helpers: add sanitizer insert13Before10

packages/helpers/src/dkim/sanitizers.ts

@@ -13,6 +13,7 @@ function setHeaderValue(email: string, header: string, value: string) {
 
  // Google sets their own Message-ID and put the original one  in X-Google-Original-Message-ID
  // when ARC forwarding
+// TODO: Add test for this
 function revertGoogleMessageId(email: string): string {
   // (Optional check) This only happens when google does ARC
   if (!email.includes("ARC-Authentication-Results")) {
@@ -31,6 +32,7 @@ function revertGoogleMessageId(email: string): string {
   return email;
 }
 
+
 // Remove labels inserted to Subject - `[ListName] Newsletter 2024` to `Newsletter 2024`
 function removeLabels(email: string): string {
   // Replace Subject: [label] with Subject:
@@ -39,9 +41,30 @@ function removeLabels(email: string): string {
 }
 
 
+// Sometimes, newline encodings re-encode \r\n as just \n, so re-insert the \r
+// TODO: Add test for this
+export function insert13Before10(a: Uint8Array): Uint8Array {
+  let ret = new Uint8Array(a.length + 1000);
+  let j = 0;
+  for (let i = 0; i < a.length; i++) {
+    // Ensure each \n is preceded by a \r
+    if (a[i] === 10 && i > 0 && a[i - 1] !== 13) {
+      ret[j] = 13;
+      j++;
+    }
+    ret[j] = a[i];
+    j++;
+  }
+
+  return ret.slice(0, j);
+}
+
+
+
 const sanitizers = [
   revertGoogleMessageId,
   removeLabels,
+  insert13Before10,
 ];