fix(gatsby-core-utils): fix 304 when file does not exists

packages/gatsby-core-utils/src/__tests__/fetch-remote-file.js

@@ -229,28 +229,28 @@ async function createMockCache(tmpDir) {
 
 describe(`fetch-remote-file`, () => {
   let cache
-  const cachePath = path.join(__dirname, `.cache-fetch`)
+  const cacheRoot = path.join(__dirname, `.cache-fetch`)
+  const cachePath = path.join(__dirname, `.cache-fetch`, `files`)
 
   beforeAll(async () => {
     // Establish requests interception layer before all tests.
     server.listen()
 
     cache = await createMockCache(cachePath)
-    await fs.ensureDir(cachePath)
-    storage.getDatabaseDir.mockReturnValue(cachePath)
+    storage.getDatabaseDir.mockReturnValue(cacheRoot)
   })
 
   afterAll(async () => {
     await storage.closeDatabase()
-    await fs.remove(cachePath)
+    await fs.remove(cacheRoot)
     delete global.__GATSBY
 
     // Clean up after all tests are done, preventing this
     // interception layer from affecting irrelevant tests.
     server.close()
   })
 
-  beforeEach(() => {
+  beforeEach(async () => {
     // simulate a new build each run
     global.__GATSBY = {
       buildId: global.__GATSBY?.buildId
@@ -260,6 +260,9 @@ describe(`fetch-remote-file`, () => {
     gotStream.mockClear()
     fsMove.mockClear()
     urlCount.clear()
+
+    await fs.remove(cachePath)
+    await fs.ensureDir(cachePath)
   })
 
   it(`downloads and create a svg file`, async () => {
@@ -359,6 +362,28 @@ describe(`fetch-remote-file`, () => {
     global.__GATSBY = currentGlobal
   })
 
+  it(`handles 304 responses correctly when file does not exists`, async () => {
+    const currentGlobal = global.__GATSBY
+    global.__GATSBY = { buildId: `304-3` }
+    const filePath = await fetchRemoteFile({
+      url: `http://external.com/dog-304.jpg`,
+      directory: cachePath,
+    })
+
+    await fs.remove(filePath)
+
+    global.__GATSBY = { buildId: `304-4` }
+    const filePathCached = await fetchRemoteFile({
+      url: `http://external.com/dog-304.jpg`,
+      directory: cachePath,
+    })
+
+    expect(filePathCached).toBe(filePath)
+    expect(fsMove).toBeCalledTimes(2)
+    expect(gotStream).toBeCalledTimes(2)
+    global.__GATSBY = currentGlobal
+  })
+
   it(`fails when 404 is triggered`, async () => {
     await expect(
       fetchRemoteFile({

packages/gatsby-core-utils/src/fetch-remote-file.ts

@@ -1,6 +1,6 @@
 import fileType from "file-type"
 import path from "path"
-import fs from "fs-extra"
+import fs, { pathExists } from "fs-extra"
 import Queue from "fastq"
 import { createContentDigest } from "./create-content-digest"
 import {
@@ -148,14 +148,6 @@ async function fetchFile({
 
     const cachedEntry = await storage.remoteFileInfo.get(url)
 
-    // See if there's response headers for this url
-    // from a previous request.
-    const headers = { ...httpHeaders }
-    if (cachedEntry?.headers?.etag) {
-      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
-      headers[`If-None-Match`] = cachedEntry.headers.etag
-    }
-
     // Add htaccess authentication if passed in. This isn't particularly
     // extensible. We should define a proper API that we validate.
     const httpOptions: Options = {}
@@ -176,14 +168,23 @@ async function fetchFile({
     await fs.ensureDir(path.join(fileDirectory, digest))
 
     const tmpFilename = createFilePath(fileDirectory, `tmp-${digest}`, ext)
+    const filename = createFilePath(path.join(fileDirectory, digest), name, ext)
+
+    // See if there's response headers for this url
+    // from a previous request.
+    const headers = { ...httpHeaders }
+    if (cachedEntry?.headers?.etag && (await pathExists(filename))) {
+      // eslint-disable-next-line @typescript-eslint/no-non-null-assertion
+      headers[`If-None-Match`] = cachedEntry.headers.etag
+    }
+
     const response = await requestRemoteNode(
       url,
       headers,
       tmpFilename,
       httpOptions
     )
 
-    const filename = createFilePath(path.join(fileDirectory, digest), name, ext)
     if (response.statusCode === 200) {
       // Save the response headers for future requests.
       // If the user did not provide an extension and we couldn't get one from remote file, try and guess one