Add strtcat[_a](), and use it instead of its pattern

lib/Makefile.am

@@ -239,6 +239,8 @@ libshadow_la_SOURCES = \
 	string/strcpy/strncat.h \
 	string/strcpy/strncpy.c \
 	string/strcpy/strncpy.h \
+	string/strcpy/strtcat.c \
+	string/strcpy/strtcat.h \
 	string/strcpy/strtcpy.c \
 	string/strcpy/strtcpy.h \
 	string/strdup/strdup.c \

lib/salt.c

@@ -27,6 +27,7 @@
 #include "prototypes.h"
 #include "shadowlog.h"
 #include "string/strcmp/streq.h"
+#include "string/strcpy/strtcat.h"
 
 
 #if (defined CRYPT_GENSALT_IMPLEMENTS_AUTO_ENTROPY && \
@@ -443,12 +444,8 @@ static /*@observer@*/const char *gensalt (size_t salt_size)
 
 	return retval;
 #else /* USE_XCRYPT_GENSALT */
-	/* Check if the result buffer is long enough. */
-	assert (GENSALT_SETTING_SIZE > strlen (result) + salt_len);
 
-	/* Concatenate a pseudo random salt. */
-	strncat (result, gensalt (salt_len),
-		 GENSALT_SETTING_SIZE - strlen (result) - 1);
+	assert(strtcat_a(result, gensalt(salt_len)) != -1);
 
 	return result;
 #endif /* USE_XCRYPT_GENSALT */

lib/string/README

@@ -189,10 +189,10 @@ strcpy/ - String copying
     STRTCPY()
 	Like strtcpy(), but takes an array.
 
-    strtcat()  // Unimplemented
+    strtcat()
 	Catenate a string after an existing string, with truncation.
 	Rarely useful.  Consider using stpecpy() instead.
-    STRTCAT()  // Unimplemented
+    strtcat_a()
 	Like strtcat(), but takes an array.
 
     stpecpy()

lib/string/strcpy/strtcat.c

@@ -0,0 +1,13 @@
+// SPDX-FileCopyrightText: 2025, Alejandro Colomar <[email protected]>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#include "config.h"
+
+#include "string/strcpy/strtcat.h"
+
+#include <stddef.h>
+
+
+extern inline ssize_t strtcat(char *restrict dst, const char *restrict src,
+    size_t dsize);

lib/string/strcpy/strtcat.h

@@ -0,0 +1,45 @@
+// SPDX-FileCopyrightText: 2025, Alejandro Colomar <[email protected]>
+// SPDX-License-Identifier: BSD-3-Clause
+
+
+#ifndef SHADOW_INCLUDE_LIB_STRING_STRCPY_STRTCAT_H_
+#define SHADOW_INCLUDE_LIB_STRING_STRCPY_STRTCAT_H_
+
+
+#include "config.h"
+
+#include <stddef.h>
+
+#include "attr.h"
+#include "sizeof.h"
+#include "string/strchr/strnul.h"
+#include "string/strcpy/stpecpy.h"
+
+
+// strtcat_a - string truncate catenate array
+#define strtcat_a(dst, src)  strtcat(dst, src, countof(dst))
+
+
+ATTR_STRING(2)
+inline ssize_t strtcat(char *restrict dst, const char *restrict src,
+    size_t dsize);
+
+
+// strtcat - string truncate catenate
+// Returns new length, or -1 on truncation.
+inline ssize_t
+strtcat(char *restrict dst, const char *restrict src, size_t dsize)
+{
+	char  *p, *end;
+
+	end = dst + dsize;
+
+	p = stpecpy(strnul(dst), end, src);
+	if (p == NULL)
+		return -1;
+
+	return p - dst;
+}
+
+
+#endif  // include guard