From: =?utf-8?b?0L3QsNCx?= <nabijaczleweli@nabijaczleweli.xyz>
Date: Wed, 15 Mar 2023 16:16:48 +0100
Subject: wall: use fputs_careful()

LINE_MAX only applies to teletypes in canonical mode: when stdin is a
file, it could still very much tear; start off at 512 for the sprintf(),
then use getline() like in write.

The line wrapping has one suboptimal edge-case:
  $ wall < all

  Broadcast message from nabijaczleweli@tarta (pts/4) (Tue Mar 14 22:31:25
  2023):

  ^N^O^P^Q^R^S^T^U^V^W^X^Y^Z^[^\^]^^^_
  !"#$%&'()*+,-./0123456789:;<=>?@ABCDEFGHIJ
  KLMNOPQRSTUVWXYZ[\]^_`abcdefghijklmnopqrstuvwxyz{|}~^?\200\201\202\203\204\205\206
  \207\210\211\212\213\214\215\216\217\220\221\222\223\224\225\226\227\230\231\232
  \233\234\235\236\237\240\241\242\243\244\245\246\247\250\251\252\253\254\255\256
  \257\260\261\262\263\264\265\266\267\270\271\272\273\274\275\276\277\300\301\302
  \303\304\305\306\307\310\311\312\313\314\315\316\317\320\321\322\323\324\325\326
  \327\330\331\332\333\334\335\336\337\340\341\342\343\344\345\346\347\350\351\352
  \353\354\355\356\357\360\361\362\363\364\365\366\367\370\371\372\373\374\375\376
  \377
but that's a pathological input, and the result is still infinitely
better than it was before, so fixing that is more trouble than it's
worth.

Bug-Debian: https://bugs.debian.org/826596
---
 include/carefulputc.h | 42 +++++++++++++++++++++++++++++++++---------
 login-utils/last.c    |  2 +-
 term-utils/wall.c     | 38 ++++++--------------------------------
 term-utils/write.c    |  2 +-
 4 files changed, 41 insertions(+), 43 deletions(-)

diff --git a/include/carefulputc.h b/include/carefulputc.h
index 4f74526..51d1c99 100644
--- a/include/carefulputc.h
+++ b/include/carefulputc.h
@@ -6,6 +6,7 @@
 #include <ctype.h>
 #ifdef HAVE_WIDECHAR
 #include <wctype.h>
+#include <wchar.h>
 #endif
 #include <stdbool.h>
 
@@ -15,18 +16,35 @@
  * A puts() for use in write and wall (that sometimes are sgid tty).
  * It avoids control and invalid characters.
  * The locale of the recipient is nominally unknown,
- * but it's a solid bet that the encoding is compatible with the author's.
+ * but it's a solid bet that it's compatible with the author's.
+ * Use soft_width=0 to disable wrapping.
  */
-static inline int fputs_careful(const char * s, FILE *fp, const char ctrl, bool cr_lf)
+static inline int fputs_careful(const char * s, FILE *fp, const char ctrl, bool cr_lf, int soft_width)
 {
-	int ret = 0;
+	int ret = 0, col = 0;
 
 	for (size_t slen = strlen(s); *s; ++s, --slen) {
-		if (*s == '\n')
+		if (*s == '\t')
+			col += (7 - (col % 8)) - 1;
+		else if (*s == '\r')
+			col = -1;
+		else if (*s == '\a')
+			--col;
+
+		if ((soft_width && col >= soft_width) || *s == '\n') {
+			if (soft_width) {
+				fprintf(fp, "%*s", soft_width - col, "");
+				col = 0;
+			}
 			ret = fputs(cr_lf ? "\r\n" : "\n", fp);
-		else if (isprint(*s) || *s == '\a' || *s == '\t' || *s == '\r')
+			if (*s == '\n' || ret < 0)
+				goto wrote;
+		}
+
+		if (isprint(*s) || *s == '\a' || *s == '\t' || *s == '\r') {
 			ret = putc(*s, fp);
-		else if (!c_isascii(*s)) {
+			++col;
+		} else if (!c_isascii(*s)) {
 #ifdef HAVE_WIDECHAR
 			wchar_t w;
 			size_t clen = mbtowc(&w, s, slen);
@@ -35,21 +53,27 @@ static inline int fputs_careful(const char * s, FILE *fp, const char ctrl, bool
 				case (size_t)-1:  // EILSEQ
 					mbtowc(NULL, NULL, 0);
 				nonprint:
-					ret = fprintf(fp, "\\%3hho", *s);
+					col += ret = fprintf(fp, "\\%3hho", *s);
 					break;
 				default:
 					if(!iswprint(w))
 						goto nonprint;
 					ret = fwrite(s, 1, clen, fp);
+					if (soft_width)
+						col += wcwidth(w);
 					s += clen - 1;
 					slen -= clen - 1;
 					break;
 			}
 #else
-			ret = fprintf(fp, "\\%3hho", *s);
+			col += ret = fprintf(fp, "\\%3hho", *s);
 #endif
-		} else
+		} else {
 			ret = fputs((char[]){ ctrl, *s ^ 0x40, '\0' }, fp);
+			col += 2;
+		}
+
+	wrote:
 		if (ret < 0)
 			return EOF;
 	}
diff --git a/login-utils/last.c b/login-utils/last.c
index c5984f1..8386f08 100644
--- a/login-utils/last.c
+++ b/login-utils/last.c
@@ -550,7 +550,7 @@ static int list(const struct last_control *ctl, struct utmpx *p, time_t logout_t
 	/*
 	 *	Print out "final" string safely.
 	 */
-	fputs_careful(final, stdout, '*', false);
+	fputs_careful(final, stdout, '*', false, 0);
 
 	if (len < 0 || (size_t)len >= sizeof(final))
 		putchar('\n');
diff --git a/term-utils/wall.c b/term-utils/wall.c
index 97623b8..fa5e027 100644
--- a/term-utils/wall.c
+++ b/term-utils/wall.c
@@ -273,29 +273,13 @@ int main(int argc, char **argv)
 	exit(EXIT_SUCCESS);
 }
 
-static void buf_putc_careful(FILE *fs, int c)
-{
-	if (isprint(c) || c == '\a' || c == '\t' || c == '\r' || c == '\n')
-		fputc(c, fs);
-	else if (!c_isascii(c))
-		fprintf(fs, "\\%3o", (unsigned char)c);
-	else
-		fputs((char[]){ '^', c ^ 0x40, '\0' }, fs);
-}
-
 static char *makemsg(char *fname, char **mvec, int mvecsz,
 		     size_t *mbufsize, int print_banner)
 {
-	register int ch, cnt;
-	char *p, *lbuf, *retbuf;
+	char *lbuf, *retbuf;
 	FILE * fs = open_memstream(&retbuf, mbufsize);
-	long line_max;
-
-	line_max = sysconf(_SC_LINE_MAX);
-	if (line_max <= 0)
-		line_max = 512;
-
-	lbuf = xmalloc(line_max);
+	size_t lbuflen = 512;
+	lbuf = xmalloc(lbuflen);
 
 	if (print_banner == TRUE) {
 		char *hostname = xgethostname();
@@ -330,7 +314,7 @@ static char *makemsg(char *fname, char **mvec, int mvecsz,
 		   will not overflow as long as %d takes at most 100 chars */
 		fprintf(fs, "\r%*s\r\n", TERM_WIDTH, " ");
 
-		snprintf(lbuf, line_max,
+		snprintf(lbuf, lbuflen,
 				_("Broadcast message from %s@%s (%s) (%s):"),
 				whom, hostname, where, date);
 		fprintf(fs, "%-*.*s\007\007\r\n", TERM_WIDTH, TERM_WIDTH, lbuf);
@@ -374,18 +358,8 @@ static char *makemsg(char *fname, char **mvec, int mvecsz,
 		/*
 		 * Read message from stdin.
 		 */
-		while (fgets(lbuf, line_max, stdin)) {
-			for (cnt = 0, p = lbuf; (ch = *p) != '\0'; ++p, ++cnt) {
-				if (cnt == TERM_WIDTH || ch == '\n') {
-					fprintf(fs, "%*s\r\n", TERM_WIDTH - cnt, "");
-					cnt = 0;
-				}
-				if (ch == '\t')
-					cnt += (7 - (cnt % 8));
-				if (ch != '\n')
-					buf_putc_careful(fs, ch);
-			}
-		}
+		while (getline(&lbuf, &lbuflen, stdin) >= 0)
+			fputs_careful(lbuf, fs, '^', true, TERM_WIDTH);
 	}
 	fprintf(fs, "%*s\r\n", TERM_WIDTH, " ");
 
diff --git a/term-utils/write.c b/term-utils/write.c
index 710a58c..1d57fce 100644
--- a/term-utils/write.c
+++ b/term-utils/write.c
@@ -276,7 +276,7 @@ static void do_write(const struct write_control *ctl)
 		if (signal_received)
 			break;
 
-		if (fputs_careful(line, stdout, '^', true) == EOF)
+		if (fputs_careful(line, stdout, '^', true, 0) == EOF)
 			err(EXIT_FAILURE, _("carefulputc failed"));
 	}
 	free(line);