rpc: eth_getLogs processes the rest of a block with a stale or nil header

[AskAlexSharov]

In getLogsV3 (rpc/jsonrpc/eth_receipts.go:380, main at 52b071b) a nil header skips only the current txNum:

if blockNumChanged {
	if header, err = api._blockReader.HeaderByNumber(ctx, tx, blockNum); err != nil {
		return nil, err
	}
	if header == nil {
		log.Warn("[rpc] header is nil", "blockNum", blockNum)
		continue
	}
}

The iterator reports blockNumChanged only for the first txNum of a block, so the remaining txNums of that block are processed with whatever header holds:

• If an earlier block in the range loaded a header, its hash and time are used: logs come back stamped with the previous block, and TryGetCachedReceipt looks up receipts under the wrong block hash.
• If the nil header is the first one in the range, header is still nil and header.Hash() panics; the call fails with "method handler crashed".

This looks reachable on a standalone rpcdaemon when a block is pruned or reorged away while the request runs. Found in the review of #23963.

Fix: when the header is nil, skip every txNum of that block (for example, remember the skipped block number and continue until it changes), or return an error.

[VBulikov]

yperbasis added Imp2 as Importance