strcpy/strncpy、strcat/strncpy的替代方案strlcpy,strlcat

strlcat.c

#include <sys/types.h>
#include <string.h>

/*
 * Appends src to string dst of size dsize (unlike strncat, dsize is the
 * full size of dst, not space left).  At most dsize-1 characters
 * will be copied.  Always NUL terminates (unless dsize <= strlen(dst)).
 * Returns strlen(src) + MIN(dsize, strlen(initial dst)).
 * If retval >= dsize, truncation occurred.
 */
size_t
strlcat(char *dst, const char *src, size_t dsize)
{
    const char *odst = dst;
    const char *osrc = src;
    size_t n = dsize;
    size_t dlen;

    /* Find the end of dst and adjust bytes left but don't go past end. */
    while (n-- != 0 && *dst != '\0')
        dst++;
    dlen = dst - odst;
    n = dsize - dlen;

    if (n-- == 0)
        return(dlen + strlen(src));
    while (*src != '\0') {
        if (n != 0) {
            *dst++ = *src;
            n--;
        }
        src++;
    }
    *dst = '\0';

    return(dlen + (src - osrc));    /* count does not include NUL */
}

测试代码 strlcattest.c

#include <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <setjmp.h>
#include <signal.h>
#include <unistd.h>

volatile sig_atomic_t got_signal;
sigjmp_buf jmpenv;

void
handler(int signo)
{
        got_signal = signo;
    siglongjmp(jmpenv, 1);
}

int
main(int argc, char *argv[])
{
    char *buf, *cp, *ep;
    struct sigaction sa;
    size_t len, bufsize;
    int failures = 0;

    bufsize = getpagesize(); /* trigger guard pages easily */
    buf = malloc(bufsize);
    if (buf == NULL) {
        fprintf(stderr, "unable to allocate memory\n");
        return 1;
    }
    memset(buf, 'z', bufsize);
    ep = buf + bufsize;

    /* Test appending to an unterminated string. */
    len = strlcat(buf, "abcd", bufsize);
    if (len != 4 + bufsize) {
        fprintf(stderr,
            "strlcat: failed unterminated buffer test (1a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    for (cp = buf; cp < ep; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcat: failed unterminated buffer test (1b)\n");
            failures++;
            break;
        }
    }

    /* Test appending to a full string. */
    ep[-1] = '\0';
    len = strlcat(buf, "abcd", bufsize);
    if (len != 4 + bufsize - 1) {
        fprintf(stderr, "strlcat: failed full buffer test (2a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    for (cp = buf; cp < ep - 1; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcat: failed full buffer test (2b)\n");
            failures++;
            break;
        }
    }

    /* Test appending to an empty string. */
    ep[-1] = 'z';
    buf[0] = '\0';
    len = strlcat(buf, "abcd", bufsize);
    if (len != 4) {
        fprintf(stderr, "strlcat: failed empty buffer test (3a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    if (memcmp(buf, "abcd", sizeof("abcd")) != 0) {
        fprintf(stderr, "strlcat: failed empty buffer test (3b)\n");
        failures++;
    }
    for (cp = buf + len + 1; cp < ep; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcat: failed empty buffer test (3c)\n");
            failures++;
            break;
        }
    }

    /* Test appending to a NUL-terminated string. */
    memcpy(buf, "abcd", sizeof("abcd"));
    len = strlcat(buf, "efgh", bufsize);
    if (len != 8) {
        fprintf(stderr, "strlcat: failed empty buffer test (4a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    if (memcmp(buf, "abcdefgh", sizeof("abcdefgh")) != 0) {
        fprintf(stderr, "strlcat: failed empty buffer test (4b)\n");
        failures++;
    }
    for (cp = buf + len + 1; cp < ep; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcat: failed empty buffer test (4c)\n");
            failures++;
            break;
        }
    }

        /*
         * The following tests should result in SIGSEGV, however some
         * systems may erroneously report SIGBUS.
         * These tests assume that strlcat() is signal-safe.
         */
        memset(&sa, 0, sizeof(sa));
        sigemptyset(&sa.sa_mask);
        sa.sa_handler = handler;
        sigaction(SIGSEGV, &sa, NULL);
        sigaction(SIGBUS, &sa, NULL);

        /* Test copying to a NULL buffer with non-zero size. */
        got_signal = 0;
        if (sigsetjmp(jmpenv, 1) == 0) {
                len = strlcat(NULL, "abcd", sizeof(buf));
                fprintf(stderr, "strlcat: failed NULL dst test (5a), "
                    "expected signal %d, got len %zu\n", SIGSEGV, len);
                failures++;
        } else if (got_signal != SIGSEGV) {
                fprintf(stderr, "strlcat: failed NULL dst test (5b), "
                    "expected signal %d, got %d\n", SIGSEGV, got_signal);
                failures++;
        }

        /* Test copying from a NULL src. */
    memcpy(buf, "abcd", sizeof("abcd"));
        got_signal = 0;
        if (sigsetjmp(jmpenv, 1) == 0) {
                len = strlcat(buf, NULL, sizeof(buf));
                fprintf(stderr, "strlcat: failed NULL src test (6a), "
                    "expected signal %d, got len %zu\n", SIGSEGV, len);
                failures++;
        } else if (got_signal != SIGSEGV) {
                fprintf(stderr, "strlcat: failed NULL src test (6b), "
                    "expected signal %d, got %d\n", SIGSEGV, got_signal);
                failures++;
        }

    return failures;
}

strlcpy.c

#include <sys/types.h>
#include <string.h>

/*
 * Copy string src to buffer dst of size dsize.  At most dsize-1
 * chars will be copied.  Always NUL terminates (unless dsize == 0).
 * Returns strlen(src); if retval >= dsize, truncation occurred.
 */
size_t
strlcpy(char *dst, const char *src, size_t dsize)
{
    const char *osrc = src;
    size_t nleft = dsize;

    /* Copy as many bytes as will fit. */
    if (nleft != 0) {
        while (--nleft != 0) {
            if ((*dst++ = *src++) == '\0')
                break;
        }
    }

    /* Not enough room in dst, add NUL and traverse rest of src. */
    if (nleft == 0) {
        if (dsize != 0)
            *dst = '\0';        /* NUL-terminate dst */
        while (*src++)
            ;
    }

    return(src - osrc - 1);    /* count does not include NUL */
}

测试代码strlcpy.c

/*    $OpenBSD: strlcpytest.c,v 1.4 2021/09/01 09:26:32 jasper Exp $ */

/*
 * Copyright (c) 2014 Todd C. Miller <millert@openbsd.org>
 *
 * Permission to use, copy, modify, and distribute this software for any
 * purpose with or without fee is hereby granted, provided that the above
 * copyright notice and this permission notice appear in all copies.
 *
 * 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 <sys/types.h>

#include <stdio.h>
#include <stdlib.h>
#include <string.h>
#include <signal.h>
#include <setjmp.h>
#include <unistd.h>

volatile sig_atomic_t got_signal;
sigjmp_buf jmpenv;

void
handler(int signo)
{
    got_signal = signo;
    siglongjmp(jmpenv, 1);
}

int
main(int argc, char *argv[])
{
    char *buf, *buf2, *cp, *ep;
    struct sigaction sa;
    size_t len, bufsize;
    int failures = 0;

    bufsize = getpagesize(); /* trigger guard pages easily */
    buf = malloc(bufsize);
    buf2 = malloc(bufsize);
    if (buf == NULL || buf2 == NULL) {
        fprintf(stderr, "unable to allocate memory\n");
        return 1;
    }
    memset(buf, 'z', bufsize);
    ep = buf + bufsize;

    /* Test copying to a zero-length NULL buffer. */
    len = strlcpy(NULL, "abcd", 0);
    if (len != 4) {
        fprintf(stderr,
            "strlcpy: failed zero-length buffer test (1a)\n");
        failures++;
    }

    /* Test copying small string to a large buffer. */
    len = strlcpy(buf, "abcd", bufsize);
    if (len != 4) {
        fprintf(stderr, "strlcpy: failed large buffer test (2a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    if (memcmp(buf, "abcd", sizeof("abcd")) != 0) {
        fprintf(stderr, "strlcpy: failed large buffer test (2b)\n");
        failures++;
    }
    for (cp = buf + len + 1; cp < ep; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcpy: failed large buffer test (2c)\n");
            failures++;
            break;
        }
    }

    /* Test copying large string to a small buffer. */
    memset(buf, 'z', bufsize);
    memset(buf2, 'x', bufsize - 1);
    buf2[bufsize - 1] = '\0';
    len = strlcpy(buf, buf2, bufsize / 2);
    if (len != bufsize - 1) {
        fprintf(stderr, "strlcpy: failed small buffer test (3a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    len = (bufsize / 2) - 1;
    if (memcmp(buf, buf2, len) != 0 || buf[len] != '\0') {
        fprintf(stderr, "strlcpy: failed small buffer test (3b)\n");
        failures++;
    }
    for (cp = buf + len + 1; cp < ep; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcpy: failed small buffer test (3c)\n");
            failures++;
            break;
        }
    }

    /* Test copying to a 1-byte buffer. */
    memset(buf, 'z', bufsize);
    len = strlcpy(buf, "abcd", 1);
    if (len != 4) {
        fprintf(stderr, "strlcpy: failed 1-byte buffer test (4a)\n");
        failures++;
    }
    /* Make sure we only wrote where expected. */
    if (buf[0] != '\0') {
        fprintf(stderr, "strlcpy: failed 1-byte buffer test (4b)\n");
        failures++;
    }
    for (cp = buf + 1; cp < ep; cp++) {
        if (*cp != 'z') {
            fprintf(stderr,
                "strlcpy: failed 1-byte buffer test (4c)\n");
            failures++;
            break;
        }
    }

    /*
     * The following tests should result in SIGSEGV, however some
     * systems may erroneously report SIGBUS.
     * These tests assume that strlcpy() is signal-safe.
     */
    memset(&sa, 0, sizeof(sa));
    sigemptyset(&sa.sa_mask);
    sa.sa_handler = handler;
    sigaction(SIGSEGV, &sa, NULL);
    sigaction(SIGBUS, &sa, NULL);

    /* Test copying to a NULL buffer with non-zero size. */
    got_signal = 0;
    if (sigsetjmp(jmpenv, 1) == 0) {
        len = strlcpy(NULL, "abcd", sizeof(buf));
        fprintf(stderr, "strlcpy: failed NULL dst test (5a), "
            "expected signal %d, got len %zu\n", SIGSEGV, len);
        failures++;
    } else if (got_signal != SIGSEGV) {
        fprintf(stderr, "strlcpy: failed NULL dst test (5b), "
            "expected signal %d, got %d\n", SIGSEGV, got_signal);
        failures++;
    }

    /* Test copying from a NULL src. */
    got_signal = 0;
    if (sigsetjmp(jmpenv, 1) == 0) {
        len = strlcpy(buf, NULL, sizeof(buf));
        fprintf(stderr, "strlcpy: failed NULL src test (6a), "
            "expected signal %d, got len %zu\n", SIGSEGV, len);
        failures++;
    } else if (got_signal != SIGSEGV) {
        fprintf(stderr, "strlcpy: failed NULL src test (6b), "
            "expected signal %d, got %d\n", SIGSEGV, got_signal);
        failures++;
    }

    return failures;
}

代码来源：http://ftp.openbsd.org/pub/OpenBSD/7.0/src.tar.gz