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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));
}
}