fix nil pointer when block does not exist

[ysk49]

This PR fixes the following thing:

When block does not exist, hash = block.Hash() will cause a panic.

internal/ethapi/api.go

// GetRawHeader retrieves the RLP encoding for a single header.
func (api *DebugAPI) GetRawHeader(ctx context.Context, blockNrOrHash rpc.BlockNumberOrHash) (hexutil.Bytes, error) {
	var hash common.Hash
	if h, ok := blockNrOrHash.Hash(); ok {
		hash = h
	} else {
		block, err := api.b.BlockByNumberOrHash(ctx, blockNrOrHash)
		if err != nil {
			return nil, err
		} 
                hash = block.Hash()
	}
	...
}

[jwasinger]

If the block body doesn't exist, an error will be returned: https://github.com/ethereum/go-ethereum/blob/master/eth/api_backend.go#L178

[s1na]

I guess you are using ethclient for this and don't handle when a block is nil. But in most of the JSON-RPC API if an item does not exist the server returns nil. It is the same e.g. in eth_getBlockByNumber.

[MariusVanDerWijden]

While I think that this PR is on the wrong track, the issue you're reporting is correct. I would fix it in the following way:

diff --git a/internal/ethapi/api.go b/internal/ethapi/api.go
index d9cec560ea..bdc1fea381 100644
--- a/internal/ethapi/api.go
+++ b/internal/ethapi/api.go
@@ -1711,6 +1711,9 @@ func (api *DebugAPI) GetRawReceipts(ctx context.Context, blockNrOrHash rpc.Block
                if err != nil {
                        return nil, err
                }
+               if block == nil {
+                       return nil, fmt.Errorf("block #%v not found", blockNrOrHash)
+               }
                hash = block.Hash()
        }
        receipts, err := api.b.GetReceipts(ctx, hash)

Please fix all four occurrences in internal/ethapi/api.go

[rjl493456442]

I think we should fix the b.BlockByNumber, by returning the error if the required block is not existent

[ysk49]

@rjl493456442
Thank you for reviewing.
I was thinking the same thing, so I'll fix it to what you said.

[ysk49]

The following GetBlockByNumber function is used in several places, but only b.BlockByNumber did not implement error handling when block is nil.

https://github.com/ethereum/go-ethereum/blob/master/eth/api_backend.go#L146

So I think we also should fix the b.BlockByNumber, by returning the error if the required block is not existent.
And I'll remake the branch and PR to do it.

func (bc *core.BlockChain) GetBlockByNumber(number uint64) *types.Block