1 files changed, 53 insertions, 0 deletions
diff --git a/security/nss/automation/taskcluster/graph/src/context_hash.js b/security/nss/automation/taskcluster/graph/src/context_hash.js
new file mode 100644
index 0000000000..0699a0590e
--- /dev/null
+++ b/security/nss/automation/taskcluster/graph/src/context_hash.js
@@ -0,0 +1,53 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+import fs from "fs";
+import path from "path";
+import crypto from "crypto";
+import flatmap from "flatmap";
+
+// Compute the SHA-256 digest.
+function sha256(data) {
+  let hash = crypto.createHash("sha256");
+  hash.update(data);
+  return hash.digest("hex");
+}
+
+// Recursively collect a list of all files of a given directory.
+function collectFilesInDirectory(dir) {
+  return flatmap(fs.readdirSync(dir), entry => {
+    let entry_path = path.join(dir, entry);
+
+    if (fs.lstatSync(entry_path).isDirectory()) {
+      return collectFilesInDirectory(entry_path);
+    }
+
+    return [entry_path];
+  });
+}
+
+// A list of hashes for each file in the given path.
+function collectFileHashes(context_path) {
+  let root = path.join(__dirname, "../../../..");
+  let dir = path.join(root, context_path);
+  let files = collectFilesInDirectory(dir).sort();
+
+  return files.map(file => {
+    return sha256(file + "|" + fs.readFileSync(file, "utf-8"));
+  });
+}
+
+// Compute a context hash for the given context path.
+export default function (context_path) {
+  // Regenerate all images when the image_builder changes.
+  let hashes = collectFileHashes("automation/taskcluster/image_builder");
+
+  // Regenerate images when the image itself changes.
+  hashes = hashes.concat(collectFileHashes(context_path));
+
+  // Generate a new prefix every month to ensure the image stays buildable.
+  let now = new Date();
+  let prefix = `${now.getUTCFullYear()}-${now.getUTCMonth() + 1}:`;
+  return sha256(prefix + hashes.join(","));
+}