path: root/interactive.c

/* SPDX-License-Identifier: GPL-2.0 */

/** \file interactive.c Readline abstraction for interactive sessions. */

#include "para.h"

#include <readline/readline.h>
#include <readline/history.h>
#include <sys/ioctl.h>
#include <signal.h>

#include "fd.h"
#include "buffer_tree.h"
#include "list.h"
#include "sched.h"
#include "interactive.h"
#include "string.h"
#include "error.h"

struct i9e_private {
	struct i9e_client_info *ici;
	FILE *stderr_stream;
	int num_columns;
	int num_key_bindings;
	char empty_line[1000];
	char key_sequence[32];
	unsigned key_sequence_length;
	struct task *task;
	struct btr_node *stdout_btrn;
	bool last_write_was_status;
	bool input_eof;
	bool caught_sigint;
	bool caught_sigterm;
	Keymap standard_km;
	Keymap bare_km;
	int fd_flags[2];
};
static struct i9e_private i9e_private, *i9ep = &i9e_private;

/**
 * Return the error state of the i9e task.
 *
 * This is mainly useful for other tasks to tell whether the i9e task is still
 * running.
 *
 * \return A negative return value of zero means the i9e task terminated. Only
 * in this case it is safe to call i9e_close().
 */
int i9e_get_error(void)
{
	return task_status(i9ep->task);
}

static bool is_prefix(const char *partial, const char *full, size_t len)
{
	if (len == 0)
		len = strlen(partial);
	return !strncmp(partial, full, len);
}

/*
 * Generator function for command completion. STATE lets us know whether
 * to start from scratch; without any state (i.e. STATE == 0), then we
 * start at the top of the list.
 */
static char *command_generator(const char *text, int state)
{
	static int list_index, len;
	const char *name;
	struct i9e_client_info *ici = i9ep->ici;

	rl_attempted_completion_over = 1; /* disable filename completion */
	/*
	 * If this is a new word to complete, initialize now. This includes
	 * saving the length of TEXT for efficiency, and initializing the index
	 * variable to 0.
	 */
	if (state == 0) {
		list_index = 0;
		len = strlen(text);
	}
	/* Return the next name which partially matches from the command list. */
	while ((name = ici->completers[list_index].name)) {
		list_index++;
		if (is_prefix(text, name, len))
			return para_strdup(name);
	}
	return NULL; /* no names matched */
}

static void reset_completion_result(struct i9e_completion_result *cr)
{
	cr->dont_append_space = false;
	cr->filename_completion_desired = false;
	cr->matches = NULL;
}

static void create_matches(struct i9e_completion_info *ci,
		const struct i9e_completer *completers,
		struct i9e_completion_result *cr)
{
	int i, ret;

	reset_completion_result(cr);

	ret = create_argv(ci->buffer, " ", &ci->argv);
	if (ret < 0 || !ci->argv[0])
		return;

	ci->argc = ret;
	ci->word_num = compute_word_num(ci->buffer, " ", ci->point);
	for (i = 0; completers[i].name; i++) {
		if (strcmp(completers[i].name, ci->argv[0]) != 0)
			continue;
		completers[i].completer(ci, cr);
		break;
	}
	PARA_DEBUG_LOG("current word: %d (%s)\n", ci->word_num,
		ci->argv[ci->word_num]);
	if (cr->matches)
		for (i = 0; cr->matches[i]; i++)
			PARA_DEBUG_LOG("match %d: %s\n", i, cr->matches[i]);
}

static char *completion_generator(const char *word, int state)
{
	static int list_index;
	static char **argv, **matches;
	const struct i9e_completer *completers = i9ep->ici->completers;
	struct i9e_completion_info ci = {
		.word = (char *)word,
		.point = rl_point,
		.buffer = rl_line_buffer,
	};
	struct i9e_completion_result cr = {.matches = NULL};

	if (state != 0)
		goto out;
	/* clean up previous matches and set defaults */
	free(matches);
	matches = NULL;
	free_argv(argv);
	argv = NULL;
	list_index = 0;
	rl_completion_append_character = ' ';
	rl_completion_suppress_append = false;
	rl_attempted_completion_over = true;

	create_matches(&ci, completers, &cr);

	matches = cr.matches;
	argv = ci.argv;
	rl_completion_suppress_append = cr.dont_append_space;
	rl_attempted_completion_over = !cr.filename_completion_desired;
out:
	if (!matches)
		return NULL;
	return matches[list_index++];
}

/**
 * Prepare writing to stdout.
 *
 * \param producer The buffer tree node which produces output.
 *
 * The i9e subsystem maintains a buffer tree node which may be attached to
 * another node which generates output (a "producer"). When attached, the i9e
 * buffer tree node copies the buffers generated by the producer to stdout.
 * This function attaches the i9e input queue to an output queue of producer.
 */
void i9e_attach_to_stdout(struct btr_node *producer)
{
	btr_remove_node(&i9ep->stdout_btrn);
	i9ep->stdout_btrn = btr_new_node(&(struct btr_node_description)
		EMBRACE(.name = "interactive_stdout", .parent = producer));
	rl_set_keymap(i9ep->bare_km);
}

static void wipe_bottom_line(void)
{
	fprintf(i9ep->stderr_stream, "\r%s\r", i9ep->empty_line);
}

#ifndef RL_FREE_KEYMAP_DECLARED
/**
 * Free all storage associated with a keymap.
 *
 * This function is not declared in the readline headers although the symbol is
 * exported and the function is documented in the readline info file. So we
 * have to declare it here.
 *
 * \param keymap The keymap to deallocate.
 */
void rl_free_keymap(Keymap keymap);
#endif

/**
 * Reset the terminal and save the in-memory command line history.
 *
 * This should be called before the caller exits.
 */
void i9e_close(void)
{
	char *hf = i9ep->ici->history_file;

	rl_free_keymap(i9ep->bare_km);
	rl_callback_handler_remove();
	if (hf)
		write_history(hf);
	clear_history();
	wipe_bottom_line();
	fcntl(i9ep->ici->fds[0], F_SETFL, i9ep->fd_flags[0]);
	fcntl(i9ep->ici->fds[1], F_SETFL, i9ep->fd_flags[1]);
}

static void clear_bottom_line(void)
{
	int point;
	char *text;

	if (rl_point == 0 && rl_end == 0)
		return wipe_bottom_line();
	/*
	 * We might have a multi-line input that needs to be wiped here, so the
	 * simple printf("\r<space>\r") is insufficient. To workaround this, we
	 * remove the whole line, redisplay and restore the killed text.
	 */
	point = rl_point;
	text = rl_copy_text(0, rl_end);
	rl_kill_full_line(0, 0);
	rl_redisplay();
	wipe_bottom_line(); /* wipe out the prompt */
	rl_insert_text(text);
	free(text);
	rl_point = point;
}

static void i9e_line_handler(char *line)
{
	int ret;
	struct btr_node *dummy;

	if (!line) {
		i9ep->input_eof = true;
		return;
	}
	if (!*line)
		goto free_line;
	rl_set_prompt("");
	dummy = btr_new_node(&(struct btr_node_description)
		EMBRACE(.name = "dummy line handler"));
	i9e_attach_to_stdout(dummy);
	ret = i9ep->ici->line_handler(line);
	if (ret < 0)
		PARA_WARNING_LOG("%s\n", para_strerror(-ret));
	add_history(line);
	btr_remove_node(&dummy);
free_line:
	free(line);
}

static int i9e_post_monitor(__a_unused struct sched *s, __a_unused void *context)
{
	int ret;
	struct i9e_client_info *ici = i9ep->ici;
	char *buf;
	size_t sz, consumed = 0;

	ret = -E_EOF;
	if (i9ep->input_eof)
		goto rm_btrn;
	ret = -E_I9E_TERM_RQ;
	if (i9ep->caught_sigterm)
		goto rm_btrn;
	ret = 0;
	if (i9ep->caught_sigint)
		goto rm_btrn;
	while (read_ok(i9ep->ici->fds[0]) > 0) {
		if (i9ep->stdout_btrn) {
			while (i9ep->key_sequence_length < sizeof(i9ep->key_sequence) - 1) {
				buf = i9ep->key_sequence + i9ep->key_sequence_length;
				ret = read(i9ep->ici->fds[0], buf, 1);
				if (ret < 0) {
					ret = -ERRNO_TO_PARA_ERROR(errno);
					goto rm_btrn;
				}
				if (ret == 0) {
					ret = -E_EOF;
					goto rm_btrn;
				}
				buf[1] = '\0';
				i9ep->key_sequence_length++;
				rl_stuff_char((int)(unsigned char)*buf);
				rl_callback_read_char();
				if (read_ok(i9ep->ici->fds[0]) <= 0)
					break;
			}
			i9ep->key_sequence_length = 0;
		} else
			rl_callback_read_char();
		ret = 0;
	}
	if (!i9ep->stdout_btrn)
		goto out;
	ret = btr_node_status(i9ep->stdout_btrn, 0, BTR_NT_LEAF);
	if (ret < 0) {
		ret = 0;
		goto rm_btrn;
	}
	if (ret == 0)
		goto out;
again:
	sz = btr_next_buffer(i9ep->stdout_btrn, &buf);
	if (sz == 0)
		goto out;
	if (i9ep->last_write_was_status)
		fprintf(i9ep->stderr_stream, "\n");
	i9ep->last_write_was_status = false;
	ret = xwrite(ici->fds[1], buf, sz);
	if (ret < 0)
		goto rm_btrn;
	btr_consume(i9ep->stdout_btrn, ret);
	consumed += ret;
	if (ret == sz && consumed < 10000)
		goto again;
	goto out;
rm_btrn:
	if (i9ep->stdout_btrn) {
		wipe_bottom_line();
		btr_remove_node(&i9ep->stdout_btrn);
		rl_set_keymap(i9ep->standard_km);
		rl_set_prompt(i9ep->ici->prompt);
		rl_redisplay();
	}
	if (ret < 0)
		wipe_bottom_line();
out:
	i9ep->caught_sigint = false;
	return ret;
}

static void i9e_pre_monitor(struct sched *s, __a_unused void *context)
{
	int ret;

	if (i9ep->input_eof || i9ep->caught_sigint || i9ep->caught_sigterm) {
		sched_min_delay(s);
		return;
	}
	if (i9ep->stdout_btrn) {
		ret = btr_node_status(i9ep->stdout_btrn, 0, BTR_NT_LEAF);
		if (ret < 0) {
			sched_min_delay(s);
			return;
		}
		if (ret > 0)
			sched_monitor_writefd(i9ep->ici->fds[1], s);
	}
	/*
	 * fd[0] might have been reset to blocking mode if our job was moved to
	 * the background due to CTRL-Z or SIGSTOP, so set the fd back to
	 * nonblocking mode.
	 */
	ret = mark_fd_nonblocking(i9ep->ici->fds[0]);
	if (ret < 0)
		PARA_WARNING_LOG("set to nonblock failed: (fd0 %d, %s)\n",
			i9ep->ici->fds[0], para_strerror(-ret));
	sched_monitor_readfd(i9ep->ici->fds[0], s);
}

static void update_winsize(void)
{
	struct winsize w;
	int ret = ioctl(i9ep->ici->fds[2], TIOCGWINSZ, (char *)&w);

	if (ret >= 0) {
		assert(w.ws_col < sizeof(i9ep->empty_line));
		i9ep->num_columns = w.ws_col;
	} else
		i9ep->num_columns = 80;

	memset(i9ep->empty_line, ' ', i9ep->num_columns);
	i9ep->empty_line[i9ep->num_columns] = '\0';
}

static int dispatch_key(__a_unused int count, __a_unused int key)
{
	int i, ret;

again:
	if (i9ep->key_sequence_length == 0)
		return 0;
	for (i = i9ep->num_key_bindings - 1; i >= 0; i--) {
		if (strcmp(i9ep->key_sequence, i9ep->ici->bound_keyseqs[i]))
			continue;
		i9ep->key_sequence[0] = '\0';
		i9ep->key_sequence_length = 0;
		ret = i9ep->ici->key_handler(i);
		return ret < 0? ret : 0;
	}
	PARA_WARNING_LOG("ignoring key %d\n", i9ep->key_sequence[0]);
	/*
	 * We received an undefined key sequence. Throw away the first byte,
	 * and try to parse the remainder.
	 */
	memmove(i9ep->key_sequence, i9ep->key_sequence + 1,
		i9ep->key_sequence_length); /* move also terminating zero byte */
	i9ep->key_sequence_length--;
	goto again;
}

/*
 * Calls either command_generator() or completion_generator() via
 * rl_completion_matches(). May set rl_attempted_completion_over to instruct
 * readline to not perform its default completion even if no matches are
 * returned.
 */
static char **attempt_completion(const char *text, int start, __a_unused int end)
{
	struct i9e_client_info *ici = i9ep->ici;

	if (!ici->completers)
		return NULL;
	/* Complete on command names if this is the first word in the line. */
	if (start == 0)
		return rl_completion_matches(text, command_generator);
	return rl_completion_matches(text, completion_generator);
}

/**
 * Register the i9e task and initialize readline.
 *
 * \param ici The i9e configuration parameters set by the caller.
 * \param s The scheduler instance to add the i9e task to.
 *
 * The i9e client info structure must be allocated and initialized by the
 * caller before this function is called.
 *
 * \return Standard.
 */
int i9e_open(struct i9e_client_info *ici, struct sched *s)
{
	int ret;

	memset(i9ep, 0, sizeof(struct i9e_private));
	if (!isatty(ici->fds[0]))
		return -E_I9E_SETUPTERM;
	ret = fcntl(ici->fds[0], F_GETFL);
	if (ret < 0)
		return -E_I9E_SETUPTERM;
	i9ep->fd_flags[0] = ret;
	ret = fcntl(ici->fds[1], F_GETFL);
	if (ret < 0)
		return -E_I9E_SETUPTERM;
	i9ep->fd_flags[1] = ret;
	ret = mark_fd_nonblocking(ici->fds[0]);
	if (ret < 0)
		return ret;
	ret = mark_fd_nonblocking(ici->fds[1]);
	if (ret < 0)
		return ret;
	i9ep->task = task_register(&(struct task_info) {
		.name = "i9e",
		.pre_monitor = i9e_pre_monitor,
		.post_monitor = i9e_post_monitor,
		.context = i9ep,
	}, s);

	rl_readline_name = "para_i9e";
	rl_basic_word_break_characters = " ";
	rl_attempted_completion_function = attempt_completion;
	i9ep->ici = ici;
	i9ep->stderr_stream = fdopen(ici->fds[2], "w");
	setvbuf(i9ep->stderr_stream, NULL, _IONBF, 0);

	i9ep->standard_km = rl_get_keymap();
	i9ep->bare_km = rl_make_bare_keymap();
	if (ici->bound_keyseqs) {
		char *seq;
		int i;
		/* bind each key sequence to our dispatcher */
		for (i = 0; (seq = ici->bound_keyseqs[i]); i++) {
			if (strlen(seq) >= sizeof(i9ep->key_sequence) - 1) {
				PARA_WARNING_LOG("ignoring overlong key %s\n",
					seq);
				continue;
			}
			if (rl_bind_keyseq_in_map(seq,
					dispatch_key, i9ep->bare_km) != 0)
				PARA_WARNING_LOG("could not bind #%d: %s\n", i, seq);
		}
		i9ep->num_key_bindings = i;
	}
	if (ici->history_file)
		read_history(ici->history_file);
	update_winsize();
	if (ici->producer) {
		rl_callback_handler_install("", i9e_line_handler);
		i9e_attach_to_stdout(ici->producer);
	} else
		rl_callback_handler_install(i9ep->ici->prompt, i9e_line_handler);
	return 1;
}

static void reset_line_state(void)
{
	if (i9ep->stdout_btrn)
		return;
	rl_on_new_line();
	rl_reset_line_state();
	rl_forced_update_display();
}

/**
 * The log function of the i9e subsystem.
 *
 * \param ll Severity log level.
 * \param fmt Printf-like format string.
 *
 * This clears the bottom line of the terminal if necessary and writes the
 * formatted string to fd[2], where fd[] is the array provided earlier in
 * \ref i9e_open().
 */
__printf_2_3 void i9e_log(int ll, const char* fmt,...)
{
	va_list argp;

	if (ll < i9ep->ici->loglevel)
		return;
	clear_bottom_line();
	va_start(argp, fmt);
	vfprintf(i9ep->stderr_stream, fmt, argp);
	va_end(argp);
	reset_line_state();
	i9ep->last_write_was_status = false;
}

/**
 * Print the current status to stderr.
 *
 * \param buf The text to print.
 * \param len The number of bytes in the buffer.
 *
 * This clears the bottom line, moves to the beginning of the line and prints
 * the given text. If the length of this text exceeds the width of the
 * terminal, the text is shortened by leaving out a part in the middle.
 */
void i9e_print_status_bar(char *buf, unsigned len)
{
	size_t x = i9ep->num_columns, y = (x - 4) / 2;

	assert(x >= 6);
	if (len > x) {
		buf[y] = '\0';
		fprintf(i9ep->stderr_stream, "\r%s", buf);
		fprintf(i9ep->stderr_stream, " .. ");
		fprintf(i9ep->stderr_stream, "%s", buf + len - y);
	} else {
		char scratch[1000];

		y = x - len;
		scratch[0] = '\r';
		strcpy(scratch + 1, buf);
		memset(scratch + 1 + len, ' ', y);
		scratch[1 + len + y] = '\r';
		scratch[2 + len + y] = '\0';
		fprintf(i9ep->stderr_stream, "\r%s", scratch);
	}
	i9ep->last_write_was_status = true;
}

/**
 * Tell i9e that the caller received a signal.
 *
 * \param sig_num The number of the signal received.
 */
void i9e_signal_dispatch(int sig_num)
{
	if (sig_num == SIGWINCH)
		return update_winsize();
	if (sig_num == SIGINT) {
		fprintf(i9ep->stderr_stream, "\n");
		rl_replace_line ("", false /* clear_undo */);
		reset_line_state();
		i9ep->caught_sigint = true;
	}
	if (sig_num == SIGTERM)
		i9ep->caught_sigterm = true;
}

/**
 * Wrapper for poll(2) which handles EINTR and returns paraslash error codes.
 *
 * \param fds See poll(2).
 * \param nfds See poll(2).
 * \param timeout See poll(2).
 *
 * \return See poll(2).
 *
 * The only difference between this function and \ref xpoll() is that \ref
 * i9e_poll() returns zero if the system call was interrupted while xpoll()
 * restarts the system call in this case.
 */
int i9e_poll(struct pollfd *fds, nfds_t nfds, int timeout)
{
	int ret = poll(fds, nfds, timeout);
	if (ret < 0) {
		if (errno == EINTR)
			ret = 0;
		else
			ret = -ERRNO_TO_PARA_ERROR(errno);
	}
	return ret;
}

/**
 * Return the possible completions for a given word.
 *
 * \param word The word to complete.
 * \param string_list All possible words in this context.
 * \param result String list is returned here.
 *
 * This function never fails. If no completion was found, a string list of
 * length zero is returned. In any case, the result must be freed by the caller
 * using \ref free_argv().
 *
 * This function is independent of readline and may be called before
 * i9e_open().
 *
 * \return The number of possible completions.
 */
int i9e_extract_completions(const char *word, char * const *string_list,
		char ***result)
{
	char **matches = alloc(sizeof(char *));
	int match_count = 0, matches_len = 1;
	int len = strlen(word);

	for (char * const *p = string_list; *p; p++) {
		if (!is_prefix(word, *p, len))
			continue;
		match_count++;
		if (match_count >= matches_len) {
			matches_len *= 2;
			matches = arr_realloc(matches, matches_len,
				sizeof(char *));
		}
		matches[match_count - 1] = para_strdup(*p);
	}
	matches[match_count] = NULL;
	*result = matches;
	return match_count;
}

/**
 * Return the list of partially matching words.
 *
 * \param word The command to complete.
 * \param completers The array containing all command names.
 *
 * This is similar to \ref i9e_extract_completions(), but completes on the
 * command names in the completers array.
 *
 * \return See \ref i9e_extract_completions().
 */
char **i9e_complete_commands(const char *word, const struct i9e_completer *completers)
{
	char **matches;
	const char *cmd;
	int i, match_count, len = strlen(word);

	/*
	 * In contrast to completing against an arbitrary string list, here we
	 * know all possible completions and expect that there will not be many
	 * of them. So it should be OK to iterate twice over all commands which
	 * simplifies the code a bit.
	 */
	for (i = 0, match_count = 0; (cmd = completers[i].name); i++) {
		if (is_prefix(word, cmd, len))
			match_count++;
	}
	matches = arr_alloc(match_count + 1, sizeof(*matches));
	for (i = 0, match_count = 0; (cmd = completers[i].name); i++)
		if (is_prefix(word, cmd, len))
			matches[match_count++] = para_strdup(cmd);
	matches[match_count] = NULL;
	return matches;
}

/**
 * Complete according to the given options.
 *
 * \param opts All available options.
 * \param ci Information which was passed to the completer.
 * \param cr Result pointer.
 *
 * This helper returns the possible tab-completions of an option. The
 * array of all possible options is passed as the first argument. Flags,
 * i.e. options without an argument, are expected as strings such as "-X"
 * while options which require an argument are expected to be of the form
 * "-X=", i.e., contain a trailing "=".
 *
 * If the word can be uniquely completed to a flag option, an additional space
 * character is appended to the output. For non-flag options no space character
 * is appended.
 */
void i9e_complete_option(char * const *opts,
		struct i9e_completion_info *ci, struct i9e_completion_result *cr)
{
	int num_matches;

	num_matches = i9e_extract_completions(ci->word, opts, &cr->matches);
	if (num_matches == 1) {
		char *opt = cr->matches[0];
		char c = opt[strlen(opt) - 1];
		if (c == '=')
			cr->dont_append_space = true;
	}
}

/**
 * Return the number of non-option arguments encountered so far.
 *
 * This counts the number of arguments up to the current word which are neither
 * options nor arguments to options.
 *
 * \param opts NULL terminated array of short and long options, may be NULL.
 * \param ci Provided by i9e in completion context.
 *
 * For convenience, NULL can be passed as the option array pointer to
 * indicate that the subcommand has no options. In this case the function
 * returns the word number stored in the completion info structure.
 *
 * \return Zero means that the cursor is positioned at the first non-option
 * argument.
 */
unsigned i9e_get_nonopt_argnum(char * const *opts,
		struct i9e_completion_info *ci)
{
	bool prev_is_option_with_arg = false;
	unsigned num_non_option_args = 0;

	if (!opts)
		return ci->word_num;
	for (unsigned n = 0; n < ci->word_num; n++) {
		unsigned m;
		const char *arg = ci->argv[n];

		if (prev_is_option_with_arg) {
			prev_is_option_with_arg = false;
			continue;
		}
		if (!strcmp(arg, "--")) {
			prev_is_option_with_arg = false;
			continue;
		}
		if (arg[0] != '-') {
			num_non_option_args++;
			prev_is_option_with_arg = false;
			continue;
		}
		for (m = 0; opts[m]; m++) {
			const char *opt = opts[m];
			size_t len = strlen(opt);
			if (opt[len - 1] != '=') {
				if (strcmp(opt, arg))
					continue;
				/* opt without arg */
				prev_is_option_with_arg = false;
				break;
			}
			if (strncmp(opt, arg, len - 1))
				continue;
			if (arg[len - 1] == '\0') { /* --opt-with-arg */
				prev_is_option_with_arg = true;
				break;
			}
			if (arg[len - 1] == '=') { /* --opt-with-arg= */
				prev_is_option_with_arg = false;
				break;
			}
			/* --opt-with-arg-garbage, no match */
		}
		if (!opts[m]) { /* no match */
			num_non_option_args++;
			prev_is_option_with_arg = false;
		}
	}
	return num_non_option_args;
}

/**
 * Find out whether the current word is an argument to an option.
 *
 * This handles both the --opt=arg and --opt arg syntax to specify option
 * arguments.
 *
 * \param opts NULL-terminated array of short and long options.
 * \param ci Provided by i9e in completion context.
 *
 * \return If the current word is an option argument, the function returns
 * the index into the option array which corresponds to the matching option.
 * Otherwise, -1 is returned.
 */
int i9e_cword_is_option_arg(char * const *opts, struct i9e_completion_info *ci)
{
	const char *prev;

	/* Return -1 if cursor is at first word or if we've seen "--". */
	if (ci->word_num == 0)
		return -1;
	for (unsigned n = 0; n < ci->word_num; n++)
		if (!strcmp(ci->argv[n], "--"))
			return -1;
	prev = ci->argv[ci->word_num - 1];
	for (unsigned n = 0; opts[n]; n++) {
		const char *opt = opts[n];
		size_t len = strlen(opt);
		assert(len > 0);
		if (opt[len - 1] != '=')
			continue;
		if (!strncmp(opt, ci->word, len))
			return n; /* --opt=arg */
		if (!strncmp(opt, prev, len - 1) && prev[len - 1] == '\0')
			return n; /* --opt arg */
	}
	return -1;
}

/**
 * Print possible completions to stdout.
 *
 * \param completers The array of completion functions.
 *
 * At the end of the output a line starting with "-o=", followed by the
 * (possibly empty) list of completion options is printed. Currently, the only
 * two completion options are "nospace" and "filenames". The former indicates
 * that no space should be appended even for a unique match while the latter
 * indicates that usual filename completion should be performed in addition to
 * the previously printed options.
 *
 * \return Standard.
 */
int i9e_print_completions(const struct i9e_completer *completers)
{
	struct i9e_completion_result cr;
	struct i9e_completion_info ci;
	char *buf;
	const char *end, *p;
	int i, n, ret;

	reset_completion_result(&cr);
	buf = getenv("COMP_POINT");
	ci.point = buf? atoi(buf) : 0;
	ci.buffer = para_strdup(getenv("COMP_LINE"));

	ci.argc = create_argv(ci.buffer, " ", &ci.argv);
	ci.word_num = compute_word_num(ci.buffer, " ", ci.point);

	/* determine the current word to complete */
	end = ci.buffer + ci.point;

	if (*end == ' ') {
		if (ci.point == 0 || ci.buffer[ci.point - 1] == ' ') {
			ci.word = para_strdup(NULL);
			goto create_matches;
		} else /* The cursor is positioned right after a word */
			end--;
	}
	for (p = end; p > ci.buffer && *p != ' '; p--)
		; /* nothing */
	if (*p == ' ')
		p++;
	n = end - p + 1;
	ci.word = alloc(n + 1);
	strncpy(ci.word, p, n);
	ci.word[n] = '\0';
create_matches:
	PARA_DEBUG_LOG("line: %s, point: %d (%c), wordnum: %d, word: %s\n",
		ci.buffer, ci.point, ci.buffer[ci.point], ci.word_num, ci.word);
	if (ci.word_num == 0)
		cr.matches = i9e_complete_commands(ci.word, completers);
	else
		create_matches(&ci, completers, &cr);
	ret = 0;
	if (cr.matches && cr.matches[0]) {
		for (i = 0; cr.matches[i]; i++)
			printf("%s\n", cr.matches[i]);
		ret = 1;
	}
	printf("-o=");
	if (cr.dont_append_space)
		printf("nospace");
	if (cr.filename_completion_desired)
		printf(",filenames");
	printf("\n");
	free_argv(cr.matches);
	free_argv(ci.argv);
	free(ci.buffer);
	free(ci.word);
	return ret;
}

/**
 * Complete on severity strings.
 *
 * \param ci See struct \ref i9e_completer.
 * \param cr See struct \ref i9e_completer.
 *
 * This is used by para_client and para_audioc which need the same completion
 * primitive for the ll server/audiod command. Both define their own completer
 * which is implemented as a trivial wrapper that calls this function.
 */
void i9e_ll_completer(struct i9e_completion_info *ci,
		struct i9e_completion_result *cr)
{
	char * const sev[] = {SEVERITIES, NULL};

	if (ci->word_num != 1) {
		cr->matches = NULL;
		return;
	}
	i9e_extract_completions(ci->word, sev, &cr->matches);
}