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Change header check constant to hex #9

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merged 4 commits into from
Jan 15, 2019
Merged

Change header check constant to hex #9

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9e2ca13
Change header check constant to hex and update comment
Jan 15, 2019
3384e06
Allow a message length of 0
Jan 15, 2019
2185efd
Add mask to magic bytes check
keepkeyjon Jan 15, 2019
df93f5e
Change max message size to 128KB. Add comments.
Jan 15, 2019
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9 changes: 6 additions & 3 deletions src/webUSBDevice.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -77,10 +77,12 @@ export default class WebUSBDevice extends Device {
protected async read (): Promise<ByteBuffer> {
let first = await this.readChunk()

// FIXME: assert that buffer starts with: [ 0x3f, 0x23, 0x23 ]
const valid = first.getUint32(0) === 1059267328
// Check that buffer starts with: "?##" [ 0x3f, 0x23, 0x23 ]
// "?" = USB marker, "##" = KeepKey magic bytes
// Message ID is bytes 4-5. Message length starts at byte 6.
const valid = (first.getUint32(0) & 0xffffff00) === 0x3f232300
const msgLength = first.getUint32(5)
if (valid && msgLength > 0 && msgLength < 4194304) { // 4 MB sanity check
if (valid && msgLength >= 0 && msgLength < 131072) { // 128KB max message size
// FIXME: why doesn't ByteBuffer.concat() work?
const buffer = new Uint8Array(9 + 2 + msgLength)
for (let k = 0; k < first.byteLength; k++) {
Expand All @@ -90,6 +92,7 @@ export default class WebUSBDevice extends Device {

while (offset < buffer.length) {
const next = await this.readChunk()
// Drop USB "?" packet identifier in the first byte
for (let k = 1; (k < next.byteLength && offset < buffer.length); k++) {
buffer[offset] = next.getUint8(k)
offset++
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