Crate mailrs_smtp_proto 

SMTP protocol parser, formatter, and session state machine.

mailrs-smtp-proto is a zero-I/O implementation of RFC 5321 (SMTP) and its common extensions: STARTTLS (RFC 3207), AUTH PLAIN / LOGIN (RFC 4954), and SMTPUTF8 (RFC 6531). It parses incoming command lines into typed Command enums, formats outgoing responses, and drives the SMTP session state machine — but it never touches the network. The caller owns all I/O.

This crate underpins the inbound SMTP server in mailrs, a Rust mail server, and is published independently so other Rust projects can reuse the parsing + state-machine layer without pulling in a full server.

Quick start

use mailrs_smtp_proto::{parse_command, Command, Session, SessionConfig, Event};

// parse a wire-format command line
let cmd = parse_command("EHLO mail.example.com").unwrap();
assert!(matches!(cmd, Command::Ehlo("mail.example.com")));

// drive the session state machine
let mut session = Session::new("smtp.example.com", SessionConfig::default());
let event = session.handle_command(&cmd);
assert!(matches!(event, Event::Reply(_)));

What this crate does

• Parsing: parse_command turns a wire-format command line into a borrowed Command<'_> enum (zero-copy).
• Formatting: Response and its constructors produce wire-format reply lines; format_ehlo_response handles multi-line EHLO.
• State machine: Session tracks the SMTP transaction state and maps Command → Event decisions (reply / open DATA / start TLS / authenticate / shut down).
• DATA helpers: unstuff_line / unstuff_data handle the dot-stuffing convention used in the DATA stage.
• SASL: auth::decode_plain / auth::decode_login_response decode AUTH PLAIN / LOGIN payloads.

What this crate does NOT do

• No I/O. No TCP, no TLS, no async runtime. The caller wires it.
• No content scanning, no message storage, no DKIM/SPF/DMARC.
• No outbound SMTP client. See mailrs-smtp-client for that.

Re-exports

pub use command::AuthMechanism;

pub use command::Command;

pub use command::ForwardPath;

pub use command::Param;

pub use command::ReversePath;

pub use data::unstuff_data;

pub use data::unstuff_line;

pub use parse::ParseError;

pub use parse::parse_command;

pub use response::EnhancedCode;

pub use response::Response;

pub use response::format_ehlo_response;

pub use session::AuthStep;

pub use session::Event;

pub use session::MAX_MESSAGE_SIZE;

pub use session::MAX_RECIPIENTS;

pub use session::Session;

pub use session::SessionConfig;

pub use session::State;

Modules

address

Minimal email address helpers (validation and local/domain split).

auth

SASL helpers for AUTH PLAIN (RFC 4616) and AUTH LOGIN.

command

Typed SMTP command representation.

data

DATA-stage helpers: remove SMTP dot-stuffing from message bodies.

parse

Wire-format command-line parser for SMTP.

response

SMTP response codes, enhanced status codes, and well-known reply constructors.

session

SMTP session state machine.