serverless-spy
Version:
CDK-based library for writing elegant integration tests on AWS serverless architecture and an additional web console to monitor events in real time.
67 lines (66 loc) • 3.07 kB
JavaScript
export function getChunkedStream(source) {
let currentMessageTotalLength = 0;
let currentMessagePendingLength = 0;
let currentMessage = null;
let messageLengthBuffer = null;
const allocateMessage = (size) => {
if (typeof size !== "number") {
throw new Error("Attempted to allocate an event message where size was not a number: " + size);
}
currentMessageTotalLength = size;
currentMessagePendingLength = 4;
currentMessage = new Uint8Array(size);
const currentMessageView = new DataView(currentMessage.buffer);
currentMessageView.setUint32(0, size, false);
};
const iterator = async function* () {
const sourceIterator = source[Symbol.asyncIterator]();
while (true) {
const { value, done } = await sourceIterator.next();
if (done) {
if (!currentMessageTotalLength) {
return;
}
else if (currentMessageTotalLength === currentMessagePendingLength) {
yield currentMessage;
}
else {
throw new Error("Truncated event message received.");
}
return;
}
const chunkLength = value.length;
let currentOffset = 0;
while (currentOffset < chunkLength) {
if (!currentMessage) {
const bytesRemaining = chunkLength - currentOffset;
if (!messageLengthBuffer) {
messageLengthBuffer = new Uint8Array(4);
}
const numBytesForTotal = Math.min(4 - currentMessagePendingLength, bytesRemaining);
messageLengthBuffer.set(value.slice(currentOffset, currentOffset + numBytesForTotal), currentMessagePendingLength);
currentMessagePendingLength += numBytesForTotal;
currentOffset += numBytesForTotal;
if (currentMessagePendingLength < 4) {
break;
}
allocateMessage(new DataView(messageLengthBuffer.buffer).getUint32(0, false));
messageLengthBuffer = null;
}
const numBytesToWrite = Math.min(currentMessageTotalLength - currentMessagePendingLength, chunkLength - currentOffset);
currentMessage.set(value.slice(currentOffset, currentOffset + numBytesToWrite), currentMessagePendingLength);
currentMessagePendingLength += numBytesToWrite;
currentOffset += numBytesToWrite;
if (currentMessageTotalLength && currentMessageTotalLength === currentMessagePendingLength) {
yield currentMessage;
currentMessage = null;
currentMessageTotalLength = 0;
currentMessagePendingLength = 0;
}
}
}
};
return {
[Symbol.asyncIterator]: iterator,
};
}