DOCKER_METADATA_SHORT_SHA_LENGTH env var to customize short commit SHA length

Signed-off-by: CrazyMax <1951866+crazy-max@users.noreply.github.com>

.github/workflows/ci.yml

@@ -549,3 +549,33 @@ jobs:
             cwd://${{ steps.docker_meta.outputs.bake-file-labels }}
           targets: |
             release
+
+  sha-short:
+    runs-on: ubuntu-latest
+    strategy:
+      fail-fast: false
+      matrix:
+        short-length:
+          - ''
+          - 16
+    steps:
+      -
+        name: Checkout
+        uses: actions/checkout@v4
+      -
+        name: Set up Docker Buildx
+        uses: docker/setup-buildx-action@v3
+        with:
+          version: ${{ env.BUILDX_VERSION }}
+          driver: docker
+      -
+        name: Docker meta
+        uses: ./
+        with:
+          images: |
+            ${{ env.DOCKER_IMAGE }}
+            ghcr.io/name/app
+          tags: |
+            type=sha
+        env:
+          DOCKER_METADATA_SHORT_SHA_LENGTH: ${{ matrix.short-length }}

README.md

@@ -361,8 +361,9 @@ So it can be used with our [Docker Build Push action](https://github.com/docker/
 ### environment variables
 
 | Name                                 | Type   | Description                                                                                                                                   |
-|--------------------------------------|--------|------------------------------------------------------------------------------------------------------------|
+|--------------------------------------|--------|-----------------------------------------------------------------------------------------------------------------------------------------------|
 | `DOCKER_METADATA_PR_HEAD_SHA`        | Bool   | If `true`, set associated head SHA instead of commit SHA that triggered the workflow on pull request event                                    |
+| `DOCKER_METADATA_SHORT_SHA_LENGTH`   | Number | Specifies the length of the [short commit SHA](#typesha) to ensure uniqueness. Default is `12`, but can be increased for larger repositories. |
 | `DOCKER_METADATA_ANNOTATIONS_LEVELS` | String | Comma separated list of annotations levels to set for annotations output separated (default `manifest`)                                       |
 
 ## `context` input
@@ -725,6 +726,24 @@ tags: |
 Output Git short commit (or long if specified) as Docker tag like
 `sha-860c1904a1ce`.
 
+By default, the length of the short commit SHA is `12` characters. You can
+increase this length for larger repositories by setting the
+[`DOCKER_METADATA_SHORT_SHA_LENGTH` environment variable](#environment-variables):
+
+```yaml
+      -
+        name: Docker meta
+        id: meta
+        uses: docker/metadata-action@v5
+        with:
+          images: |
+            name/app
+          tags: |
+            type=sha
+        env:
+          DOCKER_METADATA_SHORT_SHA_LENGTH: 16
+```
+
 Extended attributes and default values:
 
 ```yaml

src/meta.ts

@@ -14,6 +14,8 @@ import * as icl from './image';
 import * as tcl from './tag';
 import * as fcl from './flavor';
 
+const defaultShortShaLength = 12;
+
 export interface Version {
   main: string | undefined;
   partial: string[];
@@ -307,7 +309,7 @@ export class Meta {
 
     let val = this.context.sha;
     if (tag.attrs['format'] === tcl.ShaFormat.Short) {
-      val = this.context.sha.substring(0, 12);
+      val = Meta.shortSha(this.context.sha);
     }
 
     const vraw = this.setValue(val, tag);
@@ -373,7 +375,7 @@ export class Meta {
         return context.ref.replace(/^refs\/tags\//g, '');
       },
       sha: function () {
-        return context.sha.substring(0, 12);
+        return Meta.shortSha(context.sha);
       },
       base_ref: function () {
         if (/^refs\/tags\//.test(context.ref) && context.payload?.base_ref != undefined) {
@@ -593,4 +595,18 @@ export class Meta {
   private static sanitizeTag(tag: string): string {
     return tag.replace(/[^a-zA-Z0-9._-]+/g, '-');
   }
+
+  private static shortSha(sha: string): string {
+    let shortShaLength = defaultShortShaLength;
+    if (process.env.DOCKER_METADATA_SHORT_SHA_LENGTH) {
+      if (isNaN(Number(process.env.DOCKER_METADATA_SHORT_SHA_LENGTH))) {
+        throw new Error(`DOCKER_METADATA_SHORT_SHA_LENGTH is not a valid number: ${process.env.DOCKER_METADATA_SHORT_SHA_LENGTH}`);
+      }
+      shortShaLength = Number(process.env.DOCKER_METADATA_SHORT_SHA_LENGTH);
+    }
+    if (shortShaLength >= sha.length) {
+      return sha;
+    }
+    return sha.substring(0, shortShaLength);
+  }
 }