feat: support case insensitive fetch response header access

Author: alpha0010

README.md

@@ -97,6 +97,7 @@ FilesSystem.fetch(
 ): Promise<FetchResult>
 
 type FetchResult = {
+  getHeader: (header: string) => string | undefined;
   headers: { [key: string]: string };
   ok: boolean;
   redirected: boolean;

example/src/App.tsx

@@ -215,10 +215,16 @@ export function App() {
     })
       .then((res) => {
         setInfo((prev) => {
-          prev.push({
-            key: 'fetch(https://example.com)',
-            value: JSON.stringify(res),
-          });
+          prev.push(
+            {
+              key: 'fetch(https://example.com)',
+              value: JSON.stringify(res),
+            },
+            {
+              key: 'getHeader(cOntEnt-tYPe)',
+              value: res.getHeader('cOntEnt-tYPe') ?? 'undefined',
+            }
+          );
           return prev.slice();
         });
         return FileSystem.readFile(Dirs.CacheDir + '/download.html');

jest/react-native-file-access.ts

@@ -98,6 +98,7 @@ class FileSystemMock {
         this.filesystem.set(init.path, `[Mock fetch data for '${resource}']`);
       }
       return {
+        getHeader: () => undefined,
         headers: {},
         ok: true,
         redirected: false,

src/index.ts

@@ -78,7 +78,12 @@ function registerFetchListener(
         reject(new Error(event.message));
       } else if (event.state === 'complete') {
         listener.remove();
+        const headersLower = new Map<string, string>();
+        for (const [key, value] of Object.entries(event.headers)) {
+          headersLower.set(key.toLowerCase(), value);
+        }
         resolve({
+          getHeader: (header: string) => headersLower.get(header.toLowerCase()),
           headers: event.headers,
           ok: event.ok,
           redirected: event.redirected,

src/types.ts

@@ -27,6 +27,11 @@ export type FetchInit = {
 };
 
 export type FetchResult = {
+  /**
+   * Get an HTTP response header value. (Case insensitive matching.)
+   */
+  getHeader: (header: string) => string | undefined;
+
   /**
    * Response HTTP headers.
    */
@@ -61,7 +66,7 @@ export type FetchResult = {
 export type FetchCompleteEvent = {
   requestId: number;
   state: 'complete';
-} & FetchResult;
+} & Omit<FetchResult, 'getHeader'>;
 
 export type FetchErrorEvent = {
   requestId: number;