From bdd523c59c867c4ab21242b2ad6f8659105df701 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Tue, 10 Mar 2020 21:31:35 -0400
Subject: [PATCH 1/9] Initial commit, implement contextValueExecution for #894

---
 src/subscription/subscribe.d.ts |  3 +++
 src/subscription/subscribe.js   | 16 +++++++++++++---
 2 files changed, 16 insertions(+), 3 deletions(-)

diff --git a/src/subscription/subscribe.d.ts b/src/subscription/subscribe.d.ts
index a2a2d0820e..c6d97772c9 100644
--- a/src/subscription/subscribe.d.ts
+++ b/src/subscription/subscribe.d.ts
@@ -16,6 +16,7 @@ export interface SubscriptionArgs {
   operationName?: Maybe<string>;
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
   subscribeFieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
+  contextValueExecution?: Maybe<(contextValue: any) => any>;
 }
 
 /**
@@ -53,6 +54,7 @@ export function subscribe<TData = ExecutionResultDataDefault>(
   operationName?: Maybe<string>,
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>,
   subscribeFieldResolver?: Maybe<GraphQLFieldResolver<any, any>>,
+  contextValueExecution?: Maybe<(contextValue: any) => any>,
 ): Promise<
   AsyncIterableIterator<ExecutionResult<TData>> | ExecutionResult<TData>
 >;
@@ -83,4 +85,5 @@ export function createSourceEventStream<TData = ExecutionResultDataDefault>(
   variableValues?: { [key: string]: any },
   operationName?: Maybe<string>,
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>,
+  contextValueExecution?: Maybe<(contextValue: any) => any>,
 ): Promise<AsyncIterable<any> | ExecutionResult<TData>>;
diff --git a/src/subscription/subscribe.js b/src/subscription/subscribe.js
index 1b170800c6..f8f5c18620 100644
--- a/src/subscription/subscribe.js
+++ b/src/subscription/subscribe.js
@@ -37,6 +37,7 @@ export type SubscriptionArgs = {|
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
   subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
+  contextValueExecution?: ?(contextValue: mixed) => mixed,
 |};
 
 /**
@@ -74,6 +75,7 @@ declare function subscribe(
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
   subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
+  contextValueExecution?: ?(contextValue: mixed) => mixed,
 ): Promise<AsyncIterator<ExecutionResult> | ExecutionResult>;
 export function subscribe(
   argsOrSchema,
@@ -84,6 +86,7 @@ export function subscribe(
   operationName,
   fieldResolver,
   subscribeFieldResolver,
+  contextValueExecution,
 ) {
   /* eslint-enable no-redeclare */
   // Extract arguments from object args if provided.
@@ -98,6 +101,7 @@ export function subscribe(
         operationName,
         fieldResolver,
         subscribeFieldResolver,
+        contextValueExecution,
       });
 }
 
@@ -125,6 +129,7 @@ function subscribeImpl(
     operationName,
     fieldResolver,
     subscribeFieldResolver,
+    contextValueExecution,
   } = args;
 
   const sourcePromise = createSourceEventStream(
@@ -143,16 +148,21 @@ function subscribeImpl(
   // 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({
+  const mapSourceToResponse = payload => {
+    const executeContextValue =
+      typeof contextValueExecution === 'function'
+        ? contextValueExecution(contextValue)
+        : contextValue;
+    return execute({
       schema,
       document,
       rootValue: payload,
-      contextValue,
+      contextValue: executeContextValue,
       variableValues,
       operationName,
       fieldResolver,
     });
+  };
 
   // Resolve the Source Stream, then map every source value to a
   // ExecutionResult value as described above.

From 8b4b0f78b4e161cf8699407044867567796e39fe Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Tue, 10 Mar 2020 21:58:20 -0400
Subject: [PATCH 2/9] Add test for contextValueExecution

---
 src/subscription/__tests__/subscribe-test.js | 68 +++++++++++++++++++-
 src/subscription/subscribe.js                |  4 +-
 2 files changed, 69 insertions(+), 3 deletions(-)

diff --git a/src/subscription/__tests__/subscribe-test.js b/src/subscription/__tests__/subscribe-test.js
index 8586d95469..85e9f6a83e 100644
--- a/src/subscription/__tests__/subscribe-test.js
+++ b/src/subscription/__tests__/subscribe-test.js
@@ -100,6 +100,7 @@ async function createSubscription(
   pubsub,
   schema = emailSchema,
   document = defaultSubscriptionAST,
+  contextValueExecution = undefined,
 ) {
   const data = {
     inbox: {
@@ -132,7 +133,12 @@ async function createSubscription(
   return {
     sendImportantEmail,
     // $FlowFixMe
-    subscription: await subscribe({ schema, document, rootValue: data }),
+    subscription: await subscribe({
+      schema,
+      document,
+      rootValue: data,
+      contextValueExecution,
+    }),
   };
 }
 
@@ -1107,4 +1113,64 @@ describe('Subscription Publish Phase', () => {
       value: undefined,
     });
   });
+
+  it('should produce a unique context per execution via contextValueExecution', async () => {
+    const contextExecutionSchema = emailSchemaWithResolvers(
+      async function*() {
+        yield { email: { subject: 'Hello' } };
+        yield { email: { subject: 'Hello' } };
+      },
+      (data, _args, ctx) => ({
+        email: { subject: `${data.email.subject} ${ctx.contextIndex}` },
+      }),
+    );
+
+    let contextIndex = 0;
+    const subscription = await subscribe({
+      schema: contextExecutionSchema,
+      document: parse(`
+        subscription {
+          importantEmail {
+            email {
+              subject
+            }
+          }
+        }
+      `),
+      contextValue: { test: true },
+      contextValueExecution: ctx => {
+        expect(ctx.test).to.equal(true);
+        return { ...ctx, contextIndex: contextIndex++ };
+      },
+    });
+
+    // $FlowFixMe
+    const payload1 = await subscription.next();
+    expect(payload1).to.deep.equal({
+      done: false,
+      value: {
+        data: {
+          importantEmail: {
+            email: {
+              subject: 'Hello 0',
+            },
+          },
+        },
+      },
+    });
+
+    const payload2 = await subscription.next();
+    expect(payload2).to.deep.equal({
+      done: false,
+      value: {
+        data: {
+          importantEmail: {
+            email: {
+              subject: 'Hello 1',
+            },
+          },
+        },
+      },
+    });
+  });
 });
diff --git a/src/subscription/subscribe.js b/src/subscription/subscribe.js
index f8f5c18620..7c02c04218 100644
--- a/src/subscription/subscribe.js
+++ b/src/subscription/subscribe.js
@@ -37,7 +37,7 @@ export type SubscriptionArgs = {|
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
   subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
-  contextValueExecution?: ?(contextValue: mixed) => mixed,
+  contextValueExecution?: ?(contextValue: any) => mixed,
 |};
 
 /**
@@ -75,7 +75,7 @@ declare function subscribe(
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
   subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
-  contextValueExecution?: ?(contextValue: mixed) => mixed,
+  contextValueExecution?: ?(contextValue: any) => mixed,
 ): Promise<AsyncIterator<ExecutionResult> | ExecutionResult>;
 export function subscribe(
   argsOrSchema,

From 878330d15960d324bf7e7e65b5366b57c86223f2 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Mon, 16 Mar 2020 11:24:59 -0400
Subject: [PATCH 3/9] contextValueExecution -> perEventContextResolver

---
 src/subscription/__tests__/subscribe-test.js |  8 ++++----
 src/subscription/subscribe.d.ts              |  5 ++---
 src/subscription/subscribe.js                | 14 +++++++-------
 3 files changed, 13 insertions(+), 14 deletions(-)

diff --git a/src/subscription/__tests__/subscribe-test.js b/src/subscription/__tests__/subscribe-test.js
index 85e9f6a83e..5d1f54ed61 100644
--- a/src/subscription/__tests__/subscribe-test.js
+++ b/src/subscription/__tests__/subscribe-test.js
@@ -100,7 +100,7 @@ async function createSubscription(
   pubsub,
   schema = emailSchema,
   document = defaultSubscriptionAST,
-  contextValueExecution = undefined,
+  perEventContextResolver = undefined,
 ) {
   const data = {
     inbox: {
@@ -137,7 +137,7 @@ async function createSubscription(
       schema,
       document,
       rootValue: data,
-      contextValueExecution,
+      perEventContextResolver,
     }),
   };
 }
@@ -1114,7 +1114,7 @@ describe('Subscription Publish Phase', () => {
     });
   });
 
-  it('should produce a unique context per execution via contextValueExecution', async () => {
+  it('should produce a unique context per event via perEventContextResolver', async () => {
     const contextExecutionSchema = emailSchemaWithResolvers(
       async function*() {
         yield { email: { subject: 'Hello' } };
@@ -1138,7 +1138,7 @@ describe('Subscription Publish Phase', () => {
         }
       `),
       contextValue: { test: true },
-      contextValueExecution: ctx => {
+      perEventContextResolver: ctx => {
         expect(ctx.test).to.equal(true);
         return { ...ctx, contextIndex: contextIndex++ };
       },
diff --git a/src/subscription/subscribe.d.ts b/src/subscription/subscribe.d.ts
index c6d97772c9..1359a6116c 100644
--- a/src/subscription/subscribe.d.ts
+++ b/src/subscription/subscribe.d.ts
@@ -16,7 +16,7 @@ export interface SubscriptionArgs {
   operationName?: Maybe<string>;
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
   subscribeFieldResolver?: Maybe<GraphQLFieldResolver<any, any>>;
-  contextValueExecution?: Maybe<(contextValue: any) => any>;
+  perEventContextResolver?: Maybe<(contextValue: any) => any>;
 }
 
 /**
@@ -54,7 +54,7 @@ export function subscribe<TData = ExecutionResultDataDefault>(
   operationName?: Maybe<string>,
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>,
   subscribeFieldResolver?: Maybe<GraphQLFieldResolver<any, any>>,
-  contextValueExecution?: Maybe<(contextValue: any) => any>,
+  perEventContextResolver?: Maybe<(contextValue: any) => any>,
 ): Promise<
   AsyncIterableIterator<ExecutionResult<TData>> | ExecutionResult<TData>
 >;
@@ -85,5 +85,4 @@ export function createSourceEventStream<TData = ExecutionResultDataDefault>(
   variableValues?: { [key: string]: any },
   operationName?: Maybe<string>,
   fieldResolver?: Maybe<GraphQLFieldResolver<any, any>>,
-  contextValueExecution?: Maybe<(contextValue: any) => any>,
 ): Promise<AsyncIterable<any> | ExecutionResult<TData>>;
diff --git a/src/subscription/subscribe.js b/src/subscription/subscribe.js
index 7c02c04218..2540179a98 100644
--- a/src/subscription/subscribe.js
+++ b/src/subscription/subscribe.js
@@ -37,7 +37,7 @@ export type SubscriptionArgs = {|
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
   subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
-  contextValueExecution?: ?(contextValue: any) => mixed,
+  perEventContextResolver?: ?(contextValue: any) => mixed,
 |};
 
 /**
@@ -75,7 +75,7 @@ declare function subscribe(
   operationName?: ?string,
   fieldResolver?: ?GraphQLFieldResolver<any, any>,
   subscribeFieldResolver?: ?GraphQLFieldResolver<any, any>,
-  contextValueExecution?: ?(contextValue: any) => mixed,
+  perEventContextResolver?: ?(contextValue: any) => mixed,
 ): Promise<AsyncIterator<ExecutionResult> | ExecutionResult>;
 export function subscribe(
   argsOrSchema,
@@ -86,7 +86,7 @@ export function subscribe(
   operationName,
   fieldResolver,
   subscribeFieldResolver,
-  contextValueExecution,
+  perEventContextResolver,
 ) {
   /* eslint-enable no-redeclare */
   // Extract arguments from object args if provided.
@@ -101,7 +101,7 @@ export function subscribe(
         operationName,
         fieldResolver,
         subscribeFieldResolver,
-        contextValueExecution,
+        perEventContextResolver,
       });
 }
 
@@ -129,7 +129,7 @@ function subscribeImpl(
     operationName,
     fieldResolver,
     subscribeFieldResolver,
-    contextValueExecution,
+    perEventContextResolver,
   } = args;
 
   const sourcePromise = createSourceEventStream(
@@ -150,8 +150,8 @@ function subscribeImpl(
   // "ExecuteQuery" algorithm, for which `execute` is also used.
   const mapSourceToResponse = payload => {
     const executeContextValue =
-      typeof contextValueExecution === 'function'
-        ? contextValueExecution(contextValue)
+      typeof perEventContextResolver === 'function'
+        ? perEventContextResolver(contextValue)
         : contextValue;
     return execute({
       schema,

From 92929055025a1c677e8d701a504fc802d94103ed Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Mon, 16 Mar 2020 11:25:22 -0400
Subject: [PATCH 4/9] Add note about perEventContextResolver in JSDoc for
 subscribe

---
 src/subscription/subscribe.d.ts | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/src/subscription/subscribe.d.ts b/src/subscription/subscribe.d.ts
index 1359a6116c..8f952bd9c7 100644
--- a/src/subscription/subscribe.d.ts
+++ b/src/subscription/subscribe.d.ts
@@ -37,6 +37,9 @@ export interface SubscriptionArgs {
  * If the operation succeeded, the promise resolves to an AsyncIterator, which
  * yields a stream of ExecutionResults representing the response stream.
  *
+ * If a `perEventContextResolver` argument is provided, it will be invoked for
+ * each event, and return a new context value specific to that event's execution.
+ *
  * Accepts either an object with named arguments, or individual arguments.
  */
 export function subscribe<TData = ExecutionResultDataDefault>(

From 1d6b1505b6809bdba80d2663b525667a28b207d0 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Mon, 16 Mar 2020 11:32:51 -0400
Subject: [PATCH 5/9] Remove comma

---
 src/subscription/subscribe.d.ts | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/src/subscription/subscribe.d.ts b/src/subscription/subscribe.d.ts
index 8f952bd9c7..264ff73a33 100644
--- a/src/subscription/subscribe.d.ts
+++ b/src/subscription/subscribe.d.ts
@@ -38,7 +38,7 @@ export interface SubscriptionArgs {
  * yields a stream of ExecutionResults representing the response stream.
  *
  * If a `perEventContextResolver` argument is provided, it will be invoked for
- * each event, and return a new context value specific to that event's execution.
+ * each event and return a new context value specific to that event's execution.
  *
  * Accepts either an object with named arguments, or individual arguments.
  */

From 4461d7fc6548756f3b9829786790d7e913a2d141 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Mon, 16 Mar 2020 16:48:35 -0400
Subject: [PATCH 6/9] Add docs

---
 src/subscription/subscribe.js | 5 +++++
 1 file changed, 5 insertions(+)

diff --git a/src/subscription/subscribe.js b/src/subscription/subscribe.js
index 2540179a98..8873c5a2c0 100644
--- a/src/subscription/subscribe.js
+++ b/src/subscription/subscribe.js
@@ -59,6 +59,9 @@ export type SubscriptionArgs = {|
  * If the operation succeeded, the promise resolves to an AsyncIterator, which
  * yields a stream of ExecutionResults representing the response stream.
  *
+ * If a `perEventContextResolver` argument is provided, it will be invoked for
+ * each event and return a new context value specific to the event's execution.
+ *
  * Accepts either an object with named arguments, or individual arguments.
  */
 declare function subscribe(
@@ -148,6 +151,8 @@ function subscribeImpl(
   // 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.
+  // If `perEventContextResolver` is provided, it is invoked with the original
+  // `contextValue` to return a new context unique to this `execute`.
   const mapSourceToResponse = payload => {
     const executeContextValue =
       typeof perEventContextResolver === 'function'

From f759882a10d018d24498791e1be8db8670903743 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Wed, 18 Mar 2020 10:02:03 -0400
Subject: [PATCH 7/9] Update, ensure perEventContextResolverFn per stream

---
 src/subscription/subscribe.js | 16 ++++++++--------
 1 file changed, 8 insertions(+), 8 deletions(-)

diff --git a/src/subscription/subscribe.js b/src/subscription/subscribe.js
index 8873c5a2c0..c47602298c 100644
--- a/src/subscription/subscribe.js
+++ b/src/subscription/subscribe.js
@@ -153,21 +153,21 @@ function subscribeImpl(
   // "ExecuteQuery" algorithm, for which `execute` is also used.
   // If `perEventContextResolver` is provided, it is invoked with the original
   // `contextValue` to return a new context unique to this `execute`.
-  const mapSourceToResponse = payload => {
-    const executeContextValue =
-      typeof perEventContextResolver === 'function'
-        ? perEventContextResolver(contextValue)
-        : contextValue;
-    return execute({
+  const perEventContextResolverFn =
+    typeof perEventContextResolver === 'function'
+      ? perEventContextResolver
+      : ctx => ctx;
+
+  const mapSourceToResponse = payload =>
+    execute({
       schema,
       document,
       rootValue: payload,
-      contextValue: executeContextValue,
+      contextValue: perEventContextResolverFn(contextValue),
       variableValues,
       operationName,
       fieldResolver,
     });
-  };
 
   // Resolve the Source Stream, then map every source value to a
   // ExecutionResult value as described above.

From 1d0b6af7abf9c8e2962e95b810cc53fcf08eac60 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Mon, 23 Mar 2020 09:27:47 -0400
Subject: [PATCH 8/9] Use ?? for the perEventContextResolver check

---
 src/subscription/subscribe.js | 5 +----
 1 file changed, 1 insertion(+), 4 deletions(-)

diff --git a/src/subscription/subscribe.js b/src/subscription/subscribe.js
index c47602298c..5436255533 100644
--- a/src/subscription/subscribe.js
+++ b/src/subscription/subscribe.js
@@ -153,10 +153,7 @@ function subscribeImpl(
   // "ExecuteQuery" algorithm, for which `execute` is also used.
   // If `perEventContextResolver` is provided, it is invoked with the original
   // `contextValue` to return a new context unique to this `execute`.
-  const perEventContextResolverFn =
-    typeof perEventContextResolver === 'function'
-      ? perEventContextResolver
-      : ctx => ctx;
+  const perEventContextResolverFn = perEventContextResolver ?? (ctx => ctx);
 
   const mapSourceToResponse = payload =>
     execute({

From 1fb09314a64d885a21f4b9198a549f60f3eb5c53 Mon Sep 17 00:00:00 2001
From: Tim Griesser <tgriesser10@gmail.com>
Date: Fri, 13 Nov 2020 12:00:34 -0500
Subject: [PATCH 9/9] Fix flow types

---
 src/subscription/__tests__/subscribe-test.js | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)

diff --git a/src/subscription/__tests__/subscribe-test.js b/src/subscription/__tests__/subscribe-test.js
index 919614649e..7ee7395424 100644
--- a/src/subscription/__tests__/subscribe-test.js
+++ b/src/subscription/__tests__/subscribe-test.js
@@ -13,6 +13,7 @@ import { GraphQLError } from '../../error/GraphQLError';
 
 import { GraphQLSchema } from '../../type/schema';
 import { GraphQLList, GraphQLObjectType } from '../../type/definition';
+import type { GraphQLFieldResolver } from '../../type/definition';
 import { GraphQLInt, GraphQLString, GraphQLBoolean } from '../../type/scalars';
 
 import { createSourceEventStream, subscribe } from '../subscribe';
@@ -68,9 +69,9 @@ const EmailEventType = new GraphQLObjectType({
 
 const emailSchema = emailSchemaWithResolvers();
 
-function emailSchemaWithResolvers<T: mixed>(
+function emailSchemaWithResolvers<T: mixed, R: mixed, C: mixed>(
   subscribeFn?: (T) => mixed,
-  resolveFn?: (T) => mixed,
+  resolveFn?: GraphQLFieldResolver<R, C>,
 ) {
   return new GraphQLSchema({
     query: QueryType,
@@ -1133,8 +1134,8 @@ describe('Subscription Publish Phase', () => {
         return { ...ctx, contextIndex: contextIndex++ };
       },
     });
+    invariant(isAsyncIterable(subscription));
 
-    // $FlowFixMe
     const payload1 = await subscription.next();
     expect(payload1).to.deep.equal({
       done: false,