Add and use bx_strndup() in 'tools' module for cross-platform compatibility

src/tools.c

@@ -694,12 +694,11 @@ char *trimdup(char *s, char *e)
     while (e > s && (*e == ' ' || *e == '\t')) {
         --e;
     }
-    return strndup(s, e - s + 1);
+    return bx_strndup(s, e - s + 1);
 }
 
 
 
-
 int tag_is_valid(char *tag)
 {
     if (tag == NULL) {
@@ -715,4 +714,26 @@ int tag_is_valid(char *tag)
 }
 
 
+
+char *bx_strndup(const char *s, size_t n)
+{
+    if (s == NULL) {
+        return NULL;
+    }
+
+    size_t len = strlen(s);
+    if (n < len) {
+        len = n;
+    }
+
+    char *result = (char *) malloc(len + 1);
+    if (result == NULL) {
+        return NULL;
+    }
+
+    result[len] = '\0';
+    return (char *) memcpy(result, s, len);
+}
+
+
 /*EOF*/                                                  /* vim: set sw=4: */

src/tools.h

@@ -115,6 +115,17 @@ char *trimdup(char *s, char *e);
 int tag_is_valid(char *tag);
 
 
+/**
+ * Duplicate at most `n` bytes from the given string `s`.  Memory for the new string is obtained with `malloc()`, and
+ * can be freed with `free()`. A terminating null byte is added. We include this implementation because the libc's 
+ * `strndup()` is not consistently available across all platforms.
+ * @param s a string
+ * @param n maximum number of characters to copy (excluding the null byte)
+ * @returns a new string, or `NULL` if either `s` was also `NULL`, or out of memory
+ */
+char *bx_strndup(const char *s, size_t n);
+
+
 #endif
 
 /*EOF*/                                          /* vim: set cindent sw=4: */