# Beacon Node API

Lighthouse implements the standard [Eth2 Beacon Node API
specification][OpenAPI]. Please follow that link for a full description of each API endpoint.

> **Warning:** the standard API specification is still in flux and the Lighthouse implementation is partially incomplete. You can track the status of each endpoint at [#1434](https://github.com/sigp/lighthouse/issues/1434).

## Starting the server

A Lighthouse beacon node can be configured to expose a HTTP server by supplying the `--http` flag. The default listen address is `127.0.0.1:5052`.

The following CLI flags control the HTTP server:

- `--http`: enable the HTTP server (required even if the following flags are
	provided).
- `--http-port`: specify the listen port of the server.
- `--http-address`: specify the listen address of the server.
- `--http-allow-origin`: specify the value of the `Access-Control-Allow-Origin`
		header. The default is to not supply a header.

The schema of the API aligns with the standard Eth2 Beacon Node API as defined
at [github.com/ethereum/eth2.0-APIs](https://github.com/ethereum/eth2.0-APIs).
An interactive specification is available [here][OpenAPI].

### CLI Example

Start the beacon node with the HTTP server listening on [http://localhost:5052](http://localhost:5052):

```bash
lighthouse bn --http
```

## HTTP Request/Response Examples

This section contains some simple examples of using the HTTP API via `curl`.
All endpoints are documented in the [Eth2 Beacon Node API
specification][OpenAPI].

### View the head of the beacon chain

Returns the block header at the head of the canonical chain.

```bash
curl -X GET "http://localhost:5052/eth/v1/beacon/headers/head" -H  "accept:
application/json"
```

```json
{
  "data": {
    "root": "0x4381454174fc28c7095077e959dcab407ae5717b5dca447e74c340c1b743d7b2",
    "canonical": true,
    "header": {
      "message": {
        "slot": 3199,
        "proposer_index": "19077",
        "parent_root": "0xf1934973041c5896d0d608e52847c3cd9a5f809c59c64e76f6020e3d7cd0c7cd",
        "state_root": "0xe8e468f9f5961655dde91968f66480868dab8d4147de9498111df2b7e4e6fe60",
        "body_root": "0x6f183abc6c4e97f832900b00d4e08d4373bfdc819055d76b0f4ff850f559b883"
      },
      "signature": "0x988064a2f9cf13fe3aae051a3d85f6a4bca5a8ff6196f2f504e32f1203b549d5f86a39c6509f7113678880701b1881b50925a0417c1c88a750c8da7cd302dda5aabae4b941e3104d0cf19f5043c4f22a7d75d0d50dad5dbdaf6991381dc159ab"
    }
  }
}
```

### View the status of a validator

Shows the status of validator at index `1` at the `head` state.

```bash
curl -X GET "http://localhost:5052/eth/v1/beacon/states/head/validators/1" -H  "accept: application/json"
```

```json
{
  "data": {
    "index": "1",
    "balance": "63985937939",
    "status": "Active",
    "validator": {
      "pubkey": "0x873e73ee8b3e4fcf1d2fb0f1036ba996ac9910b5b348f6438b5f8ef50857d4da9075d0218a9d1b99a9eae235a39703e1",
      "withdrawal_credentials": "0x00b8cdcf79ba7e74300a07e9d8f8121dd0d8dd11dcfd6d3f2807c45b426ac968",
      "effective_balance": 32000000000,
      "slashed": false,
      "activation_eligibility_epoch": 0,
      "activation_epoch": 0,
      "exit_epoch": 18446744073709552000,
      "withdrawable_epoch": 18446744073709552000
    }
  }
}
```

## Troubleshooting

### HTTP API is unavailable or refusing connections

Ensure the `--http` flag has been supplied at the CLI.

You can quickly check that the HTTP endpoint is up using `curl`:

```bash
curl -X GET "http://localhost:5052/eth/v1/node/version" -H  "accept: application/json"
```

The beacon node should respond with its version:

```json
{"data":{"version":"Lighthouse/v0.2.9-6f7b4768a/x86_64-linux"}}
```

If this doesn't work, the server might not be started or there might be a
network connection error.

### I cannot query my node from a web browser (e.g., Swagger)

By default, the API does not provide an `Access-Control-Allow-Origin` header,
which causes browsers to reject responses with a CORS error.

The `--http-allow-origin` flag can be used to add a wild-card CORS header:

```bash
lighthouse bn --http --http-allow-origin "*"
```

> **Warning:** Adding the wild-card allow-origin flag can pose a security risk.
> Only use it in production if you understand the risks of a loose CORS policy.

[OpenAPI]: https://ethereum.github.io/eth2.0-APIs/#/
