ape: add strnlen

sys/include/ape/string.h

@@ -32,6 +32,7 @@ extern char *strtok(char *, const char *);
 extern void *memset(void *, int, size_t);
 extern char *strerror(int);
 extern size_t strlen(const char *);
+extern size_t strnlen(const char *, size_t);
 
 #ifdef _REENTRANT_SOURCE
 extern char *strerror_r(int, const char *, int);

sys/src/ape/lib/ap/gen/mkfile

@@ -43,6 +43,7 @@ ALLOFILES=\
 	strncat.$O\
 	strncmp.$O\
 	strncpy.$O\
+	strnlen.$O\
 	strpbrk.$O\
 	strrchr.$O\
 	strspn.$O\

sys/src/ape/lib/ap/gen/strlen.c

@@ -3,6 +3,5 @@
 size_t
 strlen(const char *s)
 {
-
 	return strchr(s, 0) - s;
 }

sys/src/ape/lib/ap/gen/strnlen.c

@@ -0,0 +1,11 @@
+#include <string.h>
+
+size_t
+strnlen(const char *s, size_t maxlen)
+{
+	size_t i;
+
+	for (i = 0; i < maxlen && s[i] != '\0'; i++)
+		;
+	return i;
+}