libpayload/string: add strndup() function

Change-Id: Ie509e49f21fb537692704ac6527efa09649164e3
Signed-off-by: Thomas Heijligen <src@posteo.de>
Reviewed-on: https://review.coreboot.org/c/coreboot/+/70115
Reviewed-by: Jakub Czapiga <jacz@semihalf.com>
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>

payloads/libpayload/include/string.h

@@ -59,6 +59,7 @@ char *strcat(char *d, const char *s);
 char *strchr(const char *s, int c);
 char *strrchr(const char *s, int c);
 char *strdup(const char *s);
+char *strndup(const char *s, size_t size);
 char *strstr(const char *h, const char *n);
 char *strsep(char **stringp, const char *delim);
 size_t strspn(const char *s, const char *a);

payloads/libpayload/libc/string.c

@@ -321,6 +321,25 @@ char *strdup(const char *s)
 	return p;
 }
 
+/**
+ * Duplicate a string with a max length of size
+ *
+ * @param s The string to duplicate.
+ * @param size The max length of the string
+ * @return A pointer to the copy of the original string.
+ */
+char *strndup(const char *s, size_t size)
+{
+	size_t n = strnlen(s, size);
+	char *p = malloc(n + 1);
+
+	if (p != NULL) {
+		strncpy(p, s, n);
+		p[n] = 0;
+	}
+	return p;
+}
+
 /**
  * Find a substring within a string.
  *