span><span class="special">::</span><span class="identifier">size_t</span>
<span class="identifier">callback</span><span class="special">(</span>
    <span class="identifier">std</span><span class="special">::</span><span class="identifier">uint64_t</span> <span class="identifier">remain</span><span class="special">,</span>       <span class="comment">// Octets remaining in this chunk, includes `body`</span>
    <span class="identifier">string_view</span> <span class="identifier">body</span><span class="spe