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Diffstat (limited to 'strlcpy.3')
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diff --git a/strlcpy.3 b/strlcpy.3 new file mode 100644 index 00000000..8b07d0c4 --- /dev/null +++ b/strlcpy.3 @@ -0,0 +1,202 @@ +.\" $NetBSD: strlcpy.3,v 1.11 2003/06/26 12:25:22 wiz Exp $ +.\" from OpenBSD: strlcpy.3,v 1.11 2000/11/16 23:27:41 angelos Exp +.\" +.\" Copyright (c) 1998, 2000 Todd C. Miller <Todd.Miller@courtesan.com> +.\" All rights reserved. +.\" +.\" 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. The name of the author may not be used to endorse or promote products +.\" derived from this software without specific prior written permission. +.\" +.\" THIS SOFTWARE IS PROVIDED ``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 AUTHOR 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. +.\" +.Dd March 1, 2001 +.Dt STRLCPY 3 +.Os +.Sh NAME +.Nm strlcpy , +.Nm strlcat +.Nd size-bounded string copying and concatenation +.Sh LIBRARY +.Lb libc +.Sh SYNOPSIS +.In string.h +.Ft size_t +.Fn strlcpy "char *dst" "const char *src" "size_t size" +.Ft size_t +.Fn strlcat "char *dst" "const char *src" "size_t size" +.Sh DESCRIPTION +The +.Fn strlcpy +and +.Fn strlcat +functions copy and concatenate strings respectively. +They are designed +to be safer, more consistent, and less error prone replacements for +.Xr strncpy 3 +and +.Xr strncat 3 . +Unlike those functions, +.Fn strlcpy +and +.Fn strlcat +take the full size of the buffer (not just the length) and guarantee to +NUL-terminate the result (as long as +.Fa size +is larger than 0 or, in the case of +.Fn strlcat , +as long as there is at least one byte free in +.Fa dst ) . +Note that you should include a byte for the NUL in +.Fa size . +Also note that +.Fn strlcpy +and +.Fn strlcat +only operate on true +.Dq C +strings. +This means that for +.Fn strlcpy +.Fa src +must be NUL-terminated and for +.Fn strlcat +both +.Fa src +and +.Fa dst +must be NUL-terminated. +.Pp +The +.Fn strlcpy +function copies up to +.Fa size +- 1 characters from the NUL-terminated string +.Fa src +to +.Fa dst , +NUL-terminating the result. +.Pp +The +.Fn strlcat +function appends the NUL-terminated string +.Fa src +to the end of +.Fa dst . +It will append at most +.Fa size +- strlen(dst) - 1 bytes, NUL-terminating the result. +.Sh RETURN VALUES +The +.Fn strlcpy +and +.Fn strlcat +functions return the total length of the string they tried to create. +For +.Fn strlcpy +that means the length of +.Fa src . +For +.Fn strlcat +that means the initial length of +.Fa dst +plus +the length of +.Fa src . +While this may seem somewhat confusing it was done to make +truncation detection simple. +.Pp +Note however, that if +.Fn strlcat +traverses +.Fa size +characters without finding a NUL, the length of the string is considered +to be +.Fa size +and the destination string will not be NUL-terminated (since there was +no space for the NUL). +This keeps +.Fn strlcat +from running off the end of a string. +In practice this should not happen (as it means that either +.Fa size +is incorrect or that +.Fa dst +is not a proper +.Dq C +string). +The check exists to prevent potential security problems in incorrect code. +.Sh EXAMPLES +The following code fragment illustrates the simple case: +.Bd -literal -offset indent +char *s, *p, buf[BUFSIZ]; + +\&... + +(void)strlcpy(buf, s, sizeof(buf)); +(void)strlcat(buf, p, sizeof(buf)); +.Ed +.Pp +To detect truncation, perhaps while building a pathname, something +like the following might be used: +.Bd -literal -offset indent +char *dir, *file, pname[MAXPATHLEN]; + +\&... + +if (strlcpy(pname, dir, sizeof(pname)) \*[Ge] sizeof(pname)) + goto toolong; +if (strlcat(pname, file, sizeof(pname)) \*[Ge] sizeof(pname)) + goto toolong; +.Ed +.Pp +Since we know how many characters we copied the first time, we can +speed things up a bit by using a copy instead of an append: +.Bd -literal -offset indent +char *dir, *file, pname[MAXPATHLEN]; +size_t n; + +\&... + +n = strlcpy(pname, dir, sizeof(pname)); +if (n \*[Ge] sizeof(pname)) + goto toolong; +if (strlcpy(pname + n, file, sizeof(pname) - n) \*[Ge] sizeof(pname) - n) + goto toolong; +.Ed +.Pp +However, one may question the validity of such optimizations, as they +defeat the whole purpose of +.Fn strlcpy +and +.Fn strlcat . +.Sh SEE ALSO +.Xr snprintf 3 , +.Xr strncat 3 , +.Xr strncpy 3 +.Sh HISTORY +.Fn strlcpy +and +.Fn strlcat +first appeared in +.Ox 2.4 , +then in +.Nx 1.4.3 +and +.Fx 3.3 . |