do not assume that fetch will unwrap gzip files

Author: Techatrix

src/utils.ts

@@ -2,8 +2,17 @@ import { untar } from "@andrewbranch/untar.js";
 import { Directory, File, ConsoleStdout, wasi as wasi_defs } from "@bjorn3/browser_wasi_shim";
 
 export async function getLatestZigArchive() {
-    const zigTarResponse = await fetch(new URL("../zig-out/zig.tar.gz", import.meta.url));
-    const entries = untar(await zigTarResponse.arrayBuffer());
+    const response = await fetch(new URL("../zig-out/zig.tar.gz", import.meta.url));
+    let arrayBuffer = await response.arrayBuffer();
+    const magicNumber = new Uint8Array(arrayBuffer).slice(0, 2);
+    if (magicNumber[0] == 0x1F && magicNumber[1] == 0x8B) { // gzip
+        const ds = new DecompressionStream("gzip");
+        const response = new Response(new Response(arrayBuffer).body!.pipeThrough(ds));
+        arrayBuffer = await response.arrayBuffer();
+    } else {
+        // already decompressed
+    }
+    const entries = untar(arrayBuffer);
 
     let root: TreeNode = new Map();