Rewrite to use utils.c from ponymap

I'm starting to get tired of repeatingly doing this.

6 files changed, 1358 insertions, 276 deletions

diff --git a/CMakeLists.txt b/CMakeLists.txt
index d63f3ce..3dbef75 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -26,8 +26,12 @@ find_package (LibEV REQUIRED)
 
 include_directories (${dependencies_INCLUDE_DIRS} ${LIBEV_INCLUDE_DIRS})
 
+# Generate a configuration file
+configure_file (${PROJECT_SOURCE_DIR}/config.h.in ${PROJECT_BINARY_DIR}/config.h)
+include_directories (${PROJECT_BINARY_DIR})
+
 # Build the main executable and link it
-add_executable (${PROJECT_NAME} ${PROJECT_NAME}.c)
+add_executable (${PROJECT_NAME} ${PROJECT_NAME}.c siphash.c)
 target_link_libraries (${PROJECT_NAME}
 	${dependencies_LIBRARIES} ${LIBEV_LIBRARIES} readline)
 
diff --git a/config.h.in b/config.h.in
new file mode 100644
index 0000000..89cd306
--- /dev/null
+++ b/config.h.in
@@ -0,0 +1,8 @@
+#ifndef CONFIG_H
+#define CONFIG_H
+
+#define PROGRAM_NAME "${PROJECT_NAME}"
+#define PROGRAM_VERSION "${project_VERSION}"
+
+#endif  // ! CONFIG_H
+
diff --git a/json-rpc-shell.c b/json-rpc-shell.c
index 93269e1..9fb0205 100644
--- a/json-rpc-shell.c
+++ b/json-rpc-shell.c
@@ -1,7 +1,7 @@
 /*
  * json-rpc-shell.c: trivial JSON-RPC 2.0 shell
  *
- * Copyright (c) 2014, Přemysl Janouch <p.janouch@gmail.com>
+ * 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
@@ -18,219 +18,21 @@
  *
  */
 
-#define PROGRAM_NAME "json-rpc-shell"
-#define PROGRAM_VERSION "alpha"
-
 /// Some arbitrary limit for the history file
 #define HISTORY_LIMIT 10000
 
-#define _POSIX_C_SOURCE 199309L
-#define _XOPEN_SOURCE 600
-
-#include <stdio.h>
-#include <stdlib.h>
-#include <stdarg.h>
-#include <stdbool.h>
-#include <stdint.h>
-#include <string.h>
-#include <locale.h>
-#include <errno.h>
+#include "config.h"
+#include "utils.c"
 
-#include <libgen.h>
-#include <iconv.h>
 #include <langinfo.h>
-#include <sys/stat.h>
 #include <signal.h>
-#include <unistd.h>
 
 #include <ev.h>
-#include <getopt.h>
 #include <readline/readline.h>
 #include <readline/history.h>
 #include <curl/curl.h>
 #include <jansson.h>
 
-#if defined __GNUC__
-#define ATTRIBUTE_PRINTF(x, y) __attribute__ ((format (printf, x, y)))
-#else // ! __GNUC__
-#define ATTRIBUTE_PRINTF(x, y)
-#endif // ! __GNUC__
-
-#define N_ELEMENTS(a) (sizeof (a) / sizeof ((a)[0]))
-
-#define BLOCK_START  do {
-#define BLOCK_END    } while (0)
-
-// --- Logging -----------------------------------------------------------------
-
-static void
-log_message_stdio (const char *quote, const char *fmt, va_list ap)
-{
-	FILE *stream = stderr;
-
-	fputs (quote, stream);
-	vfprintf (stream, fmt, ap);
-	fputs ("\n", stream);
-}
-
-static void
-log_message (const char *quote, const char *fmt, ...) ATTRIBUTE_PRINTF (2, 3);
-
-static void
-log_message (const char *quote, const char *fmt, ...)
-{
-	va_list ap;
-	va_start (ap, fmt);
-	log_message_stdio (quote, fmt, ap);
-	va_end (ap);
-}
-
-// `fatal' is reserved for unexpected failures that would harm further operation
-
-// TODO: colors (probably copy over from stracepkg)
-#define print_fatal(...)    log_message ("fatal: ",   __VA_ARGS__)
-#define print_error(...)    log_message ("error: ",   __VA_ARGS__)
-#define print_warning(...)  log_message ("warning: ", __VA_ARGS__)
-#define print_status(...)   log_message ("-- ",       __VA_ARGS__)
-
-#define exit_fatal(...)                                                        \
-	BLOCK_START                                                                \
-		print_fatal (__VA_ARGS__);                                             \
-		exit (EXIT_FAILURE);                                                   \
-	BLOCK_END
-
-// --- 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
-};
-
-static void
-str_init (struct str *self)
-{
-	self->alloc = 16;
-	self->len = 0;
-	self->str = strcpy (malloc (self->alloc), "");
-}
-
-static void
-str_free (struct str *self)
-{
-	free (self->str);
-	self->str = NULL;
-	self->alloc = 0;
-	self->len = 0;
-}
-
-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 = realloc (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';
-}
-
-// --- Utilities ---------------------------------------------------------------
-
-static char *strdup_printf (const char *format, ...) ATTRIBUTE_PRINTF (1, 2);
-
-static char *
-strdup_printf (const char *format, ...)
-{
-	va_list ap;
-	va_start (ap, format);
-	int size = vsnprintf (NULL, 0, format, ap);
-	va_end (ap);
-	if (size < 0)
-		return NULL;
-
-	char buf[size + 1];
-	va_start (ap, format);
-	size = vsnprintf (buf, sizeof buf, format, ap);
-	va_end (ap);
-	if (size < 0)
-		return NULL;
-
-	return strdup (buf);
-}
-
-static char *
-iconv_strdup (iconv_t conv, char *in, size_t in_len, size_t *out_len)
-{
-	char *buf, *buf_ptr;
-	size_t out_left, buf_alloc;
-
-	buf = buf_ptr = malloc (out_left = buf_alloc = 64);
-
-	char *in_ptr = in;
-	if (in_len == (size_t) -1)
-		in_len = strlen (in) + 1;
-
-	while (iconv (conv, (char **) &in_ptr, &in_len,
-		(char **) &buf_ptr, &out_left) == (size_t) -1)
-	{
-		if (errno != E2BIG)
-		{
-			free (buf);
-			return NULL;
-		}
-		out_left += buf_alloc;
-		char *new_buf = realloc (buf, buf_alloc <<= 1);
-		buf_ptr += new_buf - buf;
-		buf = new_buf;
-	}
-	if (out_len)
-		*out_len = buf_alloc - out_left;
-	return buf;
-}
-
-static bool
-ensure_directory_existence (const char *path)
-{
-	struct stat st;
-	if (stat (path, &st))
-	{
-		if (mkdir (path, S_IRWXU | S_IRWXG | S_IRWXO))
-			return false;
-	}
-	else if (!S_ISDIR (st.st_mode))
-		return false;
-	return true;
-}
-
-static bool
-mkdir_with_parents (char *path)
-{
-	char *p = path;
-	while ((p = strchr (p + 1, '/')))
-	{
-		*p = '\0';
-		bool success = ensure_directory_existence (path);
-		*p = '/';
-
-		if (!success)
-			return false;
-	}
-	return ensure_directory_existence (path);
-}
-
 // --- Main program ------------------------------------------------------------
 
 static struct app_context
@@ -306,9 +108,9 @@ parse_response (struct app_context *ctx, struct str *buf)
 			PARSE_FAIL ("invalid `%s' field in error response", "message");
 
 		json_int_t code_val = json_integer_value (code);
-		char *utf8 = strdup_printf ("error response: %" JSON_INTEGER_FORMAT
+		char *utf8 = xstrdup_printf ("error response: %" JSON_INTEGER_FORMAT
 			" (%s)", code_val, json_string_value (message));
-		char *s = iconv_strdup (ctx->term_from_utf8, utf8, -1, NULL);
+		char *s = iconv_xstrdup (ctx->term_from_utf8, utf8, -1, NULL);
 		if (!s)
 			print_error ("character conversion failed for `%s'", "error");
 		else
@@ -321,7 +123,7 @@ parse_response (struct app_context *ctx, struct str *buf)
 	if (data)
 	{
 		char *utf8 = json_dumps (data, JSON_ENCODE_ANY);
-		char *s = iconv_strdup (ctx->term_from_utf8, utf8, -1, NULL);
+		char *s = iconv_xstrdup (ctx->term_from_utf8, utf8, -1, NULL);
 		free (utf8);
 
 		if (!s)
@@ -338,7 +140,7 @@ parse_response (struct app_context *ctx, struct str *buf)
 			flags |= JSON_INDENT (2);
 
 		char *utf8 = json_dumps (result, flags);
-		char *s = iconv_strdup (ctx->term_from_utf8, utf8, -1, NULL);
+		char *s = iconv_xstrdup (ctx->term_from_utf8, utf8, -1, NULL);
 		free (utf8);
 
 		if (!s)
@@ -443,7 +245,8 @@ make_json_rpc_call (struct app_context *ctx,
 	char *req_utf8 = json_dumps (request, 0);
 	if (ctx->verbose)
 	{
-		char *req_term = iconv_strdup (ctx->term_from_utf8, req_utf8, -1, NULL);
+		char *req_term = iconv_xstrdup
+			(ctx->term_from_utf8, req_utf8, -1, NULL);
 		if (!req_term)
 			print_error ("%s: %s", "verbose", "character conversion failed");
 		else
@@ -494,7 +297,7 @@ make_json_rpc_call (struct app_context *ctx,
 
 	if (!success)
 	{
-		char *s = iconv_strdup (ctx->term_from_utf8,
+		char *s = iconv_xstrdup (ctx->term_from_utf8,
 			buf.str, buf.len + 1, NULL);
 		if (!s)
 			print_error ("character conversion failed for `%s'",
@@ -515,7 +318,7 @@ process_input (struct app_context *ctx, char *user_input)
 	char *input;
 	size_t len;
 
-	if (!(input = iconv_strdup (ctx->term_to_utf8, user_input, -1, &len)))
+	if (!(input = iconv_xstrdup (ctx->term_to_utf8, user_input, -1, &len)))
 	{
 		print_error ("character conversion failed for `%s'", "user input");
 		goto fail;
@@ -642,79 +445,81 @@ on_tty_readable (EV_P_ ev_io *handle, int revents)
 }
 
 static void
-print_usage (const char *program_name)
+parse_program_arguments (struct app_context *ctx, int argc, char **argv,
+	char **origin, char **endpoint)
 {
-	fprintf (stdout,
-		"Usage: %s [OPTION]... ENDPOINT\n"
-		"Trivial JSON-RPC shell.\n"
-		"\n"
-		"  -h, --help       display this help and exit\n"
-		"  -V, --version    output version information and exit\n"
-		"  -a, --auto-id    automatic `id' fields\n"
-		"  -o, --origin O   set the HTTP Origin header\n"
-		"  -p, --pretty     pretty-print the responses\n"
-		"  -t, --trust-all  don't care about SSL/TLS certificates\n"
-		"  -v, --verbose    print the request before sending\n",
-		program_name);
-}
-
-int
-main (int argc, char *argv[])
-{
-	const char *invocation_name = argv[0];
-
-	static struct option opts[] =
+	static const struct opt opts[] =
 	{
-		{ "help",      no_argument,       NULL, 'h' },
-		{ "version",   no_argument,       NULL, 'V' },
-		{ "auto-id",   no_argument,       NULL, 'a' },
-		{ "origin",    required_argument, NULL, 'o' },
-		{ "pretty",    no_argument,       NULL, 'p' },
-		{ "trust-all", no_argument,       NULL, 't' },
-		{ "verbose",   no_argument,       NULL, 'v' },
-		{ NULL,        0,                 NULL,  0  }
+		{ '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" },
+		{ 'a', "auto-id", NULL, 0, "automatic `id' fields" },
+		{ 'o', "origin", "O", 0, "set the HTTP Origin header" },
+		{ 'p', "pretty", NULL, 0, "pretty-print the responses" },
+		{ 't', "trust-all", NULL, 0, "don't care about SSL/TLS certificates" },
+		{ 'v', "verbose", NULL, 0, "print the request before sending" },
+		{ 0, NULL, NULL, 0, NULL }
 	};
 
-	char *origin = NULL;
-	while (1)
-	{
-		int c, opt_index;
-
-		c = getopt_long (argc, argv, "hVapvt", opts, &opt_index);
-		if (c == -1)
-			break;
-
-		switch (c)
-		{
-		case 'h':
-			print_usage (invocation_name);
-			exit (EXIT_SUCCESS);
-		case 'V':
-			printf (PROGRAM_NAME " " PROGRAM_VERSION "\n");
-			exit (EXIT_SUCCESS);
+	struct opt_handler oh;
+	opt_handler_init (&oh, argc, argv, opts,
+		"ENDPOINT", "Trivial JSON-RPC shell.");
 
-		case 'a':  g_ctx.auto_id      = true;  break;
-		case 'o':  origin = optarg;            break;
-		case 'p':  g_ctx.pretty_print = true;  break;
-		case 't':  g_ctx.trust_all    = true;  break;
-		case 'v':  g_ctx.verbose      = true;  break;
+	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 'a':
+		ctx->auto_id = true;
+		break;
+	case 'o':
+		*origin = optarg;
+		break;
+	case 'p':
+		ctx->pretty_print = true;
+		break;
+	case 't':
+		ctx->trust_all = true;
+		break;
+	case 'v':
+		ctx->verbose = true;
+		break;
 
-		default:
-			print_error ("wrong options");
-			exit (EXIT_FAILURE);
-		}
+	default:
+		print_error ("wrong options");
+		opt_handler_usage (&oh, stderr);
+		exit (EXIT_FAILURE);
 	}
 
-	argv += optind;
 	argc -= optind;
+	argv += optind;
 
 	if (argc != 1)
 	{
-		print_usage (invocation_name);
+		opt_handler_usage (&oh, stderr);
 		exit (EXIT_FAILURE);
 	}
 
-	const char *endpoint = argv[0];
+	*endpoint = argv[0];
+	opt_handler_free (&oh);
+}
+
+int
+main (int argc, char *argv[])
+{
+	char *origin = NULL;
+	char *endpoint = NULL;
+	parse_program_arguments (&g_ctx, argc, argv, &origin, &endpoint);
+
 	if (strncmp (endpoint, "http://", 7)
 	 && strncmp (endpoint, "https://", 8))
 		exit_fatal ("the endpoint address must begin with"
@@ -729,7 +534,7 @@ main (int argc, char *argv[])
 
 	if (origin)
 	{
-		origin = strdup_printf ("Origin: %s", origin);
+		origin = xstrdup_printf ("Origin: %s", origin);
 		headers = curl_slist_append (headers, origin);
 	}
 
@@ -751,12 +556,12 @@ main (int argc, char *argv[])
 #ifdef __linux__
 	// XXX: not quite sure if this is actually desirable
 	// TODO: instead retry with JSON_ENSURE_ASCII
-	encoding = strdup_printf ("%s//TRANSLIT", encoding);
+	encoding = xstrdup_printf ("%s//TRANSLIT", encoding);
 #endif // __linux__
 
-	if ((g_ctx.term_from_utf8 = iconv_open (encoding, "utf-8"))
+	if ((g_ctx.term_from_utf8 = iconv_open (encoding, "UTF-8"))
 		== (iconv_t) -1
-	 || (g_ctx.term_to_utf8 = iconv_open ("utf-8", nl_langinfo (CODESET)))
+	 || (g_ctx.term_to_utf8 = iconv_open ("UTF-8", nl_langinfo (CODESET)))
 		== (iconv_t) -1)
 		exit_fatal ("creating the UTF-8 conversion object failed: %s",
 			strerror (errno));
@@ -767,18 +572,18 @@ main (int argc, char *argv[])
 		if (!home)
 			exit_fatal ("where is your $HOME, kid?");
 
-		data_home = strdup_printf ("%s/.local/share", home);
+		data_home = xstrdup_printf ("%s/.local/share", home);
 	}
 
 	using_history ();
 	stifle_history (HISTORY_LIMIT);
 
 	char *history_path =
-		strdup_printf ("%s/" PROGRAM_NAME "/history", data_home);
+		xstrdup_printf ("%s/" PROGRAM_NAME "/history", data_home);
 	(void) read_history (history_path);
 
 	// XXX: we should use termcap/terminfo for the codes but who cares
-	char *prompt = strdup_printf ("%c\x1b[1m%cjson-rpc> %c\x1b[0m%c",
+	char *prompt = xstrdup_printf ("%c\x1b[1m%cjson-rpc> %c\x1b[0m%c",
 		RL_PROMPT_START_IGNORE, RL_PROMPT_END_IGNORE,
 		RL_PROMPT_START_IGNORE, RL_PROMPT_END_IGNORE);
 
@@ -806,8 +611,8 @@ main (int argc, char *argv[])
 	ev_loop_destroy (loop);
 
 	// User has terminated the program, let's save the history and clean up
-	char *dir = strdup (history_path);
-	(void) mkdir_with_parents (dirname (dir));
+	char *dir = xstrdup (history_path);
+	(void) mkdir_with_parents (dirname (dir), NULL);
 	free (dir);
 
 	if (write_history (history_path))
diff --git a/siphash.c b/siphash.c
new file mode 100644
index 0000000..7a5c8d4
--- /dev/null
+++ b/siphash.c
@@ -0,0 +1,87 @@
+// Code taken from https://github.com/floodyberry/siphash with some edits.
+//
+// To the extent possible under law, the author(s) have dedicated all copyright
+// and related and neighboring rights to this software to the public domain
+// worldwide. This software is distributed without any warranty.
+//
+// You should have received a copy of the CC0 Public Domain Dedication along
+// with this software. If not, see <http://creativecommons.org/publicdomain/zero/1.0/>.
+
+#include "siphash.h"
+
+inline static uint64_t
+u8to64_le (const unsigned char *p)
+{
+	return
+		(uint64_t) p[0]       |
+		(uint64_t) p[1] <<  8 |
+		(uint64_t) p[2] << 16 |
+		(uint64_t) p[3] << 24 |
+		(uint64_t) p[4] << 32 |
+		(uint64_t) p[5] << 40 |
+		(uint64_t) p[6] << 48 |
+		(uint64_t) p[7] << 56 ;
+}
+
+uint64_t
+siphash (const unsigned char key[16], const unsigned char *m, size_t len)
+{
+	uint64_t v0, v1, v2, v3;
+	uint64_t mi, k0, k1;
+	uint64_t last7;
+	size_t i, blocks;
+
+	k0 = u8to64_le (key + 0);
+	k1 = u8to64_le (key + 8);
+	v0 = k0 ^ 0x736f6d6570736575ull;
+	v1 = k1 ^ 0x646f72616e646f6dull;
+	v2 = k0 ^ 0x6c7967656e657261ull;
+	v3 = k1 ^ 0x7465646279746573ull;
+
+	last7 = (uint64_t) (len & 0xff) << 56;
+
+#define ROTL64(a,b) (((a)<<(b))|((a)>>(64-b)))
+
+#define COMPRESS                              \
+	v0 += v1; v2 += v3;                       \
+	v1 = ROTL64 (v1,13); v3 = ROTL64 (v3,16); \
+	v1 ^= v0; v3 ^= v2;                       \
+	v0 = ROTL64 (v0,32);                      \
+	v2 += v1; v0 += v3;                       \
+	v1 = ROTL64 (v1,17); v3 = ROTL64 (v3,21); \
+	v1 ^= v2; v3 ^= v0;                       \
+	v2 = ROTL64(v2,32);
+
+	for (i = 0, blocks = (len & ~(size_t) 7); i < blocks; i += 8)
+	{
+		mi = u8to64_le (m + i);
+		v3 ^= mi;
+		COMPRESS
+		COMPRESS
+		v0 ^= mi;
+	}
+
+	switch (len - blocks)
+	{
+	case 7: last7 |= (uint64_t) m[i + 6] << 48;
+	case 6: last7 |= (uint64_t) m[i + 5] << 40;
+	case 5: last7 |= (uint64_t) m[i + 4] << 32;
+	case 4: last7 |= (uint64_t) m[i + 3] << 24;
+	case 3: last7 |= (uint64_t) m[i + 2] << 16;
+	case 2: last7 |= (uint64_t) m[i + 1] <<  8;
+	case 1: last7 |= (uint64_t) m[i + 0]      ;
+	default:;
+	};
+	v3 ^= last7;
+	COMPRESS
+	COMPRESS
+	v0 ^= last7;
+	v2 ^= 0xff;
+	COMPRESS
+	COMPRESS
+	COMPRESS
+	COMPRESS
+
+	return v0 ^ v1 ^ v2 ^ v3;
+}
+
diff --git a/siphash.h b/siphash.h
new file mode 100644
index 0000000..dca7c42
--- /dev/null
+++ b/siphash.h
@@ -0,0 +1,10 @@
+#ifndef SIPHASH_H
+#define SIPHASH_H
+
+#include <stdint.h>
+#include <stdlib.h>
+
+uint64_t siphash (const unsigned char key[16],
+	const unsigned char *m, size_t len);
+
+#endif // SIPHASH_H
diff --git a/utils.c b/utils.c
new file mode 100644
index 0000000..00772f7
--- /dev/null
+++ b/utils.c
@@ -0,0 +1,1168 @@
+/*
+ * utils.c: utilities
+ *
+ * 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 600
+
+#include <stdio.h>
+#include <stdlib.h>
+#include <stdarg.h>
+#include <stdbool.h>
+#include <stdint.h>
+#include <string.h>
+#include <ctype.h>
+#include <locale.h>
+#include <errno.h>
+
+#include <unistd.h>
+#include <sys/stat.h>
+#include <libgen.h>
+#include <iconv.h>
+
+#include <getopt.h>
+#include "siphash.h"
+
+#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)
+
+// --- Logging -----------------------------------------------------------------
+
+static void
+log_message_stdio (const char *quote, const char *fmt, va_list ap)
+{
+	FILE *stream = stderr;
+
+	fputs (quote, stream);
+	vfprintf (stream, fmt, ap);
+	fputs ("\n", stream);
+}
+
+static void
+log_message (const char *quote, const char *fmt, ...) ATTRIBUTE_PRINTF (2, 3);
+
+static void
+log_message (const char *quote, const char *fmt, ...)
+{
+	va_list ap;
+	va_start (ap, fmt);
+	log_message_stdio (quote, fmt, ap);
+	va_end (ap);
+}
+
+// `fatal' is reserved for unexpected failures that would harm further operation
+
+// TODO: colors (probably copy over from stracepkg)
+#define print_fatal(...)    log_message ("fatal: ",   __VA_ARGS__)
+#define print_error(...)    log_message ("error: ",   __VA_ARGS__)
+#define print_warning(...)  log_message ("warning: ", __VA_ARGS__)
+#define print_status(...)   log_message ("-- ",       __VA_ARGS__)
+
+#define exit_fatal(...)                                                        \
+	BLOCK_START                                                                \
+		print_fatal (__VA_ARGS__);                                             \
+		exit (EXIT_FAILURE);                                                   \
+	BLOCK_END
+
+// --- 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)                                                      \
+			log_message ("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)
+		exit_fatal ("malloc: %s", strerror (errno));
+	return p;
+}
+
+static void *
+xcalloc (size_t n, size_t m)
+{
+	void *p = calloc (n, m);
+	if (!p && n && m)
+		exit_fatal ("calloc: %s", strerror (errno));
+	return p;
+}
+
+static void *
+xrealloc (void *o, size_t n)
+{
+	void *p = realloc (o, n);
+	if (!p && n)
+		exit_fatal ("realloc: %s", strerror (errno));
+	return p;
+}
+
+static void *
+xreallocarray (void *o, size_t n, size_t m)
+{
+	if (m && n > SIZE_MAX / m)
+	{
+		errno = ENOMEM;
+		exit_fatal ("reallocarray: %s", strerror (errno));
+	}
+	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 ----------------------------------------------
+
+#define LIST_HEADER(type)                                                      \
+	struct type *next;                                                         \
+	struct type *prev;
+
+#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
+
+#define LIST_APPEND_WITH_TAIL(head, tail, link)                                \
+	BLOCK_START                                                                \
+		(link)->prev = (tail);                                                 \
+		(link)->next = NULL;                                                   \
+		if ((link)->prev)                                                      \
+			(link)->prev->next = (link);                                       \
+		else                                                                   \
+			(head) = (link);                                                   \
+		(tail) = (link);                                                       \
+	BLOCK_END
+
+#define LIST_UNLINK_WITH_TAIL(head, tail, link)                                \
+	BLOCK_START                                                                \
+		if ((tail) == (link))                                                  \
+			(tail) = (link)->prev;                                             \
+		LIST_UNLINK ((head), (link));                                          \
+	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));
+}
+
+// --- 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
+};
+
+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 void *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;
+}
+
+// --- Errors ------------------------------------------------------------------
+
+// Error reporting utilities.  Inspired by GError, only much simpler.
+
+struct error
+{
+	char *message;                      ///< Textual description of the event
+};
+
+static void
+error_set (struct error **e, const char *message, ...) ATTRIBUTE_PRINTF (2, 3);
+
+static void
+error_set (struct error **e, const char *message, ...)
+{
+	if (!e)
+		return;
+
+	va_list ap;
+	va_start (ap, message);
+	int size = vsnprintf (NULL, 0, message, ap);
+	va_end (ap);
+
+	hard_assert (size >= 0);
+
+	struct error *tmp = xmalloc (sizeof *tmp);
+	tmp->message = xmalloc (size + 1);
+
+	va_start (ap, message);
+	size = vsnprintf (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);
+}
+
+// --- String hash map ---------------------------------------------------------
+
+// The most basic <string, managed pointer> map (or associative array).
+
+struct str_map_link
+{
+	LIST_HEADER (str_map_link)
+
+	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
+
+	/// Callback that transforms all key values for storage and comparison;
+	/// has to behave exactly like strxfrm().
+	size_t (*key_xfrm) (char *dest, const char *src, size_t n);
+};
+
+#define STR_MAP_MIN_ALLOC 16
+
+typedef void (*str_map_free_fn) (void *);
+
+static void
+str_map_init (struct str_map *self)
+{
+	self->alloc = STR_MAP_MIN_ALLOC;
+	self->len = 0;
+	self->free = NULL;
+	self->key_xfrm = 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_real (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_set (struct str_map *self, const char *key, void *value)
+{
+	if (!self->key_xfrm)
+	{
+		str_map_set_real (self, key, value);
+		return;
+	}
+	char tmp[self->key_xfrm (NULL, key, 0) + 1];
+	self->key_xfrm (tmp, key, sizeof tmp);
+	str_map_set_real (self, tmp, value);
+}
+
+static void *
+str_map_find_real (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, (const char *) iter + sizeof *iter))
+			return iter->data;
+	return NULL;
+}
+
+static void *
+str_map_find (struct str_map *self, const char *key)
+{
+	if (!self->key_xfrm)
+		return str_map_find_real (self, key);
+
+	char tmp[self->key_xfrm (NULL, key, 0) + 1];
+	self->key_xfrm (tmp, key, sizeof tmp);
+	return str_map_find_real (self, tmp);
+}
+
+// --- 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 *xstrdup_printf (const char *format, ...) ATTRIBUTE_PRINTF (1, 2);
+
+static char *
+xstrdup_printf (const char *format, ...)
+{
+	va_list ap;
+	va_start (ap, format);
+	int size = vsnprintf (NULL, 0, format, ap);
+	va_end (ap);
+	if (size < 0)
+		return NULL;
+
+	char buf[size + 1];
+	va_start (ap, format);
+	size = vsnprintf (buf, sizeof buf, format, ap);
+	va_end (ap);
+	if (size < 0)
+		return NULL;
+
+	return xstrdup (buf);
+}
+
+static char *
+iconv_xstrdup (iconv_t conv, char *in, size_t in_len, size_t *out_len)
+{
+	char *buf, *buf_ptr;
+	size_t out_left, buf_alloc;
+
+	buf = buf_ptr = xmalloc (out_left = buf_alloc = 64);
+
+	char *in_ptr = in;
+	if (in_len == (size_t) -1)
+		in_len = strlen (in) + 1;
+
+	while (iconv (conv, (char **) &in_ptr, &in_len,
+		(char **) &buf_ptr, &out_left) == (size_t) -1)
+	{
+		if (errno != E2BIG)
+		{
+			free (buf);
+			return NULL;
+		}
+		out_left += buf_alloc;
+		char *new_buf = xrealloc (buf, buf_alloc <<= 1);
+		buf_ptr += new_buf - buf;
+		buf = new_buf;
+	}
+	if (out_len)
+		*out_len = buf_alloc - out_left;
+	return buf;
+}
+
+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 void
+get_xdg_config_dirs (struct str_vector *out)
+{
+	struct str config_home;
+	str_init (&config_home);
+	get_xdg_home_dir (&config_home, "XDG_CONFIG_HOME", ".config");
+	str_vector_add (out, config_home.str);
+	str_free (&config_home);
+
+	const char *xdg_config_dirs;
+	if ((xdg_config_dirs = getenv ("XDG_CONFIG_DIRS")))
+		split_str_ignore_empty (xdg_config_dirs, ':', out);
+}
+
+static char *
+resolve_config_filename (const char *filename)
+{
+	// Absolute path is absolute
+	if (*filename == '/')
+		return xstrdup (filename);
+
+	struct str_vector paths;
+	str_vector_init (&paths);
+	get_xdg_config_dirs (&paths);
+
+	struct str file;
+	str_init (&file);
+
+	char *result = NULL;
+	for (unsigned i = 0; i < paths.len; i++)
+	{
+		// As per spec, relative paths are ignored
+		if (*paths.vector[i] != '/')
+			continue;
+
+		str_reset (&file);
+		str_append_printf (&file, "%s/" PROGRAM_NAME "/%s",
+			paths.vector[i], filename);
+
+		struct stat st;
+		if (!stat (file.str, &st))
+		{
+			result = str_steal (&file);
+			break;
+		}
+	}
+
+	str_vector_free (&paths);
+	str_free (&file);
+	return result;
+}
+
+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, "cannot create directory `%s': %s",
+				path, strerror (errno));
+			return false;
+		}
+	}
+	else if (!S_ISDIR (st.st_mode))
+	{
+		error_set (e, "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
+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;
+}
+
+// --- Configuration -----------------------------------------------------------
+
+// The keys are stripped of surrounding whitespace, the values are not.
+
+struct config_item
+{
+	const char *key;
+	const char *default_value;
+	const char *description;
+};
+
+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)
+{
+	char *filename = resolve_config_filename (PROGRAM_NAME ".conf");
+	if (!filename)
+		return true;
+
+	FILE *fp = fopen (filename, "r");
+	if (!fp)
+	{
+		error_set (e, "could not open `%s' for reading: %s",
+			filename, strerror (errno));
+		free (filename);
+		return false;
+	}
+
+	struct str line;
+	str_init (&line);
+
+	bool errors = false;
+	for (unsigned 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)
+		{
+			char *value = end + 1;
+			do
+				*end = '\0';
+			while (isspace (*--end));
+
+			str_map_set (config, start, xstrdup (value));
+		}
+		else if (*start)
+		{
+			error_set (e, "line %u in config: %s", line_no, "malformed input");
+			errors = true;
+			break;
+		}
+	}
+
+	str_free (&line);
+	fclose (fp);
+	free (filename);
+	return !errors;
+}
+
+static char *
+write_default_config (const char *filename, const char *prolog,
+	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, "could not open `%s' for writing: %s",
+			path.str, strerror (errno));
+		goto error;
+	}
+
+	if (prolog)
+		fputs (prolog, fp);
+
+	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, "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;
+
+}
+
+static void
+call_write_default_config (const char *hint, const struct config_item *table)
+{
+	static const char *prolog =
+	"# " PROGRAM_NAME " " PROGRAM_VERSION " configuration file\n"
+	"#\n"
+	"# Relative paths are searched for in ${XDG_CONFIG_HOME:-~/.config}\n"
+	"# /" PROGRAM_NAME " as well as in $XDG_CONFIG_DIRS/" PROGRAM_NAME "\n"
+	"\n";
+
+	struct error *e = NULL;
+	char *filename = write_default_config (hint, prolog, table, &e);
+	if (!filename)
+	{
+		print_error ("%s", e->message);
+		error_free (e);
+		exit (EXIT_FAILURE);
+	}
+	print_status ("configuration written to `%s'", filename);
+	free (filename);
+}
+
+// --- Option handler ----------------------------------------------------------
+
+// Simple wrapper for the getopt_long API to make it easier to use and maintain.
+
+#define OPT_USAGE_ALIGNMENT_COLUMN 30   ///< Alignment for option descriptions
+
+enum
+{
+	OPT_OPTIONAL_ARG  = (1 << 0),       ///< The argument is optional
+	OPT_LONG_ONLY     = (1 << 1)        ///< Ignore the short name in opt_string
+};
+
+// All options need to have both a short name, and a long name.  The short name
+// is what is returned from opt_handler_get().  It is possible to define a value
+// completely out of the character range combined with the OPT_LONG_ONLY flag.
+//
+// When `arg_hint' is defined, the option is assumed to have an argument.
+
+struct opt
+{
+	int short_name;                     ///< The single-letter name
+	const char *long_name;              ///< The long name
+	const char *arg_hint;               ///< Option argument hint
+	int flags;                          ///< Option flags
+	const char *description;            ///< Option description
+};
+
+struct opt_handler
+{
+	int argc;                           ///< The number of program arguments
+	char **argv;                        ///< Program arguments
+
+	const char *arg_hint;               ///< Program arguments hint
+	const char *description;            ///< Description of the program
+
+	const struct opt *opts;             ///< The list of options
+	size_t opts_len;                    ///< The length of the option array
+
+	struct option *options;             ///< The list of options for getopt
+	char *opt_string;                   ///< The `optstring' for getopt
+};
+
+static void
+opt_handler_free (struct opt_handler *self)
+{
+	free (self->options);
+	free (self->opt_string);
+}
+
+static void
+opt_handler_init (struct opt_handler *self, int argc, char **argv,
+	const struct opt *opts, const char *arg_hint, const char *description)
+{
+	memset (self, 0, sizeof *self);
+	self->argc = argc;
+	self->argv = argv;
+	self->arg_hint = arg_hint;
+	self->description = description;
+
+	size_t len = 0;
+	for (const struct opt *iter = opts; iter->long_name; iter++)
+		len++;
+
+	self->opts = opts;
+	self->opts_len = len;
+	self->options = xcalloc (len + 1, sizeof *self->options);
+
+	struct str opt_string;
+	str_init (&opt_string);
+
+	for (size_t i = 0; i < len; i++)
+	{
+		const struct opt *opt = opts + i;
+		struct option *mapped = self->options + i;
+
+		mapped->name = opt->long_name;
+		if (!opt->arg_hint)
+			mapped->has_arg = no_argument;
+		else if (opt->flags & OPT_OPTIONAL_ARG)
+			mapped->has_arg = optional_argument;
+		else
+			mapped->has_arg = required_argument;
+		mapped->val = opt->short_name;
+
+		if (opt->flags & OPT_LONG_ONLY)
+			continue;
+
+		str_append_c (&opt_string, opt->short_name);
+		if (opt->arg_hint)
+		{
+			str_append_c (&opt_string, ':');
+			if (opt->flags & OPT_OPTIONAL_ARG)
+				str_append_c (&opt_string, ':');
+		}
+	}
+
+	self->opt_string = str_steal (&opt_string);
+}
+
+static void
+opt_handler_usage (struct opt_handler *self, FILE *stream)
+{
+	struct str usage;
+	str_init (&usage);
+
+	str_append_printf (&usage, "Usage: %s [OPTION]... %s\n",
+		self->argv[0], self->arg_hint ? self->arg_hint : "");
+	str_append_printf (&usage, "%s\n\n", self->description);
+
+	for (size_t i = 0; i < self->opts_len; i++)
+	{
+		struct str row;
+		str_init (&row);
+
+		const struct opt *opt = self->opts + i;
+		if (!(opt->flags & OPT_LONG_ONLY))
+			str_append_printf (&row, "  -%c, ", opt->short_name);
+		else
+			str_append (&row, "      ");
+		str_append_printf (&row, "--%s", opt->long_name);
+		if (opt->arg_hint)
+			str_append_printf (&row, (opt->flags & OPT_OPTIONAL_ARG)
+				? " [%s]" : " %s", opt->arg_hint);
+
+		// TODO: keep the indent if there are multiple lines
+		if (row.len + 2 <= OPT_USAGE_ALIGNMENT_COLUMN)
+		{
+			str_append (&row, "  ");
+			str_append_printf (&usage, "%-*s%s\n",
+				OPT_USAGE_ALIGNMENT_COLUMN, row.str, opt->description);
+		}
+		else
+			str_append_printf (&usage, "%s\n%-*s%s\n", row.str,
+				OPT_USAGE_ALIGNMENT_COLUMN, "", opt->description);
+
+		str_free (&row);
+	}
+
+	fputs (usage.str, stream);
+	str_free (&usage);
+}
+
+static int
+opt_handler_get (struct opt_handler *self)
+{
+	return getopt_long (self->argc, self->argv,
+		self->opt_string, self->options, NULL);
+}