88 lines
2.6 KiB
Java
88 lines
2.6 KiB
Java
/* LoRaWAN Timeserver
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construct 7 byte timesync_answer from gateway timestamp and node's time_sync_req
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byte meaning
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1 sequence number (taken from node's time_sync_req)
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2 timezone in 15 minutes steps
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3..6 current second (from epoch time 1970)
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7 1/250ths fractions of current second
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*/
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function timecompare(a, b) {
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const timeA = a.time;
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const timeB = b.time;
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let comparison = 0;
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if (timeA > timeB) {
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comparison = 1;
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} else if (timeA < timeB) {
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comparison = -1;
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}
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return comparison;
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}
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let confidence = 2000; // max millisecond diff gateway time to server time
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// guess if we have received a valid time_sync_req command
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if (msg.payload.payload_raw.length != 1)
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return;
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var deviceMsg = { payload: msg.payload.dev_id };
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var seqNo = msg.payload.payload_raw[0];
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var seqNoMsg = { payload: seqNo };
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var gateway_list = msg.payload.metadata.gateways;
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// filter all gateway timestamps that have milliseconds part (which we assume have a ".")
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var gateways = gateway_list.filter(function (element) {
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return (element.time.includes("."));
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});
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var gateway_time = gateways.map(gw => {
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return {
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time: new Date(gw.time),
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eui: gw.gtw_id,
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}
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});
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var server_time = new Date(msg.payload.metadata.time);
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// validate all gateway timestamps against lorawan server_time (which is assumed to be recent)
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var gw_timestamps = gateway_time.filter(function (element) {
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return ((element.time > (server_time - confidence) && element.time <= server_time));
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});
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// if no timestamp left, we have no valid one and exit
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if (gw_timestamps.length === 0) {
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var notavailMsg = { payload: "n/a" };
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var notimeMsg = { payload: 0xff };
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var buf2 = Buffer.alloc(1);
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msg.payload = new Buffer(buf2.fill(0xff));
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msg.port = 9; // Paxcounter TIMEPORT
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return [notavailMsg, notavailMsg, deviceMsg, seqNoMsg, msg];}
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// sort time array in ascending order to find most recent timestamp for time answer
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gw_timestamps.sort(timecompare);
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var timestamp = gw_timestamps[0].time;
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var eui = gw_timestamps[0].eui;
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var offset = server_time - timestamp;
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var seconds = Math.floor(timestamp/1000);
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var fractions = (timestamp % 1000) / 4;
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let buf = new ArrayBuffer(7);
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new DataView(buf).setUint8(0, seqNo);
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// Timezone (in 15min steps)
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var timezone = 8; // CET = UTC+2h
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new DataView(buf).setUint8(1, timezone);
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new DataView(buf).setUint32(2, seconds);
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new DataView(buf).setUint8(6, fractions);
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msg.payload = new Buffer(new Uint8Array(buf));
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msg.port = 9; // Paxcounter TIMEPORT
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var euiMsg = { payload: eui };
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var offsetMsg = { payload: offset };
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return [euiMsg, offsetMsg, deviceMsg, seqNoMsg, msg]; |