feat: add eStargz compression support for faster image pulls (#1)

- Add estargz boolean input parameter to action.yml
- Modify buildx output arguments to include estargz compression flags when enabled
- Add buildx version check (requires >= 0.10.0) and push requirement validation
- Update README.md with usage examples and documentation
- Requires push: true to be effective
- Compatible with existing output configurations

Co-authored-by: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
Co-authored-by: Raunak Chowdhuri <raunak@reducto.ai>

README.md

@@ -100,6 +100,37 @@ jobs:
           tags: user/app:latest
 ```
 
+### eStargz compression for faster pulls
+
+```yaml
+name: ci
+
+on:
+  push:
+
+jobs:
+  docker:
+    runs-on: blacksmith
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v4
+      -
+        name: Login to Docker Hub
+        uses: docker/login-action@v3
+        with:
+          username: ${{ secrets.DOCKERHUB_USERNAME }}
+          password: ${{ secrets.DOCKERHUB_TOKEN }}
+      -
+        name: Build and push with eStargz
+        uses: useblacksmith/build-push-action@v1
+        with:
+          context: .
+          push: true
+          tags: user/app:latest
+          estargz: true
+```
+
 ## Examples
 
 * [Multi-platform image](https://docs.docker.com/build/ci/github-actions/multi-platform/)
@@ -190,6 +221,7 @@ The following inputs can be used as `step.with` keys:
 | `target`           | String      | Sets the target stage to build                                                                                                                                                    |
 | `ulimit`           | List        | [Ulimit](https://docs.docker.com/engine/reference/commandline/buildx_build/#ulimit) options (e.g., `nofile=1024:1024`)                                                            |
 | `github-token`     | String      | GitHub Token used to authenticate against a repository for [Git context](#git-context) (default `${{ github.token }}`)                                                            |
+| `estargz`          | Bool        | Enable [eStargz compression](https://github.com/containerd/stargz-snapshotter/blob/main/docs/estargz.md) for faster image pulls (requires `push: true`) (default `false`)        |
 
 ### outputs
 

action.yml

@@ -108,6 +108,10 @@ inputs:
     description: "GitHub Token used to authenticate against a repository for Git context"
     default: ${{ github.token }}
     required: false
+  estargz:
+    description: "Enable eStargz compression for faster image pulls (requires push: true)"
+    required: false
+    default: 'false'
 
 outputs:
   imageid:

src/context.ts

@@ -57,6 +57,7 @@ export interface Inputs {
   target: string;
   ulimit: string[];
   'github-token': string;
+  estargz: boolean;
 }
 
 export async function getInputs(): Promise<Inputs> {
@@ -93,7 +94,8 @@ export async function getInputs(): Promise<Inputs> {
     tags: Util.getInputList('tags'),
     target: core.getInput('target'),
     ulimit: Util.getInputList('ulimit', {ignoreComma: true}),
-    'github-token': core.getInput('github-token')
+    'github-token': core.getInput('github-token'),
+    estargz: core.getBooleanInput('estargz')
   };
 }
 
@@ -208,11 +210,33 @@ async function getBuildArgs(inputs: Inputs, context: string, toolkit: Toolkit):
     args.push('--no-cache-filter', noCacheFilter);
   });
   await Util.asyncForEach(inputs.outputs, async output => {
-    args.push('--output', output);
+    if (inputs.estargz && inputs.push) {
+      if (output.startsWith('type=registry') || output === 'type=registry') {
+        const estargzOutput = output.includes(',') 
+          ? `${output},compression=estargz,force-compression=true,oci-mediatypes=true`
+          : `${output},compression=estargz,force-compression=true,oci-mediatypes=true`;
+        args.push('--output', estargzOutput);
+      } else {
+        args.push('--output', output);
+      }
+    } else {
+      args.push('--output', output);
+    }
   });
+  
+  if (inputs.estargz && inputs.push && inputs.outputs.length === 0) {
+    args.push('--output', 'type=registry,compression=estargz,force-compression=true,oci-mediatypes=true');
+  }
   if (inputs.platforms.length > 0) {
     args.push('--platform', inputs.platforms.join(','));
   }
+  if (inputs.estargz) {
+    if (!(await toolkit.buildx.versionSatisfies('>=0.10.0'))) {
+      core.warning("eStargz compression requires buildx >= 0.10.0; the input 'estargz' is ignored.");
+    } else if (!inputs.push) {
+      core.warning("eStargz compression requires push: true; the input 'estargz' is ignored.");
+    }
+  }
   if (await toolkit.buildx.versionSatisfies('>=0.10.0')) {
     args.push(...(await getAttestArgs(inputs, toolkit)));
   } else {