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Extract SubscriptionExecutor into its own file
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,185 @@ | ||
| import { inspect } from '../jsutils/inspect'; | ||
| import { isAsyncIterable } from '../jsutils/isAsyncIterable'; | ||
| import { addPath, pathToArray } from '../jsutils/Path'; | ||
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| import { GraphQLError } from '../error/GraphQLError'; | ||
| import { locatedError } from '../error/locatedError'; | ||
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| import type { DocumentNode } from '../language/ast'; | ||
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| import type { ExecutionContext, ExecutionResult } from '../execution/execute'; | ||
| import { collectFields } from '../execution/collectFields'; | ||
| import { getArgumentValues } from '../execution/values'; | ||
| import { Executor, getFieldDef } from '../execution/executor'; | ||
| import { execute } from '../execution/execute'; | ||
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| import { getOperationRootType } from '../utilities/getOperationRootType'; | ||
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| import { mapAsyncIterator } from './mapAsyncIterator'; | ||
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| /** | ||
| * This class is exported only to assist people in implementing their own executors | ||
| * without duplicating too much code and should be used only as last resort for cases | ||
| * requiring custom execution or if certain features could not be contributed upstream. | ||
| * | ||
| * It is still part of the internal API and is versioned, so any changes to it are never | ||
| * considered breaking changes. If you still need to support multiple versions of the | ||
| * library, please use the `versionInfo` variable for version detection. | ||
| * | ||
| * @internal | ||
| */ | ||
| export class SubscriptionExecutor extends Executor { | ||
| protected _document: DocumentNode; | ||
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| constructor(exeContext: ExecutionContext, document: DocumentNode) { | ||
| super(exeContext); | ||
| this._document = document; | ||
| } | ||
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| async executeSubscription(): Promise< | ||
| AsyncGenerator<ExecutionResult, void, void> | ExecutionResult | ||
| > { | ||
| const resultOrStream = await this.createSourceEventStream(); | ||
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| if (!isAsyncIterable(resultOrStream)) { | ||
| return resultOrStream; | ||
| } | ||
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| // 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: unknown) => | ||
| execute({ | ||
| schema: this._schema, | ||
| document: this._document, | ||
| rootValue: payload, | ||
| contextValue: this._contextValue, | ||
| variableValues: this._variableValues, | ||
| fieldResolver: this._fieldResolver, | ||
| }); | ||
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| // Map every source value to a ExecutionResult value as described above. | ||
| return mapAsyncIterator(resultOrStream, mapSourceToResponse); | ||
| } | ||
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| /** | ||
| * 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. | ||
| */ | ||
| async createSourceEventStream(): Promise< | ||
| AsyncIterable<unknown> | ExecutionResult | ||
| > { | ||
| try { | ||
| const eventStream = await this._createSourceEventStream(); | ||
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| // Assert field returned an event stream, otherwise yield an error. | ||
| if (!isAsyncIterable(eventStream)) { | ||
| throw new Error( | ||
| 'Subscription field must return Async Iterable. ' + | ||
| `Received: ${inspect(eventStream)}.`, | ||
| ); | ||
| } | ||
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| return eventStream; | ||
| } catch (error) { | ||
| // If it GraphQLError, report it as an ExecutionResult, containing only errors and no data. | ||
| // Otherwise treat the error as a system-class error and re-throw it. | ||
| if (error instanceof GraphQLError) { | ||
| return { errors: [error] }; | ||
| } | ||
| throw error; | ||
| } | ||
| } | ||
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| public async _createSourceEventStream(): Promise<unknown> { | ||
| const { | ||
| _schema, | ||
| _fragments, | ||
| _rootValue, | ||
| _contextValue, | ||
| _operation, | ||
| _variableValues, | ||
| _fieldResolver, | ||
| } = this; | ||
| const type = getOperationRootType(_schema, _operation); | ||
| const fields = collectFields( | ||
| _schema, | ||
| _fragments, | ||
| _variableValues, | ||
| type, | ||
| _operation.selectionSet, | ||
| new Map(), | ||
| new Set(), | ||
| ); | ||
| const [responseName, fieldNodes] = [...fields.entries()][0]; | ||
| const fieldDef = getFieldDef(_schema, type, fieldNodes[0]); | ||
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| if (!fieldDef) { | ||
| const fieldName = fieldNodes[0].name.value; | ||
| throw new GraphQLError( | ||
| `The subscription field "${fieldName}" is not defined.`, | ||
| fieldNodes, | ||
| ); | ||
| } | ||
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| const path = addPath(undefined, responseName, type.name); | ||
| const info = this.buildResolveInfo(fieldDef, fieldNodes, type, path); | ||
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| try { | ||
| // Implements the "ResolveFieldEventStream" algorithm from GraphQL specification. | ||
| // It differs from "ResolveFieldValue" due to providing a different `resolveFn`. | ||
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| // 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); | ||
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| // Call the `subscribe()` resolver or the default resolver to produce an | ||
| // AsyncIterable yielding raw payloads. | ||
| const resolveFn = fieldDef.subscribe ?? _fieldResolver; | ||
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| // 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 eventStream = await resolveFn( | ||
| _rootValue, | ||
| args, | ||
| _contextValue, | ||
| info, | ||
| ); | ||
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| if (eventStream instanceof Error) { | ||
| throw eventStream; | ||
| } | ||
| return eventStream; | ||
| } catch (error) { | ||
| throw locatedError(error, fieldNodes, pathToArray(path)); | ||
| } | ||
| } | ||
| } |