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42 changes: 32 additions & 10 deletions lib/hci-socket/gatt.js
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Original file line number Diff line number Diff line change
Expand Up @@ -676,6 +676,17 @@ Gatt.prototype.notify = function (serviceUuid, characteristicUuid, notify) {
});
};

function reverse (src) {
const buffer = Buffer.alloc(src.length);

for (let i = 0, j = src.length - 1; i <= j; ++i, --j) {
buffer[i] = src[j];
buffer[j] = src[i];
}

return buffer;
}

Gatt.prototype.discoverDescriptors = function (serviceUuid, characteristicUuid) {
const characteristic = this._characteristics[serviceUuid][characteristicUuid];
const descriptors = [];
Expand All @@ -684,24 +695,35 @@ Gatt.prototype.discoverDescriptors = function (serviceUuid, characteristicUuid)

const callback = data => {
const opcode = data[0];
let i = 0;

if (opcode === ATT_OP_FIND_INFO_RESP) {
const format = data[1];
const elen = 2 + (format === 0x01 ? 2 : 16);
const num = (data.length - 2) / (elen);
for (i = 0; i < num; i++) {
const offset = 2 + (i * elen);
descriptors.push({
handle: data.readUInt16LE(offset + 0),
uuid: (format === 0x01) ? data.readUInt16LE(offset + 2).toString(16) : data.slice(offset + 2).slice(0, 16).toString('hex').match(/.{1,2}/g).reverse().join('')
});
let pos = 2; // skip first 2 bytes (opcode, format)

while (data.length > pos) {
switch (format) {
case 1:
descriptors.push({
handle: data.readUInt16LE(pos),
uuid: data.readUInt16LE(pos + 2).toString(16)
});
pos = pos + 4;
break;

case 2:
descriptors.push({
handle: data.readUInt16LE(pos),
uuid: reverse(data.slice(pos + 2, pos + 2 + 16)).toString('hex')
});
pos = pos + 18;
break;
}
}
}

if (opcode !== ATT_OP_FIND_INFO_RESP || descriptors[descriptors.length - 1].handle === characteristic.endHandle) {
const descriptorUuids = [];
for (i = 0; i < descriptors.length; i++) {
for (let i = 0; i < descriptors.length; i++) {
descriptorUuids.push(descriptors[i].uuid);

this._descriptors[serviceUuid][characteristicUuid][descriptors[i].uuid] = descriptors[i];
Expand Down