xmppd

A carrier-grade XMPP server written in Zig, inspired by Postfix's architecture.

Overview

xmppd is a modern XMPP server designed for carrier-grade deployments. It draws architectural inspiration from Postfix — separation of concerns, privilege separation, sensible defaults — while leveraging Zig's async I/O and compile-time polymorphism for performance at scale.

Key Features (planned)

• Hybrid process model — master daemon supervises isolated components
• Async I/O — kqueue/kevent event loop handles millions of concurrent connections
• DANE-first — TLSA certificate validation as primary trust path for S2S federation
• Pluggable storage — RocksDB (default), PostgreSQL, MariaDB, LDAP
• Pluggable auth — internal, LDAP, OIDC, PAM
• Postfix admin UX — one package, one config, one service

Target Platforms

• Primary: FreeBSD (kqueue)
• Secondary: Linux (epoll, post-MVP)

Standards Compliance

Standard	Description	Support	Tested
RFC 6120	XMPP Core (STARTTLS, SASL, resource binding)	Full	E2E, Unit
RFC 6121	XMPP IM (roster, presence, messaging)	Partial¹	Interop, E2E, Unit
XEP-0030	Service Discovery	Full	Interop
XEP-0045	Multi-User Chat	Partial²	Interop, E2E, Unit
XEP-0054	vCard-temp	Full	Interop
XEP-0077	In-Band Registration	Full	E2E, Unit
XEP-0084	User Avatar (via PEP)	Full	E2E
XEP-0085	Chat State Notifications	Full	Interop
XEP-0092	Software Version	Full	Interop
XEP-0160	Offline Message Storage	Full	E2E, Unit
XEP-0163	Personal Eventing Protocol	Partial³	E2E
XEP-0184	Message Delivery Receipts	Pass-through	E2E
XEP-0191	Blocking Command	Full	E2E, Unit
XEP-0198	Stream Management	Partial⁴	E2E
XEP-0199	XMPP Ping	Full	Interop
XEP-0220	Server Dialback	Partial	E2E
XEP-0280	Message Carbons	Full	E2E, Unit
XEP-0308	Last Message Correction	Pass-through	E2E
XEP-0313	Message Archive Management	Full	E2E, Unit
XEP-0359	Unique and Stable Stanza IDs	Full	Unit
XEP-0440	SASL Channel-Binding Type Negotiation	Full	Unit

Interop = automated smack-sint-server-extensions v1.7.2 (495 tests available), E2E = verified with Gajim, Conversations, and/or Dino, Unit = Zig unit tests (738 tests), Pass-through = server forwards stanzas without interpretation; no server-side logic required.

¹ Multi-resource routing (§8.5) implemented: priority-based delivery, full JID forwarding, chat fallback. Roster push notifications after subscription changes not yet implemented. Roster set validation (multi-item, unauthorized, duplicate groups) incomplete.

² MUC core functionality works (join, part, groupchat, kick, ban, history, MAM, disco). Missing: room configuration forms (XEP-0045 §10), invitations (§7.8), voice requests.

³ PEP supports publish, subscribe, auto-subscribe, auto-create, persistent items, and avatar metadata notifications. Not a full XEP-0060 PubSub service.

⁴ SM supports enable, ack requests (<r/>), and ack responses (<a/>). Session resume is not implemented — sessions cannot be resumed after disconnection.

Building

Requires Zig 0.15.2+.

zig build

Run tests:

zig build test

Project Structure

lib/          XMPP protocol library (reusable)
  xml/        Streaming XML parser (XMPP subset)
  xmpp/       Stanza types, JID, protocol state machine
  sasl/       SASL mechanisms (SCRAM-SHA-256, PLAIN, EXTERNAL)
  tls/        STARTTLS + DANE/TLSA
  dns/        SRV, TLSA record resolution
src/          Server daemons
  master/     Master process supervisor
  core/       C2S listener, stanza router, presence engine
  auth/       Authentication daemon
  store/      Storage daemon + backends
  s2s/        S2S federation daemon
  muc/        Multi-User Chat service
  ctl/        xmppctl admin CLI
config/       Sample configuration
doc/          Documentation
test/         Integration and compliance tests

License

BSD-2-Clause. See LICENSE.

Copyright (c) 2026, Daniel Morante.