From 016a15c9139faf9c6aabe79d05278f25fc14800e Mon Sep 17 00:00:00 2001
From: Artur Tagisow <5359825+sethidden@users.noreply.github.com>
Date: Sat, 23 Apr 2022 23:53:19 +0200
Subject: [PATCH] feat: dynamic headers (#341)

---
 README.md             | 26 ++++++++++++++++++++++++++
 src/index.ts          | 16 +++++++++++-----
 src/types.ts          |  5 +++++
 tests/headers.test.ts | 20 ++++++++++++++++++++
 4 files changed, 62 insertions(+), 5 deletions(-)

diff --git a/README.md b/README.md
index 53651e6c..eaf8f3b3 100644
--- a/README.md
+++ b/README.md
@@ -19,6 +19,7 @@ Minimal GraphQL client supporting Node and browsers for scripts or simple apps
   - [Authentication via HTTP header](#authentication-via-http-header)
     - [Incrementally setting headers](#incrementally-setting-headers)
   - [Passing Headers in each request](#passing-headers-in-each-request)
+  - [Passing dynamic headers to the client](#passing-dynamic-headers-to-the-client)
   - [Passing more options to `fetch`](#passing-more-options-to-fetch)
     - [Custom JSON serializer](#custom-json-serializer)
   - [Using GraphQL Document variables](#using-graphql-document-variables)
@@ -214,6 +215,31 @@ const requestHeaders = {
 const data = await client.request(query, variables, requestHeaders)
 ```
 
+#### Passing dynamic headers to the client
+
+It's possible to recalculate the global client headers dynamically before each request.
+To do that, pass a function that returns the headers to the `headers` property when creating a new `GraphQLClient`.
+
+```js
+import { GraphQLClient } from 'graphql-request'
+
+const client = new GraphQLClient(endpoint,
+  { 
+    headers: () => ({ 'X-Sent-At-Time': Date.now() })
+  }
+)
+
+const query = gql`
+  query getCars {
+    cars {
+      name
+    }
+  }
+
+// Function saved in the client runs and calculates fresh headers before each request
+const data = await client.request(query)
+```
+
 ### Passing more options to `fetch`
 
 ```js
diff --git a/src/index.ts b/src/index.ts
index bd327b83..72d2572b 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -24,6 +24,8 @@ import {
   RawRequestExtendedOptions,
   RequestExtendedOptions,
   Variables,
+  PatchedRequestInit,
+  MaybeFunction,
 } from './types'
 import * as Dom from './types.dom'
 
@@ -190,9 +192,9 @@ const get = async <V = Variables>({
  */
 export class GraphQLClient {
   private url: string
-  private options: Dom.RequestInit
+  private options: PatchedRequestInit
 
-  constructor(url: string, options?: Dom.RequestInit) {
+  constructor(url: string, options?: PatchedRequestInit) {
     this.url = url
     this.options = options || {}
   }
@@ -228,7 +230,7 @@ export class GraphQLClient {
       query: rawRequestOptions.query,
       variables: rawRequestOptions.variables,
       headers: {
-        ...resolveHeaders(headers),
+        ...resolveHeaders(callOrIdentity(headers)),
         ...resolveHeaders(rawRequestOptions.requestHeaders),
       },
       operationName,
@@ -267,7 +269,7 @@ export class GraphQLClient {
       query,
       variables: requestOptions.variables,
       headers: {
-        ...resolveHeaders(headers),
+        ...resolveHeaders(callOrIdentity(headers)),
         ...resolveHeaders(requestOptions.requestHeaders),
       },
       operationName,
@@ -309,7 +311,7 @@ export class GraphQLClient {
       query: queries,
       variables,
       headers: {
-        ...resolveHeaders(headers),
+        ...resolveHeaders(callOrIdentity(headers)),
         ...resolveHeaders(batchRequestOptions.requestHeaders),
       },
       operationName: undefined,
@@ -592,6 +594,10 @@ function resolveRequestDocument(document: RequestDocument): { query: string; ope
   return { query: print(document), operationName }
 }
 
+function callOrIdentity<T>(value: MaybeFunction<T>) {
+  return typeof value === 'function' ? (value as () => T)() : value;
+}
+
 /**
  * Convenience passthrough template tag to get the benefits of tooling for the gql template tag. This does not actually parse the input into a GraphQL DocumentNode like graphql-tag package does. It just returns the string with any variables given interpolated. Can save you a bit of performance and having to install another package.
  *
diff --git a/src/types.ts b/src/types.ts
index 0a77e67e..5249d446 100644
--- a/src/types.ts
+++ b/src/types.ts
@@ -55,8 +55,13 @@ export class ClientError extends Error {
   }
 }
 
+export type MaybeFunction<T> = T | (() => T);
+
 export type RequestDocument = string | DocumentNode
 
+export type PatchedRequestInit = Omit<Dom.RequestInit, "headers">
+  & {headers?: MaybeFunction<Dom.RequestInit['headers']>};
+
 export type BatchRequestDocument<V = Variables> = {
   document: RequestDocument
   variables?: V
diff --git a/tests/headers.test.ts b/tests/headers.test.ts
index 537fb59d..0837b061 100644
--- a/tests/headers.test.ts
+++ b/tests/headers.test.ts
@@ -92,6 +92,26 @@ describe('using class', () => {
       });
 
     })
+
+    describe('gets fresh dynamic headers before each request', () => {
+      test('with request method', async () => {
+        const objectChangedThroughReference = { 'x-foo': 'old' }
+        const client = new GraphQLClient(ctx.url, { headers: () => objectChangedThroughReference });
+        objectChangedThroughReference['x-foo'] = 'new';
+        const mock = ctx.res()
+        await client.request(`{ me { id } }`);
+        expect(mock.requests[0].headers['x-foo']).toEqual('new')
+      })
+
+      test('with rawRequest method', async () => {
+        const objectChangedThroughReference = { 'x-foo': 'old' }
+        const client = new GraphQLClient(ctx.url, { headers: () => objectChangedThroughReference });
+        objectChangedThroughReference['x-foo'] = 'new';
+        const mock = ctx.res()
+        await client.rawRequest(`{ me { id } }`);
+        expect(mock.requests[0].headers['x-foo']).toEqual('new')
+      })
+    })
   })
 })