use env if it existed (#360)

README.md

@@ -64,8 +64,8 @@ steps:
 >
 > Using `flutter-version-file` requires [`yq`](https://github.com/mikefarah/yq),
 > which is not pre-installed in `windows` runners. Fortunately, since version
-> 2.18.0, this action installs `yq` automatically, so no action is required from
-> you.
+> 2.18.0, this action installs `yq` automatically if `flutter-version-file`
+> is specified, so no action is required from you.
 
 ### Use latest release for particular channel
 
@@ -122,6 +122,24 @@ steps:
   - run: flutter --version
 ```
 
+### Use a Flutter mirror by set ENV
+
+You can get more infomation from [Flutter official docs](https://docs.flutter.dev/community/china).
+
+```yaml
+steps:
+  - name: Clone repository
+    uses: actions/checkout@v4
+  - name: Set up Flutter
+    env:
+      FLUTTER_STORAGE_BASE_URL: https://storage.flutter-io.cn
+    uses: subosito/flutter-action@v2
+    with:
+      channel: master
+      flutter-version: 5b12b74 # tag, commit or branch
+  - run: flutter --version
+```
+
 ### Use alternative Flutter repository
 
 This action supports "alternative Flutters" in addition to the official

action.yaml

@@ -80,11 +80,12 @@ outputs:
 runs:
   using: composite
   steps:
-    # This is a cross-platform composite action that needs yq.
+    # This is a cross-platform composite action that needs yq in order to parse
+    # the pubspec.yaml file.
     # It's not preinstalled on Windows runners.
     # See https://github.com/actions/runner-images/issues/7443#issuecomment-1514597691
     - name: Make yq tool available on Windows runners
-      if: runner.os == 'Windows'
+      if: runner.os == 'Windows' && inputs.flutter-version-file != ''
       run: choco install yq
       shell: bash
 

setup.sh

@@ -12,7 +12,7 @@ fi
 
 OS_NAME=$(echo "$RUNNER_OS" | awk '{print tolower($0)}')
 ARCH_NAME=$(echo "$RUNNER_ARCH" | awk '{print tolower($0)}')
-MANIFEST_BASE_URL="https://storage.googleapis.com/flutter_infra_release/releases"
+MANIFEST_BASE_URL="${FLUTTER_STORAGE_BASE_URL:-https://storage.googleapis.com}/flutter_infra_release/releases"
 MANIFEST_JSON_PATH="releases_$OS_NAME.json"
 MANIFEST_URL="$MANIFEST_BASE_URL/$MANIFEST_JSON_PATH"