40 lines
1 KiB
JavaScript
40 lines
1 KiB
JavaScript
/* global ReadableStream TransformStream */
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export function transformStream(readable, transformer, oncancel) {
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if (typeof TransformStream === 'function') {
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return readable.pipeThrough(new TransformStream(transformer));
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}
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const reader = readable.getReader();
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return new ReadableStream({
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start(controller) {
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if (transformer.start) {
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return transformer.start(controller);
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}
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},
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async pull(controller) {
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let enqueued = false;
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const wrappedController = {
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enqueue(d) {
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enqueued = true;
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controller.enqueue(d);
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}
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};
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while (!enqueued) {
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const data = await reader.read();
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if (data.done) {
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if (transformer.flush) {
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await transformer.flush(controller);
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}
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return controller.close();
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}
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await transformer.transform(data.value, wrappedController);
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}
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},
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cancel(reason) {
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readable.cancel(reason);
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if (oncancel) {
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oncancel(reason);
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}
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}
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});
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}
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