I need to make POST http request at exact timestamp in future, as accurate as possible, down to milliseconds. But there is network latency as well. How can I achieve such a goal?
setTimeout is not enough here, because it always takes some time resulting in latecomer request due vary network latency. And firing this request before target timestamp may result in early coming request.
My goal is to make request guaranteed came to server after target timestamp, but as soon as possible after it. Could you suggest any solutions with Nodejs?
CodePudding user response：
The best you can do in nodejs (which is not a real-time system) is to do the following:
Premeasure the expected latency so you know about how much to presend the request.
Use
setTimeout()to schedule the send at precisely the one-way latency time before your target time. There is no other mechanism in nodejs that would be more precise.If your request involves a DNS lookup, you can prefetch the TCP address for your hostname and take the DNS lookup time out of your request cycle or at least prime the local DNS cache.
Create a dedicated nodejs program that does nothing else - so its event loop will not be doing anything else at the time the
setTimeout()needs to run. You could run this as a child_process from your larger program if desired.Run a number of tests to see how the timing works and, if you are consistently off by some margin, then adjust your latency offset.
You can develop a regular latency test to determine if the latency changes with time.
As others have said, there is no way to predict what the natural response time will be of the target server (how long it takes to start processing your request from the moment your network packets arrive there). If lots of incoming requests are all racing for the same time slot, then your request will get interleaved in among all the others and served in some order that you do not control.
Other things you can consider. If the target server supports the latest http specifications, then you can have a pre-established http connection with the host (perhaps targeting some other endpoint) that will be kept alive for you to send your precise timing request on. This would take some experimentation to figure out what the target host supports and if this would work.