Merge pull request #56 from keep-network/chain-confirmation-waiter

Add chain confirmation waiter

Added the WaitForChainConfirmation function which provides the 
ability to check the chain state once the chain reaches the given block height.

pkg/chain/ethereum/ethutil/confirmations.go

@@ -0,0 +1,35 @@
+package ethutil
+
+import "fmt"
+
+// BlockHeightWaiter provides the ability to wait for a given block height.
+type BlockHeightWaiter interface {
+	WaitForBlockHeight(blockNumber uint64) error
+}
+
+// WaitForChainConfirmation ensures that after receiving specific number of block
+// confirmations the state of the chain is actually as expected. It waits for
+// predefined number of blocks since the start block number provided. After the
+// required block number is reached it performs a check of the chain state with
+// a provided function returning a boolean value.
+func WaitForChainConfirmation(
+	blockHeightWaiter BlockHeightWaiter,
+	startBlockNumber uint64,
+	blockConfirmations uint64,
+	stateCheck func() (bool, error),
+) (bool, error) {
+	blockHeight := startBlockNumber + blockConfirmations
+	logger.Infof("waiting for block [%d] to confirm chain state", blockHeight)
+
+	err := blockHeightWaiter.WaitForBlockHeight(blockHeight)
+	if err != nil {
+		return false, fmt.Errorf("failed to wait for block height: [%v]", err)
+	}
+
+	result, err := stateCheck()
+	if err != nil {
+		return false, fmt.Errorf("failed to get chain state confirmation: [%v]", err)
+	}
+
+	return result, nil
+}