node/vms/proposervm/API_EXAMPLE.md

ProposerVM GetProposedHeight API

Overview

The GetProposedHeight API endpoint returns the P-Chain height that would be proposed for the next block built on the current preferred block.

Endpoint

/v1/bc/<CHAIN_ID>/proposervm

Method

proposervm.getProposedHeight

Parameters

None

Response

{
  "jsonrpc": "2.0",
  "id": 1,
  "result": {
    "proposedHeight": 12345
  }
}

Where:

• proposedHeight (uint64): The P-Chain height that would be used for the next block

Example Usage

cURL

curl -X POST --data '{
    "jsonrpc":"2.0",
    "id"     :1,
    "method" :"proposervm.getProposedHeight",
    "params" :{}
}' -H 'content-type:application/json;' http://127.0.0.1:9650/v1/bc/C/proposervm

Response

{
  "jsonrpc": "2.0",
  "result": {
    "proposedHeight": 12345
  },
  "id": 1
}

Implementation Details

The proposed P-Chain height is calculated as:

proposedHeight = max(currentPChainHeight, parentPChainHeight)

Where:

• currentPChainHeight is obtained from the validator state
• parentPChainHeight is the P-Chain height of the preferred block

This ensures monotonic increases in P-Chain height across the blockchain.

Use Cases

1. Block Building Prediction: Determine the P-Chain height that will be used before building a block
2. Validator Set Queries: Know which validator set will be active for the next block
3. Network Monitoring: Track P-Chain height synchronization across chains
4. Testing & Debugging: Verify P-Chain height selection logic