Merge pull request #888 from iankchristie/increaseMtu

Change MTU size of BLE transfer packets

Author: iankchristie

nodejs/FatBeaconPeripheral/FatBeacon.js

@@ -13,10 +13,14 @@ var SERVICE_UUID = 'ae5946d4-e587-4ba8-b6a5-a97cca6affd3';
 var AdvertisementData =
         require('eddystone-beacon/lib/util/advertisement-data');
 var Eir = require('eddystone-beacon/lib/util/eir');
+var Gatt = require('bleno/lib/hci-socket/gatt');
 
 var FAT_BEACON_FRAME_TYPE = 0x0e;
 var MAX_URL_LENGTH = 18;
 var ADVERTISING_HEADER_UUID = 'feaa';
+var ATT_OP_MTU_RESP = 0x03;  // Refer to bleno/lib/hci-socket/gatt for doc
+var MIN_MTU = 23;
+var MAX_MTU = 505;
 
 /**
  * this patch ensures that the correct Fatbeacon eir flag (0x06) is added
@@ -52,14 +56,41 @@ AdvertisementData.makeUrlBuffer = function(name) {
   return AdvertisementData.makeEirData(serviceData);
 }
 
+/**
+ * This allows us to change the negotiate the MTU size from 0 - 505. We have
+ * set REQUESTING_MTU to 505 for maximum transfer rate.
+ */
+Gatt.prototype.handleMtuRequest = function(request) {
+  var mtu = request.readUInt16LE(1);
+ 
+  if (mtu < MIN_MTU) {
+    mtu = MIN_MTU;
+  } else if (mtu > MAX_MTU) {
+    mtu = MAX_MTU;
+  }
+
+  this._mtu = mtu;
+
+  this.emit('mtuChange', this._mtu);
+
+  var response = Buffer.alloc(3);
+
+  response.writeUInt8(ATT_OP_MTU_RESP, 0);
+  response.writeUInt16LE(mtu, 1);
+
+  return response;
+};
+
 /*********************************************************/
 
 var characteristic = new webpageCharacteristic();
 
 fs.readFile("./html/fatBeaconDefault.html", function(err, data) {
-  if(err) throw err;
+  if (err) {
+    throw err;
+  }
+
   characteristic.onWriteRequest(data, 0, null, null);
-  console.log(service);
 });
 
 var service = new bleno.PrimaryService({
@@ -71,7 +102,7 @@ var service = new bleno.PrimaryService({
 
 bleno.once('advertisingStart', function(err) {
 
-  if(err) {
+  if (err) {
     throw err;
   }
 

nodejs/FatBeaconPeripheral/webpageCharacteristic.js

@@ -12,7 +12,7 @@ var WebpageCharacteristic = function() {
   this._value = Buffer.alloc(0);
   this._updateValueCallback = null;
 
-  this._mtuSize = 251;  // 5 less than the specified mtu
+  this._mtuSize = 500;  // 5 less than the specified mtu
   this._start = 0;
   this._end = this._mtuSize;
 };
@@ -34,7 +34,7 @@ WebpageCharacteristic.prototype.onReadRequest = function(offset, callback) {
 WebpageCharacteristic.prototype.onWriteRequest = function(data, offset, withoutResponse, callback) {
   this._value = data;
 
-  console.log(`Writing - ${this._value}`);
+  console.log(`Writing ${this._value.length} bytes`);
 
   if (this._updateValueCallback) {
     console.log('WebpageCharacteristic - onWriteRequest: notifying');