fix: allow loading gzipped fixtures (#644)

When loading a file that ends in `.gz`, `sirv` will set the
`Content-Encoding` header to `gzip` which means browsers will
unzip the content before handing it back to `fetch` or `XMLHttpRequest`.

This PR adds a workaround to the asset server that sets the header
to a garbage value if a file ending in `.gz` has been requested.

It's necessary to use a garbage value because `sirv` will only set
the header if it's not been set already, so we can't simply delete it.

Refs: lukeed/sirv#158
Refs: ipfs/aegir#1462

mocks/fixtures.mocha.js

@@ -0,0 +1,12 @@
+const { equal } = require('uvu/assert')
+
+describe('fixtures', () => {
+  it('should load a gzipped tar file', async () => {
+    const resp = await fetch('mocks/fixtures/file.tar.gz')
+    const buf = await resp.arrayBuffer()
+    const ui8 = new Uint8Array(buf)
+    const base64 = btoa(String.fromCodePoint(...ui8))
+
+    equal(base64, 'H4sICIlTHVIACw==')
+  })
+})

src/utils/index.js

@@ -620,6 +620,19 @@ export async function createPolka(dir, cwd, assets) {
         // @ts-ignore
         sirv(path.join(cwd, assets), {
           dev: true,
+          setHeaders: (
+            /** @type {{ setHeader: (arg0: string, arg1: string) => void; }} */ rsp,
+            /** @type {string} */ pathname
+          ) => {
+            // workaround for https://github.com/lukeed/sirv/issues/158 - we
+            // can't unset the `Content-Encoding` header because sirv sets it
+            // after this function is invoked and will only set it if it's not
+            // already set, so we need to set it to a garbage value that will be
+            // ignored by browsers
+            if (pathname.endsWith('.gz')) {
+              rsp.setHeader('Content-Encoding', 'unsupported-encoding')
+            }
+          },
         })
       )
       .listen(port, host, (/** @type {Error} */ err) => {

test.js

@@ -15,6 +15,17 @@ describe('mocha', function () {
     ok(proc.stdout.includes('passing'), 'process stdout')
   })
 
+  it('fixtures', async () => {
+    const proc = await execa('./cli.js', [
+      'mocks/fixtures.mocha.js',
+      '--runner',
+      'mocha',
+    ])
+
+    is(proc.exitCode, 0, 'exit code')
+    ok(proc.stdout.includes('passing'), 'process stdout')
+  })
+
   it('node', async () => {
     const proc = await execa('./cli.js', [
       'mocks/test.mocha.js',