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| async function mergeResponses(responsePromises, headers) { | |
| const readers = responsePromises.map(p => Promise.resolve(p).then(r => r.body.getReader())); | |
| let doneResolve; | |
| let doneReject; | |
| const done = new Promise((r, rr) => { | |
| doneResolve = r; | |
| doneReject = rr; | |
| }); | |
| const readable = new ReadableStream({ | |
| async pull(controller) { | |
| const reader = await readers[0]; | |
| try { | |
| const {done, value} = await reader.read(); | |
| if (done) { | |
| readers.shift(); | |
| if (!readers[0]) { | |
| controller.close(); | |
| doneResolve(); | |
| return; | |
| } | |
| return this.pull(controller); | |
| } | |
| controller.enqueue(value); | |
| } | |
| catch (err) { | |
| doneReject(err); | |
| throw err; | |
| } | |
| }, | |
| cancel() { | |
| doneResolve(); | |
| } | |
| }); | |
| const response = await responsePromises[0]; | |
| return { | |
| done, | |
| response: new Response(readable, { | |
| headers: headers || response.headers | |
| }) | |
| }; | |
| } |
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| // This depends on transform streams & async iterators | |
| async function mergeResponses(responsePromises, headers) { | |
| const {readable, writable} = new TransformStream(); | |
| const done = (async function() { | |
| for await (const response of responsePromises) { | |
| await response.body.pipeTo(writable, {preventClose: true}); | |
| } | |
| writable.getWriter().close(); | |
| })(); | |
| return { | |
| done, | |
| response: new Response(readable, { | |
| headers: headers || (await responsePromises[0]).headers | |
| }) | |
| }; | |
| } |
Ah, well spotted!
can you explain why use promises here?
const readers = responsePromises.map(p => Promise.resolve(p).then(r => r.body.getReader()));instead of using simple array?
const readers = responsePromises.map(p => p.body.getReader()@PRMSA it allows responsePromises to be a mix of Promise<Response> and plain Response.
future2.js
const mergeResponses = async (
responsePromises = [Promise.resolve(new Response())],
headers = new Headers()
) => new Response(new ReadableStream({ async start(controller) {
for await (const response of responsePromises) {
// Bonus example: controller.enqueue(await response.text());
await response.body.pipeTo(new WritableStream({
write: (data) => controller.enqueue(data)
}));
}
}}),{
headers: headers.has("Content-Type") ? headers : (await responsePromises[0]).headers
});
// usage example
globalThis.onfetch = (event) => event.respondWith(mergeResponses([...responsePromises]));The function parameters got set with empty default values for typeInferencing in IDE's
so the above example is 100% Typed
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Maybe a couple of bugs in this? Not sure if you can do a PR to a gist, but I had to change these:
Line 27:
Line 41:
Thanks for writing this. Very useful for a demo I'm doing for a talk this weekend!