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app/app.go

@@ -136,7 +136,12 @@ func RequestHandler(req *msg.Request) msg.Response {
 	case msg.ResourceBlock:
 		blockNumber, ok := req.Params["blockNumber"].(uint32)
 		if ok {
-			res.Resource = chain.CopyBlockByIndex(blockNumber)
+			blk, err := chain.CopyBlockByIndex(blockNumber)
+			if err != nil {
+				res.Error = paramErr
+			} else {
+				res.Resource = blk
+			}
 		} else {
 			res.Error = paramErr
 		}

blockchain/blockchain.go

@@ -2,6 +2,7 @@ package blockchain
 
 import (
 	"encoding/gob"
+	"errors"
 	"io"
 )
 
@@ -73,10 +74,13 @@ func (bc *BlockChain) ContainsTransaction(t *Transaction, start, stop uint32) (b
 }
 
 // CopyLocalBlockByIndex returns a copy of a block in the local chain by index.
-func (bc *BlockChain) CopyBlockByIndex(i uint32) *Block {
-	blk := bc.Blocks[i]
-	b := *blk
-	b.Transactions = make([]*Transaction, len(blk.Transactions))
-	copy(b.Transactions, blk.Transactions)
-	return &b
+func (bc *BlockChain) CopyBlockByIndex(i uint32) (*Block, error) {
+	if i >= 0 && i < uint32(len(bc.Blocks)) {
+		blk := bc.Blocks[i]
+		b := *blk
+		b.Transactions = make([]*Transaction, len(blk.Transactions))
+		copy(b.Transactions, blk.Transactions)
+		return &b, nil
+	}
+	return nil, errors.New("block request out of bounds")
 }

blockchain/blockchain_test.go

@@ -27,7 +27,7 @@ func TestEncodeDecodeBlockChain(t *testing.T) {
 
 func TestCopyBlock(t *testing.T) {
 	bc, _ := NewValidTestChainAndBlock()
-	b := bc.CopyBlockByIndex(0)
+	b, _ := bc.CopyBlockByIndex(0)
 
 	if !reflect.DeepEqual(b, bc.Blocks[0]) {
 		t.FailNow()

miner/miner.go

@@ -20,9 +20,9 @@ const (
 	// MiningSuccessful is returned when the miner mines a block.
 	MiningSuccessful = iota
 	// MiningNeverStarted is returned when the block header is invalid.
-	MiningNeverStarted = iota
+	MiningNeverStarted
 	// MiningHalted is returned when the app halts the miner.
-	MiningHalted = iota
+	MiningHalted
 )
 
 // MiningResult contains the result of the mining operation.
@@ -43,7 +43,7 @@ func RestartMiner(bc *blockchain.BlockChain, b *blockchain.Block) {
 func Mine(bc *blockchain.BlockChain, b *blockchain.Block) *MiningResult {
 	setStart()
 	if valid, _ := bc.ValidBlock(b); !valid {
-		log.Error("Invalid block")
+		log.Error("miner given invalid block")
 		return &MiningResult{
 			Complete: false,
 			Info:     MiningNeverStarted,