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/*** IMPORT ------------------------------------------- ***/
import { createClient, type Client, type ClientOptions } from "graphql-sse";
/*** UTILITY ------------------------------------------ ***/
import type { Fetcher, FetcherOptions, FetcherResult } from "./types.ts";
/*** EXPORT ------------------------------------------- ***/
export type SseFetcherOptions = FetcherOptions & {
client?: Partial<Omit<ClientOptions, "url">>;
};
export function createSseFetcher(options: SseFetcherOptions): Fetcher {
const client: Client = createClient({
fetchFn: options.fetch,
headers: options.headers,
url: options.url,
...options.client
});
return (req) => {
return {
[Symbol.asyncIterator](): AsyncIterator<FetcherResult> {
const queue: FetcherResult[] = [];
const resolvers: ((step: IteratorResult<FetcherResult>) => void)[] = [];
let done = false;
let error: unknown = null;
const dispose = client.subscribe<FetcherResult, Record<string, unknown>>(
{
extensions: req.headers as Record<string, unknown> | undefined,
operationName: req.operationName ?? undefined,
query: req.query,
variables: req.variables
},
{
complete() {
done = true;
flush();
},
error(err) {
error = err;
done = true;
flush();
},
next(value) {
queue.push(value as FetcherResult);
flush();
}
}
);
function flush() {
while (resolvers.length > 0 && (queue.length > 0 || done)) {
const resolve = resolvers.shift();
if (!resolve)
break;
if (queue.length > 0)
resolve({ done: false, value: queue.shift() as FetcherResult });
else if (error)
resolve({ done: true, value: undefined });
else
resolve({ done: true, value: undefined });
}
}
return {
next(): Promise<IteratorResult<FetcherResult>> {
if (error) {
const err = error;
error = null;
return Promise.reject(err);
}
if (queue.length > 0)
return Promise.resolve({ done: false, value: queue.shift() as FetcherResult });
if (done)
return Promise.resolve({ done: true, value: undefined });
return new Promise<IteratorResult<FetcherResult>>((resolve) => {
resolvers.push(resolve);
});
},
return(): Promise<IteratorResult<FetcherResult>> {
dispose();
done = true;
flush();
return Promise.resolve({ done: true, value: undefined });
}
};
}
};
};
}
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