flow like the river

BACK_BACK/node_modules/graphql/subscription/subscribe.mjs

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+import inspect from "../jsutils/inspect.mjs";
+import isAsyncIterable from "../jsutils/isAsyncIterable.mjs";
+import { addPath, pathToArray } from "../jsutils/Path.mjs";
+import { GraphQLError } from "../error/GraphQLError.mjs";
+import { locatedError } from "../error/locatedError.mjs";
+import { getArgumentValues } from "../execution/values.mjs";
+import { assertValidExecutionArguments, buildExecutionContext, buildResolveInfo, collectFields, execute, getFieldDef } from "../execution/execute.mjs";
+import { getOperationRootType } from "../utilities/getOperationRootType.mjs";
+import mapAsyncIterator from "./mapAsyncIterator.mjs";
+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: document,
+    rootValue: rootValue,
+    contextValue: contextValue,
+    variableValues: variableValues,
+    operationName: operationName,
+    fieldResolver: fieldResolver,
+    subscribeFieldResolver: 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) {
+  var schema = args.schema,
+      document = args.document,
+      rootValue = args.rootValue,
+      contextValue = args.contextValue,
+      variableValues = args.variableValues,
+      operationName = args.operationName,
+      fieldResolver = args.fieldResolver,
+      subscribeFieldResolver = args.subscribeFieldResolver;
+  var 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.
+
+  var mapSourceToResponse = function mapSourceToResponse(payload) {
+    return execute({
+      schema: schema,
+      document: document,
+      rootValue: payload,
+      contextValue: contextValue,
+      variableValues: variableValues,
+      operationName: operationName,
+      fieldResolver: fieldResolver
+    });
+  }; // Resolve the Source Stream, then map every source value to a
+  // ExecutionResult value as described above.
+
+
+  return sourcePromise.then(function (resultOrStream) {
+    return (// Note: Flow can't refine isAsyncIterable, so explicit casts are used.
+      isAsyncIterable(resultOrStream) ? mapAsyncIterator(resultOrStream, mapSourceToResponse, reportGraphQLError) : resultOrStream
+    );
+  });
+}
+/**
+ * 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, document, rootValue, contextValue, variableValues, operationName, fieldResolver) {
+  // If arguments are missing or incorrectly typed, this is an internal
+  // developer mistake which should throw an early error.
+  assertValidExecutionArguments(schema, document, variableValues);
+  return new Promise(function (resolve) {
+    // If a valid context cannot be created due to incorrect arguments,
+    // this will throw an error.
+    var exeContext = buildExecutionContext(schema, document, rootValue, contextValue, variableValues, operationName, fieldResolver);
+    resolve( // Return early errors if execution context failed.
+    Array.isArray(exeContext) ? {
+      errors: exeContext
+    } : executeSubscription(exeContext));
+  }).catch(reportGraphQLError);
+}
+
+function executeSubscription(exeContext) {
+  var schema = exeContext.schema,
+      operation = exeContext.operation,
+      variableValues = exeContext.variableValues,
+      rootValue = exeContext.rootValue;
+  var type = getOperationRootType(schema, operation);
+  var fields = collectFields(exeContext, type, operation.selectionSet, Object.create(null), Object.create(null));
+  var responseNames = Object.keys(fields);
+  var responseName = responseNames[0];
+  var fieldNodes = fields[responseName];
+  var fieldNode = fieldNodes[0];
+  var fieldName = fieldNode.name.value;
+  var fieldDef = getFieldDef(schema, type, fieldName);
+
+  if (!fieldDef) {
+    throw new GraphQLError("The subscription field \"".concat(fieldName, "\" is not defined."), fieldNodes);
+  }
+
+  var path = addPath(undefined, responseName, type.name);
+  var info = buildResolveInfo(exeContext, fieldDef, fieldNodes, type, path); // Coerce to Promise for easier error handling and consistent return type.
+
+  return new Promise(function (resolveResult) {
+    var _fieldDef$subscribe;
+
+    // Implements the "ResolveFieldEventStream" algorithm from GraphQL specification.
+    // It differs from "ResolveFieldValue" due to providing a different `resolveFn`.
+    // Build a JS object of arguments from the field.arguments AST, using the
+    // variables scope to fulfill any variable references.
+    var args = getArgumentValues(fieldDef, fieldNodes[0], variableValues); // The resolve function's optional third argument is a context value that
+    // is provided to every resolve function within an execution. It is commonly
+    // used to represent an authenticated user, or request-specific caches.
+
+    var contextValue = exeContext.contextValue; // Call the `subscribe()` resolver or the default resolver to produce an
+    // AsyncIterable yielding raw payloads.
+
+    var resolveFn = (_fieldDef$subscribe = fieldDef.subscribe) !== null && _fieldDef$subscribe !== void 0 ? _fieldDef$subscribe : exeContext.fieldResolver;
+    resolveResult(resolveFn(rootValue, args, contextValue, info));
+  }).then(function (eventStream) {
+    if (eventStream instanceof Error) {
+      throw locatedError(eventStream, fieldNodes, pathToArray(path));
+    } // Assert field returned an event stream, otherwise yield an error.
+
+
+    if (!isAsyncIterable(eventStream)) {
+      throw new Error('Subscription field must return Async Iterable. ' + "Received: ".concat(inspect(eventStream), "."));
+    }
+
+    return eventStream;
+  }, function (error) {
+    throw locatedError(error, fieldNodes, pathToArray(path));
+  });
+}