Add and use STRNLEN() instead of more complex code

[alejandro-colomar]

---

Revisions:

v2

• Simplify static-assertions by using SIZEOF_ARRAY.

$ git rd 
1:  2a4bb60f = 1:  2a4bb60f lib/: Use simple assignment instead of memcpy(3)
2:  1a06250a = 2:  1a06250a lib/string/strlen/: STRNLEN(): Add macro
3:  a85b0961 = 3:  a85b0961 lib/utmp.c: Use countof() for the number of elements of an array
4:  475a76c0 = 4:  475a76c0 lib/utmp.c: Only write ut_syslen if we've written ut_host
5:  813f0912 = 5:  813f0912 lib/: Use STRNLEN() instead of its pattern
6:  5933a030 < -:  -------- lib/typetraits.h: is_array(): Add macro
7:  2b527cb3 ! 6:  fb1c59bd lib/string/strcpy/: MEMCPY(): Add macro
    @@ lib/string/strcpy/memcpy.h (new)
     +
     +#include <string.h>
     +
    -+#include "typetraits.h"
    ++#include "sizeof.h"
     +
     +#include <assert.h>
     +
     +
     +#define MEMCPY(dst, src)                                              \
     +({                                                                    \
    -+  static_assert(is_array(src), "");                             \
    -+  static_assert(is_array(dst), "");                             \
    -+  static_assert(sizeof(dst) == sizeof(src), "");                \
    ++  static_assert(SIZEOF_ARRAY(dst) == SIZEOF_ARRAY(src), "");    \
     +                                                                      \
    -+  memcpy(dst, src, sizeof(dst));                                \
    ++  memcpy(dst, src, SIZEOF_ARRAY(dst));                          \
     +})
     +
     +
8:  166e380a = 7:  0825296f lib/utmp.c: prepare_utmp(): Use MEMCPY() instead of its pattern

v2b

• Rebase

$ git rd 
1:  2a4bb60f = 1:  21385568 lib/: Use simple assignment instead of memcpy(3)
2:  1a06250a = 2:  4a711c5a lib/string/strlen/: STRNLEN(): Add macro
3:  a85b0961 = 3:  43454a8e lib/utmp.c: Use countof() for the number of elements of an array
4:  475a76c0 = 4:  94f310af lib/utmp.c: Only write ut_syslen if we've written ut_host
5:  813f0912 = 5:  b1698021 lib/: Use STRNLEN() instead of its pattern
6:  fb1c59bd = 6:  1c6b62eb lib/string/strcpy/: MEMCPY(): Add macro
7:  0825296f ! 7:  0fd00afd lib/utmp.c: prepare_utmp(): Use MEMCPY() instead of its pattern
    @@ Commit message
     
      ## lib/utmp.c ##
     @@
    - #include "sizeof.h"
    + #include "string/strchr/strnul.h"
      #include "string/strcmp/streq.h"
      #include "string/strcmp/strprefix.h"
     +#include "string/strcpy/memcpy.h"

v2c

• Rebase

$ git range-diff 21385568d8a6^..gh/strnlen shadow/master..strnlen 
1:  21385568 = 1:  6571d0fd lib/: Use simple assignment instead of memcpy(3)
2:  4a711c5a = 2:  dc7dcb5b lib/string/strlen/: STRNLEN(): Add macro
3:  43454a8e = 3:  06ada7ec lib/utmp.c: Use countof() for the number of elements of an array
4:  94f310af = 4:  c12b4f12 lib/utmp.c: Only write ut_syslen if we've written ut_host
5:  b1698021 = 5:  622bde1d lib/: Use STRNLEN() instead of its pattern
6:  1c6b62eb = 6:  682b8a6b lib/string/strcpy/: MEMCPY(): Add macro
7:  0fd00afd = 7:  1db02350 lib/utmp.c: prepare_utmp(): Use MEMCPY() instead of its pattern

v3

• Rebase after Clean up lib/utmp.c and lib/logind.c #1290 .

$ git range-diff shadow/master..gh/strnlen gh/logind_utmp..strnlen 
1:  6571d0fd = 1:  6a1e4f8e lib/: Use simple assignment instead of memcpy(3)
2:  dc7dcb5b = 2:  6ae9cd00 lib/string/strlen/: STRNLEN(): Add macro
3:  06ada7ec ! 3:  770bc281 lib/utmp.c: Use countof() for the number of elements of an array
    @@ Commit message
     
      ## lib/utmp.c ##
     @@ lib/utmp.c: prepare_utmp(const char *name, const char *line, const char *host,
    - #endif
    +           STRNCPY(utent->ut_host, hostname);
      #if defined(HAVE_STRUCT_UTMPX_UT_SYSLEN)
                utent->ut_syslen = MIN (strlen (hostname),
     -                                  sizeof (utent->ut_host));
4:  c12b4f12 < -:  -------- lib/utmp.c: Only write ut_syslen if we've written ut_host
5:  622bde1d ! 4:  6404cd44 lib/: Use STRNLEN() instead of its pattern
    @@ lib/string/strdup/xstrndup.h
     
      ## lib/utmp.c ##
     @@
    - #include "string/strcpy/strtcpy.h"
    + #include "string/strdup/strndup.h"
      #include "string/strdup/xstrdup.h"
      #include "string/strdup/xstrndup.h"
    --
    --#ident "$Id$"
     +#include "string/strlen/strnlen.h"
      
      
      #define UTX_LINESIZE  countof(memberof(struct utmpx, ut_line))
     @@ lib/utmp.c: prepare_utmp(const char *name, const char *line, const char *host,
    - #if defined(HAVE_STRUCT_UTMPX_UT_HOST)
    +           struct addrinfo *info = NULL;
                STRNCPY(utent->ut_host, hostname);
    - # if defined(HAVE_STRUCT_UTMPX_UT_SYSLEN)
    + #if defined(HAVE_STRUCT_UTMPX_UT_SYSLEN)
     -          utent->ut_syslen = MIN (strlen (hostname),
     -                                  countof(utent->ut_host));
     +          utent->ut_syslen = STRNLEN(utent->ut_host);
    - # endif
      #endif
      #if defined(HAVE_STRUCT_UTMPX_UT_ADDR) || defined(HAVE_STRUCT_UTMPX_UT_ADDR_V6)
    +           if (getaddrinfo (hostname, NULL, NULL, &info) == 0) {
6:  682b8a6b = 5:  213de3d3 lib/string/strcpy/: MEMCPY(): Add macro
7:  1db02350 ! 6:  1218c16f lib/utmp.c: prepare_utmp(): Use MEMCPY() instead of its pattern
    @@ lib/utmp.c
     +#include "string/strcpy/memcpy.h"
      #include "string/strcpy/strncpy.h"
      #include "string/strcpy/strtcpy.h"
    - #include "string/strdup/xstrdup.h"
    + #include "string/strdup/strndup.h"
     @@ lib/utmp.c: prepare_utmp(const char *name, const char *line, const char *host,
                        } else if (info->ai_family == AF_INET6) {
                                struct sockaddr_in6 *sa =

v4

• Move some commits to separate PRs.

$ git range-diff gh/logind_utmp gh/strnlen strnlen 
1:  6a1e4f8e < -:  -------- lib/: Use simple assignment instead of memcpy(3)
2:  6ae9cd00 = 1:  3641970d lib/string/strlen/: STRNLEN(): Add macro
3:  770bc281 = 2:  8dfd9df7 lib/utmp.c: Use countof() for the number of elements of an array
4:  6404cd44 = 3:  d2657a74 lib/: Use STRNLEN() instead of its pattern
5:  213de3d3 < -:  -------- lib/string/strcpy/: MEMCPY(): Add macro
6:  1218c16f < -:  -------- lib/utmp.c: prepare_utmp(): Use MEMCPY() instead of its pattern

v4b

• Rebase

$ git range-diff gh/logind_utmp..gh/strnlen logind_utmp..strnlen 
1:  35529f23 = 1:  bb829e7f lib/string/strlen/: STRNLEN(): Add macro
2:  bbfdfb4e = 2:  e3dad729 lib/utmp.c: Use countof() for the number of elements of an array
3:  ca7a891f = 3:  a2e44f57 lib/: Use STRNLEN() instead of its pattern

v4c

• Update lib/string/README.

$ git range-diff gh/logind_utmp gh/strnlen strnlen 
1:  bb829e7f ! 1:  92791d58 lib/string/strlen/: STRNLEN(): Add macro
    @@ lib/Makefile.am: libshadow_la_SOURCES = \
        string/strspn/stpspn.h \
        string/strspn/stprcspn.c \
     
    + ## lib/string/README ##
    +@@ lib/string/README: strsep/ - String separation
    +   Variant of strsep2ls() that allocates the array of strings.
    +   (But the strings themselves are not duplicated.)
    + 
    ++strlen/ - String length
    ++
    ++    STRNLEN()
    ++  Like strnlen(3), but take an array.
    ++
    + strftime.h
    +     STRFTIME()
    +   Like strftime(3), but takes an array.
    +
      ## lib/string/strlen/strnlen.c (new) ##
     @@
     +// SPDX-FileCopyrightText: 2025, Alejandro Colomar <[email protected]>
2:  e3dad729 = 2:  21810b5b lib/utmp.c: Use countof() for the number of elements of an array
3:  a2e44f57 = 3:  f199c2c7 lib/: Use STRNLEN() instead of its pattern

v4d

• Rebase

$ git range-diff gh/logind_utmp..gh/strnlen logind_utmp..strnlen 
1:  92791d58 = 1:  47ca1fee lib/string/strlen/: STRNLEN(): Add macro
2:  21810b5b = 2:  b0d5de65 lib/utmp.c: Use countof() for the number of elements of an array
3:  f199c2c7 = 3:  979b0aab lib/: Use STRNLEN() instead of its pattern