btcd/README.md

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](https://blog.conformal.com/btcchain-the-bitcoin-chain-package-from-bctd/).

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

```bash
$ 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.

```Go
	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"
	)

	func main() {
		// First, we 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.
		db, err := btcdb.CreateDB("sqlite", "example.db")
		if err != nil {
			fmt.Printf("Failed to create database: %v\n", err)
			return
		}
		defer db.Close()

		// 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.
		block := btcutil.NewBlock(&btcwire.GenesisBlock, btcwire.ProtocolVersion)
		err = chain.ProcessBlock(block)
		if err != nil {
			fmt.Printf("Failed to process block: %v\n", err)
			return
		}
	}
```

## TODO

- Increase test coverage
- Profile and optimize
- Expose some APIs for block verification (without actually inserting it) and
  transaction input lookups

## 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:
  ```bash
  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:
  ```bash
  git tag -v TAG_NAME
  ```

## License

Package btcchain is licensed under the liberal ISC License.