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Take the packet end from the length field, not a suffix search #711

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Take the packet end from the length field, not a suffix search #711

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17 changes: 11 additions & 6 deletions lib/message-parser.js
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Original file line number Diff line number Diff line change
Expand Up @@ -118,14 +118,19 @@ class MessageParser {
// Check for extra data
let leftover = false;

let suffixLocation = buffer.indexOf('0000AA55', 0, 'hex');
if (suffixLocation === -1) {// Couldn't find 0000AA55 during parse
suffixLocation = buffer.indexOf('00009966', 0, 'hex');
// Frame end comes from the length field: a search for the suffix bytes
// also matches a sequence number or ciphertext holding those bytes
const frameLength = prefix === 0x00006699 ?
buffer.readUInt32BE(14) + 22 : // Header (18) + length + suffix (4)
buffer.readUInt32BE(12) + 16; // Header (16) + length

if (buffer.length < frameLength) {
throw new TypeError(`Packet missing payload: frame has length ${frameLength}.`);
}

if (suffixLocation !== buffer.length - 4) {
leftover = buffer.slice(suffixLocation + 4);
buffer = buffer.slice(0, suffixLocation + 4);
if (buffer.length > frameLength) {
leftover = buffer.slice(frameLength);
buffer = buffer.slice(0, frameLength);
}

// Check for suffix
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21 changes: 21 additions & 0 deletions test/parser.js
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Expand Up @@ -209,3 +209,24 @@ test('decode message with two packets 2', t => {
t.deepEqual(parsed.payload, payload);
t.is(parsed.commandByte, 10);
});

for (const version of ['3.1', '3.3', '3.4', '3.5']) {
for (const sequenceN of [0x0000AA55, 0x00009966]) {
test(`decode two packets with protocol ${version} and sequence number holding suffix bytes 0x${sequenceN.toString(16)}`, t => {
const payload = {devId: '002004265ccf7fb1b659', dps: {1: true, 2: 0}};

const parser = new MessageParser({key: 'bbe88b3f4106d354', version});
const baseline = parser.parse(parser.encode({data: payload, commandByte: CommandType.DP_QUERY, sequenceN: 1}))[0];
const encoded = parser.encode({data: payload, commandByte: CommandType.DP_QUERY, sequenceN});

const parsed = parser.parse(Buffer.concat([encoded, encoded]));

t.is(parsed.length, 2);
for (const packet of parsed) {
t.is(packet.sequenceN, sequenceN);
t.is(packet.commandByte, CommandType.DP_QUERY);
t.deepEqual(packet.payload, baseline.payload);
}
});
}
}