author Jorg K <>
Tue, 16 Jul 2019 21:07:12 +0200
changeset 79648 7334d3e992dc16b72b65cf7131db4016957e8142
parent 23607 2ad8960eb3968db3402f21b933daa3f5376c2f32
permissions -rw-r--r--
No bug - Pin mozilla-beta version (FIREFOX_RELEASE_68_BASE, THUNDERBIRD_68_VERBRANCH) for release. a=jorgk

Code Layout

JSMime is a MIME parsing and composition library that is written completely in
JavaScript using ES6 functionality and WebAPIs (where such APIs exist). There
are a few features for which a standardized WebAPI does not exist; for these,
external JavaScript libraries are used.

The MIME parser consists of three logical phases of translation:

1. Build the MIME (and pseudo-MIME) tree.
2. Convert the MIME tree into a list of body parts and attachments.
3. Use the result to drive a displayed version of the message.

The first stage is located in `mimeparser.js`. The latter stages have yet to be


This code depends on the following ES6 features and Web APIs:
* ES6 generators
* ES6 Map and Set
* ES6 @@iterator support (especially for Map and Set)
* ES6 let
* ES6 let-destructuring
* ES6 const
* Typed arrays (predominantly Uint8Array)
* btoa, atob (found on global Windows or WorkerScopes)
* TextDecoder

Versions and API stability

As APIs require some use and experimentation to get a feel for what works best,
the APIs may change between successive version updates as uses indicate
substandard or error-prone APIs. Therefore, there will be no guarantee of API
stability until version 1.0 is released.

This code is being initially developed as an effort to replace the MIME library
within Thunderbird. New versions will be released as needed to bring new support
into the Thunderbird codebase; version 1.0 will correspond to the version where
feature-parity with the old MIME library is reached. The set of features which
will be added before 1.0 are the following:
* S/MIME encryption and decryption
* PGP encryption and decryption
* IMAP parts-on-demand support
* Support for text/plain to HTML conversion for display
* Support for HTML downgrading and sanitization for display
* Support for all major multipart types
* Ability to convert HTML documents to text/plain and multipart/related
* Support for building outgoing messages
* Support for IDN and EAI
* yEnc and uuencode decoding support
* Support for date and Message-ID/References-like headers

Other features than these may be added before version 1.0 is released (most
notably TNEF decoding support), but they are not considered necessary to release
a version 1.0.