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Avoid rescanning SSE delimiter buffers #1913

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Avoid rescanning SSE delimiter buffers #1913

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12 changes: 11 additions & 1 deletion src/core/streaming.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -250,12 +250,15 @@ export async function* _iterSSEMessages(
}
}

const DOUBLE_NEWLINE_DELIMITER_MAX_OVERLAP_BYTES = 3;

/**
* Given an async iterable iterator, iterates over it and yields full
* SSE chunks, i.e. yields when a double new-line is encountered.
*/
async function* iterSSEChunks(iterator: AsyncIterableIterator<Bytes>): AsyncGenerator<Uint8Array> {
let data = new Uint8Array();
let searchStartIndex = 0;

for await (const chunk of iterator) {
if (chunk == null) {
Expand All @@ -273,10 +276,17 @@ async function* iterSSEChunks(iterator: AsyncIterableIterator<Bytes>): AsyncGene
data = newData;

let patternIndex;
while ((patternIndex = findDoubleNewlineIndex(data)) !== -1) {
while ((patternIndex = findDoubleNewlineIndex(data.subarray(searchStartIndex))) !== -1) {
patternIndex += searchStartIndex;
yield data.slice(0, patternIndex);
data = data.slice(patternIndex);
searchStartIndex = 0;
}

searchStartIndex = Math.max(
0,
data.length - DOUBLE_NEWLINE_DELIMITER_MAX_OVERLAP_BYTES,
);
}

if (data.length > 0) {
Expand Down