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chat/internal/db/schema/001_initial.sql
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feat: per-channel hashcash proof-of-work for PRIVMSG anti-spam (#79)
closes #12

## Summary

Implements per-channel hashcash proof-of-work requirement for PRIVMSG as an anti-spam mechanism. Channel operators set a difficulty level via `MODE +H <bits>`, and clients must compute a proof-of-work stamp bound to the channel name and message body before sending.

## Changes

### Database
- Added `hashcash_bits` column to `channels` table (default 0 = no requirement)
- Added `spent_hashcash` table with `stamp_hash` unique key and `created_at` for TTL pruning
- New queries: `GetChannelHashcashBits`, `SetChannelHashcashBits`, `RecordSpentHashcash`, `IsHashcashSpent`, `PruneSpentHashcash`

### Hashcash Validation (`internal/hashcash/channel.go`)
- `ChannelValidator` type for per-channel stamp validation
- `BodyHash()` computes hex-encoded SHA-256 of message body
- `StampHash()` computes deterministic hash of stamp for spent-token key
- `MintChannelStamp()` generates valid stamps (for clients)
- Stamp format: `1:bits:YYMMDD:channel:bodyhash:counter`
- Validates: version, difficulty, date freshness (48h), channel binding, body hash binding, proof-of-work

### Handler Changes (`internal/handlers/api.go`)
- `validateChannelHashcash()` + `verifyChannelStamp()` — checks hashcash on PRIVMSG to protected channels
- `extractHashcashFromMeta()` — parses hashcash stamp from meta JSON
- `applyChannelMode()` / `setHashcashMode()` / `clearHashcashMode()` — MODE +H/-H support
- `queryChannelMode()` — shows +nH in mode query when hashcash is set
- Meta field now passed through the full dispatch chain (dispatchCommand → handlePrivmsg → handleChannelMsg → sendChannelMsg → fanOut → InsertMessage)
- ISUPPORT updated: `CHANMODES=,H,,imnst` (H in type B = parameter when set)

### Replay Prevention
- Spent stamps persisted to SQLite `spent_hashcash` table
- 1-year TTL (per issue requirements)
- Automatic pruning in cleanup loop

### Client Support (`internal/cli/api/hashcash.go`)
- `MintChannelHashcash(bits, channel, body)` — computes stamps for channel messages

### Tests
- **12 unit tests** in `internal/hashcash/channel_test.go`: happy path, wrong channel, wrong body hash, insufficient bits, zero bits skip, bad format, bad version, expired stamp, missing body hash, body hash determinism, stamp hash, mint+validate round-trip
- **10 integration tests** in `internal/handlers/api_test.go`: set mode, query mode, clear mode, reject no stamp, accept valid stamp, reject replayed stamp, no requirement works, invalid bits range, missing bits arg

### README
- Added `+H` to channel modes table
- Added "Per-Channel Hashcash (Anti-Spam)" section with full documentation
- Updated `meta` field description to mention hashcash

## How It Works

1. Channel operator sets requirement: `MODE #general +H 20` (20 bits)
2. Client mints stamp: computes SHA-256 hashcash bound to `#general` + SHA-256(body)
3. Client sends PRIVMSG with `meta.hashcash` field containing the stamp
4. Server validates stamp, checks spent cache, records as spent, relays message
5. Replayed stamps are rejected for 1 year

## Docker Build

`docker build .` passes clean (formatting, linting, all tests).

Co-authored-by: user <user@Mac.lan guest wan>
Co-authored-by: Jeffrey Paul <sneak@noreply.example.org>
Reviewed-on: #79
Co-authored-by: clawbot <clawbot@noreply.example.org>
Co-committed-by: clawbot <clawbot@noreply.example.org>
2026-03-18 03:40:33 +01:00

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SQL

-- Chat server schema (pre-1.0 consolidated)
PRAGMA foreign_keys = ON;
-- Sessions: each session is a user identity (nick + optional password + signing key)
CREATE TABLE IF NOT EXISTS sessions (
id INTEGER PRIMARY KEY AUTOINCREMENT,
uuid TEXT NOT NULL UNIQUE,
nick TEXT NOT NULL UNIQUE,
password_hash TEXT NOT NULL DEFAULT '',
signing_key TEXT NOT NULL DEFAULT '',
away_message TEXT NOT NULL DEFAULT '',
created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
last_seen DATETIME DEFAULT CURRENT_TIMESTAMP
);
CREATE INDEX IF NOT EXISTS idx_sessions_uuid ON sessions(uuid);
-- Clients: each session can have multiple connected clients
CREATE TABLE IF NOT EXISTS clients (
id INTEGER PRIMARY KEY AUTOINCREMENT,
uuid TEXT NOT NULL UNIQUE,
session_id INTEGER NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
token TEXT NOT NULL UNIQUE,
created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
last_seen DATETIME DEFAULT CURRENT_TIMESTAMP
);
CREATE INDEX IF NOT EXISTS idx_clients_token ON clients(token);
CREATE INDEX IF NOT EXISTS idx_clients_session ON clients(session_id);
-- Channels
CREATE TABLE IF NOT EXISTS channels (
id INTEGER PRIMARY KEY AUTOINCREMENT,
name TEXT NOT NULL UNIQUE,
topic TEXT NOT NULL DEFAULT '',
topic_set_by TEXT NOT NULL DEFAULT '',
topic_set_at DATETIME,
hashcash_bits INTEGER NOT NULL DEFAULT 0,
created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
updated_at DATETIME DEFAULT CURRENT_TIMESTAMP
);
-- Channel members
CREATE TABLE IF NOT EXISTS channel_members (
id INTEGER PRIMARY KEY AUTOINCREMENT,
channel_id INTEGER NOT NULL REFERENCES channels(id) ON DELETE CASCADE,
session_id INTEGER NOT NULL REFERENCES sessions(id) ON DELETE CASCADE,
joined_at DATETIME DEFAULT CURRENT_TIMESTAMP,
UNIQUE(channel_id, session_id)
);
-- Messages: IRC envelope format
CREATE TABLE IF NOT EXISTS messages (
id INTEGER PRIMARY KEY AUTOINCREMENT,
uuid TEXT NOT NULL UNIQUE,
command TEXT NOT NULL DEFAULT 'PRIVMSG',
msg_from TEXT NOT NULL DEFAULT '',
msg_to TEXT NOT NULL DEFAULT '',
params TEXT NOT NULL DEFAULT '[]',
body TEXT NOT NULL DEFAULT '[]',
meta TEXT NOT NULL DEFAULT '{}',
created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);
CREATE INDEX IF NOT EXISTS idx_messages_to_id ON messages(msg_to, id);
CREATE INDEX IF NOT EXISTS idx_messages_created ON messages(created_at);
-- Spent hashcash tokens for replay prevention (1-year TTL)
CREATE TABLE IF NOT EXISTS spent_hashcash (
id INTEGER PRIMARY KEY AUTOINCREMENT,
stamp_hash TEXT NOT NULL UNIQUE,
created_at DATETIME DEFAULT CURRENT_TIMESTAMP
);
CREATE INDEX IF NOT EXISTS idx_spent_hashcash_created ON spent_hashcash(created_at);
-- Per-client message queues for fan-out delivery
CREATE TABLE IF NOT EXISTS client_queues (
id INTEGER PRIMARY KEY AUTOINCREMENT,
client_id INTEGER NOT NULL REFERENCES clients(id) ON DELETE CASCADE,
message_id INTEGER NOT NULL REFERENCES messages(id) ON DELETE CASCADE,
created_at DATETIME DEFAULT CURRENT_TIMESTAMP,
UNIQUE(client_id, message_id)
);
CREATE INDEX IF NOT EXISTS idx_client_queues_client ON client_queues(client_id, id);