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//! Email (`.eml` / Outlook `.msg`) backend — a port of docling's
//! `EmailDocumentBackend` (#251 for `.msg`, docling#3873).
//!
//! The subject becomes the document title; `From:`/`To:`/`Date:` headers become
//! text paragraphs; the body (preferring `text/plain`) is split into paragraphs
//! on blank lines. All emitted text is HTML/underscore-escaped like docling-core
//! (so `<a@b>` renders as `<a@b>`). A CFB-magic input is an Outlook
//! `.msg`: it projects onto RFC 822 (see [`super::msg`]) and flows through the
//! **same** parse below, so `.msg` and `.eml` output match by construction —
//! docling's own architecture for the format. `list_attachments` (opt-in,
//! docling's `EmailBackendOptions.list_attachments`) appends an `Attachments`
//! section listing names and content types; payload bytes are never embedded.
use mail_parser::{Address, Message, MessageParser};
use crate::backend::markdown::escape_text;
use crate::backend::DeclarativeBackend;
use crate::error::ConversionError;
use crate::source::SourceDocument;
use docling_core::{DoclingDocument, Node};
pub struct EmailBackend {
/// Append an `Attachments` section (names + content types, never the
/// payload) — docling's opt-in `list_attachments`.
pub list_attachments: bool,
}
impl DeclarativeBackend for EmailBackend {
fn convert(&self, source: &SourceDocument) -> Result<DoclingDocument, ConversionError> {
// Outlook .msg (CFB magic): project to RFC 822 first; the projection
// also carries the attachment labels straight from MAPI.
let projected = crate::backend::cfb::CompoundFile::detect(&source.bytes)
.then(|| super::msg::project(&source.bytes))
.flatten();
let raw: &[u8] = projected.as_ref().map_or(&source.bytes, |p| &p.rfc822);
let msg = MessageParser::default()
.parse(raw)
.ok_or_else(|| ConversionError::Parse("email: could not parse message".into()))?;
let mut doc = DoclingDocument::new(&source.name);
if let Some(subject) = msg.subject().map(str::trim).filter(|s| !s.is_empty()) {
doc.push(Node::Heading {
level: 1,
text: escape_text(subject),
});
}
for (label, addrs) in [("From", msg.from()), ("To", msg.to())] {
let text = format_addresses(addrs);
if !text.is_empty() {
doc.push(Node::Paragraph {
text: escape_text(&format!("{label}: {text}")),
});
}
}
if let Some(date) = msg.date() {
// Python docling formats via datetime.isoformat(), which spells
// UTC as "+00:00" — mail-parser's RFC 3339 uses "Z". Align.
let date = date.to_rfc3339().replace('Z', "+00:00");
doc.push(Node::Paragraph {
text: escape_text(&format!("Date: {date}")),
});
}
for para in body_paragraphs(&msg) {
doc.push(Node::Paragraph {
text: escape_text(¶),
});
}
if self.list_attachments {
let labels = match &projected {
Some(p) => p.attachment_labels.clone(),
None => eml_attachment_labels(&msg),
};
if !labels.is_empty() {
// docling adds the heading at level 2 under the title → "###".
doc.push(Node::Heading {
level: 3,
text: "Attachments".into(),
});
for label in labels {
doc.push(Node::ListItem {
ordered: false,
number: 1,
first_in_list: false,
text: escape_text(&label),
level: 0,
marker: None,
location: None,
dclx: None,
href: None,
layer: None,
});
}
}
}
Ok(doc)
}
}
/// Attachment display labels for a parsed `.eml`: `name (type/subtype)`,
/// falling back to `attachment-N` for nameless parts — docling's
/// `_get_attachment_labels`.
fn eml_attachment_labels(msg: &Message) -> Vec<String> {
use mail_parser::MimeHeaders;
msg.attachments()
.enumerate()
.map(|(i, part)| {
let name = part
.attachment_name()
.map(str::trim)
.filter(|s| !s.is_empty())
.map(str::to_string)
.unwrap_or_else(|| format!("attachment-{}", i + 1));
match part.content_type() {
Some(ct) => {
let mime = match ct.subtype() {
Some(sub) => format!("{}/{sub}", ct.ctype()),
None => ct.ctype().to_string(),
};
format!("{name} ({mime})")
}
None => name,
}
})
.collect()
}
/// `"Name <email>"` per address (or bare `email`), joined with `", "`.
fn format_addresses(addr: Option<&Address>) -> String {
let Some(addr) = addr else {
return String::new();
};
addr.iter()
.filter_map(|a| {
let name = a.name().map(str::trim).filter(|s| !s.is_empty());
let email = a.address().map(str::trim).filter(|s| !s.is_empty());
match (name, email) {
(Some(n), Some(e)) => Some(format!("{n} <{e}>")),
(None, Some(e)) => Some(e.to_string()),
_ => None,
}
})
.collect::<Vec<_>>()
.join(", ")
}
/// Body paragraphs (split on blank lines), preferring `text/plain`.
fn body_paragraphs(msg: &Message) -> Vec<String> {
let re = cached_regex!(r"\n\s*\n+");
let split = |text: &str, out: &mut Vec<String>| {
for p in re.split(text.trim()) {
let p = p.trim();
if !p.is_empty() {
out.push(p.to_string());
}
}
};
let mut out = Vec::new();
let plain = msg.text_body_count();
if plain > 0 {
for i in 0..plain {
if let Some(t) = msg.body_text(i) {
split(&t.replace("\r\n", "\n"), &mut out);
}
}
return out;
}
// No plain text — fall back to the raw HTML body as text (the test corpus is
// plain-text only; full HTML→Markdown of email bodies is a later refinement).
for i in 0..msg.html_body_count() {
if let Some(t) = msg.body_html(i) {
split(&t.replace("\r\n", "\n"), &mut out);
}
}
out
}
#[cfg(test)]
mod tests {
use super::*;
use crate::format::InputFormat;
#[test]
fn title_headers_escaped_and_body_split() {
let eml = "From: Alice <a@x.com>\r\nTo: Bob <b@y.com>\r\nSubject: Hi\r\n\
Content-Type: text/plain\r\n\r\nLine one.\r\n\r\nLine two.\r\n";
let src = SourceDocument::from_bytes("m", InputFormat::Email, eml.as_bytes().to_vec());
let md = EmailBackend {
list_attachments: false,
}
.convert(&src)
.unwrap()
.export_to_markdown();
// angle brackets HTML-escaped; body split into separate paragraphs.
assert_eq!(
md.trim(),
"# Hi\n\nFrom: Alice <a@x.com>\n\nTo: Bob <b@y.com>\n\nLine one.\n\nLine two."
);
}
/// #251: `list_attachments` appends the section with `name (type)` labels
/// for `.eml` too — the docling label format, payload never embedded.
#[test]
fn eml_list_attachments_appends_labels() {
let eml = concat!(
"From: A <a@x.com>\r\n",
"To: B <b@y.com>\r\n",
"Subject: S\r\n",
"MIME-Version: 1.0\r\n",
"Content-Type: multipart/mixed; boundary=\"bb\"\r\n\r\n",
"--bb\r\nContent-Type: text/plain\r\n\r\nBody.\r\n",
"--bb\r\nContent-Type: text/plain\r\n",
"Content-Disposition: attachment; filename=\"note.txt\"\r\n\r\n",
"hi\r\n--bb--\r\n",
);
let src = SourceDocument::from_bytes("m", crate::InputFormat::Email, eml.into());
let md = EmailBackend {
list_attachments: true,
}
.convert(&src)
.unwrap()
.export_to_markdown();
assert!(md.contains("### Attachments"), "{md}");
assert!(md.contains("- note.txt (text/plain)"), "{md}");
let md_off = EmailBackend {
list_attachments: false,
}
.convert(&src)
.unwrap()
.export_to_markdown();
assert!(!md_off.contains("Attachments"), "{md_off}");
}
}