HTTP/2: implemented per request timeouts (closes #626). Previously, there were only three timeouts used globally for the whole HTTP/2 connection: 1. Idle timeout for inactivity when there are no streams in processing (the "http2_idle_timeout" directive); 2. Receive timeout for incomplete frames when there are no streams in processing (the "http2_recv_timeout" directive); 3. Send timeout when there are frames waiting in the output queue (the "send_timeout" directive on a server level). Reaching one of these timeouts leads to HTTP/2 connection close. This left a number of scenarios when a connection can get stuck without any processing and timeouts: 1. A client has sent the headers block partially so nginx starts processing a new stream but cannot continue without the rest of HEADERS and/or CONTINUATION frames; 2. When nginx waits for the request body; 3. All streams are stuck on exhausted connection or stream windows. The first idea that was rejected was to detect when the whole connection gets stuck because of these situations and set the global receive timeout. The disadvantage of such approach would be inconsistent behaviour in some typical use cases. For example, if a user never replies to the browser's question about where to save the downloaded file, the stream will be eventually closed by a timeout. On the other hand, this will not happen if there's some activity in other concurrent streams. Now almost all the request timeouts work like in HTTP/1.x connections, so the "client_header_timeout", "client_body_timeout", and "send_timeout" are respected. These timeouts close the request. The global timeouts work as before. Previously, the c->write->delayed flag was abused to avoid setting timeouts on stream events. Now, the "active" and "ready" flags are manipulated instead to control the processing of individual streams.