graphql-yoga
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JavaScript
import { isAsyncIterable } from '@envelop/core';
import { handleMaybePromise } from '@whatwg-node/promise-helpers';
import { fakePromise } from '@whatwg-node/server';
import { getResponseInitByRespectingErrors } from '../../error.js';
import { jsonStringifyResultWithoutInternals } from './stringify.js';
export function getSSEProcessor() {
return function processSSEResult(result, fetchAPI) {
let pingIntervalMs = 12_000;
// for testing the pings, reduce the timeout
if (globalThis.process?.env?.['NODE_ENV'] === 'test') {
pingIntervalMs = 300;
}
const headersInit = {
'Content-Type': 'text/event-stream',
Connection: 'keep-alive',
'Cache-Control': 'no-cache',
'Content-Encoding': 'none',
};
const responseInit = getResponseInitByRespectingErrors(result, headersInit, true);
let iterator;
let pingInterval;
const textEncoder = new fetchAPI.TextEncoder();
const readableStream = new fetchAPI.ReadableStream({
start(controller) {
// always start with a ping because some browsers dont accept a header flush
// causing the fetch to stall until something is streamed through the response
controller.enqueue(textEncoder.encode(':\n\n'));
// ping client every 12 seconds to keep the connection alive
pingInterval = setInterval(() => {
if (!controller.desiredSize) {
clearInterval(pingInterval);
return;
}
controller.enqueue(textEncoder.encode(':\n\n'));
}, pingIntervalMs);
if (isAsyncIterable(result)) {
iterator = result[Symbol.asyncIterator]();
}
else {
let finished = false;
iterator = {
next: () => {
if (finished) {
return fakePromise({ done: true, value: null });
}
finished = true;
return fakePromise({ done: false, value: result });
},
};
}
},
pull(controller) {
return handleMaybePromise(() => iterator.next(), result => {
if (result.value != null) {
controller.enqueue(textEncoder.encode(`event: next\n`));
const chunk = jsonStringifyResultWithoutInternals(result.value);
controller.enqueue(textEncoder.encode(`data: ${chunk}\n\n`));
}
if (result.done) {
controller.enqueue(textEncoder.encode(`event: complete\n`));
controller.enqueue(textEncoder.encode(`data:\n\n`));
clearInterval(pingInterval);
controller.close();
}
}, err => {
controller.error(err);
});
},
cancel(e) {
clearInterval(pingInterval);
if (iterator.return) {
return handleMaybePromise(() => iterator.return?.(e), () => { });
}
},
});
return new fetchAPI.Response(readableStream, responseInit);
};
}