30 lines
1.9 KiB
JavaScript
30 lines
1.9 KiB
JavaScript
import { Crc32 } from "@aws-crypto/crc32";
|
|
const PRELUDE_MEMBER_LENGTH = 4;
|
|
const PRELUDE_LENGTH = PRELUDE_MEMBER_LENGTH * 2;
|
|
const CHECKSUM_LENGTH = 4;
|
|
const MINIMUM_MESSAGE_LENGTH = PRELUDE_LENGTH + CHECKSUM_LENGTH * 2;
|
|
export function splitMessage({ byteLength, byteOffset, buffer }) {
|
|
if (byteLength < MINIMUM_MESSAGE_LENGTH) {
|
|
throw new Error("Provided message too short to accommodate event stream message overhead");
|
|
}
|
|
const view = new DataView(buffer, byteOffset, byteLength);
|
|
const messageLength = view.getUint32(0, false);
|
|
if (byteLength !== messageLength) {
|
|
throw new Error("Reported message length does not match received message length");
|
|
}
|
|
const headerLength = view.getUint32(PRELUDE_MEMBER_LENGTH, false);
|
|
const expectedPreludeChecksum = view.getUint32(PRELUDE_LENGTH, false);
|
|
const expectedMessageChecksum = view.getUint32(byteLength - CHECKSUM_LENGTH, false);
|
|
const checksummer = new Crc32().update(new Uint8Array(buffer, byteOffset, PRELUDE_LENGTH));
|
|
if (expectedPreludeChecksum !== checksummer.digest()) {
|
|
throw new Error(`The prelude checksum specified in the message (${expectedPreludeChecksum}) does not match the calculated CRC32 checksum (${checksummer.digest()})`);
|
|
}
|
|
checksummer.update(new Uint8Array(buffer, byteOffset + PRELUDE_LENGTH, byteLength - (PRELUDE_LENGTH + CHECKSUM_LENGTH)));
|
|
if (expectedMessageChecksum !== checksummer.digest()) {
|
|
throw new Error(`The message checksum (${checksummer.digest()}) did not match the expected value of ${expectedMessageChecksum}`);
|
|
}
|
|
return {
|
|
headers: new DataView(buffer, byteOffset + PRELUDE_LENGTH + CHECKSUM_LENGTH, headerLength),
|
|
body: new Uint8Array(buffer, byteOffset + PRELUDE_LENGTH + CHECKSUM_LENGTH + headerLength, messageLength - headerLength - (PRELUDE_LENGTH + CHECKSUM_LENGTH + CHECKSUM_LENGTH)),
|
|
};
|
|
}
|