Add uc_dstr_copy

src/dstr.c

@@ -17,6 +17,27 @@ void uc_dstr_destroy(struct DStr *str)
     free(str->str);
 }
 
+int uc_dstr_copy(struct DStr *dest, const struct DStr *src)
+{
+    char *s;
+
+    uc_dstr_init(dest);
+    if (src->allocated == 0) {
+        return 0;
+    }
+
+    s = uc_dstr_put(dest, src->len);
+    if (s == NULL) {
+        return -1;
+    }
+
+    //+1 to copy a potential nul terminator, uc_dstr_put 
+    //guarantees we have room for it.
+    memcpy(s, src->str, UC_MIN(src->len + 1, src->allocated));
+
+    return 0;
+}
+
 size_t uc_dstr_available(const struct DStr *str)
 {
     return str->allocated - str->len;