send/app/streams.js

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/* global ReadableStream */
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export function transform(readable, transformer) {
const reader = readable.getReader();
const tstream = new ReadableStream({
start(controller) {
if (transformer.start) {
return transformer.start(controller);
}
},
async pull(controller) {
let enqueued = false;
const c = {
enqueue(d) {
enqueued = true;
controller.enqueue(d);
}
};
while (!enqueued) {
const x = await reader.read();
if (x.done) {
if (transformer.flush) {
await transformer.flush(controller);
}
return controller.close();
}
await transformer.transform(x.value, c);
}
},
cancel() {
readable.cancel();
}
});
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return tstream;
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}