aarondb/command

command — deterministic replicated command-state-machine reference

This module deliberately has no transport, leader election, or local DB integration. A future consensus runtime supplies the committed index; this module deterministically applies the same command on every member.

Types

Applied

pub type Applied {
  Applied(
    idempotency_key: String,
    fingerprint: String,
    result: CommandResult,
  )
}

Constructors

Applied(
  idempotency_key: String,
  fingerprint: String,
  result: CommandResult,
)

Command

pub type Command {
  Put(key: String, value: String)
  CompareAndSet(
    key: String,
    expected: option.Option(String),
    replacement: String,
  )
  IssueFence(resource: String)
}

Constructors

```
Put(key: String, value: String)
```

CompareAndSet(
  key: String,
  expected: option.Option(String),
  replacement: String,
)

```
IssueFence(resource: String)
```

CommandError

pub type CommandError {
  IdempotencyPayloadMismatch(key: String)
  InvalidCommittedIndex(index: Int, last_applied: Int)
}

Constructors

```
IdempotencyPayloadMismatch(key: String)
```

InvalidCommittedIndex(index: Int, last_applied: Int)

CommandRequest

pub type CommandRequest {
  CommandRequest(idempotency_key: String, command: Command)
}

Constructors

CommandRequest(idempotency_key: String, command: Command)

CommandResult

pub type CommandResult {
  Written(key: String, value: String)
  CasApplied(
    key: String,
    previous: option.Option(String),
    value: String,
  )
  CasRejected(key: String, actual: option.Option(String))
  FenceIssued(resource: String, token: Int)
}

Constructors

```
Written(key: String, value: String)
```

CasApplied(
  key: String,
  previous: option.Option(String),
  value: String,
)

CasRejected(key: String, actual: option.Option(String))

FenceIssued(resource: String, token: Int)

Consistency

pub type Consistency {
  Local
  LeaseRead
  Linearizable
}

Constructors

```
Local
```
```
LeaseRead
```
```
Linearizable
```

State

pub type State {
  State(
    values: List(Value),
    fences: List(#(String, Int)),
    applied: List(Applied),
    last_applied: Int,
  )
}

Constructors

State(
  values: List(Value),
  fences: List(#(String, Int)),
  applied: List(Applied),
  last_applied: Int,
)

Value

pub type Value {
  Value(key: String, value: String)
}

Constructors

```
Value(key: String, value: String)
```

Values

apply

pub fn apply(
  index: Int,
  request: CommandRequest,
  state: State,
) -> Result(#(State, CommandResult), CommandError)

The committed index must advance exactly once. Retried idempotency requests return their original result without applying another mutation.

last_applied

pub fn last_applied(state: State) -> Int

new

pub fn new() -> State

read

pub fn read(
  state: State,
  key: String,
  mode: Consistency,
) -> #(Consistency, option.Option(String))

replay_hash

pub fn replay_hash(state: State) -> String

The hash is intentionally constructed from closed, ordered data. It is an audit/replay fingerprint, not a cryptographic signature.