Add 'mirror' input

Author: mlugg

README.md

@@ -31,6 +31,19 @@ for the latest full release. The default is `latest`.
 > Mirrors, including the official Zig website, may purge old nightly builds at their leisure. This means
 > that if you target an out-of-date nightly build, such as a `0.11.0-dev` build, the download may fail.
 
+If you want to use one specific mirror, you can set it using the `mirror` option:
+
+```yaml
+  - uses: mlugg/setup-zig@v1
+    with:
+      mirror: 'https://pkg.machengine.org/zig'
+```
+
+Please don't do this unnecessarily; it's not nice to hammer one mirror. This mirror is not permitted to
+be https://ziglang.org/download to avoid the oggicial websote being hit with large amounts of requests.
+If you've experienced issues with a default mirror, please open an issue, and I will communicate with the
+mirror's owner or remove it from the list.
+
 ## Details
 
 This action attempts to download the requested Zig tarball from a set of mirrors, in a random order. As

action.yml

@@ -5,6 +5,10 @@ inputs:
     description: 'Version of the Zig compiler, e.g. "0.13.0" or "0.13.0-dev.351+64ef45eb0". "master" uses the latest nightly build. "latest" uses the latest tagged release.'
     required: true
     default: 'latest'
+  mirror:
+    description: 'Override of Zig download mirror to use, e.g. "https://pkg.machengine.org/zig".'
+    required: false
+    default: ''
 runs:
   using: 'node20'
   main: 'main.js'

main.js

@@ -38,6 +38,12 @@ async function downloadFromMirror(mirror, tarball_name, tarball_ext) {
 }
 
 async function downloadTarball(tarball_name, tarball_ext) {
+  const preferred_mirror = core.getInput('mirror');
+  if (preferred_mirror) {
+    core.info(`Using mirror: ${preferred_mirror}`);
+    return await downloadFromMirror(preferred_mirror, tarball_name, tarball_ext);
+  }
+
   // We will attempt all mirrors before making a last-ditch attempt to the official download.
   // To avoid hammering a single mirror, we first randomize the array.
   const shuffled_mirrors = MIRRORS.map((m) => [m, Math.random()]).sort((a, b) => a[1] - b[1]).map((a) => a[0]);