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snarkos-network
The snarkOS network protocol establishes a peer-to-peer network of nodes that maintains ledger liveness by actively exchanging transactions and blocks.
Overview
snarkOS uses TCP connections to facilitate data transfers over the network. Networking on snarkOS is built with asynchronous calls in Rust and tokio.rs. Tokio tasks are spawned to handle new connections and send messages to the main event loop.
snarkOS downloads, verifies, and stores the history of valid blocks and transactions prior to becoming an active node on the network.
Peer Discovery
When a node joins the network for the first time, it needs to populate a list of active peers in the network. In order to bootstrap peer discovery, snarkOS includes a set of optional bootnodes which provides an initial set of peers. To allow users flexibility, snarkOS provides allows users to configure the initial set of nodes in the configuration file, or as a input via a command-line flag.
Once a node is connected to one or more nodes, it may scan the network to discover more peers.
This processes starts by asking peers for more connected nodes in the network with a GetPeers message,
followed by attempts to establish a connection with each newly discovered peer.
Upon success, snarkOS will store the new peer address to allow it to connect directly with this peer in the future, without needing to use bootnodes to startup in the future.
Bootnodes
Bootnodes operate like other full nodes and serve as a public access point for all peers in the network. Bootnodes are run by community members and bolster the network by enabling new nodes to connect and participate in the network effortlessly.
Connecting to Peers
Peer connections are established with an XX noise handshake.
Peer connections are maintained with a ping-pong protocol that periodically relays Ping / Pong messages to
verify that peers are still connected. snarkOS will update its peer book to account for newly-connected peers,
and disconnected peers.
Block Download/Sync
Before a node can participate in the network, it must sync itself to the latest state of the ledger. Whether a node is newly connecting to the network or simply has stale state, it must sync with its peers, and download its missing blocks and transactions.
snarkOS uses a "Header-First" approach to syncing blocks, where a node downloads and validates each block header before downloading the corresponding full block, in parallel.
When a node determines it needs to download state, it selects a peer as the sync-node and sends it a GetSync message.
The GetSync message contains information about the current block state of the node,
so the sync-node is able to determine which block headers are necessary to send as a response.
Upon receiving a GetSync message, the sync-node sends back at most 100 block headers via a Sync message.
The requester then validates these headers and downloads the blocks in parallel by sending out GetBlock messages.
After these blocks have been downloaded, the requester sends another GetSync message,
and repeats this process until its chain state is fully up to date.
Here is a basic iteration of the sync protocol:
| Message | Sender | Receiver | Data |
|---|---|---|---|
GetSync |
Node | Sync Node | 1 or more block hashes |
Sync |
Sync Node | Node | Up to 100 new block headers |
GetBlocks |
Node | Any Peer | Block headers of the requested blocks |
Block |
Any Peer | Node | A serialized block |
Transaction Broadcasting
A node may broadcast a transaction to the network by sending a Transaction message to its connected peers.
The peers receiving this transaction verify the transaction
and further propagate the transaction by broadcasting it to its connected peers.
This transaction continues through the network until it is propagated to every connected peer in the network.
Block Broadcasting
A node may broadcast a block using a Block message, in the same manner as broadcasting a transaction.
Block
Send a block to a peer.
Message Name
block
Payload
The serialized bytes of the block.
GetBlocks
A request for blocks with the specified hashes.
Message Name
getblocks
Payload
| Parameter | Type | Description |
|---|---|---|
block_hashes |
array | A list of hashes of blocks to request |
GetMemoryPool
A request for a peer's memory pool transactions.
Message Name
getmemorypool
Payload
None
GetPeers
A request for a list of the peer's connected peer addresses.
Message Name
getpeers
Payload
None
GetSync
A request for knowledge of specified block locator hashes.
Message Name
getsync
Payload
| Parameter | Type | Description |
|---|---|---|
block_locator_hashes |
array | A list of block hashes describing the state of the requester's chain |
MemoryPool
A response to a GetMemoryPool request.
Message Name
memorypool
Payload
| Parameter | Type | Description |
|---|---|---|
transactions |
array | A list of serialized memory pool transactions |
Peers
A response to a GetPeers request.
Message Name
peers
Payload
| Parameter | Type | Description |
|---|---|---|
addresses |
array | A list of listening addresses of connected peers |
Ping
A message used to check if a peer is active and calculate their RTT.
Message Name
ping
Payload
| Parameter | Type | Description |
|---|---|---|
block_height |
number | The current height of the chain |
Pong
A response to a Ping request.
Message Name
pong
Payload
None
Sync
A response to a GetSync message.
Message Name
sync
Payload
| Parameter | Type | Description |
|---|---|---|
block_hashes |
array | A list of block hashes to share with the requester |
SyncBlock
A response to a GetBlock request.
Message Name
syncblock
Payload
| Parameter | Type | Description |
|---|---|---|
data |
bytes | The serialized bytes of the requested block |
Transaction
A transaction sent by a peer.
Message Name
transaction
Payload
| Parameter | Type | Description |
|---|---|---|
data |
bytes | The serialized bytes of a transaction |
Version
Sent during the handshake.
Message Name
version
Payload
| Parameter | Type | Description |
|---|---|---|
version |
number | The version of the network protocol |
listening_port |
number | The node's listening port |
Contributing
How to Update this README
This README is auto-generated during continuous integration. To update this README, submit a pull request updating the appropriate Markdown file in documentation and the configuration file.