Changelog and docs for preserveHeaderCase (#10111)

* Changelog

* Add only to http-link doc

* Batch, httpLink constructor, and adv. networking

CHANGELOG.md

@@ -43,6 +43,8 @@
 - Support `onError` callback for `useSubscription` hook. <br/>
   [@jeroenvisser101](https://github.com/jeroenvisser101) in [#9495](https://github.com/apollographql/apollo-client/pull/9495)
 
+- Implement `preserveHeaderCase` option for `http` context object, enabling preserved header capitalization for non-http-spec-compliant servers. <br/>
+  [@mrdoombringer](https://github.com/mrdoombringer) in [#9891](https://github.com/apollographql/apollo-client/pull/9891)
 ### Improvements
 
 - Delay calling `onCompleted` and `onError` callbacks passed to `useQuery` using `Promise.resolve().then(() => ...)` to fix issue [#9794](https://github.com/apollographql/apollo-client/pull/9794). <br/>

docs/source/api/link/apollo-link-batch-http.mdx

@@ -168,6 +168,21 @@ An object representing headers to include in every HTTP request, such as `{Authe
 <tr>
 <td>
 
+###### `preserveHeaderCase`
+
+`Boolean`
+</td>
+<td>
+
+If set to true, header names won't be automatically normalized to lowercase. This allows for non-http-spec-compliant servers that might expect capitalized header names.
+
+The default value is `false`.
+</td>
+</tr>
+
+<tr>
+<td>
+
 ###### `credentials`
 
 `String`
@@ -227,11 +242,13 @@ operation.setContext({
 })
 ```
 
-The context `http` object currently supports two keys:
+From the context `http` object:
 
 * `includeExtensions`: Send the extensions object for this request.
 * `includeQuery`: Don't send the `query` field for this request.
 
+See the [http option fields](https://www.apollographql.com/docs/react/api/link/apollo-link-http/#http-option-fields) for more information.
+
 One way to use persisted queries is with [apollo-link-persisted-queries](https://www.apollographql.com/docs/react/api/link/persisted-queries) and [Apollo Server](/apollo-server/performance/apq/).
 
 ## Custom fetching

docs/source/api/link/apollo-link-http.md

@@ -99,6 +99,20 @@ An object representing headers to include in every HTTP request, such as `{Autho
 </td>
 </tr>
 
+<tr>
+<td>
+
+###### `preserveHeaderCase`
+
+`Boolean`
+</td>
+<td>
+
+If set to true, header names won't be automatically normalized to lowercase. This allows for non-http-spec-compliant servers that might expect capitalized header names.
+
+The default value is `false`.
+</td>
+</tr>
 
 <tr>
 <td>
@@ -317,6 +331,21 @@ The default value is `true`.
 </td>
 </tr>
 
+<tr>
+<td>
+
+###### `preserveHeaderCase`
+
+`Boolean`
+</td>
+<td>
+
+If set to true, header names won't be automatically normalized to lowercase. This allows for non-http-spec-compliant servers that might expect capitalized header names.
+
+The default value is `false`.
+</td>
+</tr>
+
 </tbody>
 </table>
 

docs/source/networking/advanced-http-networking.md

@@ -191,6 +191,7 @@ The `HttpLink` constructor accepts the following options:
 | `includeExtensions` | If `true`, you can pass an `extensions` field to your GraphQL server. (default: `false`) |
 | `fetch` | A `fetch`-compatible API for making a request. See [Providing a `fetch` replacement for certain environments](#providing-a-fetch-replacement-for-certain-environments). |
 | `headers` | An object containing header names and values to include in each request. |
+| `preserveHeaderCase` | If `true`, header values retain their capitalization for non-http-spec-compliant servers. (default: `false`) |
 | `credentials` | A string representing the credentials policy to use for the `fetch` call. (valid values: `omit`, `include`, `same-origin`) |
 | `fetchOptions` | Include this to override the values of certain options that are provided to the `fetch` call. |
 | `useGETForQueries` | If `true`, `HttpLink` uses `GET` requests instead of `POST` requests to execute query operations (but not mutation operations). (default: `false`) |