@catlabtech/webcvt-email

Self-written EML (RFC 5322 + MIME) parser for webcvt — turn .eml messages into structured data, plain text, or JSON, entirely client-side with zero runtime dependencies.

What it does

• RFC 5322 header parsing: folding/unfolding, case-insensitive field names, repeated headers preserved.
• RFC 2047 encoded-words (=?utf-8?B?…?= / ?Q?) decoded in header values.
• MIME (RFC 2045/2046): Content-Type + boundary, Content-Transfer-Encoding (7bit / 8bit / binary / base64 / quoted-printable), recursive multipart/* (depth-capped), text/plain + text/html parts and attachments.
• Address-list parsing for From / To / Cc.
• HTML → text (ReDoS-safe) for the eml → txt path.

Install

npm install @catlabtech/webcvt-core @catlabtech/webcvt-email

Usage

import { parseEml } from '@catlabtech/webcvt-email';

const msg = parseEml(emlStringOrBytes);
msg.subject;          // decoded subject
msg.from;             // { name?, address }
msg.to;               // EmailAddress[]
msg.textBody;         // string | undefined
msg.htmlBody;         // string | undefined
msg.attachments;      // { filename?, contentType, bytes, size, contentId? }[]

Convert via the backend (opt-in registration — the backend never auto-registers):

import { convert, defaultRegistry } from '@catlabtech/webcvt-core';
import { EmailBackend } from '@catlabtech/webcvt-email';

defaultRegistry.register(new EmailBackend());
const txt = await convert(emlBlob, { format: 'txt' });   // plain-text body
const json = await convert(emlBlob, { format: 'json' });  // lossless structured JSON

EML has no reliable magic-byte signature, so detection relies on the filename / MIME hint (message/rfc822).

Security

Hardened against adversarial input: 64 MiB input cap, ≤1000 headers, MIME nesting depth ≤20, ≤1000 parts, bounded decoded-attachment bytes, prototype-pollution-safe header maps (Object.create(null)), and hand-written scanners instead of backtracking regex.

Out of scope

RFC 2231 parameter continuations / extended filename*=, recursive message/rfc822 sub-messages (kept as opaque attachments), and group-address labels.

License

MIT