It is accessed by at least two threads:

* `[shutoff]` in `UnregisterHTTPHandler`
* `[http]` in `http_request_cb`
{
    struct evbuffer* buf = evhttp_request_get_input_buffer(req);
    if (!buf)
        return "";
    size_t size = evbuffer_get_length(buf);
    /** Trivial implementation: if this is ever a performance bottleneck,
     * internal copying can be avoided in multi-segment buffers by using
     * evbuffer_peek and an awkward loop. Though in that case, it'd be even
     * better to not copy into an intermediate string but use a stream
     * abstraction to consume the evbuffer on the fly in the parsing algorithm.
     */
    const char* data = (const char*)evbuffer_pullup(buf, size);
    if (!data) 
        return "";
    std::string rv(data, size);
    evbuffer_drain(buf, size);
    return rv;
}
void HTTPRequest::WriteHeader(const std::string& hdr, const std::string& value)
{
    struct evkeyvalq* headers = evhttp_request_get_output_headers(req);
    assert(headers);
    evhttp_add_header(headers, hdr.c_str(), value.c_str());
}
/** Closure sent to main thread to request a reply to be sent to
 * a HTTP request.
 * Replies must be sent in the main loop in the main http thread,
 * this cannot be done from worker threads.
 */
void HTTPRequest::WriteReply(int nStatus, const std::string& strReply)