btcchain

Package btcchain implements bitcoin block handling and chain selection rules. The test coverage is currently only around 60%, but will be increasing over time. See test_coverage.txt for the gocov coverage report. Alternatively, if you are running a POSIX OS, you can run the cov_report.sh script for a real-time report. Package btcchain is licensed under the liberal ISC license.

There is an associated blog post about the release of this package here.

This package is one of the core packages from btcd, an alternative full-node implementation of bitcoin which is under active development by Conformal. Although it was primarily written for btcd, this package has intentionally been designed so it can be used as a standalone package for any projects needing to handle processing of blocks into the bitcoin block chain.

Documentation

Full go doc style documentation for the project can be viewed online without installing this package by using the GoDoc site here: http://godoc.org/github.com/conformal/btcchain

You can also view the documentation locally once the package is installed with the godoc tool by running godoc -http=":6060" and pointing your browser to http://localhost:6060/pkg/github.com/conformal/btcchain

Installation

$ go get github.com/conformal/btcchain

Bitcoin Chain Processing Overview

Before a block is allowed into the block chain, it must go through an intensive series of validation rules. The following list serves as a general outline of those rules to provide some intuition into what is going on under the hood, but is by no means exhaustive:

• Reject duplicate blocks
• Perform a series of sanity checks on the block and its transactions such as verifying proof of work, timestamps, number and character of transactions, transaction amounts, script complexity, and merkle root calculations
• Compare the block against predetermined checkpoints for expected timestamps and difficulty based on elapsed time since the checkpoint
• Save the most recent orphan blocks for a limited time in case their parent blocks become available
• Stop processing if the block is an orphan as the rest of the processing depends on the block's position within the block chain
• Perform a series of more thorough checks that depend on the block's position within the block chain such as verifying block difficulties adhere to difficulty retarget rules, timestamps are after the median of the last several blocks, all transactions are finalized, checkpoint blocks match, and block versions are in line with the previous blocks
• Determine how the block fits into the chain and perform different actions accordingly in order to ensure any side chains which have higher difficulty than the main chain become the new main chain
• When a block is being connected to the main chain (either through reorganization of a side chain to the main chain or just extending the main chain), perform further checks on the block's transactions such as verifying transaction duplicates, script complexity for the combination of connected scripts, coinbase maturity, double spends, and connected transaction values
• Run the transaction scripts to verify the spender is allowed to spend the coins
• Insert the block into the block database

Block Processing Example

The following example program demonstrates processing a block. This example intentionally causes an error by attempting to process a duplicate block.

	package main

	import (
		"fmt"
		"github.com/conformal/btcchain"
		"github.com/conformal/btcdb"
		_ "github.com/conformal/btcdb/sqlite3"
		"github.com/conformal/btcutil"
		"github.com/conformal/btcwire"
		"os"
	)

	func main() {
		// Create a new database to store the accepted blocks into.  Typically
		// this would be opening an existing database, but we create a new db
		// here so this is a complete working example.  Also, typically the
		// calls to os.Remove would not be used either, but again, we want
		// a complete working example here, so we make sure to remove the
		// database.
		dbName := "example.db"
		_ = os.Remove(dbName)
		db, err := btcdb.CreateDB("sqlite", dbName)
		if err != nil {
			fmt.Printf("Failed to create database: %v\n", err)
			return
		}
		defer os.Remove(dbName) // Ignore error.
		defer db.Close()

		// Insert the main network genesis block.  This is part of the initial
		// database setup.  Like above, this typically would not be needed when
		// opening an existing database.
		genesisBlock := btcutil.NewBlock(&btcwire.GenesisBlock)
		_, err = db.InsertBlock(genesisBlock)
		if err != nil {
			fmt.Printf("Failed to insert genesis block: %v\n", err)
			return
		}

		// Create a new BlockChain instance using the underlying database for
		// the main bitcoin network and ignore notifications.
		chain := btcchain.New(db, btcwire.MainNet, nil)

		// Process a block.  For this example, we are going to intentionally
		// cause an error by trying to process the genesis block which already
		// exists.
		err = chain.ProcessBlock(genesisBlock)
		if err != nil {
			fmt.Printf("Failed to process block: %v\n", err)
			return
		}
	}

TODO

• Increase test coverage
• Expose some APIs for block verification (without actually inserting it)

GPG Verification Key

All official release tags are signed by Conformal so users can ensure the code has not been tampered with and is coming from Conformal. To verify the signature perform the following:

• Download the public key from the Conformal website at https://opensource.conformal.com/GIT-GPG-KEY-conformal.txt

• Import the public key into your GPG keyring:

  gpg --import GIT-GPG-KEY-conformal.txt
  

• Verify the release tag with the following command where TAG_NAME is a placeholder for the specific tag:

  git tag -v TAG_NAME
  

License

Package btcchain is licensed under the liberal ISC License.