multivm/sputnikvm.RequireBlockhash: ensure block exists in db

[whilei]

Fixes

panic: runtime error: invalid memory address or nil pointer dereference                                   
[signal SIGSEGV: segmentation violation code=0x1 addr=0x0 pc=0xaa0fa7]                                    

goroutine 188627 [running]:                          
sync/atomic.(*Value).Load(...)                       
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/core/types/block.go:398                 
github.com/ethereumproject/go-ethereum/core/types.(*Block).Hash(0x0, 0x0, 0x0, 0x0, 0x0)                  
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/core/types/block.go:398 +0x67           
github.com/ethereumproject/go-ethereum/core.ApplyMultiVmTransaction(0xc420427b90, 0xc421808360, 0xc43418aaa0, 0xc42bec9700, 0xc42b1b98c0, 0xc42a789400, 0xc43418a940, 0x160, 0x150, 0x10aa560, ...)                 
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/core/multivm_processor.go:122 +0x20c2   
github.com/ethereumproject/go-ethereum/core.(*StateProcessor).Process(0xc4217d23c0, 0xc433af3b00, 0xc42bec9700, 0x54154a23db5020e, 0x862a8d08c2cd782f, 0x0, 0x0, 0x0, 0x0, 0x0, ...)                                
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/core/state_processor.go:97 +0x45e       
github.com/ethereumproject/go-ethereum/core.(*BlockChain).InsertChain(0xc421808360, 0xc42c6e2000, 0x800, 0x800, 0x0, 0x0, 0x0)                                                                                      
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/core/blockchain.go:1573 +0x1ddc         
github.com/ethereumproject/go-ethereum/eth.(*ProtocolManager).insertChain(0xc420130340, 0xc42c6e2000, 0x800, 0x800, 0x1cc40c0, 0x1cc40c0, 0xc43568d440)                                                             
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/handler.go:181 +0x51                
github.com/ethereumproject/go-ethereum/eth.(*ProtocolManager).(github.com/ethereumproject/go-ethereum/eth.insertChain)-fm(0xc42c6e2000, 0x800, 0x800, 0x0, 0x0, 0x0)                                                
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/handler.go:158 +0x48                
github.com/ethereumproject/go-ethereum/eth/downloader.(*Downloader).importBlockResults(0xc42197c000, 0xc436c16000, 0x1800, 0x1800, 0x0, 0x0)                                                                        
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/downloader/downloader.go:1422 +0x17f
github.com/ethereumproject/go-ethereum/eth/downloader.(*Downloader).processFullSyncContent(0xc42197c000, 0xc428187798, 0x0)                                                                                         
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/downloader/downloader.go:1397 +0x74 
github.com/ethereumproject/go-ethereum/eth/downloader.(*Downloader).(github.com/ethereumproject/go-ethereum/eth/downloader.processFullSyncContent)-fm(0x8, 0x12205f0)                                               
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/downloader/downloader.go:550 +0x2a  
github.com/ethereumproject/go-ethereum/eth/downloader.(*Downloader).spawnSync.func1(0xc430c274e0, 0xc430caaae0, 0xc430bc1a20)                                                                                       
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/downloader/downloader.go:568 +0x51  
created by github.com/ethereumproject/go-ethereum/eth/downloader.(*Downloader).spawnSync                  
        /home/tomek/go/src/github.com/ethereumproject/go-ethereum/eth/downloader/downloader.go:568 +0xc7

from #585

[tzdybal]

This is a cure only for symptom, not for the cause ;)

But I guess that replicating logic from default EVM is the right way to go.

[sorpaas]

On this line (https://github.com/ethereumproject/go-ethereum/pull/586/files#diff-77eb77f8c5d169125764797d711f0d5eR123) you'll need to commit an empty blockhash even when the block is not found. Otherwise the client will stuck in a loop trying to fetch the next blockhash.

[sorpaas]

lgtm

[whilei]

Thanks @sorpaas :)