67 lines
3.0 KiB
JavaScript
67 lines
3.0 KiB
JavaScript
export function getChunkedStream(source) {
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let currentMessageTotalLength = 0;
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let currentMessagePendingLength = 0;
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let currentMessage = null;
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let messageLengthBuffer = null;
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const allocateMessage = (size) => {
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if (typeof size !== "number") {
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throw new Error("Attempted to allocate an event message where size was not a number: " + size);
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}
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currentMessageTotalLength = size;
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currentMessagePendingLength = 4;
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currentMessage = new Uint8Array(size);
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const currentMessageView = new DataView(currentMessage.buffer);
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currentMessageView.setUint32(0, size, false);
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};
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const iterator = async function* () {
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const sourceIterator = source[Symbol.asyncIterator]();
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while (true) {
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const { value, done } = await sourceIterator.next();
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if (done) {
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if (!currentMessageTotalLength) {
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return;
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}
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else if (currentMessageTotalLength === currentMessagePendingLength) {
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yield currentMessage;
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}
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else {
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throw new Error("Truncated event message received.");
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}
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return;
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}
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const chunkLength = value.length;
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let currentOffset = 0;
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while (currentOffset < chunkLength) {
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if (!currentMessage) {
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const bytesRemaining = chunkLength - currentOffset;
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if (!messageLengthBuffer) {
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messageLengthBuffer = new Uint8Array(4);
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}
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const numBytesForTotal = Math.min(4 - currentMessagePendingLength, bytesRemaining);
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messageLengthBuffer.set(value.slice(currentOffset, currentOffset + numBytesForTotal), currentMessagePendingLength);
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currentMessagePendingLength += numBytesForTotal;
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currentOffset += numBytesForTotal;
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if (currentMessagePendingLength < 4) {
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break;
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}
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allocateMessage(new DataView(messageLengthBuffer.buffer).getUint32(0, false));
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messageLengthBuffer = null;
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}
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const numBytesToWrite = Math.min(currentMessageTotalLength - currentMessagePendingLength, chunkLength - currentOffset);
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currentMessage.set(value.slice(currentOffset, currentOffset + numBytesToWrite), currentMessagePendingLength);
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currentMessagePendingLength += numBytesToWrite;
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currentOffset += numBytesToWrite;
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if (currentMessageTotalLength && currentMessageTotalLength === currentMessagePendingLength) {
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yield currentMessage;
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currentMessage = null;
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currentMessageTotalLength = 0;
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currentMessagePendingLength = 0;
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}
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}
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}
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};
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return {
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[Symbol.asyncIterator]: iterator,
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};
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}
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