Repository: bitcoin/bitcoin
File: src/httpserver.cpp (C++)

Code before:
     * 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) // returns nullptr in case of empty buffer
        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)
{
    assert(!replySent && req);
    if (m_interrupt) {
        WriteHeader("Connection", "close");
    }
    // Send event to main http thread to send reply message
    struct evbuffer* evb = evhttp_request_get_output_buffer(req);
    assert(evb);
    evbuffer_add(evb, strReply.data(), strReply.size());
    auto req_copy = req;
    HTTPEvent* ev = new HTTPEvent(eventBase, true, [req_copy, nStatus]{
        evhttp_send_reply(req_copy, nStatus, nullptr, nullptr);
        // Re-enable reading from the socket. This is the second part of the libevent
        // workaround above.
        if (event_get_version_number() >= 0x02010600 && event_get_version_number() < 0x02010900) {
            evhttp_connection* conn = evhttp_request_get_connection(req_copy);
            if (conn) {
                bufferevent* bev = evhttp_connection_get_bufferevent(conn);
                if (bev) {
                    bufferevent_enable(bev, EV_READ | EV_WRITE);
                }
            }
        }
    });
    ev->trigger(nullptr);

Review comment (suggestion):
Not sure if a `Span<byte>` or string_view is best suited here.  In principle we're dealing with binary data here, not necessarily a string.

Code after:
    /** 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) // returns nullptr in case of empty buffer
        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, std::span<const std::byte> reply)
{
    assert(!replySent && req);
    if (m_interrupt) {
        WriteHeader("Connection", "close");
    }
    // Send event to main http thread to send reply message
    struct evbuffer* evb = evhttp_request_get_output_buffer(req);
    assert(evb);
    evbuffer_add(evb, reply.data(), reply.size());
    auto req_copy = req;
    HTTPEvent* ev = new HTTPEvent(eventBase, true, [req_copy, nStatus]{
        evhttp_send_reply(req_copy, nStatus, nullptr, nullptr);
        // Re-enable reading from the socket. This is the second part of the libevent
        // workaround above.
        if (event_get_version_number() >= 0x02010600 && event_get_version_number() < 0x02010900) {
            evhttp_connection* conn = evhttp_request_get_connection(req_copy);
            if (conn) {
                bufferevent* bev = evhttp_connection_get_bufferevent(conn);
                if (bev) {
                    bufferevent_enable(bev, EV_READ | EV_WRITE);
                }
            }
        }
    });