fix(gmail): RFC 2047 encode subject headers for non-ASCII characters

Author: waleedlatif1

apps/sim/tools/gmail/utils.ts

@@ -294,6 +294,22 @@ function generateBoundary(): string {
   return `----=_Part_${Date.now()}_${Math.random().toString(36).substring(2, 15)}`
 }
 
+/**
+ * Encode a header value using RFC 2047 Base64 encoding if it contains non-ASCII characters.
+ * Email headers per RFC 2822 must be ASCII-only. Non-ASCII characters (emojis, accented
+ * characters, etc.) must be encoded as =?UTF-8?B?<base64>?= to avoid mojibake.
+ * @param value The header value to encode
+ * @returns The encoded header value, or the original if it's already ASCII
+ */
+export function encodeRfc2047(value: string): string {
+  // eslint-disable-next-line no-control-regex
+  if (/^[\x00-\x7F]*$/.test(value)) {
+    return value
+  }
+  const encoded = Buffer.from(value, 'utf-8').toString('base64')
+  return `=?UTF-8?B?${encoded}?=`
+}
+
 /**
  * Encode string or buffer to base64url format (URL-safe base64)
  * Gmail API requires base64url encoding for the raw message field
@@ -333,7 +349,7 @@ export function buildSimpleEmailMessage(params: {
     emailHeaders.push(`Bcc: ${bcc}`)
   }
 
-  emailHeaders.push(`Subject: ${subject || ''}`)
+  emailHeaders.push(`Subject: ${encodeRfc2047(subject || '')}`)
 
   if (inReplyTo) {
     emailHeaders.push(`In-Reply-To: ${inReplyTo}`)
@@ -380,7 +396,7 @@ export function buildMimeMessage(params: BuildMimeMessageParams): string {
   if (bcc) {
     messageParts.push(`Bcc: ${bcc}`)
   }
-  messageParts.push(`Subject: ${subject || ''}`)
+  messageParts.push(`Subject: ${encodeRfc2047(subject || '')}`)
 
   if (inReplyTo) {
     messageParts.push(`In-Reply-To: ${inReplyTo}`)