æternity node API

This document:

Provides an overview of the API exposed by the æternity node;
Defines the Channels WebSocket API of the æternity node;
Describes the intended usage of the user API of the æternity node.

Overview

The æternity node exposes the following APIs:

Peer-to-peer network API. It consists of one TCP endpoint:
- It is encrypted and authenticated using the Noise protocol;
- The schema of its payload is defined;
- It is meant to be exposed on the Internet;
- Its TCP port is configurable.
- Its static Noise key pair is configurable.
User API. It consists of the following TCP endpoints:
- External HTTP endpoint;
  - It is defined via Swagger schema;
  - It is meant to be exposed on the Internet;
  - Its TCP port is configurable.
- Internal HTTP endpoint;
  - It is defined via Swagger schema;
  - It is not meant to be exposed on the Internet;
  - Its TCP port is configurable.
- Internal Channels WebSocket endpoint.
  - It is defined in the rest of this document;
  - It is not meant to be exposed on the Internet;
  - Its TCP port is configurable.
- Range of external Channels noise endpoints. It consists of as many TCP endpoints as needed.
  - They are used for connecting as a responder role in channel communication;
  - It is up to the node operator to define the range to be used; Their configuration is not part of the æternity node;
  - They are encrypted and authenticated using the Noise protocol using dynamic keys (unauthenticated Diffie-Hellman - exact protocol name Noise_NN_25519_ChaChaPoly_BLAKE2b);
  - The schema of its payload is defined;
  - They are meant to be exposed on the Internet;

User API - intended usage

Channels WebSocket API definition

The æternity node publishes a JSON-RPC API for managing state channels over WebSocket connections. The 'legacy' protocol was removed.

Description

Channels provide means for off-chain transactions with functionality of on-chain dispute resolution. Channels require persisted connections to æternity nodes. Each participant in a channel uses one's own trusted node. For persistence of this connection, WebSockets are used. Channels have on-chain state that persists who the participants are and the total amount of coins put into the channel. Each channel also has an off-chain state representing the latest distribution of the balance of the channel. It can be updated - each new state is co-signed by both parties and only then it becomes the latest valid state of the channel. At any point in time channel can be closed either unilaterally or through mutual agreement.

Connection

The æternity node supports an endpoint with a configurable port where the WebSocket's clients connect. It is located on /channel.

The node could serve multiple channel WebSocket clients. Their number is configured in the epoch.yaml. When all WebSocket connections are consumed - any new incoming connections will be queued. The queue has a maximum size and when it is reached, any new incoming connections will be rejected with an error code 400. This is to prevent the node of being overloaded with WebSocket connections.

Messages overview

The JSON-RPC protocol supports both synchronous RPC and asynchronous notifications. An RPC is indicated by the inclusion of an 'id' parameter. The æternity API can be used both synchronously and asynchronously. When an asynchronous method is called, the reply will have 'method': '<RequestMethod>.reply'.

Implementation support exists for batch processing, however this is not yet tested.

Examples

Example, synchronous RPC

{
  "jsonrpc": "2.0",
  "id": -576460752303423475,
  "method": "channels.get.balances",
  "params": {
    "accounts": [
      "ak_KcR46Qk9aEmHnWwGZLAW7u5MT3FLsxszmkx9rphLfCZoBAzFY",
      "ak_2MpDC9D3cnHn5KDNuDDHSarZYZR988oqzLWHudZe9pHGE78duZ"
    ]
  }
}

Reply:

{
  "jsonrpc": "2.0",
  "id": -576460752303423475,
  "result": [
    {
      "account": "ak_KcR46Qk9aEmHnWwGZLAW7u5MT3FLsxszmkx9rphLfCZoBAzFY",
      "balance": 699
    },
    {
      "account": "ak_2MpDC9D3cnHn5KDNuDDHSarZYZR988oqzLWHudZe9pHGE78duZ",
      "balance": 401
    }
  ]
}

Example, asynchronous request-reply interaction

{
  "jsonrpc": "2.0",
  "method": "channels.get.contract_call",
  "params": {
    "caller": "ak_KcR46Qk9aEmHnWwGZLAW7u5MT3FLsxszmkx9rphLfCZoBAzFY",
    "contract": "ct_28pwhjFEVfuirjPzJDRTE4o4ybjKw7vjMymRdhhVrDEVTuXAtq",
    "round": 8
  }
}

Reply:

{
  "jsonrpc": "2.0",
  "method": "channels.get.contract_call.reply",
  "params": {
    "channel_id": "undefined",
    "data": {
      "caller_id": "ak_KcR46Qk9aEmHnWwGZLAW7u5MT3FLsxszmkx9rphLfCZoBAzFY",
      "caller_nonce": 8,
      "contract_id": "ct_28pwhjFEVfuirjPzJDRTE4o4ybjKw7vjMymRdhhVrDEVTuXAtq",
      "gas_price": 1,
      "gas_used": 387,
      "height": 8,
      "log": [],
      "return_type": "ok",
      "return_value": "cb_11111111111111111111111111111115rHyByZ"
    }
  }
}

Note that when the node sends an asynchronous notification, the 'params' element contains the 'channel_id' and a 'data' element. The latter contains the same information as the 'result' element in an RPC reply, and the 'payload' element in the legacy protocol (except that if the 'channel_id' was present in the payload, it is removed from 'data' and only passed as an element of 'params'.)

Error objects

If an error occurs, a JSON-RPC error object is returned. It has the following form:

{'jsonrpc': '2.0',
 'id': null,
 'error' : {
   'code': <ErrorCode>,
   'message': <ErrorMessage>,
   'data': [ ... ],
   'request': { ... }
  }
 }

The codes and error messages include those specified in the JSON-RPC 2.0 Specification [1], some used (or proposed) by Ethereum [2], and some æternity-specific [3].

Code

Message

Origin

-32700

Parse error

[1]

-32000

Invalid request

[1]

-32601

Method not found

[1]

-32602

Invalid params

[1]

-32603

Internal error

[1]

Unauthorized

[2]

Action not allowed

[2]

Rejected

[2]

The 'data' element may contain more detailed information inside 'data':

Code

Message

Parent Code

Origin

100

X doesn't exist

[2]

101

Requires coin

[2]

102

Gas too low

[2]

103

Gas limit exceeded

[2]

104

Rejected

[2]

105

Value too low

[2]

106

Timeout

[2]

107

Conflict

[2]

1001

Insufficient balance

[3]

1002

Negative amount

[3]

1003

Invalid pubkeys

[3]

1004

Call not found

[3]

1005

Broken encoding: account pubkey

[3]

1006

Broken encoding: contract pubkey

[3]

1007

Contract init failed

[3]

1008

Not a number

[3]

1009

Broken encoding: contract bytecode

[3]

1010

Broken encoding: transaction

[3]

1011

Participant not found

[3]

Example, error object

{
 "error": {
   "code": 3,
   "data": [
     {
       "code": 1004,
       "message": "Call not found"
     }
   ],
   "message": "Rejected",
   "request": {
     "jsonrpc": "2.0",
     "method": "channels.get.contract_call",
     "params": {
       "caller": "ak_KcR46Qk9aEmHnWwGZLAW7u5MT3FLsxszmkx9rphLfCZoBAzFY",
       "contract": "ct_28pwhjFEVfuirjPzJDRTE4o4ybjKw7vjMymRdhhVrDEVTuXAtq",
       "round": 8
     }
   }
 },
 "id": null,
 "jsonrpc": "2.0"
}

Detailed message transcripts from test suites can be found in the JSON-RCP section of the Websocket API examples.

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