bar: Implement terminal status bars

1 files changed, 262 insertions, 0 deletions

diff --git a/bar.c b/bar.c
new file mode 100644
index 0000000..9cb08d3
--- /dev/null
+++ b/bar.c
@@ -0,0 +1,262 @@
+/****************************************************************************
+ * bfs                                                                      *
+ * Copyright (C) 2020 Tavian Barnes <tavianator@tavianator.com>             *
+ *                                                                          *
+ * 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 "bar.h"
+#include "dstring.h"
+#include "util.h"
+#include <errno.h>
+#include <fcntl.h>
+#include <limits.h>
+#include <signal.h>
+#include <stdio.h>
+#include <string.h>
+#include <sys/ioctl.h>
+#include <unistd.h>
+
+struct bfs_bar {
+	int fd;
+	volatile sig_atomic_t width;
+	volatile sig_atomic_t height;
+};
+
+/** The global status bar instance. */
+static struct bfs_bar the_bar = {
+	.fd = -1,
+};
+
+/** Get the terminal size, if possible. */
+static int bfs_bar_getsize(struct bfs_bar *bar) {
+#ifdef TIOCGWINSZ
+	struct winsize ws;
+	if (ioctl(bar->fd, TIOCGWINSZ, &ws) != 0) {
+		return -1;
+	}
+
+	bar->width = ws.ws_col;
+	bar->height = ws.ws_row;
+	return 0;
+#else
+	errno = ENOTSUP;
+	return -1;
+#endif
+}
+
+/** Async Signal Safe puts(). */
+static int ass_puts(int fd, const char *str) {
+	size_t len = strlen(str);
+
+	while (len > 0) {
+		ssize_t ret = write(fd, str, len);
+		if (ret <= 0) {
+			return -1;
+		}
+		str += ret;
+		len -= ret;
+	}
+
+	return 0;
+}
+
+/** Number of decimal digits needed for terminal sizes. */
+#define ITOA_DIGITS ((sizeof(unsigned short) * CHAR_BIT + 2) / 3)
+
+/** Async Signal Safe itoa(). */
+static char *ass_itoa(char *str, unsigned int n) {
+	char *end = str + ITOA_DIGITS;
+	*end = '\0';
+
+	char *c = end;
+	do {
+		*--c = '0' + (n % 10);
+		n /= 10;
+	} while (n);
+
+	size_t len = end - c;
+	memmove(str, c, len + 1);
+	return str + len;
+}
+
+/** Update the size of the scrollable region. */
+static int bfs_bar_resize(struct bfs_bar *bar) {
+	char esc_seq[12 + ITOA_DIGITS] =
+		"\0337"   // DECSC: Save cursor
+		"\033[;"; // DECSTBM: Set scrollable region
+
+	// DECSTBM takes the height as the second argument
+	char *ptr = esc_seq + strlen(esc_seq);
+	ptr = ass_itoa(ptr, bar->height - 1);
+
+	strcpy(ptr,
+		"r"      // DECSTBM
+		"\0338"  // DECRC: Restore the cursor
+		"\033[J" // ED: Erase display from cursor to end
+	);
+
+	return ass_puts(bar->fd, esc_seq);
+}
+
+#ifdef SIGWINCH
+/** SIGWINCH handler. */
+static void sighand_winch(int sig) {
+	int error = errno;
+
+	bfs_bar_getsize(&the_bar);
+	bfs_bar_resize(&the_bar);
+
+	errno = error;
+}
+#endif
+
+/** Reset the scrollable region and hide the bar. */
+static int bfs_bar_reset(struct bfs_bar *bar) {
+	return ass_puts(bar->fd,
+		"\0337"  // DECSC: Save cursor
+		"\033[r" // DECSTBM: Reset scrollable region
+		"\0338"  // DECRC: Restore cursor
+		"\033[J" // ED: Erase display from cursor to end
+	);
+}
+
+/** Signal handler for process-terminating signals. */
+static void sighand_reset(int sig) {
+	bfs_bar_reset(&the_bar);
+	raise(sig);
+}
+
+/** Register sighand_reset() for a signal. */
+static void reset_before_death_by(int sig) {
+	struct sigaction sa = {
+		.sa_handler = sighand_reset,
+		.sa_flags = SA_RESETHAND,
+	};
+	sigemptyset(&sa.sa_mask);
+	sigaction(sig, &sa, NULL);
+}
+
+/** printf() to the status bar with a single write(). */
+BFS_FORMATTER(2, 3)
+static int bfs_bar_printf(struct bfs_bar *bar, const char *format, ...) {
+	va_list args;
+	va_start(args, format);
+	char *str = dstrvprintf(format, args);
+	va_end(args);
+
+	if (!str) {
+		return -1;
+	}
+
+	int ret = ass_puts(bar->fd, str);
+	dstrfree(str);
+	return ret;
+}
+
+struct bfs_bar *bfs_bar_show(void) {
+	int error;
+
+	if (the_bar.fd >= 0) {
+		error = EBUSY;
+		goto fail;
+	}
+
+	char term[L_ctermid];
+	ctermid(term);
+	if (strlen(term) == 0) {
+		error = ENOTTY;
+		goto fail;
+	}
+
+	the_bar.fd = open(term, O_RDWR | O_CLOEXEC);
+	if (the_bar.fd < 0) {
+		error = errno;
+		goto fail;
+	}
+
+	if (bfs_bar_getsize(&the_bar) != 0) {
+		error = errno;
+		goto fail_close;
+	}
+
+	reset_before_death_by(SIGABRT);
+	reset_before_death_by(SIGINT);
+	reset_before_death_by(SIGPIPE);
+	reset_before_death_by(SIGQUIT);
+	reset_before_death_by(SIGTERM);
+
+#ifdef SIGWINCH
+	struct sigaction sa = {
+		.sa_handler = sighand_winch,
+		.sa_flags = SA_RESTART,
+	};
+	sigemptyset(&sa.sa_mask);
+	sigaction(SIGWINCH, &sa, NULL);
+#endif
+
+	bfs_bar_printf(&the_bar,
+		"\n"        // Make space for the bar
+		"\0337"     // DECSC: Save cursor
+		"\033[;%ur" // DECSTBM: Set scrollable region
+		"\0338"     // DECRC: Restore cursor
+		"\033[1A",  // CUU: Move cursor up 1 row
+		(unsigned int)(the_bar.height - 1)
+	);
+
+	return &the_bar;
+
+fail_close:
+	close(the_bar.fd);
+	the_bar.fd = -1;
+fail:
+	errno = error;
+	return NULL;
+}
+
+unsigned int bfs_bar_width(const struct bfs_bar *bar) {
+	return bar->width;
+}
+
+int bfs_bar_update(struct bfs_bar *bar, const char *str) {
+	return bfs_bar_printf(bar,
+		"\0337"      // DECSC: Save cursor
+		"\033[%u;0f" // HVP: Move cursor to row, column
+		"\033[K"     // EL: Erase line
+		"\033[7m"    // SGR reverse video
+		"%s"
+		"\033[27m"   // SGR reverse video off
+		"\0338",     // DECRC: Restore cursor
+		(unsigned int)bar->height,
+		str
+	);
+}
+
+void bfs_bar_hide(struct bfs_bar *bar) {
+	if (!bar) {
+		return;
+	}
+
+	signal(SIGABRT, SIG_DFL);
+	signal(SIGINT, SIG_DFL);
+	signal(SIGPIPE, SIG_DFL);
+	signal(SIGQUIT, SIG_DFL);
+	signal(SIGTERM, SIG_DFL);
+#ifdef SIGWINCH
+	signal(SIGWINCH, SIG_DFL);
+#endif
+
+	bfs_bar_reset(bar);
+
+	close(bar->fd);
+	bar->fd = -1;
+}