fix: support .buffer method on web environments (#49)

src/environment.ts

@@ -0,0 +1,3 @@
+export function isUsingNode(): boolean {
+  return typeof process !== 'undefined' && process.release && process.release.name === 'node'
+}

src/fetcher.ts

@@ -1,6 +1,7 @@
 import * as crossFetch from 'cross-fetch'
 import { IFetchComponent, RequestOptions, Request, Response } from '@well-known-components/interfaces'
 import { FetcherOptions } from './types'
+import { isUsingNode } from './environment'
 
 const NON_RETRYABLE_STATUS_CODES = [400, 401, 403, 404]
 const IDEMPOTENT_HTTP_METHODS = ['GET', 'HEAD', 'OPTIONS', 'PUT', 'DELETE']
@@ -85,6 +86,15 @@ export function createFetchComponent(defaultOptions?: FetcherOptions): IFetchCom
       throw new Error(`Failed to fetch ${url}. Got status ${response?.status}. Response was '${responseText}'`)
     }
 
+    if (!isUsingNode() && !!response) {
+      Object.defineProperty(response, 'buffer', {
+        value: async function (): Promise<Buffer> {
+          return Buffer.from(await response!.arrayBuffer())
+        },
+        configurable: true
+      })
+    }
+
     // Parse response in case of abortion
     return signal.aborted ? undefined : (response as any)
   }

test/fetch.spec.ts

@@ -1,5 +1,6 @@
 import { IFetchComponent } from '@well-known-components/interfaces'
 import { createFetchComponent } from './../src/fetcher'
+import * as environment from '../src/environment'
 
 import fetchMock from 'jest-fetch-mock'
 
@@ -331,4 +332,46 @@ describe('fetchComponent', () => {
 
     expect(fetchMock).toHaveBeenCalledTimes(1)
   })
+
+  it('should expose .buffer function even when it is not called from a Node environment', async () => {
+    const expectedResponseBody = { mock: 'successful', ok: true }
+    jest.spyOn(environment, 'isUsingNode').mockReturnValue(false)
+
+    fetchMock.mockResolvedValue(
+      new Response(JSON.stringify(expectedResponseBody), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' }
+      })
+    )
+
+    const response = await sut.fetch('https://example.com', {
+      attempts: 3,
+      retryDelay: 10
+    } as any)
+
+    expect(response).toBeDefined()
+    expect(response.buffer).toBeDefined()
+  })
+
+  it('should read buffer correctly from .buffer function even when it is not called from a Node environment', async () => {
+    const expectedResponseBody = { mock: 'successful', ok: true }
+    jest.spyOn(environment, 'isUsingNode').mockReturnValue(false)
+
+    fetchMock.mockResolvedValue(
+      new Response(JSON.stringify(expectedResponseBody), {
+        status: 200,
+        headers: { 'Content-Type': 'application/json' }
+      })
+    )
+
+    const response = await sut.fetch('https://example.com', {
+      attempts: 3,
+      retryDelay: 10
+    } as any)
+
+    const bufferedResponse = await response.buffer()
+
+    const parsedBufferedResponse = JSON.parse(bufferedResponse.toString())
+    expect(parsedBufferedResponse).toEqual(expectedResponseBody)
+  })
 })