Initialisation

Added the packages and files for the backend server

node_modules/graphql/execution/subscribe.mjs

@@ -0,0 +1,222 @@
+import { devAssert } from '../jsutils/devAssert.mjs';
+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 { collectFields } from './collectFields.mjs';
+import {
+  assertValidExecutionArguments,
+  buildExecutionContext,
+  buildResolveInfo,
+  execute,
+  getFieldDef,
+} from './execute.mjs';
+import { mapAsyncIterator } from './mapAsyncIterator.mjs';
+import { getArgumentValues } from './values.mjs';
+/**
+ * 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
+  arguments.length < 2 ||
+    devAssert(
+      false,
+      'graphql@16 dropped long-deprecated support for positional arguments, please pass an object instead.',
+    );
+  const resultOrStream = await createSourceEventStream(args);
+
+  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({ ...args, rootValue: payload }); // Map every source value to a ExecutionResult value as described above.
+
+  return mapAsyncIterator(resultOrStream, mapSourceToResponse);
+}
+
+function toNormalizedArgs(args) {
+  const firstArg = args[0];
+
+  if (firstArg && 'document' in firstArg) {
+    return firstArg;
+  }
+
+  return {
+    schema: firstArg,
+    // FIXME: when underlying TS bug fixed, see https://github.com/microsoft/TypeScript/issues/31613
+    document: args[1],
+    rootValue: args[2],
+    contextValue: args[3],
+    variableValues: args[4],
+    operationName: args[5],
+    subscribeFieldResolver: args[6],
+  };
+}
+/**
+ * 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(...rawArgs) {
+  const args = toNormalizedArgs(rawArgs);
+  const { schema, document, variableValues } = args; // 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(args); // 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: ${inspect(eventStream)}.`,
+      );
+    }
+
+    return eventStream;
+  } catch (error) {
+    // If it GraphQLError, report it as an ExecutionResult, containing only errors and no data.
+    // Otherwise treat the error as a system-class error and re-throw it.
+    if (error instanceof GraphQLError) {
+      return {
+        errors: [error],
+      };
+    }
+
+    throw error;
+  }
+}
+
+async function executeSubscription(exeContext) {
+  const { schema, fragments, operation, variableValues, rootValue } =
+    exeContext;
+  const rootType = schema.getSubscriptionType();
+
+  if (rootType == null) {
+    throw new GraphQLError(
+      'Schema is not configured to execute subscription operation.',
+      {
+        nodes: operation,
+      },
+    );
+  }
+
+  const rootFields = collectFields(
+    schema,
+    fragments,
+    variableValues,
+    rootType,
+    operation.selectionSet,
+  );
+  const [responseName, fieldNodes] = [...rootFields.entries()][0];
+  const fieldDef = getFieldDef(schema, rootType, fieldNodes[0]);
+
+  if (!fieldDef) {
+    const fieldName = fieldNodes[0].name.value;
+    throw new GraphQLError(
+      `The subscription field "${fieldName}" is not defined.`,
+      {
+        nodes: fieldNodes,
+      },
+    );
+  }
+
+  const path = addPath(undefined, responseName, rootType.name);
+  const info = buildResolveInfo(
+    exeContext,
+    fieldDef,
+    fieldNodes,
+    rootType,
+    path,
+  );
+
+  try {
+    var _fieldDef$subscribe;
+
+    // Implements the "ResolveFieldEventStream" algorithm from GraphQL specification.
+    // It differs from "ResolveFieldValue" due to providing a different `resolveFn`.
+    // Build a JS object of arguments from the field.arguments AST, using the
+    // variables scope to fulfill any variable references.
+    const args = getArgumentValues(fieldDef, fieldNodes[0], variableValues); // The resolve function's optional third argument is a context value that
+    // is provided to every resolve function within an execution. It is commonly
+    // used to represent an authenticated user, or request-specific caches.
+
+    const contextValue = exeContext.contextValue; // Call the `subscribe()` resolver or the default resolver to produce an
+    // AsyncIterable yielding raw payloads.
+
+    const resolveFn =
+      (_fieldDef$subscribe = fieldDef.subscribe) !== null &&
+      _fieldDef$subscribe !== void 0
+        ? _fieldDef$subscribe
+        : 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));
+  }
+}