Add digest output

Fix platforms and allow inputs

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

src/buildx.ts

@@ -1,5 +1,20 @@
+import fs from 'fs';
+import path from 'path';
+import * as context from './context';
 import * as exec from './exec';
 
+export async function getImageIDFile(): Promise<string> {
+  return path.join(context.tmpDir, 'iidfile');
+}
+
+export async function getImageID(): Promise<string | undefined> {
+  const iidFile = await getImageIDFile();
+  if (!fs.existsSync(iidFile)) {
+    return undefined;
+  }
+  return fs.readFileSync(iidFile, {encoding: 'utf-8'});
+}
+
 export async function isAvailable(): Promise<Boolean> {
   return await exec.exec(`docker`, ['buildx'], true).then(res => {
     if (res.stderr != '' && !res.success) {