@graphql-tools/graphql
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Fork of GraphQL.js
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JavaScript
import { devAssert } from '../jsutils/devAssert.js';
import { inspect } from '../jsutils/inspect.js';
import { isAsyncIterable } from '../jsutils/isAsyncIterable.js';
import { addPath, pathToArray } from '../jsutils/Path.js';
import { GraphQLError } from '../error/GraphQLError.js';
import { locatedError } from '../error/locatedError.js';
import { collectFields } from './collectFields.js';
import { assertValidExecutionArguments, buildExecutionContext, buildResolveInfo, execute, getFieldDef, } from './execute.js';
import { mapAsyncIterator } from './mapAsyncIterator.js';
import { getArgumentValues } from './values.js';
/**
* Implements the "Subscribe" algorithm described in the GraphQL specification.
*
* Returns a Promise which resolves to either an AsyncIterator (if successful)
* or an ExecutionResult (error). The promise will be rejected if the schema or
* other arguments to this function are invalid, or if the resolved event stream
* is not an async iterable.
*
* If the client-provided arguments to this function do not result in a
* compliant subscription, a GraphQL Response (ExecutionResult) with
* descriptive errors and no data will be returned.
*
* If the source stream could not be created due to faulty subscription
* resolver logic or underlying systems, the promise will resolve to a single
* ExecutionResult containing `errors` and no `data`.
*
* If the operation succeeded, the promise resolves to an AsyncIterator, which
* yields a stream of ExecutionResults representing the response stream.
*
* Accepts either an object with named arguments, or individual arguments.
*/
export async function subscribe(args) {
// Temporary for v15 to v16 migration. Remove in v17
devAssert(arguments.length < 2, 'graphql@16 dropped long-deprecated support for positional arguments, please pass an object instead.');
const { schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver, subscribeFieldResolver, } = args;
const resultOrStream = await createSourceEventStream(schema, document, rootValue, contextValue, variableValues, 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);
}
/**
* Implements the "CreateSourceEventStream" algorithm described in the
* GraphQL specification, resolving the subscription source event stream.
*
* Returns a Promise which resolves to either an AsyncIterable (if successful)
* or an ExecutionResult (error). The promise will be rejected if the schema or
* other arguments to this function are invalid, or if the resolved event stream
* is not an async iterable.
*
* If the client-provided arguments to this function do not result in a
* compliant subscription, a GraphQL Response (ExecutionResult) with
* descriptive errors and no data will be returned.
*
* If the the source stream could not be created due to faulty subscription
* resolver logic or underlying systems, the promise will resolve to a single
* ExecutionResult containing `errors` and no `data`.
*
* If the operation succeeded, the promise resolves to the AsyncIterable for the
* event stream returned by the resolver.
*
* A Source Event Stream represents a sequence of events, each of which triggers
* a GraphQL execution for that event.
*
* This may be useful when hosting the stateful subscription service in a
* different process or machine than the stateless GraphQL execution engine,
* or otherwise separating these two steps. For more on this, see the
* "Supporting Subscriptions at Scale" information in the GraphQL specification.
*/
export async function createSourceEventStream(schema, document, rootValue, contextValue, variableValues, operationName, subscribeFieldResolver) {
// If arguments are missing or incorrectly typed, this is an internal
// developer mistake which should throw an early error.
assertValidExecutionArguments(schema, document, variableValues);
// If a valid execution context cannot be created due to incorrect arguments,
// a "Response" with only errors is returned.
const exeContext = buildExecutionContext({
schema,
document,
rootValue,
contextValue,
variableValues,
operationName,
subscribeFieldResolver,
});
// Return early errors if execution context failed.
if (!('schema' in exeContext)) {
return { errors: exeContext };
}
try {
const eventStream = await executeSubscription(exeContext);
// Assert field returned an event stream, otherwise yield an error.
if (!isAsyncIterable(eventStream)) {
throw new Error('Subscription field must return Async Iterable. ' + `Received: ${inspect(eventStream)}.`);
}
return eventStream;
}
catch (error) {
// If it GraphQLError, report it as an ExecutionResult, containing only errors and no data.
// Otherwise treat the error as a system-class error and re-throw it.
if (error instanceof GraphQLError) {
return { errors: [error] };
}
throw error;
}
}
async function executeSubscription(exeContext) {
var _a;
const { schema, fragments, operation, variableValues, rootValue } = exeContext;
const rootType = schema.getSubscriptionType();
if (rootType == null) {
throw new GraphQLError('Schema is not configured to execute subscription operation.', { nodes: operation });
}
const rootFields = collectFields(schema, fragments, variableValues, rootType, operation.selectionSet);
const [responseName, fieldNodes] = [...rootFields.entries()][0];
const fieldDef = getFieldDef(schema, rootType, fieldNodes[0]);
if (!fieldDef) {
const fieldName = fieldNodes[0].name.value;
throw new GraphQLError(`The subscription field "${fieldName}" is not defined.`, { nodes: fieldNodes });
}
const path = addPath(undefined, responseName, rootType.name);
const info = buildResolveInfo(exeContext, fieldDef, fieldNodes, rootType, path);
try {
// Implements the "ResolveFieldEventStream" algorithm from GraphQL specification.
// It differs from "ResolveFieldValue" due to providing a different `resolveFn`.
// Build a JS object of arguments from the field.arguments AST, using the
// variables scope to fulfill any variable references.
const args = getArgumentValues(fieldDef, fieldNodes[0], variableValues);
// The resolve function's optional third argument is a context value that
// is provided to every resolve function within an execution. It is commonly
// used to represent an authenticated user, or request-specific caches.
const contextValue = exeContext.contextValue;
// Call the `subscribe()` resolver or the default resolver to produce an
// AsyncIterable yielding raw payloads.
const resolveFn = (_a = fieldDef.subscribe) !== null && _a !== void 0 ? _a : exeContext.subscribeFieldResolver;
const eventStream = await resolveFn(rootValue, args, contextValue, info);
if (eventStream instanceof Error) {
throw eventStream;
}
return eventStream;
}
catch (error) {
throw locatedError(error, fieldNodes, pathToArray(path));
}
}