basic/in-addr-util: add IN_ADDR_TO_STRING

Since we don't need the error value, and the buffer is allocated with a fixed
size, the whole logic provided by in_addr_to_string() becomes unnecessary, so
it's enough to wrap inet_ntop() directly.

inet_ntop() can only fail with ENOSPC. But we specify a buffer that is supposed
to be large enough, so this should never fail. A bunch of tests of this are added.
This allows all the wrappers like strna(), strnull(), strempty() to be dropped.

The guard of 'if (DEBUG_LOGGING)' can be dropped from around log_debug(),
because log_debug() implements the check outside of the function call. But
log_link_debug() does not, so it we need it to avoid unnecessary evaluation of
the formatting.

src/test/test-in-addr-util.c

@@ -347,12 +347,14 @@ TEST(in_addr_prefix_range) {
 
 static void test_in_addr_to_string_one(int f, const char *addr) {
         union in_addr_union ua;
-        _cleanup_free_ char *r = NULL;
+        _cleanup_free_ char *r;
 
         assert_se(in_addr_from_string(f, addr, &ua) >= 0);
         assert_se(in_addr_to_string(f, &ua, &r) >= 0);
         printf("test_in_addr_to_string_one: %s == %s\n", addr, r);
         assert_se(streq(addr, r));
+
+        assert_se(streq(r, IN_ADDR_TO_STRING(f, &ua)));
 }
 
 TEST(in_addr_to_string) {

src/test/test-utmp.c

@@ -41,10 +41,7 @@ TEST(dump_run_utmp) {
 
                 union in_addr_union addr = {};
                 memcpy(&addr, u->ut_addr_v6, MIN(sizeof(addr), sizeof(u->ut_addr_v6)));
-                _cleanup_free_ char *pretty = NULL;
                 bool is_ipv4 = memeqzero((const uint8_t*) &addr + 4, sizeof(addr) - 4);
-                (void) in_addr_to_string(is_ipv4 ? AF_INET : AF_INET6,
-                                         &addr, &pretty);
 
                 log_info("%14s %10"PID_PRI" line=%-7.*s id=%-4.4s name=%-8.*s session=%lu host=%.*s addr=%s",
                          type,
@@ -54,7 +51,7 @@ TEST(dump_run_utmp) {
                          UT_NAMESIZE, u->ut_user,
                          (long unsigned) u->ut_session,
                          UT_HOSTSIZE, u->ut_host,
-                         strempty(pretty));
+                         IN_ADDR_TO_STRING(is_ipv4 ? AF_INET : AF_INET6, &addr));
         }
 }