CoffeeChat

A private, end-to-end encrypted desktop messenger for a small circle of close friends.

Discord, Teams, Slack, Messenger and iMessage all hold your conversations on their servers. With CoffeeChat, our messages are encrypted on our own PCs before they leave, and only the recipients can decrypt them. The relay server we host ourselves only ever sees ciphertext, deletes it once it's delivered, and history lives only on our own machines.

This is a learning project. It's being built milestone by milestone (see Roadmap).

Target design

Area	Choice
Architecture	Self-hosted relay server (sees only ciphertext) + desktop clients
Server	Go, Docker on a small VPS, Caddy for TLS
Client	Wails v2 (Go) + React + TypeScript
Crypto	Signal protocol (X3DH + Double Ratchet) via go.mau.fi/libsignal
Groups	Pairwise fan-out (each group message is encrypted once per member)
Onboarding	Admin-issued single-use invite codes
Devices	One PC per person (MVP)
Storage	Server deletes after delivery; local history is encrypted with a passphrase-derived key

flowchart LR
  A[Friend A: Wails app] <-- WSS ciphertext --> R[Go relay in Docker behind Caddy]
  B[Friend B: Wails app] <-- WSS ciphertext --> R
  R --> DB[(SQLite: users, prekeys, queued ciphertext)]

Loading

Repo layout

cmd/server/          relay server entry point
internal/protocol/   wire types shared by server and client
internal/server/     relay server implementation
client/              Wails + React desktop app (created in M8)
playground/          throwaway crypto learning exercises (M2, M3)
docs/                threat model, protocol, deployment

Development

Requires Go 1.24+.

The runnable skeleton serves only GET /healthz (and HEAD /healthz), returning {"status":"ok"}. It does not yet accept or relay messages. It listens on 127.0.0.1:8080 by default; press Ctrl+C to shut down gracefully. To choose a different address, run go run ./cmd/server -addr 127.0.0.1:9090. The health endpoint reports process liveness, not database or messaging readiness.

On Windows, use the PowerShell helper (no make required):

.\dev.ps1         # list available tasks
.\dev.ps1 build   # build the relay into .\bin
.\dev.ps1 run     # build and run the relay
.\dev.ps1 test    # go test ./...
.\dev.ps1 vet     # go vet ./...
.\dev.ps1 check   # build, test, and vet in one command
.\dev.ps1 clean   # remove build output

The helper also supports tidy and can be invoked from any working directory. If script execution is disabled, use powershell -ExecutionPolicy Bypass -File .\dev.ps1 check for a one-off run.

With make installed:

make build   # build the relay into ./bin
make run     # build and run the relay
make test    # go test ./...
make vet     # go vet ./...

Roadmap

The details of each milestone (concepts, exercises, done-when criteria) are in docs/roadmap.md.

• M0 Clean slate: purge the old code and lay down the skeleton
• M1 Threat model (docs/threat-model.md)
• M2 Crypto primitives playground: AEAD, X25519, Ed25519, HKDF, Argon2id
• M3 Signal protocol concepts: X3DH, Double Ratchet, a first libsignal test
• M4 Wire protocol design (internal/protocol, docs/protocol.md)
• M5 Relay: SQLite store + invite-code admin CLI
• M6 Relay: challenge-response auth, WebSocket hub, offline queue
• M7 Relay: prekey directory + group routing
• M8 Wails + React client skeleton
• M9 Encrypted local storage
• M10 End-to-end encrypted DMs
• M11 Group chats
• M12 UI polish
• M13 Deploy to a VPS

Stretch: safety-number verification, attachments, multi-device, Sender Keys groups, sealed sender, notifications.