From 4d10abcc2c026f1d932efd96e740e5c1d899d322 Mon Sep 17 00:00:00 2001
From: Halla Moore <halla@nylas.com>
Date: Fri, 20 Jan 2017 13:54:26 -0800
Subject: [PATCH] [local-sync] Be more permissive with content transfer
 encodings (CTEs)

Summary:
Rather than having a strict model where we don't decode the message if we
don't specifically recognize the CTE, treat any CTEs we don't recognize as
having no encoding. There are several CTE strings that could mean this (e.g.
7bit, 7BITS, 8-bit, binary, NONE, utf8), and we don't want to check for them
all. Additionally, if there is a CTE we don't support, the user will likely
see rendering issues and contact support. This will allow us to obtain more
concrete information about these messages.

Test Plan: manual

Reviewers: spang

Reviewed By: spang

Differential Revision: https://phab.nylas.com/D3748
---
 .../local-sync/src/shared/message-factory.js  | 21 ++++++++-----------
 1 file changed, 9 insertions(+), 12 deletions(-)

diff --git a/packages/local-sync/src/shared/message-factory.js b/packages/local-sync/src/shared/message-factory.js
index 4542932a7..a5a3f8f2b 100644
--- a/packages/local-sync/src/shared/message-factory.js
+++ b/packages/local-sync/src/shared/message-factory.js
@@ -187,9 +187,12 @@ function bodyFromParts(imapMessage, desiredParts) {
   for (const {id, mimeType, transferEncoding, charset} of desiredParts) {
     let decoded = '';
     // see https://www.w3.org/Protocols/rfc1341/5_Content-Transfer-Encoding.html
-    if (!transferEncoding || new Set(['7bit', '8bit', 'binary']).has(transferEncoding.toLowerCase())) {
-      // NO transfer encoding has been performed --- how to decode to a string
-      // depends ONLY on the charset,
+    if ((/quot(ed)?[-/]print(ed|able)?/gi).test(transferEncoding)) {
+      decoded = mimelib.decodeQuotedPrintable(imapMessage.parts[id], charset);
+    } else if ((/base64/gi).test(transferEncoding)) {
+      decoded = mimelib.decodeBase64(imapMessage.parts[id], charset);
+    } else {
+      // Treat this as having no encoding and decode based only on the charset
       //
       // According to https://tools.ietf.org/html/rfc2045#section-5.2,
       // this should default to ascii; however, if we don't get a charset,
@@ -197,16 +200,10 @@ function bodyFromParts(imapMessage, desiredParts) {
       // anyway. Since ascii is a strict subset of utf-8, it's safer to
       // try and decode as utf-8 if we don't have the charset.
       //
-      // This applies to decoding quoted-printable and base64 as well. The
-      // mimelib library, if charset is null, will default to utf-8
+      // (This applies to decoding quoted-printable and base64 as well. The
+      // mimelib library, if charset is null, will default to utf-8)
+      //
       decoded = encoding.convert(imapMessage.parts[id], 'utf-8', charset).toString('utf-8');
-    } else if (transferEncoding.toLowerCase() === 'quoted-printable') {
-      decoded = mimelib.decodeQuotedPrintable(imapMessage.parts[id], charset);
-    } else if (transferEncoding.toLowerCase() === 'base64') {
-      decoded = mimelib.decodeBase64(imapMessage.parts[id], charset);
-    } else {
-      // custom x-token content-transfer-encodings
-      return Promise.reject(new Error(`Unsupported Content-Transfer-Encoding ${transferEncoding}, mimetype ${mimeType}`))
     }
     // desiredParts are in order of the MIME tree walk, e.g. 1.1, 1.2, 2...,
     // and for multipart/alternative arrays, we have already pulled out the