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Move subscription implementation alongside execution #3299

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107 changes: 107 additions & 0 deletions src/execution/execute.ts
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Original file line number Diff line number Diff line change
Expand Up @@ -11,6 +11,7 @@ import { isObjectLike } from '../jsutils/isObjectLike';
import { promiseReduce } from '../jsutils/promiseReduce';
import { promiseForObject } from '../jsutils/promiseForObject';
import { addPath, pathToArray } from '../jsutils/Path';
import { isAsyncIterable } from '../jsutils/isAsyncIterable';
import { isIterableObject } from '../jsutils/isIterableObject';

import type { GraphQLFormattedError } from '../error/GraphQLError';
Expand Down Expand Up @@ -58,6 +59,7 @@ import {
collectFields,
collectSubfields as _collectSubfields,
} from './collectFields';
import { mapAsyncIterator } from './mapAsyncIterator';

/**
* A memoized collection of relevant subfields with regard to the return
Expand Down Expand Up @@ -1032,3 +1034,108 @@ export function getFieldDef(
}
return parentType.getFields()[fieldName];
}

export async function executeSubscription(
exeContext: ExecutionContext,
): Promise<AsyncGenerator<ExecutionResult, void, void> | ExecutionResult> {
const resultOrStream = await createSourceEventStreamImpl(exeContext);

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: unknown) =>
executeQueryOrMutation({
...exeContext,
rootValue: payload,
errors: [],
});

// Map every source value to a ExecutionResult value as described above.
return mapAsyncIterator(resultOrStream, mapSourceToResponse);
}

export async function createSourceEventStreamImpl(
exeContext: ExecutionContext,
): Promise<AsyncIterable<unknown> | ExecutionResult> {
try {
const eventStream = await executeSubscriptionRootField(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 executeSubscriptionRootField(
exeContext: ExecutionContext,
): Promise<unknown> {
const { schema, fragments, operation, variableValues, rootValue } =
exeContext;
const type = getOperationRootType(schema, operation);
const fields = collectFields(
schema,
fragments,
variableValues,
type,
operation.selectionSet,
);
const [responseName, fieldNodes] = [...fields.entries()][0];
const fieldDef = getFieldDef(schema, type, fieldNodes[0]);

if (!fieldDef) {
const fieldName = fieldNodes[0].name.value;
throw new GraphQLError(
`The subscription field "${fieldName}" is not defined.`,
fieldNodes,
);
}

const path = addPath(undefined, responseName, type.name);
const info = buildResolveInfo(exeContext, fieldDef, fieldNodes, type, path);

try {
// 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 ?? 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));
}
}
127 changes: 3 additions & 124 deletions src/execution/subscribe.ts
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Original file line number Diff line number Diff line change
@@ -1,32 +1,16 @@
import { inspect } from '../jsutils/inspect';
import { isAsyncIterable } from '../jsutils/isAsyncIterable';
import { addPath, pathToArray } from '../jsutils/Path';
import type { Maybe } from '../jsutils/Maybe';

import { GraphQLError } from '../error/GraphQLError';
import { locatedError } from '../error/locatedError';

import type { DocumentNode } from '../language/ast';

import type { GraphQLSchema } from '../type/schema';
import type { GraphQLFieldResolver } from '../type/definition';

import { getOperationRootType } from '../utilities/getOperationRootType';

import type {
ExecutionArgs,
ExecutionResult,
ExecutionContext,
} from './execute';
import { collectFields } from './collectFields';
import { getArgumentValues } from './values';
import type { ExecutionArgs, ExecutionResult } from './execute';
import {
buildExecutionContext,
buildResolveInfo,
executeQueryOrMutation,
getFieldDef,
createSourceEventStreamImpl,
executeSubscription,
} from './execute';
import { mapAsyncIterator } from './mapAsyncIterator';

/**
* @deprecated use ExecutionArgs instead.
Expand Down Expand Up @@ -75,32 +59,6 @@ export async function subscribe(
return executeSubscription(exeContext);
}

async function executeSubscription(
exeContext: ExecutionContext,
): Promise<AsyncGenerator<ExecutionResult, void, void> | ExecutionResult> {
const resultOrStream = await createSourceEventStreamImpl(exeContext);

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: unknown) =>
executeQueryOrMutation({
...exeContext,
rootValue: payload,
errors: [],
});

// Map every source value to a ExecutionResult value as described above.
return mapAsyncIterator(resultOrStream, mapSourceToResponse);
}

/**
* Implements the "CreateSourceEventStream" algorithm described in the
* GraphQL specification, resolving the subscription source event stream.
Expand Down Expand Up @@ -157,82 +115,3 @@ export async function createSourceEventStream(

return createSourceEventStreamImpl(exeContext);
}

export async function createSourceEventStreamImpl(
exeContext: ExecutionContext,
): Promise<AsyncIterable<unknown> | ExecutionResult> {
try {
const eventStream = await executeSubscriptionRootField(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 executeSubscriptionRootField(
exeContext: ExecutionContext,
): Promise<unknown> {
const { schema, fragments, operation, variableValues, rootValue } =
exeContext;
const type = getOperationRootType(schema, operation);
const fields = collectFields(
schema,
fragments,
variableValues,
type,
operation.selectionSet,
);
const [responseName, fieldNodes] = [...fields.entries()][0];
const fieldDef = getFieldDef(schema, type, fieldNodes[0]);

if (!fieldDef) {
const fieldName = fieldNodes[0].name.value;
throw new GraphQLError(
`The subscription field "${fieldName}" is not defined.`,
fieldNodes,
);
}

const path = addPath(undefined, responseName, type.name);
const info = buildResolveInfo(exeContext, fieldDef, fieldNodes, type, path);

try {
// 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 ?? 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));
}
}