neetdraw/neetdraw.c

/*
 * neetdraw.c: terminal drawing application with multiplayer support
 *
 * Copyright (c) 2014 - 2023, Přemysl Eric Janouch <p@janouch.name>
 *
 * Permission to use, copy, modify, and/or distribute this software for any
 * purpose with or without fee is hereby granted.
 *
 * THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
 * WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
 * MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY
 * SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
 * WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN ACTION
 * OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF OR IN
 * CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.
 *
 */

#include "config.h"
#include "liberty/liberty.c"
#include "termo.h"

#include <locale.h>
#include <termios.h>
#ifndef TIOCGWINSZ
#include <sys/ioctl.h>
#endif  // ! TIOCGWINSZ

#include <ev.h>
#include <curses.h>

#define PALETTE_WIDTH       9           ///< Width of the palette
#define TOP_BAR_CUTOFF      3           ///< Height of the top bar

#define BITMAP_BLOCK_SIZE  50           ///< Step for extending bitmap size

#define PROTOCOL_VERSION    1           ///< Network protocol version

enum
{
	MESSAGE_HELLO,                      ///< Server/client hello
	MESSAGE_GET_BITMAP,                 ///< Request bitmap data
	MESSAGE_PUT_POINT,                  ///< Request to place a point

	MESSAGE_COUNT                       ///< Total number of messages
};

enum network_mode
{
	NETWORK_MODE_STANDALONE,            ///< No networking taking place
	NETWORK_MODE_SERVER,                ///< We're the server
	NETWORK_MODE_CLIENT                 ///< We're a client
};

struct client
{
	LIST_HEADER (struct client)

	int fd;                             ///< Client connection
	ev_io read_watcher;                 ///< Client readability watcher
	ev_io write_watcher;                ///< Client writability watcher
	struct msg_reader msg_reader;       ///< Client message reader
	struct write_queue write_queue;     ///< Write queue
};

#define BITMAP_PIXEL(app, x, y) (app)->bitmap[(y) * (app)->bitmap_w + (x)]

struct app_context
{
	termo_t *tk;                        ///< Termo instance

	ev_io tty_watcher;                  ///< TTY input watcher
	ev_timer tty_timer;                 ///< TTY timeout timer
	ev_signal winch_watcher;            ///< SIGWINCH watcher

	enum network_mode mode;             ///< Networking mode

	// Client:
	int server_fd;                      ///< Server connection
	ev_io server_read_watcher;          ///< Server readability watcher
	ev_io server_write_watcher;         ///< Server writability watcher
	struct msg_reader msg_reader;       ///< Server message reader
	struct write_queue write_queue;     ///< Server write queue

	bool no_wait;                       ///< Don't wait for server confirmations

	// Server:
	int listen_fd;                      ///< Listening FD
	ev_io listen_watcher;               ///< Listening FD watcher
	struct client *clients;             ///< Client connections

	chtype palette[2 * 9];              ///< Attribute palette

	uint8_t *bitmap;                    ///< Canvas data for drawing
	int bitmap_x;                       ///< X coord. of left top bitmap corner
	int bitmap_y;                       ///< Y coord. of left top bitmap corner
	size_t bitmap_w;                    ///< Canvas data width
	size_t bitmap_h;                    ///< Canvas data height

	int center_x;                       ///< X coordinate at center
	int center_y;                       ///< Y coordinate at center

	// These two are computed from `center_x' and `center_y':

	int corner_x;                       ///< X coordinate of LT screen corner
	int corner_y;                       ///< Y coordinate of LT screen corner

	int move_saved_x;                   ///< Saved X coord. for moving
	int move_saved_y;                   ///< Saved Y coord. for moving

	uint8_t current_color_left;         ///< Left mouse button color
	uint8_t current_color_right;        ///< Right mouse button color
};

static void remove_client (struct app_context *app, struct client *client);
static void on_server_disconnected (struct app_context *app);

static void
app_init (struct app_context *self)
{
	memset (self, 0, sizeof *self);
	self->server_fd = -1;
	self->listen_fd = -1;
	self->msg_reader = msg_reader_make ();
	self->write_queue = write_queue_make ();
}

static void
app_free (struct app_context *self)
{
	if (self->tk)
		termo_destroy (self->tk);
	while (self->clients)
		// XXX: we probably shouldn't do this from here
		remove_client (self, self->clients);

	free (self->bitmap);
	msg_reader_free (&self->msg_reader);
	write_queue_free (&self->write_queue);
}

// --- Server-client messaging -------------------------------------------------

static bool
read_loop (EV_P_ ev_io *watcher,
	bool (*cb) (EV_P_ ev_io *, const void *, ssize_t))
{
	char buf[8192];
	while (true)
	{
		ssize_t n_read = recv (watcher->fd, buf, sizeof buf, 0);
		if (n_read < 0)
		{
			if (errno == EAGAIN)
				break;
			if (errno == EINTR)
				continue;
		}
		if (n_read <= 0 || !cb (EV_A_ watcher, buf, n_read))
			return false;
	}
	return true;
}

static bool
flush_queue (struct write_queue *queue, ev_io *watcher)
{
	struct iovec vec[queue->len], *vec_iter = vec;
	for (struct write_req *iter = queue->head; iter; iter = iter->next)
		*vec_iter++ = iter->data;

	ssize_t written;
again:
	written = writev (watcher->fd, vec, N_ELEMENTS (vec));
	if (written < 0)
	{
		if (errno == EAGAIN)
			goto skip;
		if (errno == EINTR)
			goto again;
		return false;
	}

	write_queue_processed (queue, written);

skip:
	if (write_queue_is_empty (queue))
		ev_io_stop (EV_DEFAULT_ watcher);
	else
		ev_io_start (EV_DEFAULT_ watcher);
	return true;
}

static struct write_req *
flush_writer (struct msg_writer *writer)
{
	struct write_req *req = xcalloc (1, sizeof *req);
	req->data.iov_base = msg_writer_flush (writer, &req->data.iov_len);
	return req;
}

static void
flush_writer_to_client (struct msg_writer *writer, struct client *client)
{
	write_queue_add (&client->write_queue, flush_writer (writer));
	ev_io_start (EV_DEFAULT_ &client->write_watcher);
}

static void
flush_writer_to_server (struct msg_writer *writer, struct app_context *app)
{
	write_queue_add (&app->write_queue, flush_writer (writer));
	ev_io_start (EV_DEFAULT_ &app->server_write_watcher);
}

static void
send_draw_point_response (struct client *client, int x, int y, uint8_t color)
{
	struct msg_writer writer = msg_writer_make ();
	str_pack_u8 (&writer.buf, MESSAGE_PUT_POINT);
	str_pack_i32 (&writer.buf, x);
	str_pack_i32 (&writer.buf, y);
	str_pack_u8 (&writer.buf, color);

	flush_writer_to_client (&writer, client);
}

static void
send_draw_point_request (struct app_context *app, int x, int y, uint8_t color)
{
	struct msg_writer writer = msg_writer_make ();
	str_pack_u8 (&writer.buf, MESSAGE_PUT_POINT);
	str_pack_i32 (&writer.buf, x);
	str_pack_i32 (&writer.buf, y);
	str_pack_u8 (&writer.buf, color);

	flush_writer_to_server (&writer, app);
}

static void
send_hello_request (struct app_context *app)
{
	struct msg_writer writer = msg_writer_make ();
	str_pack_u8 (&writer.buf, MESSAGE_HELLO);
	str_pack_u8 (&writer.buf, PROTOCOL_VERSION);

	flush_writer_to_server (&writer, app);
}

static void
send_hello_response (struct client *client)
{
	struct msg_writer writer = msg_writer_make ();
	str_pack_u8 (&writer.buf, MESSAGE_HELLO);
	str_pack_u8 (&writer.buf, PROTOCOL_VERSION);

	flush_writer_to_client (&writer, client);
}

static void
send_get_bitmap_request (struct app_context *app)
{
	struct msg_writer writer = msg_writer_make ();
	str_pack_u8 (&writer.buf, MESSAGE_GET_BITMAP);

	flush_writer_to_server (&writer, app);
}

static void
send_get_bitmap_response (struct client *client, struct app_context *app)
{
	struct msg_writer writer = msg_writer_make ();
	str_pack_u8 (&writer.buf, MESSAGE_GET_BITMAP);
	str_pack_i32 (&writer.buf, app->bitmap_x);
	str_pack_i32 (&writer.buf, app->bitmap_y);
	str_pack_u64 (&writer.buf, app->bitmap_w);
	str_pack_u64 (&writer.buf, app->bitmap_h);

	// Simple RLE compression
	size_t size = app->bitmap_w * app->bitmap_h;
	uint8_t last_value = 0, count = 0;
	for (size_t i = 0; i < size; i++)
	{
		uint8_t value = app->bitmap[i];
		if ((count && value != last_value) || count == 0xFF)
		{
			str_pack_u8 (&writer.buf, count);
			str_pack_u8 (&writer.buf, last_value);
			count = 0;
		}
		count++;
		last_value = value;
	}
	if (count)
	{
		str_pack_u8 (&writer.buf, count);
		str_pack_u8 (&writer.buf, last_value);
	}

	flush_writer_to_client (&writer, client);
}

// --- Server-client messaging -------------------------------------------------

static void
display (const char *format, ...)
{
	va_list ap;

	mvwhline (stdscr, 0, 0, A_REVERSE, COLS);
	attron (A_REVERSE);

	va_start (ap, format);
	vw_printw (stdscr, format, ap);
	va_end (ap);

	attroff (A_REVERSE);
	refresh ();
}

static void
init_palette (struct app_context *app)
{
	start_color ();

	// Also does init_pair (0, -1, -1);
	use_default_colors ();
	// Duplicate it for convenience.
	init_pair (9, -1, -1);

	// Add the basic 8 colors to the default pair.  Once normally, once
	// inverted to workaround VTE's inability to set a bright background.
	for (int i = 0; i < 8; i++)
	{
		init_pair (1  + i, COLOR_WHITE, COLOR_BLACK + i);
		init_pair (10 + i, COLOR_BLACK + i, COLOR_WHITE);
	}

	// Initialize the palette of characters with attributes
	for (int i = 0; i < PALETTE_WIDTH; i++)
	{
		app->palette[i]     = ' ' | COLOR_PAIR (i);
		app->palette[i + 9] = ' ' | COLOR_PAIR (i + 9) | A_REVERSE | A_BOLD;
	}

	// This usually creates a solid black or white.
	app->current_color_left = app->current_color_right = 9;
}

static void
update_canvas_for_screen (struct app_context *app)
{
	app->corner_x = app->center_x - COLS / 2;
	app->corner_y = app->center_y - (LINES - TOP_BAR_CUTOFF) / 2;
}

static void
redraw (struct app_context *app)
{
	int i;

	mvwhline (stdscr, 1, 0, A_REVERSE, COLS);
	mvwhline (stdscr, 2, 0, A_REVERSE, COLS);

	for (i = 0; i < COLS; i++)
	{
		int pair = (float) i / COLS * PALETTE_WIDTH;
		mvaddch (1, i, app->palette[pair]);
		mvaddch (2, i, app->palette[pair + PALETTE_WIDTH]);
	}

	display ("Choose a color from the palette and draw.  "
		"Press Escape or ^C to quit.");
	refresh ();
}

static bool
is_in_bitmap_data (struct app_context *app, int x, int y)
{
	return x >= app->bitmap_x
		&& y >= app->bitmap_y
		&& x <  app->bitmap_x + (int) app->bitmap_w
		&& y <  app->bitmap_y + (int) app->bitmap_h;
}

static void
redraw_canvas (struct app_context *app)
{
	int y = app->corner_y;
	for (int screen_y = TOP_BAR_CUTOFF; screen_y < LINES; screen_y++, y++)
	{
		move (screen_y, 0);

		int x = app->corner_x;
		for (int screen_x = 0; screen_x < COLS; screen_x++, x++)
		{
			uint8_t color = 0;
			if (is_in_bitmap_data (app, x, y))
				color = BITMAP_PIXEL (app,
					x - app->bitmap_x, y - app->bitmap_y);

			addch (app->palette[color]);
		}
	}
	refresh ();
}

static bool
is_visible (struct app_context *app, int x, int y)
{
	return x >= app->corner_x
		&& y >= app->corner_y
		&& x <  app->corner_x + COLS
		&& y <  app->corner_y + LINES - TOP_BAR_CUTOFF;
}

static void
make_place_for_point (struct app_context *app, int x, int y)
{
	if (is_in_bitmap_data (app, x, y))
		return;

	// Make sure the point has some place to go
	int new_bitmap_x = app->bitmap_x;
	int new_bitmap_y = app->bitmap_y;

	while (new_bitmap_x > x)
		new_bitmap_x -= BITMAP_BLOCK_SIZE;
	while (new_bitmap_y > y)
		new_bitmap_y -= BITMAP_BLOCK_SIZE;

	int new_bitmap_w = app->bitmap_w + (app->bitmap_x - new_bitmap_x);
	int new_bitmap_h = app->bitmap_h + (app->bitmap_y - new_bitmap_y);

	while (new_bitmap_x + new_bitmap_w <= x)
		new_bitmap_w += BITMAP_BLOCK_SIZE;
	while (new_bitmap_y + new_bitmap_h <= y)
		new_bitmap_h += BITMAP_BLOCK_SIZE;

	uint8_t *new_bitmap = xcalloc (new_bitmap_w * new_bitmap_h,
		sizeof *new_bitmap);
	if (app->bitmap)
	{
		// Copy data, assuming that the area can only get larger
		for (size_t data_y = 0; data_y < app->bitmap_h; data_y++)
			memcpy (new_bitmap
				+ ((data_y + app->bitmap_y - new_bitmap_y) * new_bitmap_w)
				+ (app->bitmap_x - new_bitmap_x),
				app->bitmap + (data_y * app->bitmap_w),
				app->bitmap_w * sizeof *new_bitmap);

		free (app->bitmap);
	}

	// Replace the bitmap with the reallocated version
	app->bitmap_x = new_bitmap_x;
	app->bitmap_y = new_bitmap_y;
	app->bitmap_w = new_bitmap_w;
	app->bitmap_h = new_bitmap_h;
	app->bitmap   = new_bitmap;
}

static void
draw_point_internal (struct app_context *app, int x, int y, uint8_t color)
{
	make_place_for_point (app, x, y);
	BITMAP_PIXEL (app, x - app->bitmap_x, y - app->bitmap_y) = color;

	if (is_visible (app, x, y))
	{
		int screen_x = x - app->corner_x;
		int screen_y = y - app->corner_y + TOP_BAR_CUTOFF;

		move (screen_y, screen_x);
		addch (app->palette[color]);
		refresh ();
	}
}

static void
draw_point (struct app_context *app, int x, int y, uint8_t color)
{
	if (app->mode == NETWORK_MODE_CLIENT)
	{
		send_draw_point_request (app, x, y, color);

		// We don't usually draw anything immediately in client mode,
		// instead we wait for confirmation from the server
		if (!app->no_wait)
			return;
	}

	draw_point_internal (app, x, y, color);

	// Broadcast clients about the event
	if (app->mode == NETWORK_MODE_SERVER)
		for (struct client *iter = app->clients; iter; iter = iter->next)
			send_draw_point_response (iter, x, y, color);
}

static void
draw_line (struct app_context *app, int x0, int x1, int y0, int y1,
	uint8_t color)
{
	// Integer version of Bresenham's line drawing algorithm,
	// loosely based on code from libcaca because screw math
	int dx = abs (x1 - x0);
	int dy = abs (y1 - y0);

	bool steep = dx < dy;
	if (steep)
	{
		// Flip the coordinate system on input
		int tmp;
		tmp = x0; x0 = y0; y0 = tmp;
		tmp = x1; x1 = y1; y1 = tmp;
		tmp = dx; dx = dy; dy = tmp;
	}

	int step_x = x0 > x1 ? -1 : 1;
	int step_y = y0 > y1 ? -1 : 1;

	int dpr = dy * 2;
	int delta = dpr - dx;
	int dpru = delta - dx;

	while (dx-- >= 0)
	{
		// Unflip the coordinate system on output
		if (steep)
			draw_point (app, y0, x0, color);
		else
			draw_point (app, x0, y0, color);

		x0 += step_x;
		if (delta > 0)
		{
			y0 += step_y;
			delta += dpru;
		}
		else
			delta += dpr;
	}
}

// --- Exports -----------------------------------------------------------------

static bool
is_data_row_empty (struct app_context *app, int y)
{
	for (size_t x = 0; x < app->bitmap_w; x++)
		if (app->bitmap[y * app->bitmap_w + x])
			return false;
	return true;
}

static bool
is_data_column_empty (struct app_context *app, int x)
{
	for (size_t y = 0; y < app->bitmap_h; y++)
		if (app->bitmap[y * app->bitmap_w + x])
			return false;
	return true;
}

static void
find_data_bounding_rect (struct app_context *app,
	size_t *x, size_t *y, size_t *w, size_t *h)
{
	size_t my_x = 0, my_y = 0;
	size_t my_w = app->bitmap_w, my_h = app->bitmap_h;
	size_t i;

	i = 0;
	while (i < app->bitmap_h && is_data_row_empty (app, i++))
		my_y++;

	// Special case: the whole canvas is empty
	if (my_y == my_h)
	{
		my_x = my_w;
		goto end;
	}

	i = app->bitmap_h;
	while (i-- && is_data_row_empty (app, i))
		my_h--;

	i = 0;
	while (i < app->bitmap_w && is_data_column_empty (app, i++))
		my_x++;

	i = app->bitmap_w;
	while (i-- && is_data_column_empty (app, i))
		my_w--;

end:
	*x = my_x;
	*y = my_y;
	*w = my_w - my_x;
	*h = my_h - my_y;
}

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

static const char *g_ansi_table[2 * PALETTE_WIDTH] =
{
	"\033[0m",
	"\033[0;40m",
	"\033[0;41m",
	"\033[0;42m",
	"\033[0;43m",
	"\033[0;44m",
	"\033[0;45m",
	"\033[0;46m",
	"\033[0;47m",
	"\033[0;1;7m",
	"\033[0;1;7;30m",
	"\033[0;1;7;31m",
	"\033[0;1;7;32m",
	"\033[0;1;7;33m",
	"\033[0;1;7;34m",
	"\033[0;1;7;35m",
	"\033[0;1;7;36m",
	"\033[0;1;7;37m",
};

static const char *
color_to_ansi (uint8_t color)
{
	if (color < N_ELEMENTS (g_ansi_table))
		return g_ansi_table[color];
	return NULL;
}

static void
export_ansi (struct app_context *app)
{
	FILE *fp = fopen ("export-ansi.asc", "wb");
	if (!fp)
	{
		display ("Error opening file for writing.");
		beep ();
		return;
	}

	size_t x, y, w, h;
	find_data_bounding_rect (app, &x, &y, &w, &h);

	for (size_t row = 0; row < h; row++)
	{
		const char *color = NULL;
		for (size_t column = 0; column < w; column++)
		{
			const char *new_color = color_to_ansi
				(BITMAP_PIXEL (app, x + column, y + row));
			if (color != new_color)
				fputs (new_color, fp);
			color = new_color;
			fputc (' ', fp);
		}

		// We need to reset the attributes
		fputs (color_to_ansi (0), fp);
		fputc ('\n', fp);
	}

	fclose (fp);
}

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

enum
{
	MIRC_NONE        = -1,

	MIRC_WHITE       = 0,
	MIRC_BLACK       = 1,
	MIRC_BLUE        = 2,
	MIRC_GREEN       = 3,
	MIRC_L_RED       = 4,
	MIRC_RED         = 5,
	MIRC_PURPLE      = 6,
	MIRC_ORANGE      = 7,
	MIRC_YELLOW      = 8,
	MIRC_L_GREEN     = 9,
	MIRC_CYAN        = 10,
	MIRC_L_CYAN      = 11,
	MIRC_L_BLUE      = 12,
	MIRC_L_PURPLE    = 13,
	MIRC_GRAY        = 14,
	MIRC_L_GRAY      = 15,

	MIRC_TRANSPARENT = 99
};

static int
color_to_mirc (uint8_t color)
{
	static const int table[2 * PALETTE_WIDTH] =
	{
		// XXX: not sure what to map the default color pair to;
		//   the mIRC code for reverse colours seems to not be well supported
		MIRC_TRANSPARENT, MIRC_BLACK, MIRC_RED, MIRC_GREEN, MIRC_YELLOW,
		MIRC_BLUE, MIRC_PURPLE, MIRC_CYAN, MIRC_L_GRAY,
		MIRC_BLACK, MIRC_GRAY, MIRC_L_RED, MIRC_L_GREEN, MIRC_YELLOW,
		MIRC_L_BLUE, MIRC_L_PURPLE, MIRC_L_CYAN, MIRC_WHITE
	};

	if (color >= sizeof table / sizeof table[0])
		return MIRC_NONE;
	return table[color];
}

static void
export_irc (struct app_context *app)
{
	FILE *fp = fopen ("export-irc.asc", "wb");
	if (!fp)
	{
		display ("Error opening file for writing.");
		beep ();
		return;
	}

	size_t x, y, w, h;
	find_data_bounding_rect (app, &x, &y, &w, &h);

	// This is tricky and needs to be tested with major IRC clients.  Currently
	// works with: weechat 1.0, xchat 2.8.8, freenode's qwebirc.

	// We cannot use the same non-space character for transparent and opaque
	// pixels because many clients don't understand the transparent 99 colour
	// that is needed for the foreground of transparent pixels.  Therefore it
	// is not possible to display correctly using non-monospace fonts.

	for (size_t row = 0; row < h; row++)
	{
		// qwebirc is retarded and in some cases it reduces spaces, misaligning
		// the picture.  Appending two spaces after the attribute reset and
		// rendering opaque pixels as something different from a space seems
		// to prevent that behaviour.
		int color = MIRC_TRANSPARENT;
		fprintf (fp, "\x0f  ");

		for (size_t column = 0; column < w; column++)
		{
			int new_color = color_to_mirc
				(BITMAP_PIXEL (app, x + column, y + row));
			if (color != new_color)
			{
				color = new_color;
				if (color == MIRC_TRANSPARENT)
					fprintf (fp, "\x0f");
				else
					fprintf (fp, "\x03%02d,%02d", color, color);
			}
			fputc ("# "[color == MIRC_TRANSPARENT], fp);
		}
		fputc ('\n', fp);
	}

	fclose (fp);
}

// --- Loading, saving ---------------------------------------------------------

static void
load (struct app_context *app, const char *filename)
{
	// Client cannot load at all, the server would have send the new bitmap out
	if (app->mode != NETWORK_MODE_STANDALONE)
	{
		display ("Cannot load bitmaps in networked mode.");
		beep ();
		return;
	}

	FILE *fp = fopen (filename, "rb");
	if (!fp)
	{
		display ("Error opening file for reading.");
		beep ();
		return;
	}

	// Some way of loading/saving is better than no way, let's just do our job.
	// The format neither standardised nor effective but it works for us.
	// We just eat everything and make sure to not crash.

	int x, y;
	size_t w, h;
	if (fscanf (fp, "%d %d %zu %zu", &x, &y, &w, &h) != 4)
		goto error;

	if (w && h > SIZE_MAX / w)
		goto error;
	size_t size = w * h;

	uint8_t *bitmap = calloc (size, sizeof *bitmap);
	if (!bitmap)
		goto error;

	int c;
	uint8_t pixel = 0;
	bool have_nibble = false;
	size_t loaded = 0;

	while (loaded < size && (c = fgetc (fp)) != EOF)
	{
		static const char digits[] = "0123456789abcdef";
		const char *value = strchr (digits, c);
		if (value && c != '\0')
		{
			pixel = pixel << 4 | (value - digits);
			if (have_nibble)
				bitmap[loaded++] = pixel;
			have_nibble = !have_nibble;
		}
	}

	free (app->bitmap);
	app->bitmap = bitmap;
	app->bitmap_h = h;  app->bitmap_x = x;
	app->bitmap_w = w;  app->bitmap_y = y;
	redraw_canvas (app);

error:
	fclose (fp);
}

static void
save (struct app_context *app, const char *filename)
{
	FILE *fp = fopen (filename, "wb");
	if (!fp)
	{
		display ("Error opening file for writing.");
		return;
	}

	int x = app->bitmap_x, y = app->bitmap_y;
	size_t w = app->bitmap_w, h = app->bitmap_h;
	fprintf (fp, "%d %d %zu %zu\n", x, y, w, h);

	for (size_t row = 0; row < h; row++)
	{
		for (size_t column = 0; column < w; column++)
			fprintf (fp, "%02x", BITMAP_PIXEL (app, column, row));
		fputc ('\n', fp);
	}

	fclose (fp);
}

// --- Event handlers ----------------------------------------------------------

static void
move_canvas (struct app_context *app, int x, int y)
{
	app->corner_x += x;
	app->corner_y += y;

	app->center_x += x;
	app->center_y += y;

	redraw_canvas (app);
}

static void
on_mouse (struct app_context *app, termo_key_t *key)
{
	int screen_y, screen_x, button;
	termo_mouse_event_t event;

	termo_interpret_mouse (app->tk, key, &event, &button, &screen_y, &screen_x);
	if (event != TERMO_MOUSE_PRESS && event != TERMO_MOUSE_DRAG)
		return;

	// Middle mouse button, or Ctrl + left mouse button, moves the canvas
	if (button == 2 || (button == 1 && key->modifiers == TERMO_KEYMOD_CTRL))
	{
		if (event == TERMO_MOUSE_DRAG)
			move_canvas (app,
				app->move_saved_x - screen_x,
				app->move_saved_y - screen_y);

		app->move_saved_x = screen_x;
		app->move_saved_y = screen_y;
		return;
	}

	uint8_t *color;
	if (button == 1)
		color = &app->current_color_left;
	else if (button == 3)
		color = &app->current_color_right;
	else
		return;

	int canvas_x = app->corner_x + screen_x;
	int canvas_y = app->corner_y + screen_y - TOP_BAR_CUTOFF;

	if (screen_y >= TOP_BAR_CUTOFF)
	{
		if (event == TERMO_MOUSE_DRAG)
			draw_line (app,
				app->move_saved_x, canvas_x,
				app->move_saved_y, canvas_y,
				*color);
		else
			draw_point (app, canvas_x, canvas_y, *color);

		app->move_saved_x = canvas_x;
		app->move_saved_y = canvas_y;
	}
	else if (screen_y > 0 && event != TERMO_MOUSE_DRAG)
	{
		int pair = (float) screen_x / COLS * PALETTE_WIDTH;
		*color = pair + (screen_y - 1) * PALETTE_WIDTH;
	}
}

static bool
on_key (struct app_context *app, termo_key_t *key)
{
	if (key->type == TERMO_TYPE_KEYSYM)
	{
		if (key->code.sym == TERMO_SYM_ESCAPE)
			return false;

		if (key->modifiers)
			return true;

		switch (key->code.sym)
		{
		case TERMO_SYM_UP:     move_canvas (app,  0, -1);  break;
		case TERMO_SYM_DOWN:   move_canvas (app,  0,  1);  break;
		case TERMO_SYM_LEFT:   move_canvas (app, -1,  0);  break;
		case TERMO_SYM_RIGHT:  move_canvas (app,  1,  0);  break;
		default:                                           break;
		}
		return true;
	}

	if (key->type == TERMO_TYPE_KEY)
	{
		if ((key->modifiers & TERMO_KEYMOD_CTRL)
		 && (key->code.codepoint == 'C' || key->code.codepoint == 'c'))
			return false;

		if (key->modifiers)
			return true;

		if (key->code.codepoint == 'l')  load (app, "drawing.bin");
		if (key->code.codepoint == 's')  save (app, "drawing.bin");
		if (key->code.codepoint == 'e')  export_ansi (app);
		if (key->code.codepoint == 'E')  export_irc (app);
		return true;
	}

	if (key->type == TERMO_TYPE_MOUSE)
		on_mouse (app, key);

	return true;
}

static void
on_winch (EV_P_ ev_signal *handle, int revents)
{
	struct app_context *app = ev_userdata (loop);
	(void) handle;
	(void) revents;

#if defined HAVE_RESIZETERM && defined TIOCGWINSZ
	struct winsize size;
	if (!ioctl (STDOUT_FILENO, TIOCGWINSZ, (char *) &size))
	{
		char *row = getenv ("LINES");
		char *col = getenv ("COLUMNS");
		unsigned long tmp;
		resizeterm (
			(row && xstrtoul (&tmp, row, 10)) ? (int) tmp : size.ws_row,
			(col && xstrtoul (&tmp, col, 10)) ? (int) tmp : size.ws_col);
	}
#else  // ! HAVE_RESIZETERM || ! TIOCGWINSZ
	endwin ();
	refresh ();
#endif  // ! HAVE_RESIZETERM || ! TIOCGWINSZ

	update_canvas_for_screen (app);
	redraw (app);
	redraw_canvas (app);
}

static void
on_key_timer (EV_P_ ev_timer *handle, int revents)
{
	struct app_context *app = ev_userdata (loop);
	(void) handle;
	(void) revents;

	termo_key_t key;
	if (termo_getkey_force (app->tk, &key) == TERMO_RES_KEY)
		if (!on_key (app, &key))
			ev_break (EV_A_ EVBREAK_ONE);
}

static void
on_tty_readable (EV_P_ ev_io *handle, int revents)
{
	// Ignoring and hoping for the best
	(void) handle;
	(void) revents;

	struct app_context *app = ev_userdata (loop);

	ev_timer_stop (EV_A_ &app->tty_timer);
	termo_advisereadable (app->tk);

	termo_key_t key;
	termo_result_t ret;
	while ((ret = termo_getkey (app->tk, &key)) == TERMO_RES_KEY)
		if (!on_key (app, &key))
			ev_break (EV_A_ EVBREAK_ONE);

	if (ret == TERMO_RES_AGAIN)
		ev_timer_start (EV_A_ &app->tty_timer);
}

// --- Client-specific stuff ---------------------------------------------------

typedef bool (*server_handler_fn) (struct app_context *, struct msg_unpacker *);

static void
on_server_disconnected (struct app_context *app)
{
	write_queue_free (&app->write_queue);
	app->write_queue = write_queue_make ();

	ev_io_stop (EV_DEFAULT_ &app->server_read_watcher);
	ev_io_stop (EV_DEFAULT_ &app->server_write_watcher);
	xclose (app->server_fd);
	app->server_fd = -1;

	display ("Disconnected!");
	beep ();  // Beep beep!  Made a boo-boo.

	// Let the user save the picture at least.
	// Also prevents us from trying to use the dead server handle.
	app->mode = NETWORK_MODE_STANDALONE;
}

static bool
on_server_hello (struct app_context *app, struct msg_unpacker *unpacker)
{
	(void) app;

	uint8_t version;
	if (!msg_unpacker_u8 (unpacker, &version))
		return false;  // Not enough data
	if (version != PROTOCOL_VERSION)
		return false;  // Incompatible version
	return true;
}

static bool
on_server_get_bitmap (struct app_context *app, struct msg_unpacker *unpacker)
{
	int32_t x, y;
	uint64_t w, h;
	if (!msg_unpacker_i32 (unpacker, &x)
	 || !msg_unpacker_i32 (unpacker, &y)
	 || !msg_unpacker_u64 (unpacker, &w)
	 || !msg_unpacker_u64 (unpacker, &h))
		return false;  // Not enough data

	size_t size = w * h;
	if ((h && w > SIZE_MAX / h) || w > SIZE_MAX || h > SIZE_MAX)
		return false;  // The server is flooding us

	uint8_t *bitmap = xcalloc (size, sizeof *app->bitmap);

	// RLE decompression
	size_t i = 0;
	uint8_t len, value;
	while (msg_unpacker_u8 (unpacker, &len)
		&& msg_unpacker_u8 (unpacker, &value))
	{
		// Don't allow overflow
		if (i + len > size || i + len < i)
			break;
		for (size_t x = 0; x < len; x++)
			bitmap[i++] = value;
	}

	free (app->bitmap);
	app->bitmap = bitmap;
	app->bitmap_x = x;
	app->bitmap_y = y;
	app->bitmap_w = w;
	app->bitmap_h = h;

	redraw_canvas (app);
	return true;
}

static bool
on_server_put_point (struct app_context *app, struct msg_unpacker *unpacker)
{
	int32_t x, y;
	uint8_t color;

	if (!msg_unpacker_i32 (unpacker, &x)
	 || !msg_unpacker_i32 (unpacker, &y)
	 || !msg_unpacker_u8 (unpacker, &color))
		return false;  // Not enough data

	// Either a confirmation of our own request, or an event notification;
	// let's just put the pixel in place without further ado
	draw_point_internal (app, x, y, color);
	return true;
}

static bool
on_server_data (EV_P_ ev_io *watcher, const void *buf, ssize_t n_read)
{
	struct app_context *app = ev_userdata (loop);
	(void) watcher;

	msg_reader_feed (&app->msg_reader, buf, n_read);

	static const server_handler_fn handlers[MESSAGE_COUNT] =
	{
		[MESSAGE_HELLO]      = on_server_hello,
		[MESSAGE_GET_BITMAP] = on_server_get_bitmap,
		[MESSAGE_PUT_POINT]  = on_server_put_point,
	};

	void *msg;
	size_t len;
	while ((msg = msg_reader_get (&app->msg_reader, &len)))
	{
		struct msg_unpacker unpacker = msg_unpacker_make (msg, len);

		uint8_t type;
		if (!msg_unpacker_u8 (&unpacker, &type)
		 || type >= MESSAGE_COUNT)
			return false;  // Unknown message

		server_handler_fn handler = handlers[type];
		if (!handler)
			return false;  // Unknown message
		if (!handler (app, &unpacker))
			return false;  // Invalid message
		if (msg_unpacker_get_available (&unpacker) > 0)
			return false;  // Overlong message
	}
	return true;
}

static void
on_server_ready (EV_P_ ev_io *watcher, int revents)
{
	struct app_context *app = ev_userdata (loop);

	if (revents & EV_READ)
		if (!read_loop (EV_A_ watcher, on_server_data))
			goto error;
	if (revents & EV_WRITE)
		if (!flush_queue (&app->write_queue, watcher))
			goto error;
	return;

error:
	on_server_disconnected (app);
}

// --- Server-specific stuff ---------------------------------------------------

typedef bool (*client_handler_fn)
	(struct app_context *, struct client *, struct msg_unpacker *);

static void
remove_client (struct app_context *app, struct client *client)
{
	ev_io_stop (EV_DEFAULT_ &client->read_watcher);
	ev_io_stop (EV_DEFAULT_ &client->write_watcher);
	xclose (client->fd);
	msg_reader_free (&client->msg_reader);
	write_queue_free (&client->write_queue);
	LIST_UNLINK (app->clients, client);
	free (client);
}

static bool
on_client_hello (struct app_context *app, struct client *client,
	struct msg_unpacker *unpacker)
{
	(void) app;

	uint8_t version;
	if (!msg_unpacker_u8 (unpacker, &version)
	 || version != PROTOCOL_VERSION)
		// Nope, I don't like you
		return false;

	send_hello_response (client);
	return true;
}

static bool
on_client_get_bitmap (struct app_context *app, struct client *client,
	struct msg_unpacker *unpacker)
{
	(void) unpacker;

	send_get_bitmap_response (client, app);
	return true;
}

static bool
on_client_put_point (struct app_context *app, struct client *client,
	struct msg_unpacker *unpacker)
{
	(void) client;

	int32_t x, y;
	uint8_t color;
	if (!msg_unpacker_i32 (unpacker, &x)
	 || !msg_unpacker_i32 (unpacker, &y)
	 || !msg_unpacker_u8 (unpacker, &color))
		return false;

	// The function takes care of broadcasting to all the other clients,
	// as well as back to the original sender
	draw_point (app, x, y, color);
	return true;
}

static bool
on_client_data (EV_P_ ev_io *watcher, const void *buf, ssize_t n_read)
{
	struct app_context *app = ev_userdata (loop);
	struct client *client = watcher->data;

	msg_reader_feed (&client->msg_reader, buf, n_read);

	static const client_handler_fn handlers[MESSAGE_COUNT] =
	{
		[MESSAGE_HELLO]      = on_client_hello,
		[MESSAGE_GET_BITMAP] = on_client_get_bitmap,
		[MESSAGE_PUT_POINT]  = on_client_put_point,
	};

	void *msg;
	size_t len;
	while ((msg = msg_reader_get (&client->msg_reader, &len)))
	{
		struct msg_unpacker unpacker = msg_unpacker_make (msg, len);

		uint8_t type;
		if (!msg_unpacker_u8 (&unpacker, &type))
			return false;  // Invalid message
		if (type >= MESSAGE_COUNT)
			return false;  // Unknown message

		client_handler_fn handler = handlers[type];
		if (!handler)
			return false;  // Unknown message
		if (!handler (app, client, &unpacker))
			return false;  // Invalid message
		if (msg_unpacker_get_available (&unpacker) > 0)
			return false;  // Overlong message data
	}
	return true;
}

static void
on_client_ready (EV_P_ ev_io *watcher, int revents)
{
	struct app_context *app = ev_userdata (loop);
	struct client *client = watcher->data;

	if (revents & EV_READ)
		if (!read_loop (EV_A_ watcher, on_client_data))
			goto error;
	if (revents & EV_WRITE)
		if (!flush_queue (&client->write_queue, watcher))
			goto error;
	return;

error:
	remove_client (app, client);
}

static void
on_new_client (EV_P_ ev_io *watcher, int revents)
{
	struct app_context *app = ev_userdata (loop);
	(void) revents;

	while (true)
	{
		int sock_fd = accept (watcher->fd, NULL, NULL);
		if (sock_fd == -1)
		{
			if (errno == EAGAIN)
				break;
			if (errno == EINTR
			 || errno == ECONNABORTED)
				continue;

			// Stop accepting connections to prevent busy looping
			// TODO: indicate the error to the user
			ev_io_stop (EV_A_ watcher);
			break;
		}

		struct client *client = xcalloc (1, sizeof *client);
		client->fd = sock_fd;
		client->msg_reader = msg_reader_make ();
		client->write_queue = write_queue_make ();

		set_blocking (sock_fd, false);
		ev_io_init (&client->read_watcher,  on_client_ready, sock_fd, EV_READ);
		ev_io_init (&client->write_watcher, on_client_ready, sock_fd, EV_WRITE);
		client->read_watcher.data = client;
		client->write_watcher.data = client;

		// We're only interested in reading as the write queue is empty now
		ev_io_start (EV_A_ &client->read_watcher);

		LIST_PREPEND (app->clients, client);
	}
}

// --- Program startup ---------------------------------------------------------

struct app_options
{
	struct addrinfo *client_address;    ///< Address to connect to
	struct addrinfo *server_address;    ///< Address to listen at
	bool no_wait;                       ///< Don't wait for server confirmations
	const char *filename;               ///< A filename to preload
};

static void
app_options_init (struct app_options *self)
{
	memset (self, 0, sizeof *self);
}

static void
app_options_free (struct app_options *self)
{
	if (self->client_address)  freeaddrinfo (self->client_address);
	if (self->server_address)  freeaddrinfo (self->server_address);
}

static struct addrinfo *
parse_address (const char *address, int flags)
{
	char address_copy[strlen (address) + 1];
	strcpy (address_copy, address);

	char *colon = strrchr (address_copy, ':');
	if (!colon)
	{
		print_error ("no port number specified in `%s'", address);
		return false;
	}

	char *host = address_copy, *service = colon + 1;

	if (host == colon)
		host = NULL;
	else if (host < colon && *host == '[' && colon[-1] == ']')
	{
		// Remove IPv6 RFC 2732-style [] brackets from the host, if present.
		// This also makes it possible to take the usage string literally. :))
		host++;
		colon[-1] = '\0';
	}
	else
		*colon = '\0';

	struct addrinfo *result, hints =
	{
		.ai_socktype = SOCK_STREAM,
		.ai_protocol = IPPROTO_TCP,
		.ai_flags = flags,
	};
	int err = getaddrinfo (host, service, &hints, &result);
	if (err)
	{
		print_error ("cannot resolve `%s', port `%s': %s",
			host, service, gai_strerror (err));
		return false;
	}
	return result;
}

static void
parse_program_arguments (struct app_options *options, int argc, char **argv)
{
	static const struct opt opts[] =
	{
		{ 'h', "help", NULL, 0, "display this help and exit" },
		{ 'V', "version", NULL, 0, "output version information and exit" },
		{ 's', "server", "[ADDRESS]:PORT", 0, "start a server" },
		{ 'c', "client", "[ADDRESS]:PORT", 0, "connect to a server" },
		{ 'n', "no-wait", NULL, OPT_LONG_ONLY,
		  "don't wait for server confirmations" },
		{ 0, NULL, NULL, 0, NULL }
	};

	struct opt_handler oh = opt_handler_make (argc, argv, opts, "[drawing.bin]",
		"Terminal drawing application with multiplayer support");

	int c;
	while ((c = opt_handler_get (&oh)) != -1)
	switch (c)
	{
	case 'h':
		opt_handler_usage (&oh, stdout);
		exit (EXIT_SUCCESS);
	case 'V':
		printf (PROGRAM_NAME " " PROGRAM_VERSION "\n");
		exit (EXIT_SUCCESS);
	case 's':
		if (options->server_address)
			exit_fatal ("cannot specify multiple listening addresses");
		if (!(options->server_address = parse_address (optarg, AI_PASSIVE)))
			exit (EXIT_FAILURE);
		break;
	case 'c':
		if (options->client_address)
			exit_fatal ("cannot specify multiple addresses to connect to");
		if (!(options->client_address = parse_address (optarg, 0)))
			exit (EXIT_FAILURE);
		break;
	case 'n':
		options->no_wait = true;
		break;
	default:
		print_error ("wrong options");
		opt_handler_usage (&oh, stderr);
		exit (EXIT_FAILURE);
	}

	if (options->client_address && options->server_address)
		exit_fatal ("cannot be both a server and a client");

	argc -= optind;
	argv += optind;

	options->filename = argv[0];
	if (argc > 1)
	{
		opt_handler_usage (&oh, stderr);
		exit (EXIT_FAILURE);
	}

	opt_handler_free (&oh);
}

static void
initialize_client (struct app_context *app, struct addrinfo *address)
{
	app->mode = NETWORK_MODE_CLIENT;

	int sock_fd, err;
	for (; address; address = address->ai_next)
	{
		sock_fd = socket (address->ai_family,
			address->ai_socktype, address->ai_protocol);
		if (sock_fd == -1)
			continue;

		char host_buf[NI_MAXHOST], serv_buf[NI_MAXSERV];
		err = getnameinfo (address->ai_addr, address->ai_addrlen,
			host_buf, sizeof host_buf, serv_buf, sizeof serv_buf,
			NI_NUMERICHOST | NI_NUMERICSERV);
		if (err)
		{
			print_error ("%s: %s", "getnameinfo", gai_strerror (err));
			print_status ("connecting...");
		}
		else
		{
			char *x = format_host_port_pair (host_buf, serv_buf);
			print_status ("connecting to %s...", x);
			free (x);
		}

		if (!connect (sock_fd, address->ai_addr, address->ai_addrlen))
			break;

		xclose (sock_fd);
	}

	if (!address)
		exit_fatal ("connection failed");

	int yes = 1;
	(void) setsockopt (sock_fd, SOL_SOCKET, SO_KEEPALIVE, &yes, sizeof yes);

	set_blocking (sock_fd, false);
	app->server_fd = sock_fd;
	ev_io_init (&app->server_read_watcher,  on_server_ready, sock_fd, EV_READ);
	ev_io_init (&app->server_write_watcher, on_server_ready, sock_fd, EV_WRITE);

	// We're only interested in reading as the write queue is empty now
	ev_io_start (EV_DEFAULT_ &app->server_read_watcher);

	send_hello_request (app);
	send_get_bitmap_request (app);
}

static void
initialize_server (struct app_context *app, struct addrinfo *address)
{
	app->mode = NETWORK_MODE_SERVER;

	int sock_fd = socket (address->ai_family,
		address->ai_socktype, address->ai_protocol);
	if (sock_fd == -1)
		goto fail_socket;

	if (bind (sock_fd, address->ai_addr, address->ai_addrlen)
	 || listen (sock_fd, 10))
		goto fail;

	int yes = 1;
	(void) setsockopt (sock_fd, SOL_SOCKET, SO_KEEPALIVE, &yes, sizeof yes);
	(void) setsockopt (sock_fd, SOL_SOCKET, SO_REUSEADDR, &yes, sizeof yes);

	set_blocking (sock_fd, false);
	app->listen_fd = sock_fd;
	ev_io_init (&app->listen_watcher, on_new_client, sock_fd, EV_READ);
	ev_io_start (EV_DEFAULT_ &app->listen_watcher);
	return;

fail:
	xclose (sock_fd);
fail_socket:
	exit_fatal ("%s: %s", "initialization failed", strerror (errno));
}

int
main (int argc, char *argv[])
{
	TERMO_CHECK_VERSION;
	setlocale (LC_CTYPE, "");

	struct app_context app;
	app_init (&app);

	struct ev_loop *loop = EV_DEFAULT;
	if (!loop)
		exit_fatal ("cannot initialize libev");

	struct app_options options;
	app_options_init (&options);
	parse_program_arguments (&options, argc, argv);

	if      (options.client_address)
		initialize_client (&app, options.client_address);
	else if (options.server_address)
		initialize_server (&app, options.server_address);
	else
		app.mode = NETWORK_MODE_STANDALONE;

	app.no_wait = options.no_wait;
	app_options_free (&options);

	termo_t *tk = termo_new (STDIN_FILENO, NULL, 0);
	if (!tk)
		exit_fatal ("cannot allocate termo instance");

	app.tk = tk;
	termo_set_mouse_tracking_mode (tk, TERMO_MOUSE_TRACKING_DRAG);

	// Set up curses for our drawing needs
	if (!initscr () || nonl () == ERR || curs_set (0) == ERR)
		exit_fatal ("cannot initialize curses");

	ev_set_userdata (loop, &app);

	ev_signal_init (&app.winch_watcher, on_winch, SIGWINCH);
	ev_signal_start (EV_DEFAULT_ &app.winch_watcher);
	ev_io_init (&app.tty_watcher, on_tty_readable, STDIN_FILENO, EV_READ);
	ev_io_start (EV_DEFAULT_ &app.tty_watcher);
	ev_timer_init (&app.tty_timer, on_key_timer,
		termo_get_waittime (app.tk) / 1000., 0);

	init_palette (&app);
	update_canvas_for_screen (&app);
	redraw (&app);
	redraw_canvas (&app);

	if (options.filename)
		load (&app, options.filename);

	ev_run (loop, 0);
	endwin ();

	app_free (&app);
	ev_loop_destroy (loop);
	return 0;
}