/*
 * zyklonb.c: the experimental IRC bot
 *
 * Copyright (c) 2014 - 2015, Přemysl Janouch <p.janouch@gmail.com>
 * All rights reserved.
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * 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"

#include "common.c"
#include <arpa/inet.h>

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

static struct 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"         },
	{ "ssl",             "off",             "Whether to use SSL"             },
	{ "ssl_cert",        NULL,              "Client SSL certificate (PEM)"   },
	{ "ssl_verify",      "on",              "Whether to verify certificates" },
	{ "ssl_ca_file",     NULL,              "OpenSSL CA bundle file"         },
	{ "ssl_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",      PLUGIN_DIR,        "Where to search for plugins"    },
	{ "recover",         "on",              "Whether to re-launch on crash"  },

	{ NULL,              NULL,              NULL                             }
};

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

struct plugin_data
{
	LIST_HEADER (struct plugin_data)
	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 void
plugin_data_init (struct plugin_data *self)
{
	memset (self, 0, sizeof *self);

	self->pid = -1;
	str_init (&self->queued_output);

	self->read_fd = -1;
	str_init (&self->read_buffer);
	self->write_fd = -1;
	str_init (&self->write_buffer);
}

static void
plugin_data_free (struct plugin_data *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);
}

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_ready;                     ///< 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_data *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)
{
	str_map_init (&self->config);
	self->config.free = free;
	load_config_defaults (&self->config, g_config_table);
	self->admin_re = NULL;

	self->irc_fd = -1;
	str_init (&self->read_buffer);
	self->irc_ready = false;

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

	self->plugins = NULL;
	str_map_init (&self->plugins_by_name);

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

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

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

	poller_timer_init (&self->reconnect_tmr, &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
	struct plugin_data *link, *tmp;
	for (link = self->plugins; link; link = tmp)
	{
		tmp = link->next;
		plugin_data_free (link);
		free (link);
	}

	if (self->irc_fd != -1)
	{
		xclose (self->irc_fd);
		poller_fd_reset (&self->irc_event);
	}
	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_data *);

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_data *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_init (&str);
	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
		if (SSL_write (ctx->ssl, str.str, str.len) != (int) str.len)
		{
			print_debug ("%s: %s: %s", __func__, "SSL_write",
				ERR_error_string (ERR_get_error (), NULL));
			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;

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

static bool
irc_initialize_ssl_ctx (struct bot_context *ctx, struct error **e)
{
	// XXX: maybe we should call SSL_CTX_set_options() for some workarounds

	bool verify;
	if (!irc_get_boolean_from_config (ctx, "ssl_verify", &verify, e))
		return false;

	if (!verify)
		SSL_CTX_set_verify (ctx->ssl_ctx, SSL_VERIFY_NONE, NULL);

	const char *ca_file = str_map_find (&ctx->config, "ca_file");
	const char *ca_path = str_map_find (&ctx->config, "ca_path");

	struct error *error = NULL;
	if (ca_file || ca_path)
	{
		if (SSL_CTX_load_verify_locations (ctx->ssl_ctx, ca_file, ca_path))
			return true;

		error_set (&error, "%s: %s",
			"failed to set locations for the CA certificate bundle",
			ERR_reason_error_string (ERR_get_error ()));
		goto ca_error;
	}

	if (!SSL_CTX_set_default_verify_paths (ctx->ssl_ctx))
	{
		error_set (&error, "%s: %s",
			"couldn't load the default CA certificate bundle",
			ERR_reason_error_string (ERR_get_error ()));
		goto ca_error;
	}
	return true;

ca_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_ssl (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 *ssl_cert = str_map_find (&ctx->config, "ssl_cert");
	if (ssl_cert)
	{
		char *path = resolve_config_filename (ssl_cert);
		if (!path)
			print_error ("%s: %s", "cannot open file", ssl_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 SSL client certificate failed",
				ERR_error_string (ERR_get_error (), NULL));
		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:
	// XXX: these error strings are really nasty; also there could be
	//   multiple errors on the OpenSSL stack.
	if (!error_info)
		error_info = ERR_error_string (ERR_get_error (), NULL);
	error_set (e, "%s: %s", "could not initialize SSL", error_info);
	return false;
}

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)
	{
		error_set (e, "%s: %s: %s",
			"connection failed", "getaddrinfo", gai_strerror (err));
		return false;
	}

	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)
	{
		error_set (e, "connection failed");
		return false;
	}

	ctx->irc_fd = sockfd;
	return true;
}

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

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

static struct str_vector
	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;

	// 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)
{
	str_vector_init (&g_recovery_env);
	str_vector_add_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
	{
		str_vector_add (&g_recovery_env, "");
		g_startup_reason_location =
			g_recovery_env.vector + g_recovery_env.len - 1;
	}
}

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;
}

// --- SOCKS 5/4a (blocking implementation) ------------------------------------

// These are awkward protocols.  Note that the `username' is used differently
// in SOCKS 4a and 5.  In the former version, it is the username that you can
// get ident'ed against.  In the latter version, it forms a pair with the
// password field and doesn't need to be an actual user on your machine.

// TODO: make a non-blocking poller-based version of this;
//   either use c-ares or (even better) start another thread to do resolution

struct socks_addr
{
	enum socks_addr_type
	{
		SOCKS_IPV4 = 1,                 ///< IPv4 address
		SOCKS_DOMAIN = 3,               ///< Domain name to be resolved
		SOCKS_IPV6 = 4                  ///< IPv6 address
	}
	type;                               ///< The type of this address
	union
	{
		uint8_t ipv4[4];                ///< IPv4 address, network octet order
		const char *domain;             ///< Domain name
		uint8_t ipv6[16];               ///< IPv6 address, network octet order
	}
	data;                               ///< The address itself
};

struct socks_data
{
	struct socks_addr address;          ///< Target address
	uint16_t port;                      ///< Target port
	const char *username;               ///< Authentication username
	const char *password;               ///< Authentication password

	struct socks_addr bound_address;    ///< Bound address at the server
	uint16_t bound_port;                ///< Bound port at the server
};

static bool
socks_get_socket (struct addrinfo *addresses, int *fd, struct error **e)
{
	int sockfd;
	for (; addresses; addresses = addresses->ai_next)
	{
		sockfd = socket (addresses->ai_family,
			addresses->ai_socktype, addresses->ai_protocol);
		if (sockfd == -1)
			continue;
		set_cloexec (sockfd);

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

		if (!connect (sockfd, addresses->ai_addr, addresses->ai_addrlen))
			break;
		xclose (sockfd);
	}
	if (!addresses)
	{
		error_set (e, "couldn't connect to the SOCKS server");
		return false;
	}
	*fd = sockfd;
	return true;
}

#define SOCKS_FAIL(...)                                                        \
	BLOCK_START                                                                \
		error_set (e, __VA_ARGS__);                                            \
		goto fail;                                                             \
	BLOCK_END
#define SOCKS_RECV(buf, len)                                                   \
	BLOCK_START                                                                \
		if ((n = recv (sockfd, (buf), (len), 0)) == -1)                        \
			SOCKS_FAIL ("%s: %s", "recv", strerror (errno));                   \
		if (n != (len))                                                        \
			SOCKS_FAIL ("%s: %s", "protocol error", "unexpected EOF");         \
	BLOCK_END

static bool
socks_4a_connect (struct addrinfo *addresses, struct socks_data *data,
	int *fd, struct error **e)
{
	int sockfd;
	if (!socks_get_socket (addresses, &sockfd, e))
		return false;

	const void *dest_ipv4 = "\x00\x00\x00\x01";
	const char *dest_domain = NULL;

	char buf[INET6_ADDRSTRLEN];
	switch (data->address.type)
	{
	case SOCKS_IPV4:
		dest_ipv4 = data->address.data.ipv4;
		break;
	case SOCKS_IPV6:
		// About the best thing we can do, not sure if it works anywhere at all
		if (!inet_ntop (AF_INET6, &data->address.data.ipv6, buf, sizeof buf))
			SOCKS_FAIL ("%s: %s", "inet_ntop", strerror (errno));
		dest_domain = buf;
		break;
	case SOCKS_DOMAIN:
		dest_domain = data->address.data.domain;
	}

	struct str req;
	str_init (&req);
	str_append_c (&req, 4);                // version
	str_append_c (&req, 1);                // connect

	str_append_c (&req, data->port >> 8);  // higher bits of port
	str_append_c (&req, data->port);       // lower bits of port
	str_append_data (&req, dest_ipv4, 4);  // destination address

	if (data->username)
		str_append (&req, data->username);
	str_append_c (&req, '\0');

	if (dest_domain)
	{
		str_append (&req, dest_domain);
		str_append_c (&req, '\0');
	}

	ssize_t n = send (sockfd, req.str, req.len, 0);
	str_free (&req);
	if (n == -1)
		SOCKS_FAIL ("%s: %s", "send", strerror (errno));

	uint8_t resp[8];
	SOCKS_RECV (resp, sizeof resp);
	if (resp[0] != 0)
		SOCKS_FAIL ("protocol error");

	switch (resp[1])
	{
	case 90:
		break;
	case 91:
		SOCKS_FAIL ("request rejected or failed");
	case 92:
		SOCKS_FAIL ("%s: %s", "request rejected",
			"SOCKS server cannot connect to identd on the client");
	case 93:
		SOCKS_FAIL ("%s: %s", "request rejected",
			"identd reports different user-id");
	default:
		SOCKS_FAIL ("protocol error");
	}

	*fd = sockfd;
	return true;

fail:
	xclose (sockfd);
	return false;
}

#undef SOCKS_FAIL
#define SOCKS_FAIL(...)                                                        \
	BLOCK_START                                                                \
		error_set (e, __VA_ARGS__);                                            \
		return false;                                                          \
	BLOCK_END

static bool
socks_5_userpass_auth (int sockfd, struct socks_data *data, struct error **e)
{
	size_t ulen = strlen (data->username);
	if (ulen > 255)
		ulen = 255;

	size_t plen = strlen (data->password);
	if (plen > 255)
		plen = 255;

	uint8_t req[3 + ulen + plen], *p = req;
	*p++ = 0x01;  // version
	*p++ = ulen;  // username length
	memcpy (p, data->username, ulen);
	p += ulen;
	*p++ = plen;  // password length
	memcpy (p, data->password, plen);
	p += plen;

	ssize_t n = send (sockfd, req, p - req, 0);
	if (n == -1)
		SOCKS_FAIL ("%s: %s", "send", strerror (errno));

	uint8_t resp[2];
	SOCKS_RECV (resp, sizeof resp);
	if (resp[0] != 0x01)
		SOCKS_FAIL ("protocol error");
	if (resp[1] != 0x00)
		SOCKS_FAIL ("authentication failure");
	return true;
}

static bool
socks_5_auth (int sockfd, struct socks_data *data, struct error **e)
{
	bool can_auth = data->username && data->password;

	uint8_t hello[4];
	hello[0] = 0x05;          // version
	hello[1] = 1 + can_auth;  // number of authentication methods
	hello[2] = 0x00;          // no authentication required
	hello[3] = 0x02;          // username/password

	ssize_t n = send (sockfd, hello, 3 + can_auth, 0);
	if (n == -1)
		SOCKS_FAIL ("%s: %s", "send", strerror (errno));

	uint8_t resp[2];
	SOCKS_RECV (resp, sizeof resp);
	if (resp[0] != 0x05)
		SOCKS_FAIL ("protocol error");

	switch (resp[1])
	{
	case 0x02:
		if (!can_auth)
			SOCKS_FAIL ("protocol error");
		if (!socks_5_userpass_auth (sockfd, data, e))
			return false;
	case 0x00:
		break;
	case 0xFF:
		SOCKS_FAIL ("no acceptable authentication methods");
	default:
		SOCKS_FAIL ("protocol error");
	}
	return true;
}

static bool
socks_5_send_req (int sockfd, struct socks_data *data, struct error **e)
{
	uint8_t req[4 + 256 + 2], *p = req;
	*p++ = 0x05;  // version
	*p++ = 0x01;  // connect
	*p++ = 0x00;  // reserved
	*p++ = data->address.type;

	switch (data->address.type)
	{
	case SOCKS_IPV4:
		memcpy (p, data->address.data.ipv4, sizeof data->address.data.ipv4);
		p += sizeof data->address.data.ipv4;
		break;
	case SOCKS_DOMAIN:
	{
		size_t dlen = strlen (data->address.data.domain);
		if (dlen > 255)
			dlen = 255;

		*p++ = dlen;
		memcpy (p, data->address.data.domain, dlen);
		p += dlen;
		break;
	}
	case SOCKS_IPV6:
		memcpy (p, data->address.data.ipv6, sizeof data->address.data.ipv6);
		p += sizeof data->address.data.ipv6;
		break;
	}
	*p++ = data->port >> 8;
	*p++ = data->port;

	if (send (sockfd, req, p - req, 0) == -1)
		SOCKS_FAIL ("%s: %s", "send", strerror (errno));
	return true;
}

static bool
socks_5_process_resp (int sockfd, struct socks_data *data, struct error **e)
{
	uint8_t resp_header[4];
	ssize_t n;
	SOCKS_RECV (resp_header, sizeof resp_header);
	if (resp_header[0] != 0x05)
		SOCKS_FAIL ("protocol error");

	switch (resp_header[1])
	{
	case 0x00:
		break;
	case 0x01:  SOCKS_FAIL ("general SOCKS server failure");
	case 0x02:  SOCKS_FAIL ("connection not allowed by ruleset");
	case 0x03:  SOCKS_FAIL ("network unreachable");
	case 0x04:  SOCKS_FAIL ("host unreachable");
	case 0x05:  SOCKS_FAIL ("connection refused");
	case 0x06:  SOCKS_FAIL ("TTL expired");
	case 0x07:  SOCKS_FAIL ("command not supported");
	case 0x08:  SOCKS_FAIL ("address type not supported");
	default:    SOCKS_FAIL ("protocol error");
	}

	switch ((data->bound_address.type = resp_header[3]))
	{
	case SOCKS_IPV4:
		SOCKS_RECV (data->bound_address.data.ipv4,
			sizeof data->bound_address.data.ipv4);
		break;
	case SOCKS_IPV6:
		SOCKS_RECV (data->bound_address.data.ipv6,
			sizeof data->bound_address.data.ipv6);
		break;
	case SOCKS_DOMAIN:
	{
		uint8_t len;
		SOCKS_RECV (&len, sizeof len);

		char domain[len + 1];
		SOCKS_RECV (domain, len);
		domain[len] = '\0';

		data->bound_address.data.domain = xstrdup (domain);
		break;
	}
	default:
		SOCKS_FAIL ("protocol error");
	}

	uint16_t port;
	SOCKS_RECV (&port, sizeof port);
	data->bound_port = ntohs (port);
	return true;
}

#undef SOCKS_FAIL
#undef SOCKS_RECV

static bool
socks_5_connect (struct addrinfo *addresses, struct socks_data *data,
	int *fd, struct error **e)
{
	int sockfd;
	if (!socks_get_socket (addresses, &sockfd, e))
		return false;

	if (!socks_5_auth (sockfd, data, e)
	 || !socks_5_send_req (sockfd, data, e)
	 || !socks_5_process_resp (sockfd, data, e))
	{
		xclose (sockfd);
		return false;
	}

	*fd = sockfd;
	return true;
}

static int
socks_connect (const char *socks_host, const char *socks_port,
	const char *host, const char *port,
	const char *username, const char *password, struct error **e)
{
	int result = -1;
	struct addrinfo gai_hints, *gai_result;
	memset (&gai_hints, 0, sizeof gai_hints);
	gai_hints.ai_socktype = SOCK_STREAM;

	unsigned long port_no;
	const struct servent *serv;
	if ((serv = getservbyname (port, "tcp")))
		port_no = (uint16_t) ntohs (serv->s_port);
	else if (!xstrtoul (&port_no, port, 10) || !port_no || port_no > UINT16_MAX)
	{
		error_set (e, "invalid port number");
		goto fail;
	}

	int err = getaddrinfo (socks_host, socks_port, &gai_hints, &gai_result);
	if (err)
	{
		error_set (e, "%s: %s", "getaddrinfo", gai_strerror (err));
		goto fail;
	}

	struct socks_data data =
		{ .username = username, .password = password, .port = port_no };

	if      (inet_pton (AF_INET,  host, &data.address.data.ipv4) == 1)
		data.address.type = SOCKS_IPV4;
	else if (inet_pton (AF_INET6, host, &data.address.data.ipv6) == 1)
		data.address.type = SOCKS_IPV6;
	else
	{
		data.address.type = SOCKS_DOMAIN;
		data.address.data.domain = host;
	}

	if (!socks_5_connect (gai_result, &data, &result, NULL))
		socks_4a_connect (gai_result, &data, &result, e);

	if (data.bound_address.type == SOCKS_DOMAIN)
		free ((char *) data.bound_address.data.domain);
	freeaddrinfo (gai_result);
fail:
	return result;
}

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

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

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

static bool
plugin_zombify (struct plugin_data *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_data *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_data *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_data *plugin, const char *format, ...)
	ATTRIBUTE_PRINTF (2, 3);

static void
plugin_send (struct plugin_data *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_message (const struct irc_message *msg,
	const char *raw, void *user_data)
{
	struct plugin_data *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))
	{
		// 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 (&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]);
		}
	}
	else if (plugin->initialized && ctx->irc_ready)
	{
		// 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_data *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_ensure_space (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 bool
plugin_load (struct bot_context *ctx, const char *name, struct error **e)
{
	const char *plugin_dir = str_map_find (&ctx->config, "plugin_dir");
	if (!plugin_dir)
	{
		error_set (e, "plugin directory not set");
		return false;
	}

	if (!is_valid_plugin_name (name))
	{
		error_set (e, "invalid plugin name");
		return false;
	}

	if (str_map_find (&ctx->plugins_by_name, name))
	{
		error_set (e, "the plugin has already been loaded");
		return false;
	}

	int stdin_pipe[2];
	if (pipe (stdin_pipe) == -1)
	{
		error_set (e, "%s: %s: %s",
			"failed to load the plugin", "pipe", strerror (errno));
		goto fail_1;
	}

	int stdout_pipe[2];
	if (pipe (stdout_pipe) == -1)
	{
		error_set (e, "%s: %s: %s",
			"failed to load the plugin", "pipe", strerror (errno));
		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: %s",
			"failed to load the plugin", "fork", strerror (errno));
		goto fail_3;
	}

	if (pid == 0)
	{
		// Redirect the child's stdin and stdout to the pipes
		hard_assert (dup2 (stdin_pipe[0],  STDIN_FILENO)  != -1);
		hard_assert (dup2 (stdout_pipe[1], STDOUT_FILENO) != -1);

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

		struct str pathname;
		str_init (&pathname);
		str_append (&pathname, plugin_dir);
		str_append_c (&pathname, '/');
		str_append (&pathname, name);

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

		char *const argv[] = { pathname.str, 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);
	}

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

	set_blocking (stdout_pipe[0], false);
	set_blocking (stdin_pipe[1], false);

	struct plugin_data *plugin = xmalloc (sizeof *plugin);
	plugin_data_init (plugin);
	plugin->ctx = ctx;
	plugin->pid = pid;
	plugin->name = xstrdup (name);
	plugin->read_fd = stdout_pipe[0];
	plugin->write_fd = stdin_pipe[1];

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

	poller_fd_init (&plugin->write_event, &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;

fail_3:
	xclose (stdout_pipe[0]);
	xclose (stdout_pipe[1]);
fail_2:
	xclose (stdin_pipe[0]);
	xclose (stdin_pipe[1]);
fail_1:
	return false;
}

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

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

	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 str_vector plugins;
	str_vector_init (&plugins);

	split_str_ignore_empty (plugin_list, ',', &plugins);
	for (size_t i = 0; i < plugins.len; i++)
	{
		char *name = strip_str_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);
		}
	}

	str_vector_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 str_vector *out)
{
	split_str_ignore_empty (arguments, ',', out);
	for (size_t i = 0; i < out->len; )
	{
		if (!*strip_str_in_place (out->vector[i], " \t"))
			str_vector_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';

	struct str text;
	va_list ap;

	str_init (&text);
	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 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 str_vector list;
	str_vector_init (&list);

	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))
	{
		struct str report;
		str_init (&report);

		const char *reason = getenv (g_startup_reason_str);
		if (!reason)
			reason = "launched normally";
		str_append_printf (&report,
			"\x02startup reason:\x0f %s; \x02plugins:\x0f ", reason);
		size_t zombies = 0;
		const char *prepend = "";
		for (struct plugin_data *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 (&report, "\x02none\x0f");
		str_append_printf (&report, "; \x02zombies:\x0f %zu", zombies);

		respond_to_user (ctx, msg, "%s", report.str);
		str_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]);
	}

	str_vector_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_ready)
		return;

	for (struct plugin_data *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_ready && (!strcasecmp (msg->command, "MODE")
		|| !strcasecmp (msg->command, "376")    // RPL_ENDOFMOTD
		|| !strcasecmp (msg->command, "422")))  // ERR_NOMOTD
	{
		print_status ("successfully connected");
		ctx->irc_ready = 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_ssl (struct bot_context *ctx, struct str *buf)
{
	int n_read;
start:
	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;
	}

	xclose (ctx->irc_fd);
	ctx->irc_fd = -1;
	ctx->irc_ready = false;

	ctx->irc_event.closed = true;
	poller_fd_reset (&ctx->irc_event);

	// 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_ssl
		: irc_fill_read_buffer;
	bool disconnected = false;
	while (true)
	{
		str_ensure_space (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);
}

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 *socks_username = str_map_find (&ctx->config, "socks_username");
	const char *socks_password = str_map_find (&ctx->config, "socks_password");

	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)
	{
		error_set (e, "no hostname specified in configuration");
		return false;
	}

	bool use_ssl;
	if (!irc_get_boolean_from_config (ctx, "ssl", &use_ssl, e))
		return false;

	if (socks_host)
	{
		char *address = format_host_port_pair (irc_host, irc_port);
		char *socks_address = format_host_port_pair (socks_host, socks_port);
		print_status ("connecting to %s via %s...", address, socks_address);
		free (socks_address);
		free (address);

		struct error *error = NULL;
		int fd = socks_connect (socks_host, socks_port, irc_host, irc_port,
			socks_username, socks_password, &error);
		if (fd == -1)
		{
			error_set (e, "%s: %s", "SOCKS connection failed", error->message);
			error_free (error);
			return false;
		}
		ctx->irc_fd = fd;
	}
	else if (!irc_establish_connection (ctx, irc_host, irc_port, e))
		return false;

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

	poller_fd_init (&ctx->irc_event, &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))
	{
		error_set (e, "invalid configuration value for `%s'",
			"reconnect_delay");
		return false;
	}

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

	if (g_termination_requested && !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);
	}

	// Reap all dead children (since the pipe may overflow, we ask waitpid()
	// to return all the zombies it knows about).
	while (true)
	{
		int status;
		pid_t zombie = waitpid (-1, &status, WNOHANG);

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

			hard_assert (errno == EINTR);
			continue;
		}

		if (zombie == 0)
			break;

		struct plugin_data *plugin = plugin_find_by_pid (ctx, zombie);
		// Something has died but we don't recognize it (re-exec?)
		if (!soft_assert (plugin != NULL))
			continue;

		// 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_data_free (plugin);
		free (plugin);

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

int
main (int argc, char *argv[])
{
	str_vector_init (&g_original_argv);
	str_vector_add_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_init (&oh, 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_write_default_config (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 ();

	SSL_library_init ();
	atexit (EVP_cleanup);
	SSL_load_error_strings ();
	// XXX: ERR_load_BIO_strings()?  Anything else?
	atexit (ERR_free_strings);

	struct bot_context ctx;
	bot_context_init (&ctx);

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

	poller_fd_init (&ctx.signal_event, &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);

	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);
	str_vector_free (&g_original_argv);
	return EXIT_SUCCESS;
}