Add strnvis(3) -- a length-bounded version of strvis(3) with a return

value similar to snprintf(3) and strlcpy(3).

2 files changed, 104 insertions, 18 deletions

diff --git a/lib/libc/gen/vis.3 b/lib/libc/gen/vis.3
index 6ca6afd7c1d..96b6996c290 100644
--- a/lib/libc/gen/vis.3
+++ b/lib/libc/gen/vis.3
@@ -1,4 +1,4 @@
-.\"	$OpenBSD: vis.3,v 1.12 2000/09/14 17:47:09 aaron Exp $
+.\"	$OpenBSD: vis.3,v 1.13 2000/11/21 00:47:28 millert Exp $
 .\"
 .\" Copyright (c) 1989, 1991, 1993
 .\"	The Regents of the University of California.  All rights reserved.
@@ -37,6 +37,7 @@
 .Sh NAME
 .Nm vis ,
 .Nm strvis ,
+.Nm strnvis ,
 .Nm strvisx
 .Nd visually encode characters
 .Sh SYNOPSIS
@@ -46,7 +47,9 @@
 .Ft int
 .Fn strvis "char *dst" "char *src" "int flag"
 .Ft int
-.Fn strvisx "char *dst" "char *src" "int len" "int flag"
+.Fn strnvis "char *dst" "char *src" "size_t size" "int flag"
+.Ft int
+.Fn strvisx "char *dst" "char *src" "size_t len" "int flag"
 .Sh DESCRIPTION
 The
 .Fn vis
@@ -78,7 +81,8 @@ is only used when selecting the
 encoding format (explained below).
 .Pp
 The
-.Fn strvis
+.Fn strvis ,
+.Fn strnvis
 and
 .Fn strvisx
 functions copy into
@@ -92,6 +96,14 @@ function encodes characters from
 .Fa src
 up to the first NUL.
 The
+.Fn strnvis
+function encodes characters from
+.Fa src
+up to the first NUL or the end of
+.Fa dst ,
+as indicated by
+.Fa siz .
+The
 .Fn strvisx
 function encodes exactly
 .Fa len
@@ -99,18 +111,36 @@ characters from
 .Fa src
 (this
 is useful for encoding a block of data that may contain NULs).
-Both forms null terminate
+All three forms NUL terminate
 .Fa dst .
-The size of
+For
+.Fn strvis
+and
+.Fn strvisx ,
+the size of
 .Fa dst
 must be four times the number
 of characters encoded from
 .Fa src
 (plus one for the NUL).
-Both
-forms return the number of characters in
+.Fn strvis
+and
+.Fn strvisx
+return the number of characters in
 .Fa dst
 (not including the trailing NUL).
+.Fn strnvis
+returns the length that
+.Fa dst
+would become if it were of unlimited size (similar to
+.Xr snprintf 3
+or
+.Xr strlcpy 3 ) .
+This can be used to detect truncation but it also means that
+the return value of
+.Fn strnvis
+must not be used without checking it against
+.Fa siz .
 .Pp
 The encoding is a unique, invertible representation composed entirely of
 graphic characters; it can be decoded back into the original form using
@@ -259,7 +289,19 @@ ambiguous and non-invertible.
 .Sh SEE ALSO
 .Xr unvis 1 ,
 .Xr vis 1 ,
+.Xr snprintf 3 ,
+.Xr strlcpy 3 ,
 .Xr unvis 3
 .Sh HISTORY
-These functions first appeared in
+The
+.Fn vis ,
+.Fn strvis
+and
+.Fn strvisx
+functions first appeared in
 .Bx 4.4 .
+.br
+The
+.Fn strnvis
+function first appeared in
+.Ox 2.9 .
diff --git a/lib/libc/gen/vis.c b/lib/libc/gen/vis.c
index 1c8028fb9b6..e15a7427d11 100644
--- a/lib/libc/gen/vis.c
+++ b/lib/libc/gen/vis.c
@@ -32,7 +32,7 @@
  */
 
 #if defined(LIBC_SCCS) && !defined(lint)
-static char rcsid[] = "$OpenBSD: vis.c,v 1.5 2000/07/19 15:25:13 deraadt Exp $";
+static char rcsid[] = "$OpenBSD: vis.c,v 1.6 2000/11/21 00:47:28 millert Exp $";
 #endif /* LIBC_SCCS and not lint */
 
 #include <sys/types.h>
@@ -41,6 +41,13 @@ static char rcsid[] = "$OpenBSD: vis.c,v 1.5 2000/07/19 15:25:13 deraadt Exp $";
 #include <vis.h>
 
 #define	isoctal(c)	(((u_char)(c)) >= '0' && ((u_char)(c)) <= '7')
+#define isvisible(c)	(((u_int)(c) <= UCHAR_MAX && isascii((u_char)(c)) && \
+				isgraph((u_char)(c))) ||		     \
+				((flag & VIS_SP) == 0 && (c) == ' ') ||	     \
+				((flag & VIS_TAB) == 0 && (c) == '\t') ||    \
+				((flag & VIS_NL) == 0 && (c) == '\n') ||     \
+				((flag & VIS_SAFE) &&			     \
+				((c) == '\b' || (c) == '\007' || (c) == '\r')))
 
 /*
  * vis - visually encode characters
@@ -51,12 +58,7 @@ vis(dst, c, flag, nextc)
 	int c, nextc;
 	register int flag;
 {
-	if (((u_int)c <= UCHAR_MAX && isascii((u_char)c) &&
-	    isgraph((u_char)c)) ||
-	   ((flag & VIS_SP) == 0 && c == ' ') ||
-	   ((flag & VIS_TAB) == 0 && c == '\t') ||
-	   ((flag & VIS_NL) == 0 && c == '\n') ||
-	   ((flag & VIS_SAFE) && (c == '\b' || c == '\007' || c == '\r'))) {
+	if (isvisible(c)) {
 		*dst++ = c;
 		if (c == '\\' && (flag & VIS_NOSLASH) == 0)
 			*dst++ = '\\';
@@ -141,12 +143,15 @@ done:
 }
 
 /*
- * strvis, strvisx - visually encode characters from src into dst
+ * strvis, strnvis, strvisx - visually encode characters from src into dst
  *	
  *	Dst must be 4 times the size of src to account for possible
  *	expansion.  The length of dst, not including the trailing NULL,
  *	is returned. 
  *
+ *	Strnvis will write no more than siz-1 bytes (and will NULL terminate).
+ *	The number of bytes needed to fully encode the string is returned.
+ *
  *	Strvisx encodes exactly len bytes from src into dst.
  *	This is useful for encoding a block of data.
  */
@@ -161,7 +166,48 @@ strvis(dst, src, flag)
 
 	for (start = dst; (c = *src);)
 		dst = vis(dst, c, flag, *++src);
+	return (dst - start);
+}
+
+int
+strnvis(dst, src, siz, flag)
+	register char *dst;
+	register const char *src;
+	size_t siz;
+	int flag;
+{
+	register char c;
+	char *start, *end;
+
+	for (start = dst, end = start + siz - 1; (c = *src) && dst < end; ) {
+		if (isvisible(c)) {
+			*dst++ = c;
+			if (c == '\\' && (flag & VIS_NOSLASH) == 0) {
+				/* need space for the extra '\\' */
+				if (dst < end)
+					*dst++ = '\\';
+				else {
+					dst--;
+					break;
+				}
+			}
+			src++;
+		} else {
+			/* vis(3) requires up to 4 chars */
+			if (dst + 3 < end)
+				dst = vis(dst, c, flag, *++src);
+			else
+				break;
+		}
+	}
 	*dst = '\0';
+	if (dst >= end) {
+		char tbuf[5];
+
+		/* adjust return value for truncation */
+		while ((c = *src))
+			dst += vis(tbuf, c, flag, *++src) - tbuf;
+	}
 	return (dst - start);
 }
 
@@ -181,7 +227,5 @@ strvisx(dst, src, len, flag)
 	}
 	if (len)
 		dst = vis(dst, *src, flag, '\0');
-	*dst = '\0';
-
 	return (dst - start);
 }