@envelop/execute-subscription-event/esm/subscribe.js

Utilities for hooking into the [ExecuteSubscriptionEvent](<https://spec.graphql.org/draft/#ExecuteSubscriptionEvent()>) phase.

import { createSourceEventStream } from 'graphql';
import { isAsyncIterable, makeSubscribe, mapAsyncIterator, } from '@envelop/core';
/**
 * This is a almost identical port from graphql-js subscribe.
 * The only difference is that a custom `execute` function can be injected for customizing the behavior.
 */
export const subscribe = (execute) => makeSubscribe(async (args) => {
    const { schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, subscribeFieldResolver, } = args;
    const resultOrStream = await createSourceEventStream(schema, document, rootValue, contextValue, variableValues ?? undefined, operationName, subscribeFieldResolver);
    if (!isAsyncIterable(resultOrStream)) {
        return resultOrStream;
    }
    // For each payload yielded from a subscription, map it over the normal
    // GraphQL `execute` function, with `payload` as the rootValue.
    // This implements the "MapSourceToResponseEvent" algorithm described in
    // the GraphQL specification. The `execute` function provides the
    // "ExecuteSubscriptionEvent" algorithm, as it is nearly identical to the
    // "ExecuteQuery" algorithm, for which `execute` is also used.
    const mapSourceToResponse = (payload) => execute({
        schema,
        document,
        rootValue: payload,
        contextValue,
        variableValues,
        operationName,
        fieldResolver,
    });
    // Map every source value to a ExecutionResult value as described above.
    return mapAsyncIterator(resultOrStream, mapSourceToResponse);
});