Cache data from the serial buffer to try and improve reliability

Author: Jbithell

package-lock.json

@@ -1,4 +1,5 @@
 {
+  "name": "PSCWeather",
   "scripts": {
     "start": "node ./src/main.js"
   },

package.json

@@ -2,6 +2,7 @@ const SerialPort = require('serialport')
 const Delimiter = require('@serialport/parser-delimiter')
 const logger = require("./logger")
 const responseParser = require("./parser")
+const responseValidator = require("./validator")
 const sleep = require("./sleep")
 const windy = require("./targets/windy")
 const windguru = require("./targets/windguru")
@@ -44,17 +45,43 @@ function querySerial() {
     querySerial() //Request again
   })
 }
+/***
+ * Cache the serial connection as the messages can come through from the device in chunks
+ */
+let serialCache = { 
+  "cache": Buffer.from([]),
+  "updated": Date.now()
+}
+function cacheSerial(message) { //Build up a bit of a cache of serial messages because they seem to come in chunks
+  if (serialCache["updated"] < (Date.now() - 65000)) { //If the cache is older than 65 seconds
+    serialCache["cache"] = Buffer.from([]) //Reset the cache
+  }
+  serialCache["updated"] = Date.now()
+  serialCache["cache"] = Buffer.concat([serialCache["cache"],message]) //Add the new message to the cache
+
+  let offset = responseValidator(serialCache["cache"]) //Check if the cache is a complete message
+  if (offset !== false) { // If we have a full message then parse it, otherwise wait and let the cache build up a bit
+    const response = responseParser(serialCache["cache"], offset) //Parse the message
+    serialCache = { //Reset the serialCache
+      "cache": Buffer.from([]),
+      "updated": Date.now()
+    }
+    if (response) {
+      logger.log("debug","Received parsed weather data", response)
+      windy(response) // Send the data to windy
+      windguru(response) // Send the data to windguru
+    }
+  }
+}
+/**
+ * Handle messages from the device
+ */
 parser.on('data', function(message) {
   if (notHeadFromDevice) {
     notHeadFromDevice = false
     querySerial() // Trigger the first query, function then starts calling itself
   }
-  const response = responseParser(message)
-  if (response) {
-    logger.log("debug","Received parsed weather data", response)
-    windy(response)
-    windguru(response)
-  }
+  cacheSerial(message)
 })
 
 

src/main.js

@@ -3,25 +3,7 @@ const logger = require("./logger")
  * Script to parse a buffer of the format "loop" and turn it into to an object
  * @param {Buffer} inputBuffer
  */
-const parser = (inputBuffer) => {
-  let offset = false
-  if (inputBuffer.length < 40) {
-    logger.log("warn",`Buffer received too short - length is ${inputBuffer.length}`,inputBuffer)
-    return false
-  }
-  for (let thisOffset = 0; thisOffset < (inputBuffer.length-3); thisOffset++) {
-    if (inputBuffer.slice(thisOffset,thisOffset+3).toString('utf8') === "LOO") {
-      offset = thisOffset
-      break
-    }
-  }
-  if (!offset) { 
-    logger.log("warn","Buffer received doesn't contain LOO (76,79,79)",inputBuffer)
-    return false
-  } else {
-    logger.log("debug",`This offset is ${offset}`)
-  }
-  
+const parser = (inputBuffer, offset) => {
   const data = {
     temperatureRaw: inputBuffer.readUInt16LE(offset+12), // In degrees F multiplied by 10
     windDirection: inputBuffer.readUInt16LE(offset+16), //In degrees

src/parser.js

@@ -0,0 +1,31 @@
+const logger = require("./logger")
+/**
+ * Script to validate a buffer is of the format "loop"
+ * @param {Buffer} inputBuffer
+ */
+const validator = (inputBuffer) => {
+  let offset = false
+  const inputBufferLength = inputBuffer.length
+  if (inputBufferLength < 40) {
+    logger.log("debug",`Buffer received too short - length is ${inputBufferLength}`,inputBuffer)
+    return false
+  }
+  for (let thisOffset = 0; thisOffset < (inputBufferLength-3); thisOffset++) {
+    if (inputBuffer.slice(thisOffset,thisOffset+3).toString('utf8') === "LOO") {
+      offset = thisOffset
+      break
+    }
+  }
+  if (!offset) { 
+    logger.log("debug","Buffer received doesn't contain LOO (76,79,79)",inputBuffer)
+    return false
+  }
+  if ((inputBufferLength-offset) < 40) {
+    logger.log("debug",`Buffer received too short - length is ${inputBufferLength} and offset is ${offset} so there is not 40 after the offset`,inputBuffer)
+    return false
+  }
+
+  logger.log("debug",`This offset is ${offset}`)
+  return offset
+}
+module.exports = validator