📫 mml-lib

Rust implementation of the Emacs MIME message Meta Language, as known as MML.

Features

• Compiles MML to MIME messages
• Interprets MIME messages as MML
• Supports multiple parts <#multipart>…<#/multipart>
• Supports inline part <#part text=mime/type>…<#/part>
• Supports attachment <#part disposition=attachment filename=/path/to/attachment.ext><#/part>
• Supports comment <#!part>This will not be compiled<#!/part>
• Supports tokio and async-std async runtimes
• Supports rustls and native-tls crypto libs
• Supports PGP: shell commands, GPG bindings or native implem with pgp-lib
• Retrieves PGP secret keys and passphrases from shell commands or global keyring via secret-lib
• Supports serde (de)serialization

The library comes with 13 cargo features, including 4 default ones:

• tokio: enables the tokio async runtime
• async-std: enables the async-std async runtime
• rustls: enables the rustls crypto
• native-tls: enables the native-tls crypto
• compiler: enables MML to MIME compilation
• interpreter: enables MIME to MML interpretation
• pgp-commands: enables PGP using shell commands
• pgp-gpg: enables PGP using GPG bindings
• pgp-native: enables native PGP using pgp-lib
• command: enables command-based secrets for pgp-native
• keyring: enables keyring-based secrets for pgp-native
• derive: enables serde support
• vendored: compiles and statically link to a copy of non-Rust vendors like OpenSSL

Definition

From the Emacs documentation:

Creating a MIME message is boring and non-trivial. Therefore, a library called mml has been defined that parses a language called MML (MIME Meta Language) and generates MIME messages.

The MML language is very simple. It looks a bit like an SGML application, but it’s not.

The main concept of MML is the part. Each part can be of a different type or use a different charset. The way to delineate a part is with a ‘<#part ...>’ tag. Multipart parts can be introduced with the ‘<#multipart ...>’ tag. Parts are ended by the ‘<#/part>’ or ‘<#/multipart>’ tags. Parts started with the ‘<#part ...>’ tags are also closed by the next open tag.

[…]

Each tag can contain zero or more parameters on the form ‘parameter=value’. The values may be enclosed in quotation marks, but that’s not necessary unless the value contains white space. So ‘filename=/home/user/#hello$^yes’ is perfectly valid.

Examples

From: alice@localhost
To: bob@localhost
Subject: MML examples

This is a plain text part.

<#part type=text/html>
<h1>This is a HTML part.</h1>
<#/part>

<#part description="This is an attachment." filename=./examples/attachment.png><#/part>

compiles to:

MIME-Version: 1.0
From: <alice@localhost>
To: <bob@localhost>
Subject: MML examples
Message-ID: <17886a741feef4a2.f9706245cd3a3f97.3b41d60ef9e2fbfb@soywod>
Date: Tue, 26 Sep 2023 09:58:26 +0000
Content-Type: multipart/mixed; 
	boundary="17886a741fef2cb2_97a7dbff4c84bbac_3b41d60ef9e2fbfb"


--17886a741fef2cb2_97a7dbff4c84bbac_3b41d60ef9e2fbfb
Content-Type: text/plain; charset="utf-8"
Content-Transfer-Encoding: 7bit

This is a plain text part.


--17886a741fef2cb2_97a7dbff4c84bbac_3b41d60ef9e2fbfb
Content-Type: text/html; charset="utf-8"
Content-Transfer-Encoding: 7bit

<h1>This is a HTML part.</h1>

Content-Type: application/octet-stream
Content-Disposition: attachment; filename="attachment.png"
Content-Transfer-Encoding: base64

iVBORw0KGgo…

--17886a741fef2cb2_97a7dbff4c84bbac_3b41d60ef9e2fbfb--

Other examples can be found at ./examples:

cargo run --example

See the full API documentation on docs.rs.

Sponsoring

Special thanks to the NLnet foundation and the European Commission that helped the project to receive financial support from various programs:

• NGI Assure in 2022
• NGI Zero Entrust in 2023
• NGI Zero Core in 2024 (still ongoing)

If you appreciate the project, feel free to donate using one of the following providers: