Reth's stage-based sync format not supported, leads to NaN sync percentage

[segunjkf]

Problem

The metrics exporter doesn't properly handle Reth's stage-based sync status format, resulting in sync percentage showing as NaN and incorrect sync blocks.

Current Output

When using Reth, the /metrics endpoint shows:

eth_exe_sync_current_block{ethereum_role="execution",module="sync",node_name="execution"} 0
eth_exe_sync_highest_block{ethereum_role="execution",module="sync",node_name="execution"} 0
eth_exe_sync_percentage{ethereum_role="execution",module="sync",node_name="execution"} NaN
eth_exe_sync_is_syncing{ethereum_role="execution",module="sync",node_name="execution"} 1

How to Reproduce

• Run metrics exporter with Reth as execution client
• Check eth_syncing RPC endpoint response from Reth:

curl -X POST -H "Content-Type: application/json" --data '{"jsonrpc":"2.0","method":"eth_syncing","params":[],"id":1}' http://localhost:8545

Reth returns stage-based format:

{
  "result": {
    "stages": [
      {
        "name": "Headers",
        "block": "0x2f22e5"  // Target block
      },
      {
        "name": "Bodies",
        "block": "0xbb418"   // Current progress
      },
      {
        "name": "Execution",
        "block": "0x0"
      }
    ]
  }
}

• Observe that sync percentage shows as NaN in /metrics output

Additional Context

Reth also exposes sync progress via its own metrics:

prometheusCopyreth_sync_checkpoint{stage="Headers"} 3088189
reth_sync_checkpoint{stage="Execution"} 1011014

This could be an alternative data source for calculating sync progress.

Environment

• ethereum-metrics-exporter: 0.26.0-debian
• Reth: v1.1.4
• Network: Holesky