Check SHA1 hashes for blobs locally (#55)

* Check SHA1 hashes for blobs locally
Fixes #53

* Adding functional test

* Realized I was trying to hash the encoded contents

* Turns out git prefixes the file and then hashes it

* Let's try that again

* Debugging

* 🤦

* Fine I just won't use if

* I don't know anymore

.github/workflows/test.yml

@@ -51,8 +51,10 @@ jobs:
     steps:
       - name: Checkout repo
         uses: actions/checkout@v2
-      - name: Generate file to commit
-        run: 'echo "$(date): Testing ${GITHUB_SHA}" > test.txt'
+      - name: Generate files to commit
+        run: |
+          echo "$(date): Testing ${GITHUB_SHA}" > test.txt
+          echo "static value" > static.txt
       - name: Run action against test with default token
         uses: ./
         with:
@@ -66,3 +68,17 @@ jobs:
           branch: protected-test
           message: ':robot: Test commit'
           glob-patterns: test.txt
+      - name: Run action against unchanged file
+        id: unchanged-commit
+        uses: ./
+        with:
+          branch: test
+          message: ':robot: Test commit of static.txt'
+          glob-patterns: static.txt
+      - name: Fail if unchanged file was committed
+        run: |
+          if [[ -n "${{steps.unchanged-commit.outputs.sha}}" ]]
+          then
+            echo "::error::Action commited the unchanged file"
+            exit 1
+          fi

src/commitFiles.ts

@@ -2,6 +2,7 @@ import {GitHub} from '@actions/github/lib/utils';
 import {Endpoints} from '@octokit/types';
 import * as core from '@actions/core';
 import _ from 'lodash';
+import {computeBlobHashB64String} from './utils/hash';
 
 export type Octokit = InstanceType<typeof GitHub>;
 type Tree = Endpoints['POST /repos/:owner/:repo/git/trees']['parameters']['tree'];
@@ -48,13 +49,15 @@ export async function createOrUpdateFiles(
       throw Error('Refusing to replace non-blob tree entry');
     }
 
-    const {data: blob} = await octokit.git.createBlob({owner, repo, content, encoding: 'base64'});
-    if (previousEntry?.sha !== blob.sha) {
+    const hash = computeBlobHashB64String(content);
+    if (hash !== previousEntry?.sha) {
+      const {data: blob} = await octokit.git.createBlob({owner, repo, content, encoding: 'base64'});
+
       tree.push({
         path,
         sha: blob.sha,
         type: 'blob',
-        // TODO: Grab previous mode if it exists. Right now types are getting in the way
+        // TODO(#44): Set to 100755 if file is executable
         mode: '100644',
       });
     } else {

src/utils/hash.ts

@@ -0,0 +1,12 @@
+import {createHash} from 'crypto';
+
+/**
+ * Compute the git blob hash for a base64 encoded string
+ * @param b64string Base64 encoded string
+ */
+export function computeBlobHashB64String(b64string: string): string {
+  const contents = Buffer.from(b64string, 'base64');
+  const buf = Buffer.concat([Buffer.from(`blob ${contents.length}\0`), contents]);
+  const hasher = createHash('sha1');
+  return hasher.update(buf).digest('hex');
+}