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node_modules/graphql/subscription/subscribe.js.flow

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+// @flow strict
+
+import { isAsyncIterable } from 'iterall';
+
+import inspect from '../jsutils/inspect';
+import { addPath, pathToArray } from '../jsutils/Path';
+
+import { GraphQLError } from '../error/GraphQLError';
+import { locatedError } from '../error/locatedError';
+
+import { type DocumentNode } from '../language/ast';
+
+import {
+  type ExecutionResult,
+  assertValidExecutionArguments,
+  buildExecutionContext,
+  buildResolveInfo,
+  collectFields,
+  execute,
+  getFieldDef,
+  resolveFieldValueOrError,
+} from '../execution/execute';
+
+import { type GraphQLSchema } from '../type/schema';
+import { type GraphQLFieldResolver } from '../type/definition';
+
+import { getOperationRootType } from '../utilities/getOperationRootType';
+
+import mapAsyncIterator from './mapAsyncIterator';
+
+export type SubscriptionArgs = {|
+  schema: GraphQLSchema,
+  document: DocumentNode,
+  rootValue?: mixed,
+  contextValue?: mixed,
+  variableValues?: ?{ +[variable: string]: mixed, ... },
+  operationName?: ?string,
+  fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
+|};
+
+/**
+ * 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.
+ */
+declare function subscribe(
+  SubscriptionArgs,
+  ..._: []
+): Promise<AsyncIterator<ExecutionResult> | ExecutionResult>;
+/* eslint-disable no-redeclare */
+declare function subscribe(
+  schema: GraphQLSchema,
+  document: DocumentNode,
+  rootValue?: mixed,
+  contextValue?: mixed,
+  variableValues?: ?{ +[variable: string]: mixed, ... },
+  operationName?: ?string,
+  fieldResolver?: ?GraphQLFieldResolver<any, any>,
+  subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
+): Promise<AsyncIterator<ExecutionResult> | ExecutionResult>;
+export function subscribe(
+  argsOrSchema,
+  document,
+  rootValue,
+  contextValue,
+  variableValues,
+  operationName,
+  fieldResolver,
+  subscribeFieldResolver,
+) {
+  /* eslint-enable no-redeclare */
+  // Extract arguments from object args if provided.
+  return arguments.length === 1
+    ? subscribeImpl(argsOrSchema)
+    : subscribeImpl({
+        schema: argsOrSchema,
+        document,
+        rootValue,
+        contextValue,
+        variableValues,
+        operationName,
+        fieldResolver,
+        subscribeFieldResolver,
+      });
+}
+
+/**
+ * This function checks if the error is a GraphQLError. If it is, report it as
+ * an ExecutionResult, containing only errors and no data. Otherwise treat the
+ * error as a system-class error and re-throw it.
+ */
+function reportGraphQLError(error) {
+  if (error instanceof GraphQLError) {
+    return { errors: [error] };
+  }
+  throw error;
+}
+
+function subscribeImpl(
+  args: SubscriptionArgs,
+): Promise<AsyncIterator<ExecutionResult> | ExecutionResult> {
+  const {
+    schema,
+    document,
+    rootValue,
+    contextValue,
+    variableValues,
+    operationName,
+    fieldResolver,
+    subscribeFieldResolver,
+  } = args;
+
+  const sourcePromise = createSourceEventStream(
+    schema,
+    document,
+    rootValue,
+    contextValue,
+    variableValues,
+    operationName,
+    subscribeFieldResolver,
+  );
+
+  // 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,
+      payload,
+      contextValue,
+      variableValues,
+      operationName,
+      fieldResolver,
+    );
+
+  // Resolve the Source Stream, then map every source value to a
+  // ExecutionResult value as described above.
+  return sourcePromise.then(resultOrStream =>
+    // Note: Flow can't refine isAsyncIterable, so explicit casts are used.
+    isAsyncIterable(resultOrStream)
+      ? mapAsyncIterator(
+          ((resultOrStream: any): AsyncIterable<mixed>),
+          mapSourceToResponse,
+          reportGraphQLError,
+        )
+      : ((resultOrStream: any): ExecutionResult),
+  );
+}
+
+/**
+ * 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 function createSourceEventStream(
+  schema: GraphQLSchema,
+  document: DocumentNode,
+  rootValue?: mixed,
+  contextValue?: mixed,
+  variableValues?: ?{ +[variable: string]: mixed, ... },
+  operationName?: ?string,
+  fieldResolver?: ?GraphQLFieldResolver<any, any>,
+): Promise<AsyncIterable<mixed> | ExecutionResult> {
+  // If arguments are missing or incorrectly typed, this is an internal
+  // developer mistake which should throw an early error.
+  assertValidExecutionArguments(schema, document, variableValues);
+
+  try {
+    // If a valid context cannot be created due to incorrect arguments,
+    // this will throw an error.
+    const exeContext = buildExecutionContext(
+      schema,
+      document,
+      rootValue,
+      contextValue,
+      variableValues,
+      operationName,
+      fieldResolver,
+    );
+
+    // Return early errors if execution context failed.
+    if (Array.isArray(exeContext)) {
+      return Promise.resolve({ errors: exeContext });
+    }
+
+    const type = getOperationRootType(schema, exeContext.operation);
+    const fields = collectFields(
+      exeContext,
+      type,
+      exeContext.operation.selectionSet,
+      Object.create(null),
+      Object.create(null),
+    );
+    const responseNames = Object.keys(fields);
+    const responseName = responseNames[0];
+    const fieldNodes = fields[responseName];
+    const fieldNode = fieldNodes[0];
+    const fieldName = fieldNode.name.value;
+    const fieldDef = getFieldDef(schema, type, fieldName);
+
+    if (!fieldDef) {
+      throw new GraphQLError(
+        `The subscription field "${fieldName}" is not defined.`,
+        fieldNodes,
+      );
+    }
+
+    // Call the `subscribe()` resolver or the default resolver to produce an
+    // AsyncIterable yielding raw payloads.
+    const resolveFn = fieldDef.subscribe || exeContext.fieldResolver;
+
+    const path = addPath(undefined, responseName);
+
+    const info = buildResolveInfo(exeContext, fieldDef, fieldNodes, type, path);
+
+    // resolveFieldValueOrError implements the "ResolveFieldEventStream"
+    // algorithm from GraphQL specification. It differs from
+    // "ResolveFieldValue" due to providing a different `resolveFn`.
+    const result = resolveFieldValueOrError(
+      exeContext,
+      fieldDef,
+      fieldNodes,
+      resolveFn,
+      rootValue,
+      info,
+    );
+
+    // Coerce to Promise for easier error handling and consistent return type.
+    return Promise.resolve(result).then(eventStream => {
+      // If eventStream is an Error, rethrow a located error.
+      if (eventStream instanceof Error) {
+        return {
+          errors: [locatedError(eventStream, fieldNodes, pathToArray(path))],
+        };
+      }
+
+      // Assert field returned an event stream, otherwise yield an error.
+      if (isAsyncIterable(eventStream)) {
+        // Note: isAsyncIterable above ensures this will be correct.
+        return ((eventStream: any): AsyncIterable<mixed>);
+      }
+      throw new Error(
+        'Subscription field must return Async Iterable. Received: ' +
+          inspect(eventStream),
+      );
+    });
+  } catch (error) {
+    // As with reportGraphQLError above, if the error is a GraphQLError, report
+    // it as an ExecutionResult; otherwise treat it as a system-class error and
+    // re-throw it.
+    return error instanceof GraphQLError
+      ? Promise.resolve({ errors: [error] })
+      : Promise.reject(error);
+  }
+}