From 37d524bb0adce198d36ff589d0e330583e108b6d Mon Sep 17 00:00:00 2001
From: Waleed <walif6@gmail.com>
Date: Wed, 11 Mar 2026 15:48:07 -0700
Subject: [PATCH] fix(gmail): RFC 2047 encode subject headers for non-ASCII
 characters (#3526)

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

* Fix RFC 2047 encoded word length limit

Split long email subjects into multiple RFC 2047 encoded words to comply with the 75-character limit per RFC 2047 Section 2. Each encoded word now contains at most 45 bytes of UTF-8 content (producing max 60 chars of base64 + 12 chars overhead = 72 total). Multiple encoded words are separated by CRLF + space (folding whitespace).

Applied via @cursor push command

* fix(gmail): split RFC 2047 encoded words on character boundaries

* fix(gmail): simplify RFC 2047 encoding to match Google's own sample

---------

Co-authored-by: Cursor Agent <cursoragent@cursor.com>
---
 apps/sim/tools/gmail/utils.test.ts | 36 ++++++++++++++++++++++++++++++
 apps/sim/tools/gmail/utils.ts      | 17 ++++++++++++--
 2 files changed, 51 insertions(+), 2 deletions(-)
 create mode 100644 apps/sim/tools/gmail/utils.test.ts

diff --git a/apps/sim/tools/gmail/utils.test.ts b/apps/sim/tools/gmail/utils.test.ts
new file mode 100644
index 0000000000..5c28ac9a13
--- /dev/null
+++ b/apps/sim/tools/gmail/utils.test.ts
@@ -0,0 +1,36 @@
+/**
+ * @vitest-environment node
+ */
+import { describe, expect, it } from 'vitest'
+import { encodeRfc2047 } from './utils'
+
+describe('encodeRfc2047', () => {
+  it('returns ASCII text unchanged', () => {
+    expect(encodeRfc2047('Simple ASCII Subject')).toBe('Simple ASCII Subject')
+  })
+
+  it('returns empty string unchanged', () => {
+    expect(encodeRfc2047('')).toBe('')
+  })
+
+  it('encodes emojis as RFC 2047 base64', () => {
+    const result = encodeRfc2047('Time to Stretch! 🧘')
+    expect(result).toBe('=?UTF-8?B?VGltZSB0byBTdHJldGNoISDwn6eY?=')
+  })
+
+  it('round-trips non-ASCII subjects correctly', () => {
+    const subjects = ['Hello 世界', 'Café résumé', '🎉🎊🎈 Party!', '今週のミーティング']
+    for (const subject of subjects) {
+      const encoded = encodeRfc2047(subject)
+      const match = encoded.match(/^=\?UTF-8\?B\?(.+)\?=$/)
+      expect(match).not.toBeNull()
+      const decoded = Buffer.from(match![1], 'base64').toString('utf-8')
+      expect(decoded).toBe(subject)
+    }
+  })
+
+  it('does not double-encode already-encoded subjects', () => {
+    const alreadyEncoded = '=?UTF-8?B?VGltZSB0byBTdHJldGNoISDwn6eY?='
+    expect(encodeRfc2047(alreadyEncoded)).toBe(alreadyEncoded)
+  })
+})
diff --git a/apps/sim/tools/gmail/utils.ts b/apps/sim/tools/gmail/utils.ts
index 4d856db1d5..f374a4e00f 100644
--- a/apps/sim/tools/gmail/utils.ts
+++ b/apps/sim/tools/gmail/utils.ts
@@ -294,6 +294,19 @@ function generateBoundary(): string {
   return `----=_Part_${Date.now()}_${Math.random().toString(36).substring(2, 15)}`
 }
 
+/**
+ * Encode a header value using RFC 2047 Base64 encoding if it contains non-ASCII characters.
+ * This matches Google's own Gmail API sample: `=?utf-8?B?${Buffer.from(subject).toString('base64')}?=`
+ * @see https://github.com/googleapis/google-api-nodejs-client/blob/main/samples/gmail/send.js
+ */
+export function encodeRfc2047(value: string): string {
+  // eslint-disable-next-line no-control-regex
+  if (/^[\x00-\x7F]*$/.test(value)) {
+    return value
+  }
+  return `=?UTF-8?B?${Buffer.from(value, 'utf-8').toString('base64')}?=`
+}
+
 /**
  * Encode string or buffer to base64url format (URL-safe base64)
  * Gmail API requires base64url encoding for the raw message field
@@ -333,7 +346,7 @@ 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 +393,7 @@ 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}`)