docs(migration): minor fixes and additions (content-type header and `…

…didResolveOperation` errors) (#7423)

* Add note about content-type response header change
* Add note about status code behavior change when errors are thrown from
`didResolveOperation`
* Add example for handling doubly-encoded `variables` (and show it works
in a test)

---------

Co-authored-by: David Glasser <glasser@apollographql.com>

.changeset/good-flies-peel.md

@@ -0,0 +1,2 @@
+---
+---

docs/source/migration.mdx

@@ -466,7 +466,7 @@ class MoviesAPI extends RESTDataSource { // highlight-line
   }
 
   override willSendRequest(path: string, request: AugmentedRequest) {
-    request.headers['authorization'] = this.token;
+    request.headers.authorization = this.token;
   }
 
   async getMovie(id: string): Promise<Movie> {
@@ -1080,6 +1080,24 @@ Whereas this query would be invalid:
 
 (Moreover, Apollo Server 4 responds with a 400 status code if `variables` and `extensions` are provided in a `POST` body with any type other than object, such as array, boolean, or null. Similarly, it responds with a 400 status code if `operationName` is provided in a `POST` body with any type other than string.)
 
+If you'd like to restore the previous behavior, you can `JSON.parse` the `variables` and `extensions` fields after your framework has parsed the request body. In Express that might look like:
+
+```ts
+app.use(json());
+app.use((req, res, next) => {
+  if (typeof req.body?.variables === 'string') {
+    try {
+      req.body.variables = JSON.parse(req.body.variables);
+    } catch (e) {
+      // https://github.com/graphql/graphql-over-http/blob/main/spec/GraphQLOverHTTP.md#json-parsing-failure
+      res.status(400).send(e instanceof Error ? e.message : e);
+    }
+  }
+  next();
+});
+app.use(expressMiddleware(server));
+```
+
 
 ## Changed features
 
@@ -1504,6 +1522,10 @@ new ApolloServer({
 });
 ```
 
+### Content-Type response header
+
+In Apollo Server 3, the `Content-Type` response header is `application/json`. Apollo Server 4 includes the encoding via the `charset` parameter: `application/json; charset=utf-8` as recommended by the [GraphQL over HTTP spec](https://github.com/graphql/graphql-over-http/blob/main/spec/GraphQLOverHTTP.md#media-types).
+
 ## "Disabled" plugins cannot be combined with their enabled counterpart
 
 Apollo Server has several plugins that are installed by default in certain conditions. To override this behavior, each of these plugins has a "disabled" counterpart that prevents this default installation.
@@ -1618,6 +1640,8 @@ In Apollo Server 4, `requestDidStart` hooks are called in parallel rather than i
 
 Apollo Server 4 more consistently handles errors thrown by multiple plugin hooks.  Each error is wrapped in an "Unexpected error handling request" error and invoked using the new `unexpectedErrorProcessingRequest` plugin hook.
 
+In Apollo Server 3, if a `didResolveOperation` hook threw a `GraphQLError`, the server would return a 400 error by default. In Apollo Server 4, the server will return a 500 by default, but this can be configured by setting [`extensions.http`](./data/errors/#setting-http-status-code-and-headers) on the `GraphQLError` object.
+
 ### Custom `gateway` and `GraphQLDataSource` implementations
 
 The `gateway` option to the `ApolloServer` constructor is designed to be used with the `ApolloGateway` class from the `@apollo/gateway` package. Apollo Server 4 changes the details of how Apollo Server interacts with this object. If you use [any version of `@apollo/gateway` that supports `graphql` 16](#graphql) as your server's `gateway`, these changes won't affect you. However, if you provide something _other_ than an `ApolloGateway` instance to this option, you might need to adjust your custom code.

packages/server/src/__tests__/express4/expressSpecific.test.ts

@@ -141,3 +141,59 @@ it('incremental delivery works with compression', async () => {
 
   await server.stop();
 });
+
+it('supporting doubly-encoded variables example from migration guide', async () => {
+  const server = new ApolloServer({
+    typeDefs: 'type Query {hello(s: String!): String!}',
+    resolvers: {
+      Query: {
+        hello: (_root, { s }) => s,
+      },
+    },
+  });
+  await server.start();
+  const app = express();
+
+  app.use(json());
+
+  // Test will fail if you remove this middleware.
+  app.use((req, res, next) => {
+    if (typeof req.body?.variables === 'string') {
+      try {
+        req.body.variables = JSON.parse(req.body.variables);
+      } catch (e) {
+        // https://github.com/graphql/graphql-over-http/blob/main/spec/GraphQLOverHTTP.md#json-parsing-failure
+        res.status(400).send(e instanceof Error ? e.message : e);
+      }
+    }
+    next();
+  });
+
+  app.use(expressMiddleware(server));
+
+  await request(app)
+    .post('/')
+    .send({
+      query: 'query Hello($s: String!){hello(s: $s)}',
+      variables: { s: 'normally encoded' },
+    })
+    .expect(200, { data: { hello: 'normally encoded' } });
+
+  await request(app)
+    .post('/')
+    .send({
+      query: 'query Hello($s: String!){hello(s: $s)}',
+      variables: JSON.stringify({ s: 'doubly-encoded' }),
+    })
+    .expect(200, { data: { hello: 'doubly-encoded' } });
+
+  await request(app)
+    .post('/')
+    .send({
+      query: 'query Hello($s: String!){hello(s: $s)}',
+      variables: '{malformed JSON}',
+    })
+    .expect(400, 'Unexpected token m in JSON at position 1');
+
+  await server.stop();
+});