point operation";
		if (code == FPE_FLTSUB)  *reason = "subscript out of range";
		break;
	case SIGSEGV:
		*name = "SIGSEGV";
		if (code == SEGV_MAPERR)
			*reason = "address not mapped to object";
		if (code == SEGV_ACCERR)
			*reason = "invalid permissions for mapped object";
		break;
	case SIGBUS:
		*name = "SIGBUS";
		if (code == BUS_ADRALN)  *reason = "invalid address alignment";
		if (code == BUS_ADRERR)  *reason = "nonexistent physical address";
		if (code == BUS_OBJERR)  *reason = "object-specific hardware error";
		break;
	default:
		*name = NULL;
	}
}

static void
recovery_handler (int signum, siginfo_t *info, void *context)
{
	(void) context;

	// TODO: maybe try to force a core dump like this: if (fork() == 0) return;
	// TODO: maybe we could even send "\r\nQUIT :reason\r\n" to the server. >_>
	//   As long as we're not connected via TLS, that is.

	const char *signal_name = NULL, *reason = NULL;
	translate_signal_info (signum, &signal_name, info->si_code, &reason);

	char buf[128], numbuf[8];
	if (!signal_name)
	{
		snprintf (numbuf, sizeof numbuf, "%d", signum);
		signal_name = numbuf;
	}

	if (reason)
		snprintf (buf, sizeof buf, "%s=%s: %s: %s", g_startup_reason_str,
			"signal received", signal_name, reason);
	else
		snprintf (buf, sizeof buf, "%s=%s: %s", g_startup_reason_str,
			"signal received", signal_name);
	*g_startup_reason_location = buf;

	// Avoid annoying resource intensive infinite loops by sleeping for a bit
	(void) sleep (1);

	// TODO: maybe pregenerate the path, see the following for some other ways
	//   that would be illegal to do from within a signal handler:
	//     http://stackoverflow.com/a/1024937
	//     http://stackoverflow.com/q/799679
	//   Especially if we change the current working directory in the program.
	//
	//   Note that I can just overwrite g_orig_argv[0].

	// NOTE: our children will read EOF on the read ends of their pipes as a
	//   a result of O_CLOEXEC.  That should be enough to make them terminate.

	char **argv = g_original_argv.vector, **argp = g_recovery_env.vector;
	execve ("/proc/self/exe",        argv, argp);  // Linux
	execve ("/proc/curproc/file",    argv, argp);  // BSD
	execve ("/proc/curproc/exe",     argv, argp);  // BSD
	execve ("/proc/self/path/a.out", argv, argp);  // Solaris
	execve (argv[0],                 argv, argp);  // unreliable fallback

	// Let's just crash
	perror ("execve");
	signal (signum, SIG_DFL);
	raise (signum);
}

static void
prepare_recovery_environment (void)
{
	g_recovery_env = strv_make ();
	strv_append_vector (&g_recovery_env, environ);

	// Prepare a location within the environment where we will put the startup
	// (or maybe rather restart) reason in case of an irrecoverable error.
	char **iter;
	for (iter = g_recovery_env.vector; *iter; iter++)
	{
		const size_t len = sizeof g_startup_reason_str - 1;
		if (!strncmp (*iter, g_startup_reason_str, len) && (*iter)[len] == '=')
			break;
	}

	if (*iter)
		g_startup_reason_location = iter;
	else
	{
		g_startup_reason_location = g_recovery_env.vector + g_recovery_env.len;
		strv_append (&g_recovery_env, "");
	}
}

static bool
setup_recovery_handler (struct bot_context *ctx, struct error **e)
{
	bool recover;
	if (!irc_get_boolean_from_config (ctx, "recover", &recover, e))
		return false;
	if (!recover)
		return true;

	// Make sure these signals aren't blocked, otherwise we would be unable
	// to handle them, making the critical conditions fatal.
	sigset_t mask;
	sigemptyset (&mask);
	sigaddset (&mask, SIGSEGV);
	sigaddset (&mask, SIGBUS);
	sigaddset (&mask, SIGFPE);
	sigaddset (&mask, SIGILL);
	sigprocmask (SIG_UNBLOCK, &mask, NULL);

	struct sigaction sa;
	sa.sa_flags = SA_SIGINFO;
	sa.sa_sigaction = recovery_handler;
	sigemptyset (&sa.sa_mask);

	prepare_recovery_environment ();

	// TODO: also handle SIGABRT... or avoid doing abort() in the first place?
	if (sigaction (SIGSEGV, &sa, NULL) == -1
	 || sigaction (SIGBUS,  &sa, NULL) == -1
	 || sigaction (SIGFPE,  &sa, NULL) == -1
	 || sigaction (SIGILL,  &sa, NULL) == -1)
		print_error ("sigaction: %s", strerror (errno));
	return true;
}

// --- Plugins -----------------------------------------------------------------

/// The name of the special IRC command for interprocess communication
static const char *plugin_ipc_command = "ZYKLONB";

static struct plugin *
plugin_find_by_pid (struct bot_context *ctx, pid_t pid)
{
	struct plugin *iter;
	for (iter = ctx->plugins; iter; iter = iter->next)
		if (iter->pid == pid)
			return iter;
	return NULL;
}

static bool
plugin_zombify (struct plugin *plugin)
{
	if (plugin->is_zombie)
		return false;

	// FIXME: make sure that we don't remove entries from the poller while we
	//   still may have stuff to read; maybe just check that the read pipe is
	//   empty before closing it... and then on EOF check if `pid == -1' and
	//   only then dispose of it (it'd be best to simulate that both of these
	//   cases may happen).
	poller_fd_reset (&plugin->write_event);

	// TODO: try to flush the write buffer (non-blocking)?

	// The plugin should terminate itself after it receives EOF.
	xclose (plugin->write_fd);
	plugin->write_fd = -1;

	// Make it a pseudo-anonymous zombie.  In this state we process any
	// remaining commands it attempts to send to us before it finally dies.
	str_map_set (&plugin->ctx->plugins_by_name, plugin->name, NULL);
	plugin->is_zombie = true;

	// TODO: wait a few seconds and then send SIGKILL to the plugin
	return true;
}

static void
on_plugin_writable (const struct pollfd *fd, struct plugin *plugin)
{
	struct str *buf = &plugin->write_buffer;
	size_t written_total = 0;

	if (fd->revents & ~(POLLOUT | POLLHUP | POLLERR))
		print_debug ("fd %d: unexpected revents: %d", fd->fd, fd->revents);

	while (written_total != buf->len)
	{
		ssize_t n_written = write (fd->fd, buf->str + written_total,
			buf->len - written_total);

		if (n_written < 0)
		{
			if (errno == EAGAIN)
				break;
			if (errno == EINTR)
				continue;

			soft_assert (errno == EPIPE);
			// Zombies shouldn't get dispatched for writability
			hard_assert (!plugin->is_zombie);

			print_debug ("%s: %s", "write", strerror (errno));
			print_error ("failure on writing to plugin `%s',"
				" therefore I'm unloading it", plugin->name);
			plugin_zombify (plugin);
			break;
		}

		// This may be equivalent to EAGAIN on some implementations
		if (n_written == 0)
			break;

		written_total += n_written;
	}

	if (written_total != 0)
		str_remove_slice (buf, 0, written_total);

	if (buf->len == 0)
		// Everything has been written, there's no need to end up in here again
		poller_fd_reset (&plugin->write_event);
}

static void
plugin_queue_write (struct plugin *plugin)
{
	if (plugin->is_zombie)
		return;

	// Don't let the write buffer grow indefinitely.  If there's a ton of data
	// waiting to be processed by the plugin, it usually means there's something
	// wrong with it (such as someone stopping the process).
	if (plugin->write_buffer.len >= (1 << 20))
	{
		print_warning ("plugin `%s' does not seem to process messages fast"
			" enough, I'm unloading it", plugin->name);
		plugin_zombify (plugin);
		return;
	}
	poller_fd_set (&plugin->write_event, POLLOUT);
}

static void
plugin_send (struct plugin *plugin, const char *format, ...)
	ATTRIBUTE_PRINTF (2, 3);

static void
plugin_send (struct plugin *plugin, const char *format, ...)
{
	va_list ap;

	if (g_debug_mode)
	{
		fprintf (stderr, "[%s] <-- \"", plugin->name);
		va_start (ap, format);
		vfprintf (stderr, format, ap);
		va_end (ap);
		fputs ("\"\n", stderr);
	}

	va_start (ap, format);
	str_append_vprintf (&plugin->write_buffer, format, ap);
	va_end (ap);
	str_append (&plugin->write_buffer, "\r\n");

	plugin_queue_write (plugin);
}

static void
plugin_process_ipc (struct plugin *plugin, const struct irc_message *msg)
{
	// Replies are sent in the order in which they came in, so there's
	// no need to attach a special identifier to them.  It might be
	// desirable in some cases, though.

	if (msg->params.len < 1)
		return;

	const char *command = msg->params.vector[0];
	if (!plugin->initialized && !strcasecmp (command, "register"))
	{
		// Register for relaying of IRC traffic
		plugin->initialized = true;

		// Flush any queued up traffic here.  The point of queuing it in
		// the first place is so that we don't have to wait for plugin
		// initialization during startup.
		//
		// Note that if we start filtering data coming to the plugins e.g.
		// based on what it tells us upon registration, we might need to
		// filter `queued_output' as well.
		str_append_str (&plugin->write_buffer, &plugin->queued_output);
		str_free (&plugin->queued_output);

		// NOTE: this may trigger the buffer length check
		plugin_queue_write (plugin);
	}
	else if (!strcasecmp (command, "get_config"))
	{
		if (msg->params.len < 2)
			return;

		const char *value =
			str_map_find (&plugin->ctx->config, msg->params.vector[1]);
		// TODO: escape the value (although there's no need to ATM)
		plugin_send (plugin, "%s :%s",
			plugin_ipc_command, value ? value : "");
	}
	else if (!strcasecmp (command, "print"))
	{
		if (msg->params.len < 2)
			return;

		printf ("%s\n", msg->params.vector[1]);
	}
}

static void
plugin_process_message (const struct irc_message *msg,
	const char *raw, void *user_data)
{
	struct plugin *plugin = user_data;
	struct bot_context *ctx = plugin->ctx;

	if (g_debug_mode)
		fprintf (stderr, "[%s] --> \"%s\"\n", plugin->name, raw);

	if (!strcasecmp (msg->command, plugin_ipc_command))
		plugin_process_ipc (plugin, msg);
	else if (plugin->initialized && ctx->irc_registered)
	{
		// Pass everything else through to the IRC server
		// XXX: when the server isn't ready yet, these messages get silently
		//   discarded, which shouldn't pose a problem most of the time.
		//   Perhaps we could send a "connected" notification on `register'
		//   if `irc_ready' is true, or after it becomes true later, so that
		//   plugins know when to start sending unprovoked IRC messages.
		// XXX: another case is when the connection gets interrupted and the
		//   plugin tries to send something back while we're reconnecting.
		//   For that we might set up a global buffer that gets flushed out
		//   after `irc_ready' becomes true.  Note that there is always some
		//   chance of messages getting lost without us even noticing it.
		irc_send (ctx, "%s", raw);
	}
}

static void
on_plugin_readable (const struct pollfd *fd, struct plugin *plugin)
{
	if (fd->revents & ~(POLLIN | POLLHUP | POLLERR))
		print_debug ("fd %d: unexpected revents: %d", fd->fd, fd->revents);

	// TODO: see if I can reuse irc_fill_read_buffer()
	struct str *buf = &plugin->read_buffer;
	while (true)
	{
		str_reserve (buf, 512 + 1);
		ssize_t n_read = read (fd->fd, buf->str + buf->len,
			buf->alloc - buf->len - 1);

		if (n_read < 0)
		{
			if (errno == EAGAIN)
				break;
			if (soft_assert (errno == EINTR))
				continue;

			if (!plugin->is_zombie)
			{
				print_error ("failure on reading from plugin `%s',"
					" therefore I'm unloading it", plugin->name);
				plugin_zombify (plugin);
			}
			return;
		}

		// EOF; hopefully it will die soon (maybe it already has)
		if (n_read == 0)
			break;

		buf->str[buf->len += n_read] = '\0';
		if (buf->len >= (1 << 20))
		{
			// XXX: this isn't really the best flood prevention mechanism,
			//   but it wasn't even supposed to be one.
			if (plugin->is_zombie)
			{
				print_error ("a zombie of plugin `%s' is trying to flood us,"
					" therefore I'm killing it", plugin->name);
				kill (plugin->pid, SIGKILL);
			}
			else
			{
				print_error ("plugin `%s' seems to spew out data frantically,"
					" therefore I'm unloading it", plugin->name);
				plugin_zombify (plugin);
			}
			return;
		}
	}

	irc_process_buffer (buf, plugin_process_message, plugin);
}

static bool
is_valid_plugin_name (const char *name)
{
	if (!*name)
		return false;
	for (const char *p = name; *p; p++)
		if (!isgraph (*p) || *p == '/')
			return false;
	return true;
}

static char *
plugin_resolve_relative_filename (const char *filename)
{
	struct strv paths = strv_make ();
	get_xdg_data_dirs (&paths);
	char *result = resolve_relative_filename_generic
		(&paths, PROGRAM_NAME "/plugins/", filename);
	strv_free (&paths);
	return result;
}

static struct plugin *
plugin_launch (struct bot_context *ctx, const char *name, struct error **e)
{
	char *path = NULL;
	const char *plugin_dir = str_map_find (&ctx->config, "plugin_dir");
	if (plugin_dir)
	{
		// resolve_relative_filename_generic() won't accept relative paths,
		// so just keep the old behaviour and expect the file to exist.
		// We could use resolve_filename() on "plugin_dir" with paths=getcwd().
		path = xstrdup_printf ("%s/%s", plugin_dir, name);
	}
	else if (!(path = plugin_resolve_relative_filename (name)))
	{
		error_set (e, "plugin not found");
		goto fail_0;
	}

	int stdin_pipe[2];
	if (pipe (stdin_pipe) == -1)
	{
		error_set (e, "%s: %s", "pipe", strerror (errno));
		goto fail_0;
	}

	int stdout_pipe[2];
	if (pipe (stdout_pipe) == -1)
	{
		error_set (e, "%s: %s", "pipe", strerror (errno));
		goto fail_1;
	}

	struct str work_dir = str_make ();
	get_xdg_home_dir (&work_dir, "XDG_DATA_HOME", ".local/share");
	str_append_printf (&work_dir, "/%s", PROGRAM_NAME);

	if (!mkdir_with_parents (work_dir.str, e))
		goto fail_2;

	set_cloexec (stdin_pipe[1]);
	set_cloexec (stdout_pipe[0]);

	pid_t pid = fork ();
	if (pid == -1)
	{
		error_set (e, "%s: %s", "fork", strerror (errno));
		goto fail_2;
	}

	if (pid == 0)
	{
		// Redirect the child's stdin and stdout to the pipes
		if (dup2 (stdin_pipe[0], STDIN_FILENO) == -1
		 || dup2 (stdout_pipe[1], STDOUT_FILENO) == -1)
		{
			print_error ("%s: %s: %s", "failed to load the plugin",
				"dup2", strerror (errno));
			_exit (EXIT_FAILURE);
		}
		if (chdir (work_dir.str))
		{
			print_error ("%s: %s: %s", "failed to load the plugin",
				"chdir", strerror (errno));
			_exit (EXIT_FAILURE);
		}

		xclose (stdin_pipe[0]);
		xclose (stdout_pipe[1]);

		// Restore some of the signal handling
		signal (SIGPIPE, SIG_DFL);

		char *argv[] = { path, NULL };
		execve (argv[0], argv, environ);

		// We will collect the failure later via SIGCHLD
		print_error ("%s: %s: %s", "failed to load the plugin",
			"exec", strerror (errno));
		_exit (EXIT_FAILURE);
	}

	str_free (&work_dir);
	free (path);

	xclose (stdin_pipe[0]);
	xclose (stdout_pipe[1]);

	struct plugin *plugin = plugin_new ();
	plugin->ctx = ctx;
	plugin->pid = pid;
	plugin->name = xstrdup (name);
	plugin->read_fd = stdout_pipe[0];
	plugin->write_fd = stdin_pipe[1];
	return plugin;

fail_2:
	str_free (&work_dir);
	xclose (stdout_pipe[0]);
	xclose (stdout_pipe[1]);
fail_1:
	xclose (stdin_pipe[0]);
	xclose (stdin_pipe[1]);
fail_0:
	free (path);
	return NULL;
}

static bool
plugin_load (struct bot_context *ctx, const char *name, struct error **e)
{
	if (!is_valid_plugin_name (name))
		return error_set (e, "invalid plugin name");
	if (str_map_find (&ctx->plugins_by_name, name))
		return error_set (e, "the plugin has already been loaded");

	struct plugin *plugin;
	if (!(plugin = plugin_launch (ctx, name, e)))
		return false;

	set_blocking (plugin->read_fd, false);
	set_blocking (plugin->write_fd, false);

	plugin->read_event = poller_fd_make (&ctx->poller, plugin->read_fd);
	plugin->read_event.dispatcher = (poller_fd_fn) on_plugin_readable;
	plugin->read_event.user_data = plugin;

	plugin->write_event = poller_fd_make (&ctx->poller, plugin->write_fd);
	plugin->write_event.dispatcher = (poller_fd_fn) on_plugin_writable;
	plugin->write_event.user_data = plugin;

	LIST_PREPEND (ctx->plugins, plugin);
	str_map_set (&ctx->plugins_by_name, name, plugin);

	poller_fd_set (&plugin->read_event, POLLIN);
	return true;
}

static bool
plugin_unload (struct bot_context *ctx, const char *name, struct error **e)
{
	struct plugin *plugin = str_map_find (&ctx->plugins_by_name, name);

	if (!plugin)
		return error_set (e, "no such plugin is loaded");

	plugin_zombify (plugin);

	// TODO: add a `kill zombies' command to forcefully get rid of processes
	//   that do not understand the request.
	return true;
}

static void
plugin_load_all_from_config (struct bot_context *ctx)
{
	const char *plugin_list = str_map_find (&ctx->config, "plugins");
	if (!plugin_list)
		return;

	struct strv plugins = strv_make ();
	cstr_split (plugin_list, ",", true, &plugins);
	for (size_t i = 0; i < plugins.len; i++)
	{
		char *name = cstr_strip_in_place (plugins.vector[i], " ");

		struct error *e = NULL;
		if (!plugin_load (ctx, name, &e))
		{
			print_error ("plugin `%s' failed to load: %s", name, e->message);
			error_free (e);
		}
	}

	strv_free (&plugins);
}

// --- Main program ------------------------------------------------------------

static bool
parse_bot_command (const char *s, const char *command, const char **following)
{
	size_t command_len = strlen (command);
	if (strncasecmp (s, command, command_len))
		return false;
	s += command_len;

	// Expect a word boundary, so that we don't respond to invalid things
	if (isalnum (*s))
		return false;

	// Ignore any initial spaces; the rest is the command's argument
	while (isblank (*s))
		s++;
	*following = s;
	return true;
}

static void
split_bot_command_argument_list (const char *arguments, struct strv *out)
{
	cstr_split (arguments, ",", true, out);
	for (size_t i = 0; i < out->len; )
	{
		if (!*cstr_strip_in_place (out->vector[i], " \t"))
			strv_remove (out, i);
		else
			i++;
	}
}

static bool
is_private_message (const struct irc_message *msg)
{
	hard_assert (msg->params.len);
	return !strchr ("#&+!", *msg->params.vector[0]);
}

static bool
is_sent_by_admin (struct bot_context *ctx, const struct irc_message *msg)
{
	// No administrator set -> everyone is an administrator
	if (!ctx->admin_re)
		return true;
	return regexec (ctx->admin_re, msg->prefix, 0, NULL, 0) != REG_NOMATCH;
}

static void respond_to_user (struct bot_context *ctx, const struct
	irc_message *msg, const char *format, ...) ATTRIBUTE_PRINTF (3, 4);

static void
respond_to_user (struct bot_context *ctx, const struct irc_message *msg,
	const char *format, ...)
{
	if (!soft_assert (msg->prefix && msg->params.len))
		return;

	char nick[strcspn (msg->prefix, "!") + 1];
	strncpy (nick, msg->prefix, sizeof nick - 1);
	nick[sizeof nick - 1] = '\0';

	va_list ap;
	struct str text = str_make ();
	va_start (ap, format);
	str_append_vprintf (&text, format, ap);
	va_end (ap);

	if (is_private_message (msg))
		irc_send (ctx, "PRIVMSG %s :%s", nick, text.str);
	else
		irc_send (ctx, "PRIVMSG %s :%s: %s",
			msg->params.vector[0], nick, text.str);

	str_free (&text);
}

static void
process_plugin_load (struct bot_context *ctx,
	const struct irc_message *msg, const char *name)
{
	struct error *e = NULL;
	if (plugin_load (ctx, name, &e))
		respond_to_user (ctx, msg, "plugin `%s' queued for loading", name);
	else
	{
		respond_to_user (ctx, msg, "plugin `%s' could not be loaded: %s",
			name, e->message);
		error_free (e);
	}
}

static void
process_plugin_unload (struct bot_context *ctx,
	const struct irc_message *msg, const char *name)
{
	struct error *e = NULL;
	if (plugin_unload (ctx, name, &e))
		respond_to_user (ctx, msg, "plugin `%s' unloaded", name);
	else
	{
		respond_to_user (ctx, msg, "plugin `%s' could not be unloaded: %s",
			name, e->message);
		error_free (e);
	}
}

static void
process_plugin_reload (struct bot_context *ctx,
	const struct irc_message *msg, const char *name)
{
	// XXX: we might want to wait until the plugin terminates before we try
	//   to reload it (so that it can save its configuration or whatever)

	// So far the only error that can occur is that the plugin hasn't been
	// loaded, which in this case doesn't really matter.
	plugin_unload (ctx, name, NULL);

	process_plugin_load (ctx, msg, name);
}

static char *
make_status_report (struct bot_context *ctx)
{
	struct str report = str_make ();
	const char *reason = getenv (g_startup_reason_str);
	if (!reason)
		reason = "launched normally";
	str_append_printf (&report, "\x02startup reason:\x0f %s", reason);

	size_t zombies = 0;
	const char *prepend = "; \x02plugins:\x0f ";
	for (struct plugin *plugin = ctx->plugins; plugin; plugin = plugin->next)
	{
		if (plugin->is_zombie)
			zombies++;
		else
		{
			str_append_printf (&report, "%s%s", prepend, plugin->name);
			prepend = ", ";
		}
	}
	if (!ctx->plugins)
		str_append_printf (&report, "%s\x02none\x0f", prepend);

	str_append_printf (&report, "; \x02zombies:\x0f %zu", zombies);
	return str_steal (&report);
}

static void
process_privmsg (struct bot_context *ctx, const struct irc_message *msg)
{
	if (!is_sent_by_admin (ctx, msg))
		return;
	if (msg->params.len < 2)
		return;

	const char *prefix = str_map_find (&ctx->config, "prefix");
	hard_assert (prefix != NULL);  // We have a default value for this

	// For us to recognize the command, it has to start with the prefix,
	// with the exception of PM's sent directly to us.
	const char *text = msg->params.vector[1];
	if (!strncmp (text, prefix, strlen (prefix)))
		text += strlen (prefix);
	else if (!is_private_message (msg))
		return;

	const char *following;
	struct strv list = strv_make ();

	if (parse_bot_command (text, "quote", &following))
		// This seems to replace tons of random stupid commands
		irc_send (ctx, "%s", following);
	else if (parse_bot_command (text, "quit", &following))
	{
		// We actually need this command (instead of just `quote') because we
		// could try to reconnect to the server automatically otherwise.
		if (*following)
			irc_send (ctx, "QUIT :%s", following);
		else
			irc_send (ctx, "QUIT");
		initiate_quit (ctx);
	}
	else if (parse_bot_command (text, "status", &following))
	{
		char *report = make_status_report (ctx);
		respond_to_user (ctx, msg, "%s", report);
		free (report);
	}
	else if (parse_bot_command (text, "load", &following))
	{
		split_bot_command_argument_list (following, &list);
		for (size_t i = 0; i < list.len; i++)
			process_plugin_load (ctx, msg, list.vector[i]);
	}
	else if (parse_bot_command (text, "reload", &following))
	{
		split_bot_command_argument_list (following, &list);
		for (size_t i = 0; i < list.len; i++)
			process_plugin_reload (ctx, msg, list.vector[i]);
	}
	else if (parse_bot_command (text, "unload", &following))
	{
		split_bot_command_argument_list (following, &list);
		for (size_t i = 0; i < list.len; i++)
			process_plugin_unload (ctx, msg, list.vector[i]);
	}

	strv_free (&list);
}

static void
irc_forward_message_to_plugins (struct bot_context *ctx, const char *raw)
{
	// For consistency with plugin_process_message()
	if (!ctx->irc_registered)
		return;

	for (struct plugin *plugin = ctx->plugins;
		 plugin; plugin = plugin->next)
	{
		if (plugin->is_zombie)
			continue;

		if (plugin->initialized)
			plugin_send (plugin, "%s", raw);
		else
			// TODO: make sure that this buffer doesn't get too large either
			str_append_printf (&plugin->queued_output, "%s\r\n", raw);
	}
}

static void
irc_process_message (const struct irc_message *msg,
	const char *raw, void *user_data)
{
	struct bot_context *ctx = user_data;
	if (g_debug_mode)
		fprintf (stderr, "[%s] ==> \"%s\"\n", "IRC", raw);

	// This should be as minimal as possible, I don't want to have the whole bot
	// written in C, especially when I have this overengineered plugin system.
	// Therefore the very basic functionality only.
	//
	// I should probably even rip out the autojoin...

	irc_forward_message_to_plugins (ctx, raw);

	if (!strcasecmp (msg->command, "PING"))
	{
		if (msg->params.len)
			irc_send (ctx, "PONG :%s", msg->params.vector[0]);
		else
			irc_send (ctx, "PONG");
	}
	else if (!ctx->irc_registered && !strcasecmp (msg->command, "001"))
	{
		print_status ("successfully connected");
		ctx->irc_registered = true;

		const char *autojoin = str_map_find (&ctx->config, "autojoin");
		if (autojoin)
			irc_send (ctx, "JOIN :%s", autojoin);
	}
	else if (!strcasecmp (msg->command, "PRIVMSG"))
		process_privmsg (ctx, msg);
}

enum irc_read_result
{
	IRC_READ_OK,                        ///< Some data were read successfully
	IRC_READ_EOF,                       ///< The server has closed connection
	IRC_READ_AGAIN,                     ///< No more data at the moment
	IRC_READ_ERROR                      ///< General connection failure
};

static enum irc_read_result
irc_fill_read_buffer_tls (struct bot_context *ctx, struct str *buf)
{
	int n_read;
start:
	ERR_clear_error ();
	n_read = SSL_read (ctx->ssl, buf->str + buf->len,
		buf->alloc - buf->len - 1 /* null byte */);

	const char *error_info = NULL;
	switch (xssl_get_error (ctx->ssl, n_read, &error_info))
	{
	case SSL_ERROR_NONE:
		buf->str[buf->len += n_read] = '\0';
		return IRC_READ_OK;
	case SSL_ERROR_ZERO_RETURN:
		return IRC_READ_EOF;
	case SSL_ERROR_WANT_READ:
		return IRC_READ_AGAIN;
	case SSL_ERROR_WANT_WRITE:
	{
		// Let it finish the handshake as we don't poll for writability;
		// any errors are to be collected by SSL_read() in the next iteration
		struct pollfd pfd = { .fd = ctx->irc_fd, .events = POLLOUT };
		soft_assert (poll (&pfd, 1, 0) > 0);
		goto start;
	}
	case XSSL_ERROR_TRY_AGAIN:
		goto start;
	default:
		print_debug ("%s: %s: %s", __func__, "SSL_read", error_info);
		return IRC_READ_ERROR;
	}
}

static enum irc_read_result
irc_fill_read_buffer (struct bot_context *ctx, struct str *buf)
{
	ssize_t n_read;
start:
	n_read = recv (ctx->irc_fd, buf->str + buf->len,
		buf->alloc - buf->len - 1 /* null byte */, 0);

	if (n_read > 0)
	{
		buf->str[buf->len += n_read] = '\0';
		return IRC_READ_OK;
	}
	if (n_read == 0)
		return IRC_READ_EOF;

	if (errno == EAGAIN)
		return IRC_READ_AGAIN;
	if (errno == EINTR)
		goto start;

	print_debug ("%s: %s: %s", __func__, "recv", strerror (errno));
	return IRC_READ_ERROR;
}

static bool irc_connect (struct bot_context *, struct error **);
static void irc_queue_reconnect (struct bot_context *);

static void
irc_cancel_timers (struct bot_context *ctx)
{
	poller_timer_reset (&ctx->timeout_tmr);
	poller_timer_reset (&ctx->ping_tmr);
	poller_timer_reset (&ctx->reconnect_tmr);
}

static void
on_irc_reconnect_timeout (void *user_data)
{
	struct bot_context *ctx = user_data;

	struct error *e = NULL;
	if (irc_connect (ctx, &e))
	{
		// TODO: inform plugins about the new connection
		return;
	}

	print_error ("%s", e->message);
	error_free (e);
	irc_queue_reconnect (ctx);
}

static void
irc_queue_reconnect (struct bot_context *ctx)
{
	hard_assert (ctx->irc_fd == -1);
	print_status ("trying to reconnect in %ld seconds...",
		ctx->reconnect_delay);
	poller_timer_set (&ctx->reconnect_tmr, ctx->reconnect_delay * 1000);
}

static void
on_irc_disconnected (struct bot_context *ctx)
{
	// Get rid of the dead socket and related things
	if (ctx->ssl)
	{
		SSL_free (ctx->ssl);
		ctx->ssl = NULL;
		SSL_CTX_free (ctx->ssl_ctx);
		ctx->ssl_ctx = NULL;
	}

	poller_fd_reset (&ctx->irc_event);
	xclose (ctx->irc_fd);
	ctx->irc_fd = -1;
	ctx->irc_registered = false;

	// TODO: inform plugins about the disconnect event

	// All of our timers have lost their meaning now
	irc_cancel_timers (ctx);

	if (ctx->quitting)
		try_finish_quit (ctx);
	else if (!ctx->reconnect)
		initiate_quit (ctx);
	else
		irc_queue_reconnect (ctx);
}

static void
on_irc_ping_timeout (void *user_data)
{
	struct bot_context *ctx = user_data;
	print_error ("connection timeout");
	on_irc_disconnected (ctx);
}

static void
on_irc_timeout (void *user_data)
{
	// Provoke a response from the server
	struct bot_context *ctx = user_data;
	irc_send (ctx, "PING :%s",
		(char *) str_map_find (&ctx->config, "nickname"));
}

static void
irc_reset_connection_timeouts (struct bot_context *ctx)
{
	irc_cancel_timers (ctx);
	poller_timer_set (&ctx->timeout_tmr, 3 * 60 * 1000);
	poller_timer_set (&ctx->ping_tmr, (3 * 60 + 30) * 1000);
}

static void
on_irc_readable (const struct pollfd *fd, struct bot_context *ctx)
{
	if (fd->revents & ~(POLLIN | POLLHUP | POLLERR))
		print_debug ("fd %d: unexpected revents: %d", fd->fd, fd->revents);

	(void) set_blocking (ctx->irc_fd, false);

	struct str *buf = &ctx->read_buffer;
	enum irc_read_result (*fill_buffer)(struct bot_context *, struct str *)
		= ctx->ssl
		? irc_fill_read_buffer_tls
		: irc_fill_read_buffer;
	bool disconnected = false;
	while (true)
	{
		str_reserve (buf, 512);
		switch (fill_buffer (ctx, buf))
		{
		case IRC_READ_AGAIN:
			goto end;
		case IRC_READ_ERROR:
			print_error ("reading from the IRC server failed");
			disconnected = true;
			goto end;
		case IRC_READ_EOF:
			print_status ("the IRC server closed the connection");
			disconnected = true;
			goto end;
		case IRC_READ_OK:
			break;
		}

		if (buf->len >= (1 << 20))
		{
			print_error ("the IRC server seems to spew out data frantically");
			irc_shutdown (ctx);
			goto end;
		}
	}
end:
	(void) set_blocking (ctx->irc_fd, true);
	irc_process_buffer (buf, irc_process_message, ctx);

	if (disconnected)
		on_irc_disconnected (ctx);
	else
		irc_reset_connection_timeouts (ctx);
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

// The bot is currently mostly synchronous (which also makes it shorter),
// however our current SOCKS code is not, hence we must wrap it.

struct irc_socks_data
{
	struct bot_context *ctx;            ///< Bot context
	struct poller inner_poller;         ///< Special inner poller
	bool polling;                       ///< Inner poller is no longer needed
	struct socks_connector connector;   ///< SOCKS connector
	bool succeeded;                     ///< Were we successful in connecting?
};

static void
irc_on_socks_connected (void *user_data, int socket, const char *hostname)
{
	(void) hostname;

	struct irc_socks_data *data = user_data;
	data->ctx->irc_fd = socket;
	data->succeeded = true;
	data->polling = false;
}

static void
irc_on_socks_failure (void *user_data)
{
	struct irc_socks_data *data = user_data;
	data->succeeded = false;
	data->polling = false;
}

static void
irc_on_socks_connecting (void *user_data,
	const char *address, const char *via, const char *version)
{
	(void) user_data;
	print_status ("connecting to %s via %s (%s)...", address, via, version);
}

static void
irc_on_socks_error (void *user_data, const char *error)
{
	(void) user_data;
	print_error ("%s: %s", "SOCKS connection failed", error);
}

static bool
irc_establish_connection_socks (struct bot_context *ctx,
	const char *socks_host, const char *socks_port,
	const char *host, const char *service, struct error **e)
{
	struct irc_socks_data data;
	struct poller *poller = &data.inner_poller;
	struct socks_connector *connector = &data.connector;

	data.ctx = ctx;
	poller_init (poller);
	data.polling = true;
	socks_connector_init (connector, poller);
	data.succeeded = false;

	connector->on_connected  = irc_on_socks_connected;
	connector->on_connecting = irc_on_socks_connecting;
	connector->on_error      = irc_on_socks_error;
	connector->on_failure    = irc_on_socks_failure;
	connector->user_data     = &data;

	if (socks_connector_add_target (connector, host, service, e))
	{
		socks_connector_run (connector, socks_host, socks_port,
			str_map_find (&ctx->config, "socks_username"),
			str_map_find (&ctx->config, "socks_password"));
		while (data.polling)
			poller_run (poller);
		if (!data.succeeded)
			error_set (e, "connection failed");
	}

	socks_connector_free (connector);
	poller_free (poller);
	return data.succeeded;
}

// - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

static bool
irc_connect (struct bot_context *ctx, struct error **e)
{
	const char *irc_host = str_map_find (&ctx->config, "irc_host");
	const char *irc_port = str_map_find (&ctx->config, "irc_port");
	const char *socks_host = str_map_find (&ctx->config, "socks_host");
	const char *socks_port = str_map_find (&ctx->config, "socks_port");

	const char *nickname = str_map_find (&ctx->config, "nickname");
	const char *username = str_map_find (&ctx->config, "username");
	const char *realname = str_map_find (&ctx->config, "realname");

	// We have a default value for these
	hard_assert (irc_port && socks_port);
	hard_assert (nickname && username && realname);

	// TODO: again, get rid of `struct error' in here.  The question is: how
	//   do we tell our caller that he should not try to reconnect?
	if (!irc_host)
		return error_set (e, "no hostname specified in configuration");

	bool use_tls;
	if (!irc_get_boolean_from_config (ctx, "tls", &use_tls, e))
		return false;

	bool connected = socks_host
		? irc_establish_connection_socks (ctx,
			socks_host, socks_port, irc_host, irc_port, e)
		: irc_establish_connection (ctx, irc_host, irc_port, e);
	if (!connected)
		return false;

	if (use_tls && !irc_initialize_tls (ctx, e))
	{
		xclose (ctx->irc_fd);
		ctx->irc_fd = -1;
		return false;
	}
	print_status ("connection established");

	ctx->irc_event = poller_fd_make (&ctx->poller, ctx->irc_fd);
	ctx->irc_event.dispatcher = (poller_fd_fn) on_irc_readable;
	ctx->irc_event.user_data = ctx;

	// TODO: in exec try: 1/ set blocking, 2/ setsockopt() SO_LINGER,
	//   (struct linger) { .l_onoff = true; .l_linger = 1 /* 1s should do */; }
	//   3/ /* O_CLOEXEC */  But only if the QUIT message proves unreliable.
	poller_fd_set (&ctx->irc_event, POLLIN);
	irc_reset_connection_timeouts (ctx);

	irc_send (ctx, "NICK %s", nickname);
	irc_send (ctx, "USER %s 8 * :%s", username, realname);
	return true;
}

static bool
parse_config (struct bot_context *ctx, struct error **e)
{
	if (!irc_get_boolean_from_config (ctx, "reconnect", &ctx->reconnect, e))
		return false;

	const char *delay_str = str_map_find (&ctx->config, "reconnect_delay");
	hard_assert (delay_str != NULL);  // We have a default value for this
	if (!xstrtoul (&ctx->reconnect_delay, delay_str, 10))
	{
		return error_set (e,
			"invalid configuration value for `%s'", "reconnect_delay");
	}

	hard_assert (!ctx->admin_re);
	const char *admin = str_map_find (&ctx->config, "admin");
	if (!admin)
		return true;

	struct error *error = NULL;
	ctx->admin_re = regex_compile (admin, REG_EXTENDED | REG_NOSUB, &error);
	if (!error)
		return true;

	error_set (e, "invalid configuration value for `%s': %s",
		"admin", error->message);
	error_free (error);
	return false;
}

static void
on_plugin_death (struct plugin *plugin, int status)
{
	struct bot_context *ctx = plugin->ctx;

	// TODO: callbacks on children death, so that we may tell the user
	//       "plugin `name' died like a dirty jewish pig"; use `status'
	if (!plugin->is_zombie && WIFSIGNALED (status))
	{
		const char *notes = "";
#ifdef WCOREDUMP
		if (WCOREDUMP (status))
			notes = " (core dumped)";
#endif
		print_warning ("Plugin `%s' died from signal %d%s",
			plugin->name, WTERMSIG (status), notes);
	}

	// Let's go through the zombie state to simplify things a bit
	// TODO: might not be a completely bad idea to restart the plugin
	plugin_zombify (plugin);

	plugin->pid = -1;

	// In theory we could close `read_fd', set `read_event->closed' to true
	// and expect epoll to no longer return events for the descriptor, as
	// all the pipe ends should be closed by then (the child is dead, so its
	// pipe FDs have been closed [assuming it hasn't forked without closing
	// the descriptors, which would be evil], and we would have closed all
	// of our FDs for this pipe as well).  In practice that doesn't work.
	poller_fd_reset (&plugin->read_event);

	xclose (plugin->read_fd);
	plugin->read_fd = -1;

	LIST_UNLINK (ctx->plugins, plugin);
	plugin_destroy (plugin);

	// Living child processes block us from quitting
	try_finish_quit (ctx);
}

static bool
try_reap_plugin (struct bot_context *ctx)
{
	int status;
	pid_t zombie = waitpid (-1, &status, WNOHANG);

	if (zombie == -1)
	{
		// No children to wait on
		if (errno == ECHILD)
			return false;

		hard_assert (errno == EINTR);
		return true;
	}

	if (zombie == 0)
		return false;

	struct plugin *plugin = plugin_find_by_pid (ctx, zombie);
	// XXX: re-exec if something has died that we don't recognize?
	if (soft_assert (plugin != NULL))
		on_plugin_death (plugin, status);
	return true;
}

static void
kill_all_zombies (struct bot_context *ctx)
{
	for (struct plugin *plugin = ctx->plugins; plugin; plugin = plugin->next)
	{
		if (!plugin->is_zombie)
			continue;

		print_status ("forcefully killing a zombie of `%s' (PID %d)",
			plugin->name, (int) plugin->pid);
		kill (plugin->pid, SIGKILL);
	}
}

static void
on_signal_pipe_readable (const struct pollfd *fd, struct bot_context *ctx)
{
	char dummy;
	(void) read (fd->fd, &dummy, 1);

	if (g_termination_requested)
	{
		g_termination_requested = false;
		if (!ctx->quitting)
		{
			// There may be a timer set to reconnect to the server
			irc_cancel_timers (ctx);

			if (ctx->irc_fd != -1)
				irc_send (ctx, "QUIT :Terminated by signal");
			initiate_quit (ctx);
		}
		else
			// Disregard proper termination, just kill all the children
			kill_all_zombies (ctx);
	}

	// Reap all dead children (since the signal pipe may overflow etc. we run
	// waitpid() in a loop to return all the zombies it knows about).
	while (try_reap_plugin (ctx))
		;
}

int
main (int argc, char *argv[])
{
	g_original_argv = strv_make ();
	strv_append_vector (&g_original_argv, argv);

	static const struct opt opts[] =
	{
		{ 'd', "debug", NULL, 0, "run in debug mode" },
		{ 'h', "help", NULL, 0, "display this help and exit" },
		{ 'V', "version", NULL, 0, "output version information and exit" },
		{ 'w', "write-default-cfg", "FILENAME",
		  OPT_OPTIONAL_ARG | OPT_LONG_ONLY,
		  "write a default configuration file and exit" },
		{ 0, NULL, NULL, 0, NULL }
	};

	struct opt_handler oh =
		opt_handler_make (argc, argv, opts, NULL, "Experimental IRC bot.");

	int c;
	while ((c = opt_handler_get (&oh)) != -1)
	switch (c)
	{
	case 'd':
		g_debug_mode = true;
		break;
	case 'h':
		opt_handler_usage (&oh, stdout);
		exit (EXIT_SUCCESS);
	case 'V':
		printf (PROGRAM_NAME " " PROGRAM_VERSION "\n");
		exit (EXIT_SUCCESS);
	case 'w':
		call_simple_config_write_default (optarg, g_config_table);
		exit (EXIT_SUCCESS);
	default:
		print_error ("wrong options");
		opt_handler_usage (&oh, stderr);
		exit (EXIT_FAILURE);
	}

	opt_handler_free (&oh);

	print_status (PROGRAM_NAME " " PROGRAM_VERSION " starting");
	setup_signal_handlers ();
	init_openssl ();

	struct bot_context ctx;
	bot_context_init (&ctx);

	struct error *e = NULL;
	if (!simple_config_update_from_file (&ctx.config, &e)
	 || !setup_recovery_handler (&ctx, &e))
	{
		print_error ("%s", e->message);
		error_free (e);
		exit (EXIT_FAILURE);
	}

	ctx.signal_event = poller_fd_make (&ctx.poller, g_signal_pipe[0]);
	ctx.signal_event.dispatcher = (poller_fd_fn) on_signal_pipe_readable;
	ctx.signal_event.user_data = &ctx;
	poller_fd_set (&ctx.signal_event, POLLIN);

#if OpenBSD >= 201605
	// cpath is for creating the plugin home directory
	if (pledge ("stdio rpath cpath inet proc exec", NULL))
		exit_fatal ("%s: %s", "pledge", strerror (errno));
#endif

	plugin_load_all_from_config (&ctx);
	if (!parse_config (&ctx, &e)
	 || !irc_connect (&ctx, &e))
	{
		print_error ("%s", e->message);
		error_free (e);
		exit (EXIT_FAILURE);
	}

	// TODO: clean re-exec support; to save the state I can either use argv,
	//   argp, or I can create a temporary file, unlink it and use the FD
	//   (mkstemp() on a `struct str' constructed from XDG_RUNTIME_DIR, TMPDIR
	//   or /tmp as a last resort + PROGRAM_NAME + ".XXXXXX" -> unlink();
	//   remember to use O_CREAT | O_EXCL).  The state needs to be versioned.
	//   Unfortunately I cannot de/serialize SSL state.

	ctx.polling = true;
	while (ctx.polling)
		poller_run (&ctx.poller);

	bot_context_free (&ctx);
	strv_free (&g_original_argv);
	return EXIT_SUCCESS;
}