WIP: add a stub IRC daemon named `kike'

As it is going to share a great lot of functionality with ZyklonB, I have
decided to extract the common parts into `common.c' and make the two subprojects
include this file.

The Single Compile Unit concept has proven valuable (sub-second compile times,
dead code warnings, almost no need for function declarations, whole-program
optimizations), and the sources aren't that long so far anyway.

I am probably going to add CMake support later but so far it's not a priority.
This project is meant to be portable and freely relocatable (ie. no hardcoded
paths if I can avoid it).

1 files changed, 1772 insertions, 0 deletions

diff --git a/src/common.c b/src/common.c
new file mode 100644
index 0000000..be523a9
--- /dev/null
+++ b/src/common.c
@@ -0,0 +1,1772 @@
+/*
+ * common.c: common functionality
+ *
+ * Copyright (c) 2014, 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.
+ *
+ */
+
+#define _POSIX_C_SOURCE 199309L
+#define _XOPEN_SOURCE 500
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <errno.h>
+#include <string.h>
+#include <stdarg.h>
+#include <stdint.h>
+#include <stdbool.h>
+#include <ctype.h>
+#include <time.h>
+#include <limits.h>
+
+#include <unistd.h>
+#include <sys/wait.h>
+#include <sys/stat.h>
+#include <sys/time.h>
+#include <fcntl.h>
+#include <poll.h>
+#include <signal.h>
+#include <strings.h>
+#include <regex.h>
+#include <libgen.h>
+
+#include <sys/socket.h>
+#include <sys/types.h>
+#include <netinet/in.h>
+#include <netdb.h>
+
+#ifndef NI_MAXHOST
+#define NI_MAXHOST 1025
+#endif // ! NI_MAXHOST
+
+#ifndef NI_MAXSERV
+#define NI_MAXSERV 32
+#endif // ! NI_MAXSERV
+
+#include <getopt.h>
+#include <openssl/ssl.h>
+#include <openssl/err.h>
+#include "siphash.h"
+
+extern char **environ;
+
+#ifdef _POSIX_MONOTONIC_CLOCK
+#define CLOCK_BEST CLOCK_MONOTONIC
+#else // ! _POSIX_MONOTIC_CLOCK
+#define CLOCK_BEST CLOCK_REALTIME
+#endif // ! _POSIX_MONOTONIC_CLOCK
+
+#if defined __GNUC__
+#define ATTRIBUTE_PRINTF(x, y) __attribute__ ((format (printf, x, y)))
+#else // ! __GNUC__
+#define ATTRIBUTE_PRINTF(x, y)
+#endif // ! __GNUC__
+
+#if defined __GNUC__ && __GNUC__ >= 4
+#define ATTRIBUTE_SENTINEL __attribute__ ((sentinel))
+#else // ! __GNUC__ || __GNUC__ < 4
+#define ATTRIBUTE_SENTINEL
+#endif // ! __GNUC__ || __GNUC__ < 4
+
+#define N_ELEMENTS(a) (sizeof (a) / sizeof ((a)[0]))
+
+#define BLOCK_START  do {
+#define BLOCK_END    } while (0)
+
+// --- Utilities ---------------------------------------------------------------
+
+static void
+print_message (FILE *stream, const char *type, const char *fmt, ...)
+	ATTRIBUTE_PRINTF (3, 4);
+
+static void
+print_message (FILE *stream, const char *type, const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start (ap, fmt);
+	fprintf (stream, "%s ", type);
+	vfprintf (stream, fmt, ap);
+	fputs ("\n", stream);
+	va_end (ap);
+}
+
+#define print_fatal(...)    print_message (stderr, "fatal:",   __VA_ARGS__)
+#define print_error(...)    print_message (stderr, "error:",   __VA_ARGS__)
+#define print_warning(...)  print_message (stderr, "warning:", __VA_ARGS__)
+#define print_status(...)   print_message (stdout, "--",       __VA_ARGS__)
+
+// --- Debugging and assertions ------------------------------------------------
+
+// We should check everything that may possibly fail with at least a soft
+// assertion, so that any causes for problems don't slip us by silently.
+//
+// `g_soft_asserts_are_deadly' may be useful while running inside a debugger.
+
+static bool g_debug_mode;               ///< Debug messages are printed
+static bool g_soft_asserts_are_deadly;  ///< soft_assert() aborts as well
+
+#define print_debug(...)                                                       \
+	BLOCK_START                                                                \
+		if (g_debug_mode)                                                      \
+			print_message (stderr, "debug:", __VA_ARGS__);                     \
+	BLOCK_END
+
+static void
+assertion_failure_handler (bool is_fatal, const char *file, int line,
+	const char *function, const char *condition)
+{
+	if (is_fatal)
+	{
+		print_fatal ("assertion failed [%s:%d in function %s]: %s",
+			file, line, function, condition);
+		abort ();
+	}
+	else
+		print_debug ("assertion failed [%s:%d in function %s]: %s",
+			file, line, function, condition);
+}
+
+#define soft_assert(condition)                                                 \
+	((condition) ? true :                                                      \
+		(assertion_failure_handler (g_soft_asserts_are_deadly,                 \
+		__FILE__, __LINE__, __func__, #condition), false))
+
+#define hard_assert(condition)                                                 \
+	((condition) ? (void) 0 :                                                  \
+		assertion_failure_handler (true,                                       \
+		__FILE__, __LINE__, __func__, #condition))
+
+// --- Safe memory management --------------------------------------------------
+
+// When a memory allocation fails and we need the memory, we're usually pretty
+// much fucked.  Use the non-prefixed versions when there's a legitimate
+// worry that an unrealistic amount of memory may be requested for allocation.
+
+// XXX: it's not a good idea to use print_message() as it may want to allocate
+//   further memory for printf() and the output streams.  That may fail.
+
+static void *
+xmalloc (size_t n)
+{
+	void *p = malloc (n);
+	if (!p)
+	{
+		print_fatal ("malloc: %s", strerror (errno));
+		exit (EXIT_FAILURE);
+	}
+	return p;
+}
+
+static void *
+xcalloc (size_t n, size_t m)
+{
+	void *p = calloc (n, m);
+	if (!p && n && m)
+	{
+		print_fatal ("calloc: %s", strerror (errno));
+		exit (EXIT_FAILURE);
+	}
+	return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+	void *p = realloc (o, n);
+	if (!p && n)
+	{
+		print_fatal ("realloc: %s", strerror (errno));
+		exit (EXIT_FAILURE);
+	}
+	return p;
+}
+
+static void *
+xreallocarray (void *o, size_t n, size_t m)
+{
+	if (m && n > SIZE_MAX / m)
+	{
+		errno = ENOMEM;
+		print_fatal ("reallocarray: %s", strerror (errno));
+		exit (EXIT_FAILURE);
+	}
+	return xrealloc (o, n * m);
+}
+
+static char *
+xstrdup (const char *s)
+{
+	return strcpy (xmalloc (strlen (s) + 1), s);
+}
+
+static char *
+xstrndup (const char *s, size_t n)
+{
+	size_t size = strlen (s);
+	if (n > size)
+		n = size;
+
+	char *copy = xmalloc (n + 1);
+	memcpy (copy, s, n);
+	copy[n] = '\0';
+	return copy;
+}
+
+// --- Double-linked list helpers ----------------------------------------------
+
+// The links of the list need to have the members `prev' and `next'.
+
+#define LIST_PREPEND(head, link)                                               \
+	BLOCK_START                                                                \
+		(link)->prev = NULL;                                                   \
+		(link)->next = (head);                                                 \
+		if ((link)->next)                                                      \
+			(link)->next->prev = (link);                                       \
+		(head) = (link);                                                       \
+	BLOCK_END
+
+#define LIST_UNLINK(head, link)                                                \
+	BLOCK_START                                                                \
+		if ((link)->prev)                                                      \
+			(link)->prev->next = (link)->next;                                 \
+		else                                                                   \
+			(head) = (link)->next;                                             \
+		if ((link)->next)                                                      \
+			(link)->next->prev = (link)->prev;                                 \
+	BLOCK_END
+
+// --- Dynamically allocated string array --------------------------------------
+
+struct str_vector
+{
+	char **vector;
+	size_t len;
+	size_t alloc;
+};
+
+static void
+str_vector_init (struct str_vector *self)
+{
+	self->alloc = 4;
+	self->len = 0;
+	self->vector = xcalloc (sizeof *self->vector, self->alloc);
+}
+
+static void
+str_vector_free (struct str_vector *self)
+{
+	unsigned i;
+	for (i = 0; i < self->len; i++)
+		free (self->vector[i]);
+
+	free (self->vector);
+	self->vector = NULL;
+}
+
+static void
+str_vector_add_owned (struct str_vector *self, char *s)
+{
+	self->vector[self->len] = s;
+	if (++self->len >= self->alloc)
+		self->vector = xreallocarray (self->vector,
+			sizeof *self->vector, (self->alloc <<= 1));
+	self->vector[self->len] = NULL;
+}
+
+static void
+str_vector_add (struct str_vector *self, const char *s)
+{
+	str_vector_add_owned (self, xstrdup (s));
+}
+
+static void
+str_vector_add_args (struct str_vector *self, const char *s, ...)
+	ATTRIBUTE_SENTINEL;
+
+static void
+str_vector_add_args (struct str_vector *self, const char *s, ...)
+{
+	va_list ap;
+
+	va_start (ap, s);
+	while (s)
+	{
+		str_vector_add (self, s);
+		s = va_arg (ap, const char *);
+	}
+	va_end (ap);
+}
+
+static void
+str_vector_add_vector (struct str_vector *self, char **vector)
+{
+	while (*vector)
+		str_vector_add (self, *vector++);
+}
+
+static void
+str_vector_remove (struct str_vector *self, size_t i)
+{
+	hard_assert (i < self->len);
+	free (self->vector[i]);
+	memmove (self->vector + i, self->vector + i + 1,
+		(self->len-- - i) * sizeof *self->vector);
+}
+
+// --- Dynamically allocated strings -------------------------------------------
+
+// Basically a string builder to abstract away manual memory management.
+
+struct str
+{
+	char *str;                          ///< String data, null terminated
+	size_t alloc;                       ///< How many bytes are allocated
+	size_t len;                         ///< How long the string actually is
+};
+
+/// We don't care about allocations that are way too large for the content, as
+/// long as the allocation is below the given threshold.  (Trivial heuristics.)
+#define STR_SHRINK_THRESHOLD (1 << 20)
+
+static void
+str_init (struct str *self)
+{
+	self->alloc = 16;
+	self->len = 0;
+	self->str = strcpy (xmalloc (self->alloc), "");
+}
+
+static void
+str_free (struct str *self)
+{
+	free (self->str);
+	self->str = NULL;
+	self->alloc = 0;
+	self->len = 0;
+}
+
+static void
+str_reset (struct str *self)
+{
+	str_free (self);
+	str_init (self);
+}
+
+static char *
+str_steal (struct str *self)
+{
+	char *str = self->str;
+	self->str = NULL;
+	str_free (self);
+	return str;
+}
+
+static void
+str_ensure_space (struct str *self, size_t n)
+{
+	// We allocate at least one more byte for the terminating null character
+	size_t new_alloc = self->alloc;
+	while (new_alloc <= self->len + n)
+		new_alloc <<= 1;
+	if (new_alloc != self->alloc)
+		self->str = xrealloc (self->str, (self->alloc = new_alloc));
+}
+
+static void
+str_append_data (struct str *self, const char *data, size_t n)
+{
+	str_ensure_space (self, n);
+	memcpy (self->str + self->len, data, n);
+	self->len += n;
+	self->str[self->len] = '\0';
+}
+
+static void
+str_append_c (struct str *self, char c)
+{
+	str_append_data (self, &c, 1);
+}
+
+static void
+str_append (struct str *self, const char *s)
+{
+	str_append_data (self, s, strlen (s));
+}
+
+static void
+str_append_str (struct str *self, const struct str *another)
+{
+	str_append_data (self, another->str, another->len);
+}
+
+static int
+str_append_vprintf (struct str *self, const char *fmt, va_list va)
+{
+	va_list ap;
+	int size;
+
+	va_copy (ap, va);
+	size = vsnprintf (NULL, 0, fmt, ap);
+	va_end (ap);
+
+	if (size < 0)
+		return -1;
+
+	va_copy (ap, va);
+	str_ensure_space (self, size);
+	size = vsnprintf (self->str + self->len, self->alloc - self->len, fmt, ap);
+	va_end (ap);
+
+	if (size > 0)
+		self->len += size;
+
+	return size;
+}
+
+static int
+str_append_printf (struct str *self, const char *fmt, ...)
+	ATTRIBUTE_PRINTF (2, 3);
+
+static int
+str_append_printf (struct str *self, const char *fmt, ...)
+{
+	va_list ap;
+
+	va_start (ap, fmt);
+	int size = str_append_vprintf (self, fmt, ap);
+	va_end (ap);
+	return size;
+}
+
+static void
+str_remove_slice (struct str *self, size_t start, size_t length)
+{
+	size_t end = start + length;
+	hard_assert (end <= self->len);
+	memmove (self->str + start, self->str + end, self->len - end);
+	self->str[self->len -= length] = '\0';
+
+	// Shrink the string if the allocation becomes way too large
+	if (self->alloc >= STR_SHRINK_THRESHOLD && self->len < (self->alloc >> 2))
+		self->str = xrealloc (self->str, self->alloc >>= 2);
+}
+
+// --- Errors ------------------------------------------------------------------
+
+// Error reporting utilities.  Inspired by GError, only much simpler.
+
+struct error
+{
+	size_t domain;                      ///< The domain of the error
+	int id;                             ///< The concrete error ID
+	char *message;                      ///< Textual description of the event
+};
+
+static size_t
+error_resolve_domain (size_t *tag)
+{
+	// This method is fairly sensitive to the order in which resolution
+	// requests come in, does not provide a good way of decoding the number
+	// back to a meaningful identifier, and may not play all too well with
+	// dynamic libraries when a module is e.g. statically linked into multiple
+	// libraries, but it's fast, simple, and more than enough for our purposes.
+	static size_t domain_counter;
+
+	if (!*tag)
+		*tag = ++domain_counter;
+	return *tag;
+}
+
+static void
+error_set (struct error **e, size_t domain, int id,
+	const char *message, ...) ATTRIBUTE_PRINTF (4, 5);
+
+static void
+error_set (struct error **e, size_t domain, int id,
+	const char *message, ...)
+{
+	if (!e)
+		return;
+
+	va_list ap;
+	va_start (ap, message);
+	int size = snprintf (NULL, 0, message, ap);
+	va_end (ap);
+
+	hard_assert (size >= 0);
+
+	struct error *tmp = xmalloc (sizeof *tmp);
+	tmp->domain = domain;
+	tmp->id = id;
+	tmp->message = xmalloc (size + 1);
+
+	va_start (ap, message);
+	size = snprintf (tmp->message, size + 1, message, ap);
+	va_end (ap);
+
+	hard_assert (size >= 0);
+
+	soft_assert (*e == NULL);
+	*e = tmp;
+}
+
+static void
+error_free (struct error *e)
+{
+	free (e->message);
+	free (e);
+}
+
+static void
+error_propagate (struct error **destination, struct error *source)
+{
+	if (!destination)
+	{
+		error_free (source);
+		return;
+	}
+
+	soft_assert (*destination == NULL);
+	*destination = source;
+}
+
+// --- String hash map ---------------------------------------------------------
+
+// The most basic <string, managed pointer> map (or associative array).
+
+struct str_map_link
+{
+	struct str_map_link *next;          ///< The next link in a chain
+	struct str_map_link *prev;          ///< The previous link in a chain
+
+	void *data;                         ///< Payload
+	size_t key_length;                  ///< Length of the key without '\0'
+	char key[];                         ///< The key for this link
+};
+
+struct str_map
+{
+	struct str_map_link **map;          ///< The hash table data itself
+	size_t alloc;                       ///< Number of allocated entries
+	size_t len;                         ///< Number of entries in the table
+	void (*free) (void *);              ///< Callback to destruct the payload
+};
+
+#define STR_MAP_MIN_ALLOC 16
+
+typedef void (*str_map_free_func) (void *);
+
+static void
+str_map_init (struct str_map *self)
+{
+	self->alloc = STR_MAP_MIN_ALLOC;
+	self->len = 0;
+	self->free = NULL;
+	self->map = xcalloc (self->alloc, sizeof *self->map);
+}
+
+static void
+str_map_free (struct str_map *self)
+{
+	struct str_map_link **iter, **end = self->map + self->alloc;
+	struct str_map_link *link, *tmp;
+
+	for (iter = self->map; iter < end; iter++)
+		for (link = *iter; link; link = tmp)
+		{
+			tmp = link->next;
+			if (self->free)
+				self->free (link->data);
+			free (link);
+		}
+
+	free (self->map);
+	self->map = NULL;
+}
+
+static uint64_t
+str_map_hash (const char *s, size_t len)
+{
+	static unsigned char key[16] = "SipHash 2-4 key!";
+	return siphash (key, (const void *) s, len);
+}
+
+static uint64_t
+str_map_pos (struct str_map *self, const char *s)
+{
+	size_t mask = self->alloc - 1;
+	return str_map_hash (s, strlen (s)) & mask;
+}
+
+static uint64_t
+str_map_link_hash (struct str_map_link *self)
+{
+	return str_map_hash (self->key, self->key_length);
+}
+
+static void
+str_map_resize (struct str_map *self, size_t new_size)
+{
+	struct str_map_link **old_map = self->map;
+	size_t i, old_size = self->alloc;
+
+	// Only powers of two, so that we don't need to compute the modulo
+	hard_assert ((new_size & (new_size - 1)) == 0);
+	size_t mask = new_size - 1;
+
+	self->alloc = new_size;
+	self->map = xcalloc (self->alloc, sizeof *self->map);
+	for (i = 0; i < old_size; i++)
+	{
+		struct str_map_link *iter = old_map[i], *next_iter;
+		while (iter)
+		{
+			next_iter = iter->next;
+			uint64_t pos = str_map_link_hash (iter) & mask;
+			LIST_PREPEND (self->map[pos], iter);
+			iter = next_iter;
+		}
+	}
+
+	free (old_map);
+}
+
+static void
+str_map_set (struct str_map *self, const char *key, void *value)
+{
+	uint64_t pos = str_map_pos (self, key);
+	struct str_map_link *iter = self->map[pos];
+	for (; iter; iter = iter->next)
+	{
+		if (strcmp (key, iter->key))
+			continue;
+
+		// Storing the same data doesn't destroy it
+		if (self->free && value != iter->data)
+			self->free (iter->data);
+
+		if (value)
+		{
+			iter->data = value;
+			return;
+		}
+
+		LIST_UNLINK (self->map[pos], iter);
+		free (iter);
+		self->len--;
+
+		// The array should be at least 1/4 full
+		if (self->alloc >= (STR_MAP_MIN_ALLOC << 2)
+		 && self->len < (self->alloc >> 2))
+			str_map_resize (self, self->alloc >> 2);
+		return;
+	}
+
+	if (!value)
+		return;
+
+	if (self->len >= self->alloc)
+	{
+		str_map_resize (self, self->alloc << 1);
+		pos = str_map_pos (self, key);
+	}
+
+	// Link in a new element for the given <key, value> pair
+	size_t key_length = strlen (key);
+	struct str_map_link *link = xmalloc (sizeof *link + key_length + 1);
+	link->data = value;
+	link->key_length = key_length;
+	memcpy (link->key, key, key_length + 1);
+
+	LIST_PREPEND (self->map[pos], link);
+	self->len++;
+}
+
+static void *
+str_map_find (struct str_map *self, const char *key)
+{
+	struct str_map_link *iter = self->map[str_map_pos (self, key)];
+	for (; iter; iter = iter->next)
+		if (!strcmp (key, (char *) iter + sizeof *iter))
+			return iter->data;
+	return NULL;
+}
+
+// --- File descriptor utilities -----------------------------------------------
+
+static void
+set_cloexec (int fd)
+{
+	soft_assert (fcntl (fd, F_SETFD, fcntl (fd, F_GETFD) | FD_CLOEXEC) != -1);
+}
+
+static bool
+set_blocking (int fd, bool blocking)
+{
+	int flags = fcntl (fd, F_GETFL);
+	hard_assert (flags != -1);
+
+	bool prev = !(flags & O_NONBLOCK);
+	if (blocking)
+		flags &= ~O_NONBLOCK;
+	else
+		flags |=  O_NONBLOCK;
+
+	hard_assert (fcntl (fd, F_SETFL, flags) != -1);
+	return prev;
+}
+
+static void
+xclose (int fd)
+{
+	while (close (fd) == -1)
+		if (!soft_assert (errno == EINTR))
+			break;
+}
+
+// --- Polling -----------------------------------------------------------------
+
+// Basically the poor man's GMainLoop/libev/libuv.  It might make some sense
+// to instead use those tested and proven libraries but we don't need much
+// and it's interesting to implement.
+
+// At the moment the FD's are stored in an unsorted array.  This is not ideal
+// complexity-wise but I don't think I have much of a choice with poll(),
+// and neither with epoll for that matter.
+//
+//                         unsorted array       sorted array
+//           search             O(n)       O(log n) [O(log log n)]
+//           insert by fd       O(n)                O(n)
+//           delete by fd       O(n)                O(n)
+//
+// Insertion in the unsorted array can be reduced to O(1) if I maintain a
+// bitmap of present FD's but that's still not a huge win.
+//
+// I don't expect this to be much of an issue, as there are typically not going
+// to be that many FD's to watch, and the linear approach is cache-friendly.
+
+typedef void (*poller_dispatcher_func) (const struct pollfd *, void *);
+typedef void (*poller_timer_func) (void *);
+
+#define POLLER_MIN_ALLOC 16
+
+struct poller_timer_info
+{
+	int64_t when;                       ///< When is the timer to expire
+	poller_timer_func dispatcher;       ///< Event dispatcher
+	void *user_data;                    ///< User data
+};
+
+struct poller_timers
+{
+	struct poller_timer_info *info;     ///< Min-heap of timers
+	size_t len;                         ///< Number of scheduled timers
+	size_t alloc;                       ///< Number of timers allocated
+};
+
+static void
+poller_timers_init (struct poller_timers *self)
+{
+	self->alloc = POLLER_MIN_ALLOC;
+	self->len = 0;
+	self->info = xmalloc (self->alloc * sizeof *self->info);
+}
+
+static void
+poller_timers_free (struct poller_timers *self)
+{
+	free (self->info);
+}
+
+static int64_t
+poller_timers_get_current_time (void)
+{
+#ifdef _POSIX_TIMERS
+	struct timespec tp;
+	hard_assert (clock_gettime (CLOCK_BEST, &tp) != -1);
+	return (int64_t) tp.tv_sec * 1000 + (int64_t) tp.tv_nsec / 1000000;
+#else
+	struct timeval tp;
+	gettimeofday (&tp, NULL);
+	return (int64_t) tp.tv_sec * 1000 + (int64_t) tp.tv_usec / 1000;
+#endif
+}
+
+static void
+poller_timers_heapify_down (struct poller_timers *self, size_t index)
+{
+	typedef struct poller_timer_info info_t;
+	info_t *end = self->info + self->len;
+
+	while (true)
+	{
+		info_t *parent = self->info + index;
+		info_t *left   = self->info + 2 * index + 1;
+		info_t *right  = self->info + 2 * index + 2;
+
+		info_t *largest = parent;
+		if (left  < end && left->when  > largest->when)
+			largest = left;
+		if (right < end && right->when > largest->when)
+			largest = right;
+		if (parent == largest)
+			break;
+
+		info_t tmp = *parent;
+		*parent = *largest;
+		*largest = tmp;
+
+		index = largest - self->info;
+	}
+}
+
+static void
+poller_timers_remove_at_index (struct poller_timers *self, size_t index)
+{
+	hard_assert (index < self->len);
+	if (index == --self->len)
+		return;
+
+	self->info[index] = self->info[self->len];
+	poller_timers_heapify_down (self, index);
+}
+
+static void
+poller_timers_dispatch (struct poller_timers *self)
+{
+	int64_t now = poller_timers_get_current_time ();
+	while (self->len && self->info->when <= now)
+	{
+		struct poller_timer_info info = *self->info;
+		poller_timers_remove_at_index (self, 0);
+		info.dispatcher (info.user_data);
+	}
+}
+
+static void
+poller_timers_heapify_up (struct poller_timers *self, size_t index)
+{
+	while (index != 0)
+	{
+		size_t parent = (index - 1) / 2;
+		if (self->info[parent].when <= self->info[index].when)
+			break;
+
+		struct poller_timer_info tmp = self->info[parent];
+		self->info[parent] = self->info[index];
+		self->info[index] = tmp;
+
+		index = parent;
+	}
+}
+
+static ssize_t
+poller_timers_find (struct poller_timers *self,
+	poller_timer_func dispatcher, void *data)
+{
+	// NOTE: there may be duplicates.
+	for (size_t i = 0; i < self->len; i++)
+		if (self->info[i].dispatcher == dispatcher
+		 && self->info[i].user_data == data)
+			return i;
+	return -1;
+}
+
+static void
+poller_timers_add (struct poller_timers *self,
+	poller_timer_func dispatcher, void *data, int timeout_ms)
+{
+	if (self->len == self->alloc)
+		self->info = xreallocarray (self->info,
+			self->alloc <<= 1, sizeof *self->info);
+
+	self->info[self->len] = (struct poller_timer_info) {
+		.when = poller_timers_get_current_time () + timeout_ms,
+		.dispatcher = dispatcher, .user_data = data };
+	poller_timers_heapify_up (self, self->len++);
+}
+
+static int
+poller_timers_get_poll_timeout (struct poller_timers *self)
+{
+	if (!self->len)
+		return -1;
+
+	int64_t timeout = self->info->when - poller_timers_get_current_time ();
+	return timeout >= 0 ? timeout : 0;
+}
+
+#ifdef __linux__
+
+// I don't really need this, I've basically implemented this just because I can.
+
+#include <sys/epoll.h>
+
+struct poller_info
+{
+	int fd;                             ///< Our file descriptor
+	uint32_t events;                    ///< The events we registered
+	poller_dispatcher_func dispatcher;  ///< Event dispatcher
+	void *user_data;                    ///< User data
+};
+
+struct poller
+{
+	int epoll_fd;                       ///< The epoll FD
+	struct poller_info **info;          ///< Information associated with each FD
+	struct epoll_event *revents;        ///< Output array for epoll_wait()
+	size_t len;                         ///< Number of polled descriptors
+	size_t alloc;                       ///< Number of entries allocated
+
+	struct poller_timers timers;        ///< Timeouts
+
+	/// Index of the element in `revents' that's about to be dispatched next.
+	int dispatch_next;
+
+	/// The total number of entries stored in `revents' by epoll_wait().
+	int dispatch_total;
+};
+
+static void
+poller_init (struct poller *self)
+{
+	self->epoll_fd = epoll_create (POLLER_MIN_ALLOC);
+	hard_assert (self->epoll_fd != -1);
+	set_cloexec (self->epoll_fd);
+
+	self->len = 0;
+	self->alloc = POLLER_MIN_ALLOC;
+	self->info = xcalloc (self->alloc, sizeof *self->info);
+	self->revents = xcalloc (self->alloc, sizeof *self->revents);
+
+	poller_timers_init (&self->timers);
+
+	self->dispatch_next = 0;
+	self->dispatch_total = 0;
+}
+
+static void
+poller_free (struct poller *self)
+{
+	for (size_t i = 0; i < self->len; i++)
+	{
+		struct poller_info *info = self->info[i];
+		hard_assert (epoll_ctl (self->epoll_fd,
+			EPOLL_CTL_DEL, info->fd, (void *) "") != -1);
+		free (info);
+	}
+
+	poller_timers_free (&self->timers);
+
+	xclose (self->epoll_fd);
+	free (self->info);
+	free (self->revents);
+}
+
+static ssize_t
+poller_find_by_fd (struct poller *self, int fd)
+{
+	for (size_t i = 0; i < self->len; i++)
+		if (self->info[i]->fd == fd)
+			return i;
+	return -1;
+}
+
+static void
+poller_ensure_space (struct poller *self)
+{
+	if (self->len < self->alloc)
+		return;
+
+	self->alloc <<= 1;
+	self->revents = xreallocarray
+		(self->revents, sizeof *self->revents, self->alloc);
+	self->info = xreallocarray
+		(self->info, sizeof *self->info, self->alloc);
+}
+
+static int
+poller_epoll_to_poll_events (int events)
+{
+	int result = 0;
+	if (events & EPOLLIN)   result |= POLLIN;
+	if (events & EPOLLOUT)  result |= POLLOUT;
+	if (events & EPOLLERR)  result |= POLLERR;
+	if (events & EPOLLHUP)  result |= POLLHUP;
+	if (events & EPOLLPRI)  result |= POLLPRI;
+	return result;
+}
+
+static uint32_t
+poller_poll_to_epoll_events (uint32_t events)
+{
+	uint32_t result = 0;
+	if (events & POLLIN)   result |= EPOLLIN;
+	if (events & POLLOUT)  result |= EPOLLOUT;
+	if (events & POLLERR)  result |= EPOLLERR;
+	if (events & POLLHUP)  result |= EPOLLHUP;
+	if (events & POLLPRI)  result |= EPOLLPRI;
+	return result;
+}
+
+static void
+poller_set (struct poller *self, int fd, short int events,
+	poller_dispatcher_func dispatcher, void *data)
+{
+	ssize_t index = poller_find_by_fd (self, fd);
+	bool modifying = true;
+	if (index == -1)
+	{
+		poller_ensure_space (self);
+		self->info[index = self->len++] = xcalloc (1, sizeof **self->info);
+		modifying = false;
+	}
+
+	struct poller_info *info = self->info[index];
+	info->fd = fd;
+	info->dispatcher = dispatcher;
+	info->user_data = data;
+
+	struct epoll_event event;
+	event.events = poller_poll_to_epoll_events (events);
+	event.data.ptr = info;
+	hard_assert (epoll_ctl (self->epoll_fd,
+		modifying ? EPOLL_CTL_MOD : EPOLL_CTL_ADD, fd, &event) != -1);
+}
+
+static void
+poller_remove_from_dispatch (struct poller *self,
+	const struct poller_info *info)
+{
+	if (!self->dispatch_total)
+		return;
+
+	int i;
+	for (i = self->dispatch_next; i < self->dispatch_total; i++)
+		if (self->revents[i].data.ptr == info)
+			break;
+	if (i == self->dispatch_total)
+		return;
+
+	if (i != --self->dispatch_total)
+		self->revents[i] = self->revents[self->dispatch_total];
+}
+
+static void
+poller_remove_at_index (struct poller *self, size_t index)
+{
+	hard_assert (index < self->len);
+	struct poller_info *info = self->info[index];
+
+	poller_remove_from_dispatch (self, info);
+	hard_assert (epoll_ctl (self->epoll_fd,
+		EPOLL_CTL_DEL, info->fd, (void *) "") != -1);
+
+	free (info);
+	if (index != --self->len)
+		self->info[index] = self->info[self->len];
+}
+
+static void
+poller_run (struct poller *self)
+{
+	// Not reentrant
+	hard_assert (!self->dispatch_total);
+
+	int n_fds;
+	do
+		n_fds = epoll_wait (self->epoll_fd, self->revents, self->len,
+			poller_timers_get_poll_timeout (&self->timers));
+	while (n_fds == -1 && errno == EINTR);
+
+	if (n_fds == -1)
+	{
+		print_fatal ("%s: %s", "epoll", strerror (errno));
+		exit (EXIT_FAILURE);
+	}
+
+	poller_timers_dispatch (&self->timers);
+
+	self->dispatch_next = 0;
+	self->dispatch_total = n_fds;
+
+	while (self->dispatch_next < self->dispatch_total)
+	{
+		struct epoll_event *revents = self->revents + self->dispatch_next;
+		struct poller_info *info = revents->data.ptr;
+
+		struct pollfd pfd;
+		pfd.fd = info->fd;
+		pfd.revents = poller_epoll_to_poll_events (revents->events);
+		pfd.events = poller_epoll_to_poll_events (info->events);
+
+		self->dispatch_next++;
+		info->dispatcher (&pfd, info->user_data);
+	}
+
+	self->dispatch_next = 0;
+	self->dispatch_total = 0;
+}
+
+#else  // !__linux__
+
+struct poller_info
+{
+	poller_dispatcher_func dispatcher;  ///< Event dispatcher
+	void *user_data;                    ///< User data
+};
+
+struct poller
+{
+	struct pollfd *fds;                 ///< Polled descriptors
+	struct poller_info *fds_info;       ///< Additional information for each FD
+	size_t len;                         ///< Number of polled descriptors
+	size_t alloc;                       ///< Number of entries allocated
+
+	struct poller_timers timers;        ///< Timers
+	int dispatch_next;                  ///< The next dispatched FD or -1
+};
+
+static void
+poller_init (struct poller *self)
+{
+	self->alloc = POLLER_MIN_ALLOC;
+	self->len = 0;
+	self->fds = xcalloc (self->alloc, sizeof *self->fds);
+	self->fds_info = xcalloc (self->alloc, sizeof *self->fds_info);
+	poller_timers_init (&self->timers);
+	self->dispatch_next = -1;
+}
+
+static void
+poller_free (struct poller *self)
+{
+	free (self->fds);
+	free (self->fds_info);
+	poller_timers_free (&self->timers);
+}
+
+static ssize_t
+poller_find_by_fd (struct poller *self, int fd)
+{
+	for (size_t i = 0; i < self->len; i++)
+		if (self->fds[i].fd == fd)
+			return i;
+	return -1;
+}
+
+static void
+poller_ensure_space (struct poller *self)
+{
+	if (self->len < self->alloc)
+		return;
+
+	self->alloc <<= 1;
+	self->fds = xreallocarray (self->fds, sizeof *self->fds, self->alloc);
+	self->fds_info = xreallocarray
+		(self->fds_info, sizeof *self->fds_info, self->alloc);
+}
+
+static void
+poller_set (struct poller *self, int fd, short int events,
+	poller_dispatcher_func dispatcher, void *data)
+{
+	ssize_t index = poller_find_by_fd (self, fd);
+	if (index == -1)
+	{
+		poller_ensure_space (self);
+		index = self->len++;
+	}
+
+	struct pollfd *new_entry = self->fds + index;
+	memset (new_entry, 0, sizeof *new_entry);
+	new_entry->fd = fd;
+	new_entry->events = events;
+
+	self->fds_info[self->len] = (struct poller_info) { dispatcher, data };
+}
+
+static void
+poller_remove_at_index (struct poller *self, size_t index)
+{
+	hard_assert (index < self->len);
+	if (index == --self->len)
+		return;
+
+	// Make sure that we don't disrupt the dispatch loop; kind of crude
+	if ((int) index < self->dispatch_next)
+	{
+		memmove (self->fds + index, self->fds + index + 1,
+			(self->len - index) * sizeof *self->fds);
+		memmove (self->fds_info + index, self->fds_info + index + 1,
+			(self->len - index) * sizeof *self->fds_info);
+		self->dispatch_next--;
+	}
+	else
+	{
+		self->fds[index]      = self->fds[self->len];
+		self->fds_info[index] = self->fds_info[self->len];
+	}
+}
+
+static void
+poller_run (struct poller *self)
+{
+	// Not reentrant
+	hard_assert (self->dispatch_next == -1);
+
+	int result;
+	do
+		result = poll (self->fds, self->len,
+			poller_timers_get_poll_timeout (&self->timers));
+	while (result == -1 && errno == EINTR);
+
+	if (result == -1)
+	{
+		print_fatal ("%s: %s", "poll", strerror (errno));
+		exit (EXIT_FAILURE);
+	}
+
+	poller_timers_dispatch (&self->timers);
+
+	for (int i = 0; i < (int) self->len; )
+	{
+		struct pollfd pfd = self->fds[i];
+		if (!pfd.revents)
+			continue;
+
+		struct poller_info *info = self->fds_info + i;
+		self->dispatch_next = ++i;
+		info->dispatcher (&pfd, info->user_data);
+		i = self->dispatch_next;
+	}
+
+	self->dispatch_next = -1;
+}
+
+#endif  // !__linux__
+
+// --- Utilities ---------------------------------------------------------------
+
+static void
+split_str_ignore_empty (const char *s, char delimiter, struct str_vector *out)
+{
+	const char *begin = s, *end;
+
+	while ((end = strchr (begin, delimiter)))
+	{
+		if (begin != end)
+			str_vector_add_owned (out, xstrndup (begin, end - begin));
+		begin = ++end;
+	}
+
+	if (*begin)
+		str_vector_add (out, begin);
+}
+
+static char *
+strip_str_in_place (char *s, const char *stripped_chars)
+{
+	char *end = s + strlen (s);
+	while (end > s && strchr (stripped_chars, end[-1]))
+		*--end = '\0';
+
+	char *start = s + strspn (s, stripped_chars);
+	if (start > s)
+		memmove (s, start, end - start + 1);
+	return s;
+}
+
+static bool
+str_append_env_path (struct str *output, const char *var, bool only_absolute)
+{
+	const char *value = getenv (var);
+
+	if (!value || (only_absolute && *value != '/'))
+		return false;
+
+	str_append (output, value);
+	return true;
+}
+
+static void
+get_xdg_home_dir (struct str *output, const char *var, const char *def)
+{
+	str_reset (output);
+	if (!str_append_env_path (output, var, true))
+	{
+		str_append_env_path (output, "HOME", false);
+		str_append_c (output, '/');
+		str_append (output, def);
+	}
+}
+
+static size_t io_error_domain_tag;
+#define IO_ERROR (error_resolve_domain (&io_error_domain_tag))
+
+enum
+{
+	IO_ERROR_FAILED
+};
+
+static bool
+ensure_directory_existence (const char *path, struct error **e)
+{
+	struct stat st;
+
+	if (stat (path, &st))
+	{
+		if (mkdir (path, S_IRWXU | S_IRWXG | S_IRWXO))
+		{
+			error_set (e, IO_ERROR, IO_ERROR_FAILED,
+				"cannot create directory `%s': %s",
+				path, strerror (errno));
+			return false;
+		}
+	}
+	else if (!S_ISDIR (st.st_mode))
+	{
+		error_set (e, IO_ERROR, IO_ERROR_FAILED,
+			"cannot create directory `%s': %s",
+			path, "file exists but is not a directory");
+		return false;
+	}
+	return true;
+}
+
+static bool
+mkdir_with_parents (char *path, struct error **e)
+{
+	char *p = path;
+
+	// XXX: This is prone to the TOCTTOU problem.  The solution would be to
+	//   rewrite the function using the {mkdir,fstat}at() functions from
+	//   POSIX.1-2008, ideally returning a file descriptor to the open
+	//   directory, with the current code as a fallback.  Or to use chdir().
+	while ((p = strchr (p + 1, '/')))
+	{
+		*p = '\0';
+		bool success = ensure_directory_existence (path, e);
+		*p = '/';
+
+		if (!success)
+			return false;
+	}
+
+	return ensure_directory_existence (path, e);
+}
+
+static bool
+set_boolean_if_valid (bool *out, const char *s)
+{
+	if      (!strcasecmp (s, "yes"))    *out = true;
+	else if (!strcasecmp (s, "no"))     *out = false;
+	else if (!strcasecmp (s, "on"))     *out = true;
+	else if (!strcasecmp (s, "off"))    *out = false;
+	else if (!strcasecmp (s, "true"))   *out = true;
+	else if (!strcasecmp (s, "false"))  *out = false;
+	else return false;
+
+	return true;
+}
+
+static void
+regerror_to_str (int code, const regex_t *preg, struct str *out)
+{
+	size_t required = regerror (code, preg, NULL, 0);
+	str_ensure_space (out, required);
+	out->len += regerror (code, preg,
+		out->str + out->len, out->alloc - out->len) - 1;
+}
+
+static size_t regex_error_domain_tag;
+#define REGEX_ERROR (error_resolve_domain (&regex_error_domain_tag))
+
+enum
+{
+	REGEX_ERROR_COMPILATION_FAILED
+};
+
+static bool
+regex_match (const char *regex, const char *s, struct error **e)
+{
+	regex_t re;
+	int err = regcomp (&re, regex, REG_EXTENDED | REG_NOSUB);
+	if (err)
+	{
+		struct str desc;
+
+		str_init (&desc);
+		regerror_to_str (err, &re, &desc);
+		error_set (e, REGEX_ERROR, REGEX_ERROR_COMPILATION_FAILED,
+			"failed to compile regular expression: %s", desc.str);
+		str_free (&desc);
+		return false;
+	}
+
+	bool result = regexec (&re, s, 0, NULL, 0) != REG_NOMATCH;
+	regfree (&re);
+	return result;
+}
+
+static bool
+read_line (FILE *fp, struct str *s)
+{
+	int c;
+	bool at_end = true;
+
+	str_reset (s);
+	while ((c = fgetc (fp)) != EOF)
+	{
+		at_end = false;
+		if (c == '\r')
+			continue;
+		if (c == '\n')
+			break;
+		str_append_c (s, c);
+	}
+
+	return !at_end;
+}
+
+#define XSSL_ERROR_TRY_AGAIN INT_MAX
+
+/// A small wrapper around SSL_get_error() to simplify further handling
+static int
+xssl_get_error (SSL *ssl, int result, const char **error_info)
+{
+	int error = SSL_get_error (ssl, result);
+	switch (error)
+	{
+	case SSL_ERROR_NONE:
+	case SSL_ERROR_ZERO_RETURN:
+	case SSL_ERROR_WANT_READ:
+	case SSL_ERROR_WANT_WRITE:
+		return error;
+	case SSL_ERROR_SYSCALL:
+		if ((error = ERR_get_error ()))
+			*error_info = ERR_error_string (error, NULL);
+		else if (result == 0)
+			// An EOF that's not according to the protocol is still an EOF
+			return SSL_ERROR_ZERO_RETURN;
+		else
+		{
+			if (errno == EINTR)
+				return XSSL_ERROR_TRY_AGAIN;
+			*error_info = strerror (errno);
+		}
+		return SSL_ERROR_SSL;
+	default:
+		if ((error = ERR_get_error ()))
+			*error_info = ERR_error_string (error, NULL);
+		else
+			*error_info = "Unknown error";
+		return SSL_ERROR_SSL;
+	}
+}
+
+// --- IRC utilities -----------------------------------------------------------
+
+struct irc_message
+{
+	char *prefix;
+	char *command;
+	struct str_vector params;
+};
+
+static void
+irc_parse_message (struct irc_message *msg, const char *line)
+{
+	msg->prefix = NULL;
+	msg->command = NULL;
+	str_vector_init (&msg->params);
+
+	// Prefix
+	if (*line == ':')
+	{
+		size_t prefix_len = strcspn (++line, " ");
+		msg->prefix = xstrndup (line, prefix_len);
+		line += prefix_len;
+	}
+
+	// Command name
+	{
+		while (*line == ' ')
+			line++;
+
+		size_t cmd_len = strcspn (line, " ");
+		msg->command = xstrndup (line, cmd_len);
+		line += cmd_len;
+	}
+
+	// Arguments
+	while (true)
+	{
+		while (*line == ' ')
+			line++;
+
+		if (*line == ':')
+		{
+			str_vector_add (&msg->params, ++line);
+			break;
+		}
+
+		size_t param_len = strcspn (line, " ");
+		if (!param_len)
+			break;
+
+		str_vector_add_owned (&msg->params, xstrndup (line, param_len));
+		line += param_len;
+	}
+}
+
+static void
+irc_free_message (struct irc_message *msg)
+{
+	free (msg->prefix);
+	free (msg->command);
+	str_vector_free (&msg->params);
+}
+
+static void
+irc_process_buffer (struct str *buf,
+	void (*callback)(const struct irc_message *, const char *, void *),
+	void *user_data)
+{
+	char *start = buf->str, *end = start + buf->len;
+	for (char *p = start; p + 1 < end; p++)
+	{
+		// Split the input on newlines
+		if (p[0] != '\r' || p[1] != '\n')
+			continue;
+
+		*p = 0;
+
+		struct irc_message msg;
+		irc_parse_message (&msg, start);
+		callback (&msg, start, user_data);
+		irc_free_message (&msg);
+
+		start = p + 2;
+	}
+
+	// XXX: we might want to just advance some kind of an offset to avoid
+	//   moving memory around unnecessarily.
+	str_remove_slice (buf, 0, start - buf->str);
+}
+
+static int
+irc_tolower (char c)
+{
+	if (c == '[')   return '{';
+	if (c == ']')   return '}';
+	if (c == '\\')  return '|';
+	if (c == '~')   return '^';
+	return c >= 'A' && c <= 'Z' ? c + ('a' - 'A') : c;
+}
+
+static int
+irc_strcmp (const char *a, const char *b)
+{
+	int x;
+	while (*a || *b)
+		if ((x = irc_tolower (*a++) - irc_tolower (*b++)))
+			return x;
+	return 0;
+}
+
+// --- Configuration -----------------------------------------------------------
+
+// The keys are stripped of surrounding whitespace, the values are not.
+
+static size_t config_error_domain_tag;
+#define CONFIG_ERROR (error_resolve_domain (&config_error_domain_tag))
+
+enum
+{
+	CONFIG_ERROR_MALFORMED
+};
+
+struct config_item
+{
+	const char *key;
+	const char *default_value;
+	const char *description;
+};
+
+static FILE *
+get_config_file (void)
+{
+	struct str_vector paths;
+	struct str config_home, file;
+	const char *xdg_config_dirs;
+	unsigned i;
+	FILE *fp = NULL;
+
+	str_vector_init (&paths);
+
+	str_init (&config_home);
+	get_xdg_home_dir (&config_home, "XDG_CONFIG_HOME", ".config");
+	str_vector_add (&paths, config_home.str);
+	str_free (&config_home);
+
+	if ((xdg_config_dirs = getenv ("XDG_CONFIG_DIRS")))
+		split_str_ignore_empty (xdg_config_dirs, ':', &paths);
+
+	str_init (&file);
+	for (i = 0; i < paths.len; i++)
+	{
+		// As per spec, relative paths are ignored
+		if (*paths.vector[i] != '/')
+			continue;
+
+		str_reset (&file);
+		str_append (&file, paths.vector[i]);
+		str_append (&file, "/" PROGRAM_NAME "/" PROGRAM_NAME ".conf");
+
+		if ((fp = fopen (file.str, "r")))
+			break;
+	}
+
+	str_free (&file);
+	str_vector_free (&paths);
+	return fp;
+}
+
+static void
+load_config_defaults (struct str_map *config, const struct config_item *table)
+{
+	for (; table->key != NULL; table++)
+		if (table->default_value)
+			str_map_set (config, table->key, xstrdup (table->default_value));
+		else
+			str_map_set (config, table->key, NULL);
+}
+
+static bool
+read_config_file (struct str_map *config, struct error **e)
+{
+	struct str line;
+	FILE *fp = get_config_file ();
+	unsigned line_no = 0;
+	bool errors = false;
+
+	if (!fp)
+		return true;
+
+	str_init (&line);
+	for (line_no = 1; read_line (fp, &line); line_no++)
+	{
+		char *start = line.str;
+		if (*start == '#')
+			continue;
+
+		while (isspace (*start))
+			start++;
+
+		char *end = strchr (start, '=');
+		if (!end)
+		{
+			if (*start)
+			{
+				error_set (e, CONFIG_ERROR, CONFIG_ERROR_MALFORMED,
+					"line %u in config: %s", line_no, "malformed input");
+				errors = true;
+				break;
+			}
+		}
+		else
+		{
+			char *value = end + 1;
+			do
+				*end = '\0';
+			while (isspace (*--end));
+
+			str_map_set (config, start, xstrdup (value));
+		}
+	}
+
+	str_free (&line);
+	fclose (fp);
+
+	return !errors;
+}
+
+static char *
+write_default_config (const char *filename, const struct config_item *table,
+	struct error **e)
+{
+	struct str path, base;
+
+	str_init (&path);
+	str_init (&base);
+
+	if (filename)
+	{
+		char *tmp = xstrdup (filename);
+		str_append (&path, dirname (tmp));
+		strcpy (tmp, filename);
+		str_append (&base, basename (tmp));
+		free (tmp);
+	}
+	else
+	{
+		get_xdg_home_dir (&path, "XDG_CONFIG_HOME", ".config");
+		str_append (&path, "/" PROGRAM_NAME);
+		str_append (&base, PROGRAM_NAME ".conf");
+	}
+
+	if (!mkdir_with_parents (path.str, e))
+		goto error;
+
+	str_append_c (&path, '/');
+	str_append_str (&path, &base);
+
+	FILE *fp = fopen (path.str, "w");
+	if (!fp)
+	{
+		error_set (e, IO_ERROR, IO_ERROR_FAILED,
+			"could not open `%s' for writing: %s", path.str, strerror (errno));
+		goto error;
+	}
+
+	errno = 0;
+	for (; table->key != NULL; table++)
+	{
+		fprintf (fp, "# %s\n", table->description);
+		if (table->default_value)
+			fprintf (fp, "%s=%s\n", table->key, table->default_value);
+		else
+			fprintf (fp, "#%s=\n", table->key);
+	}
+	fclose (fp);
+	if (errno)
+	{
+		error_set (e, IO_ERROR, IO_ERROR_FAILED,
+			"writing to `%s' failed: %s", path.str, strerror (errno));
+		goto error;
+	}
+
+	str_free (&base);
+	return str_steal (&path);
+
+error:
+	str_free (&base);
+	str_free (&path);
+	return NULL;
+
+}