cs350/kern/lib/kgets.c

/*
 * Copyright (c) 2001
 *	The President and Fellows of Harvard College.
 *
 * Redistribution and use in source and binary forms, with or without
 * modification, are permitted provided that the following conditions
 * are met:
 * 1. Redistributions of source code must retain the above copyright
 *    notice, this list of conditions and the following disclaimer.
 * 2. Redistributions in binary form must reproduce the above copyright
 *    notice, this list of conditions and the following disclaimer in the
 *    documentation and/or other materials provided with the distribution.
 * 3. Neither the name of the University nor the names of its contributors
 *    may be used to endorse or promote products derived from this software
 *    without specific prior written permission.
 *
 * THIS SOFTWARE IS PROVIDED BY THE UNIVERSITY AND CONTRIBUTORS ``AS IS'' AND
 * ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE
 * IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE
 * ARE DISCLAIMED.  IN NO EVENT SHALL THE UNIVERSITY OR CONTRIBUTORS BE LIABLE
 * FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL
 * DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS
 * OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION)
 * HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
 * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
 * OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF
 * SUCH DAMAGE.
 */


#include <types.h>
#include <lib.h>

/*
 * Do a backspace in typed input.
 * We overwrite the current character with a space in case we're on
 * a terminal where backspace is nondestructive.
 */
static
void
backsp(void)
{
	putch('\b');
	putch(' ');
	putch('\b');
}

/*
 * Read a string off the console. Support a few of the more useful
 * common control characters. Do not include the terminating newline
 * in the buffer passed back.
 */
void
kgets(char *buf, size_t maxlen)
{
	size_t pos = 0;
	int ch;

	while (1) {
		ch = getch();
		if (ch=='\n' || ch=='\r') {
			putch('\n');
			break;
		}

		/* Only allow the normal 7-bit ascii */
		if (ch>=32 && ch<127 && pos < maxlen-1) {
			putch(ch);
			buf[pos++] = ch;
		}
		else if ((ch=='\b' || ch==127) && pos>0) {
			/* backspace */
			backsp();
			pos--;
		}
		else if (ch==3) {
			/* ^C - return empty string */
			putch('^');
			putch('C');
			putch('\n');
			pos = 0;
			break;
		}
		else if (ch==18) {
			/* ^R - reprint input */
			buf[pos] = 0;
			kprintf("^R\n%s", buf);
		}
		else if (ch==21) {
			/* ^U - erase line */
			while (pos > 0) {
				backsp();
				pos--;
			}
		}
		else if (ch==23) {
			/* ^W - erase word */
			while (pos > 0 && buf[pos-1]==' ') {
				backsp();
				pos--;
			}
			while (pos > 0 && buf[pos-1]!=' ') {
				backsp();
				pos--;
			}
		}
		else {
			beep();
		}
	}

	buf[pos] = 0;
}