292 lines
8.7 KiB
Markdown
292 lines
8.7 KiB
Markdown
# Eth 2.0 Networking Spec - RPC Interface
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## Abstract
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The Ethereum 2.0 networking stack uses two modes of communication: a broadcast protocol that gossips information to interested parties via GossipSub, and an RPC protocol that retrieves information from specific clients. This specification defines the RPC protocol.
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The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL", NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in [RFC 2119](https://tools.ietf.org/html/rfc2119).
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## Dependencies
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This specification assumes familiarity with the [Messaging](./messaging.md), [Node Identification](./node-identification.md), and [Beacon Chain](../core/0_beacon-chain.md) specifications.
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# Specification
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## Message schemas
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Message body schemas are notated like this:
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```
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(
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field_name_1: type
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field_name_2: type
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)
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```
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Embedded types are serialized as SSZ Containers unless otherwise noted.
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All referenced data structures can be found in the [Beacon Chain](../core/0_beacon-chain.md#data-structures) specification.
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## `libp2p` protocol names
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A "Protocol ID" in `libp2p` parlance refers to a human-readable identifier `libp2p` uses in order to identify sub-protocols and stream messages of different types over the same connection. Peers exchange supported protocol IDs via the `Identify` protocol upon connection. When opening a new stream, peers pin a particular protocol ID to it, and the stream remains contextualized thereafter. Since messages are sent inside a stream, they do not need to bear the protocol ID.
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## RPC-over-`libp2p`
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To facilitate RPC-over-`libp2p`, a single protocol name is used: `/eth/serenity/beacon/rpc/1`. The version number in the protocol name is neither backwards or forwards compatible, and will be incremented whenever changes to the below structures are required.
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Remote method calls are wrapped in a "request" structure:
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```
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(
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id: uint64
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method_id: uint16
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body: Request
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)
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```
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and their corresponding responses are wrapped in a "response" structure:
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```
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(
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id: uint64
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response_code: uint16
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result: bytes
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)
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```
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If an error occurs, a variant of the response structure is returned:
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```
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(
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id: uint64
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response_code: uint16
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result: bytes
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)
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```
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The details of the RPC-Over-`libp2p` protocol are similar to [JSON-RPC 2.0](https://www.jsonrpc.org/specification). Specifically:
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1. The `id` member is REQUIRED.
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2. The `id` member in the response MUST be the same as the value of the `id` in the request.
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3. The `id` member MUST be unique within the context of a single connection. Monotonically increasing `id`s are RECOMMENDED.
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4. The `method_id` member is REQUIRED.
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5. The `result` member is REQUIRED on success.
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6. The `result` member is OPTIONAL on errors, and MAY contain additional information about the error.
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7. `response_code` MUST be `0` on success.
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Structuring RPC requests in this manner allows multiple calls and responses to be multiplexed over the same stream without switching. Note that this implies that responses MAY arrive in a different order than requests.
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The "method ID" fields in the below messages refer to the `method` field in the request structure above.
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The first 1,000 values in `response_code` are reserved for system use. The following response codes are predefined:
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1. `0`: No error.
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2. `10`: Parse error.
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2. `20`: Invalid request.
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3. `30`: Method not found.
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4. `40`: Server error.
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### Alternative for non-`libp2p` clients
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Since some clients are waiting for `libp2p` implementations in their respective languages. As such, they MAY listen for raw TCP messages on port `9000`. To distinguish RPC messages from other messages on that port, a byte prefix of `ETH` (`0x455448`) MUST be prepended to all messages. This option will be removed once `libp2p` is ready in all supported languages.
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## Messages
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### Hello
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**Method ID:** `0`
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**Body**:
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```
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(
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network_id: uint8
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chain_id: uint64
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latest_finalized_root: bytes32
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latest_finalized_epoch: uint64
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best_root: bytes32
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best_slot: uint64
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)
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```
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Clients exchange `hello` messages upon connection, forming a two-phase handshake. The first message the initiating client sends MUST be the `hello` message. In response, the receiving client MUST respond with its own `hello` message.
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Clients SHOULD immediately disconnect from one another following the handshake above under the following conditions:
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1. If `network_id` belongs to a different chain, since the client definitionally cannot sync with this client.
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2. If the `latest_finalized_root` shared by the peer is not in the client's chain at the expected epoch. For example, if Peer 1 in the diagram below has `(root, epoch)` of `(A, 5)` and Peer 2 has `(B, 3)`, Peer 1 would disconnect because it knows that `B` is not the root in their chain at epoch 3:
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```
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Root A
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+---+
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|xxx| +----+ Epoch 5
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+-+-+
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^
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+-+-+
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+-+-+
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Root B ^
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+---+ +-+-+
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|xxx+<---+--->+ | +----+ Epoch 3
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+---+ | +---+
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+-+-+
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+-+-+
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^
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+-+-+
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+---+
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```
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Once the handshake completes, the client with the higher `latest_finalized_epoch` or `best_slot` (if the clients have equal `latest_finalized_epoch`s) SHOULD request beacon block roots from its counterparty via `beacon_block_roots` (i.e. RPC method `10`).
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### Goodbye
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**Method ID:** `1`
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**Body:**
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```
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(
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reason: uint64
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)
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```
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Client MAY send `goodbye` messages upon disconnection. The reason field MAY be one of the following values:
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- `1`: Client shut down.
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- `2`: Irrelevant network.
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- `3`: Fault/error.
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Clients MAY define custom goodbye reasons as long as the value is larger than `1000`.
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### Get status
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**Method ID:** `2`
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**Request body:**
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```
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(
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sha: bytes32
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user_agent: bytes
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timestamp: uint64
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)
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```
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**Response body:**
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```
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(
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sha: bytes32
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user_agent: bytes
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timestamp: uint64
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)
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```
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Returns metadata about the remote node.
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### Request beacon block roots
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**Method ID:** `10`
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**Request body**
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```
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(
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start_slot: uint64
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count: uint64
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)
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```
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**Response body:**
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```
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# BlockRootSlot
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(
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block_root: bytes32
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slot: uint64
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)
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roots: []BlockRootSlot
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)
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```
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Requests a list of block roots and slots from the peer. The `count` parameter MUST be less than or equal to `32768`. The slots MUST be returned in ascending slot order.
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### Beacon block headers
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**Method ID:** `11`
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**Request body**
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```
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start_root: HashTreeRoot
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start_slot: uint64
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max_headers: uint64
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skip_slots: uint64
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)
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```
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**Response body:**
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```
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headers: []BeaconBlockHeader
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)
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```
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Requests beacon block headers from the peer starting from `(start_root, start_slot)`. The response MUST contain no more than `max_headers` headers. `skip_slots` defines the maximum number of slots to skip between blocks. For example, requesting blocks starting at slots `2` a `skip_slots` value of `1` would return the blocks at `[2, 4, 6, 8, 10]`. In cases where a slot is empty for a given slot number, the closest previous block MUST be returned. For example, if slot `4` were empty in the previous example, the returned array would contain `[2, 3, 6, 8, 10]`. If slot three were further empty, the array would contain `[2, 6, 8, 10]`—i.e. duplicate blocks MUST be collapsed. A `skip_slots` value of `0` returns all blocks.
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The function of the `skip_slots` parameter helps facilitate light client sync - for example, in [#459](https://github.com/ethereum/eth2.0-specs/issues/459) - and allows clients to balance the peers from whom they request headers. Clients could, for instance, request every 10th block from a set of peers where each peer has a different starting block in order to populate block data.
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### Beacon block bodies
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**Method ID:** `12`
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**Request body:**
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```
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block_roots: []HashTreeRoot
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)
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```
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**Response body:**
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```
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(
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block_bodies: []BeaconBlockBody
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)
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```
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Requests the `block_bodies` associated with the provided `block_roots` from the peer. Responses MUST return `block_roots` in the order provided in the request. If the receiver does not have a particular `block_root`, it must return a zero-value `block_body` (i.e. a `block_body` container with all zero fields).
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### Beacon chain state
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*Note*: This section is preliminary, pending the definition of the data structures to be transferred over the wire during fast sync operations.
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**Method ID:** `13`
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**Request body:**
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```
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(
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hashes: []HashTreeRoot
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)
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```
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**Response body:** TBD
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Requests contain the hashes of Merkle tree nodes that when merkleized yield the block's `state_root`.
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The response will contain the values that, when hashed, yield the hashes inside the request body.
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