Avalanche C-Chain missing method-spec override → eth_baseFee unroutable via nodecore

[pxlvre]

Description

eth_baseFee is an Avalanche C-Chain JSON-RPC extension (Avalanche Builder Hub docs) for reading the base fee of the next block. Calling it through a nodecore instance configured with an avalanche/avalanche-fuji upstream returns:

{"jsonrpc":"2.0","error":{"code":-32601,"message":"the method eth_baseFee does not exist/is not available"},"id":...}

with a response-provider: NoUpstream response header — even though every configured upstream answers the same call correctly when hit directly:

$ curl -s https://api.avax-test.network/ext/bc/C/rpc \
    -H 'Content-Type: application/json' \
    -d '{"jsonrpc":"2.0","method":"eth_baseFee","params":[],"id":1}'
{"jsonrpc":"2.0","id":1,"result":"0xa"}

$ curl -s https://avalanche-fuji-c-chain-rpc.publicnode.com \
    -H 'Content-Type: application/json' \
    -d '{"jsonrpc":"2.0","method":"eth_baseFee","params":[],"id":1}'
{"jsonrpc":"2.0","id":1,"result":"0xa"}

Root cause (confirmed by reading nodecore's source, drpcorg/nodecore @ tag 1.13.0)

nodecore's MethodMatcher (internal/upstreams/flow/matchers.go) only routes a call to an upstream if the method is present in the chain's method spec, resolved via specs.GetSpecMethodsByConnectors(methodSpecName, ...) from this repo. Avalanche's entry in chains.yaml is:

- id: avalanche
  label: Avalanche
  type: eth
  settings:
    expected-block-time: 2s
    ...

There's no method-spec override, so it falls back to the bare eth spec, which has no knowledge of eth_baseFee (an Avalanche-only extension).

This is exactly the situation method-spec overrides exist to solve, and ~18 other EVM chains already use this pattern for their own vendor-specific extension methods. The closest analog is fantom:

- id: fantom
  ...
  settings:
    method-spec: "fantom"

whose fantom.json does "spec-imports": ["eth"] and adds ftm_effectiveBaseFee — Fantom's own base-fee extension, functionally identical to what Avalanche needs for eth_baseFee. Avalanche was simply never given the equivalent spec file, so it inherits only the generic eth method set that every other plain EVM chain gets.

Proposed fix

Opening a PR that:

• adds pkg/methods/specs/avalanche.json (imports eth, adds eth_baseFee as a non-cacheable method — it reflects the next block, so it must never be cached)
• sets method-spec: "avalanche" on Avalanche's chains.yaml entry
• updates docs/method-specs.md's spec table
• adds a TestAvalancheSpecLoads test

mirroring the fantom pattern exactly.

Workaround in the meantime

nodecore's per-upstream methods.enable config (documented in nodecore's docs/nodecore/05-upstream-config.md) already provides an immediate workaround without needing this repo changed, e.g.:

methods:
  enable: [eth_baseFee]

on the avalanche upstream config. This repo-level fix removes the need for that override and matches how every other chain with its own extension methods is already handled.

Environment

• nodecore version: 1.13.0
• Chain: avalanche / avalanche-fuji (Avalanche C-Chain)
• Connector type: json-rpc

[pxlvre]

PR: #274