.
   A return value between 0 and <code class="code">len</code> exclusive means that
   not all requested <code class="code">len</code> characters were read, either because
   no more characters were available at that time, or because
   the implementation found it convenient to do a partial read;
   <code class="code">input</code> must be called again to read the remaining characters,
   if desired.  (See also <a href="Pervasives.html#VALreally_input"><code class="code">really_input</code></a> for reading
