81 lines
2.2 KiB
TypeScript
81 lines
2.2 KiB
TypeScript
import { StreamPartType, parseStreamPart } from './stream-parts';
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const NEWLINE = '\n'.charCodeAt(0);
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// concatenates all the chunks into a single Uint8Array
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function concatChunks(chunks: Uint8Array[], totalLength: number) {
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const concatenatedChunks = new Uint8Array(totalLength);
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let offset = 0;
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for (const chunk of chunks) {
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concatenatedChunks.set(chunk, offset);
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offset += chunk.length;
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}
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chunks.length = 0;
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return concatenatedChunks;
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}
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/**
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Converts a ReadableStreamDefaultReader into an async generator that yields
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StreamPart objects.
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@param reader
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Reader for the stream to read from.
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@param isAborted
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Optional function that returns true if the request has been aborted.
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If the function returns true, the generator will stop reading the stream.
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If the function is not provided, the generator will not stop reading the stream.
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*/
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export async function* readDataStream(
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reader: ReadableStreamDefaultReader<Uint8Array>,
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{
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isAborted,
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}: {
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isAborted?: () => boolean;
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} = {},
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): AsyncGenerator<StreamPartType> {
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// implementation note: this slightly more complex algorithm is required
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// to pass the tests in the edge environment.
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const decoder = new TextDecoder();
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const chunks: Uint8Array[] = [];
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let totalLength = 0;
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while (true) {
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const { value } = await reader.read();
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if (value) {
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chunks.push(value);
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totalLength += value.length;
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if (value[value.length - 1] !== NEWLINE) {
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// if the last character is not a newline, we have not read the whole JSON value
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continue;
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}
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}
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if (chunks.length === 0) {
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break; // we have reached the end of the stream
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}
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const concatenatedChunks = concatChunks(chunks, totalLength);
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totalLength = 0;
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const streamParts = decoder
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.decode(concatenatedChunks, { stream: true })
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.split('\n')
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.filter(line => line !== '') // splitting leaves an empty string at the end
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.map(parseStreamPart);
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for (const streamPart of streamParts) {
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yield streamPart;
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}
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// The request has been aborted, stop reading the stream.
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if (isAborted?.()) {
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reader.cancel();
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break;
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}
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}
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}
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