Blockchain

This is the documentation of Blockchain a simple implementation in Python to get familiar with Python and the basic concepts of Blockchains.

Short Disclaimer: It is just a private Python 3.7.2 project. Its purposes is to get a little bit familiar with the Python projects and the concepts of Blockchains. Therefore it is not intended for production usage, and any warranties are excluded.

Getting Started

The easiest way to get up a single miner or a whole blockchain network is to use Docker. This repository offers the needed Dockerfile and docker-compose.yaml in the directory docker. Do the following steps:

1. Change to docker directory
2. Run docker build --no-cache -t blockchain .
3. Run docker-compose up

This starts a Blockchain network with 3 miners and forwards their ports (12345, 12346, 12347) to your host system. It uses the directory ~/.blockchain/ on your host system to save the created files for each miner.

Install the CLI Locally

1. Clone this repository: git clone git@github.com:se-jaeger/blockchain.git
2. Open the clone directory: cd blockchain
3. Create a virtual env: python -m venv venv
4. Activate the virtual env: source venv/bin/activate
5. Install all dependencies: pip install -r requirements.txt
6. Install the blockchain CLI, run the following in the root directory of this project: pip install -e .
7. Check available commands: blockchain --help

How Does This Blockchain Implementation Work?

This implementation produces a simple CLI, Miner and UI. It is necessary to get up and running a local Miner. The CLI, as well as the UI, uses the Miners REST interface to interact with it. Created messages get synchronized with all other known Miners (neighbours) in the Blockchain network. A Miner asks all its neighbours periodically (if not max amount of neighbours is reached) to send unknown Miner and connects to them. Also in a periodical manner, Miner synchronizes their local Blockchain with the chains of there neighbours and use the longest valid chain in the network.

Miner Implementation

This Miner implementation offers a REST API with the following endpoints:

• /add (PUT): needs the URL parameter message. Adds the message to the local cache of unprocessed data.

  • response (200): JSON with message: ‘Message added!’
  • response (400): JSON with message: ‘No Message added!’

• /chain (GET): Returns the miners local chain.

  • response (200): JSON with the actual chain and its length.

• /neighbours (GET): Returns the miners neighbours.

  • response (200): JSON with the actual neighbours and its length.

• /data (GET): Returns the miners local cache of unprocessed data.

  • response (200): JSON with the actual list of unprocessed data.

The miner uses a set of files for normal operation:

• <filename>.chain: Representation of the actual file.
• <filename>.hash: SHA-256 of the actual chain file. Is used to check if the local chain differs from its on disc representation.
• <filename>_<date>_<time>: Older versions of the chain file. Created at <date>_<time>.
• miner.log: Log file and up to three backup files named miner.log.x where x is a number.

The Miner runs several Threads and a Process to run parallel and periodical tasks:

• Gossip Job (Thread): Implementation of a simple Gossip Protocol. Fetches periodical all neighbours of its neighbours.
• Sync Chain Job (Thread): To get the actual longest global chain. Fetches periodical the chain of all neighbours.
• Sync Unprocessed Data Job (Thread): To propagate unprocessed data through the network. Fetches periodical the set of unprocessed data of all neighbours.
• Backup Local Chain Job (Thread): To backup the local chain to disc. Backups periodical the local chain to disc if they differ from each other.
• Server Process (Process): Servers the Miners REST API in a separate process.
• Communication Job (Thread): Communication thread to exchange message with the server process.

Web-based User Interface

The CLI offers a subcommand ui, this allows to start an webserver for convenient interaction with the blockchain system.

Proof of Work

A very simple implementation of a Proof of Work algorithm. The SHA-256 hash value of the concatenation of the previous proof and the proof of the new Block has to start with difficulty trailing 0s.

Improvements

• Miner endpoint (health) to check availability and provide opportunity to delete a neighbour
• More Error handling -> chain probably gets corrupt when killing miner
• Use locking for (chain, neighbours, data)

Contents

License

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Contributors

• Sebastian Jäger <se.jaeger@web.de>

Changelog

Version 0.1

• Implement core functionality

Version 0.2

• Implement Web-based user interface

src

blockchain package

Subpackages

blockchain.blockchain package

Submodules

blockchain.blockchain.block module

class blockchain.blockchain.block.Block(index: int, data: blockchain.blockchain.data.Data, proof: int, previous_hash: str)

Bases: object

__bytes__() → bytes

Uses the encoded string representation of this Block object as bytes representation.

Returns:byte representation of Block object. Return type:bytes

__eq__(other: object) → bool

Method for comparing two Block objects.

Parameters:other (Block) – Block object to compare with self. Returns:True if blocks are equal. False otherwise. Return type:bool

__repr__() → str

String representation of Block object.

Returns:String representation of Block object. Return type:str

data

index

previous_hash

proof

timestamp

blockchain.blockchain.blockchain module

class blockchain.blockchain.blockchain.Blockchain(path_to_chain: str, json_format: bool, force_new_chain: bool)

Bases: object

_load_chain() → None

Helper method to load chain from disk. Raises an error if no chain is found.

Raises:ChainNotFoundError – Will be raised if no local chain could be found.

add_new_block(data: blockchain.blockchain.data.Data, proof: int, previous_hash: str) → blockchain.blockchain.block.Block

Adds a new Block to the existing chain.

Parameters:

• data (Data) – Data that is attached to this block.
• proof (int) – The proof value for this block.
• previous_hash (str) – Hash value of previous block in chain.

chain

genesis_block = | ================================================================================ | index: 0 | time: 1581268484.244806 | proof: None | prev. hash: None | __________________________________________________________________ | data: | id: 324dc066e690437fa68e8afc810e9617 | | message: This is the workload of the very first Block in this chain! | _________________________________________________________________ | ================================================================================

genesis_block_hash = 'c0f0de3647e32b3b129e4ca3c329dd7584fa375366106b4c22c31c55f8c1ab94'

json_format

last_block

path_to_chain

save_chain() → None

Helper method to save chain to disk. Creates intermediate directories and backups an existing chain file if necessary.

blockchain.blockchain.data module

class blockchain.blockchain.data.Data(message: str)

Bases: object

__hash__()

Needed to use Set``s of ``Data objects.

id

message

Module contents

blockchain.cli package

Submodules

blockchain.cli.cli module

Module contents

blockchain.client package

Submodules

blockchain.client.miner module

class blockchain.client.miner.Miner(path_to_chain: str, json_format: bool, port: int, difficulty: int, neighbours: list, force_new_chain: bool)

Bases: object

_backup_local_chain() → None

Periodical thread to backup the local chain to disc.

_check_for_longest_chain() → None

Consensus Algorithm:

Ask each neighbour for that neighbours. Add all unknown miner to neighbours set until maximum amount of neighbours is reached.

_communicate() → None

Periodical thread to communicate with server process.

_fetch_unprocessed_data() → None

Periodical thread to get unprocessed data form neighbours. => Broadcasts unprocessed data around the network.

static _hash(block: blockchain.blockchain.block.Block) → str

Hash a Block object with SHA-256.

Parameters:block (Block) – Object of class Block to hash. Returns:Hex representation of block hash. Return type:str Raises:ValueError – Will be raised if no Block object is passed.

_is_chain_valid(chain: list = None) → bool

Checks if the given chain satisfies the following rules:

1. The first (genesis) block:

   • index = 0
   • previous_hash = None
   • proof = None

2. each and every following block:

   • index: step size 1 and monotonically increasing (1, 2, 3, 4, …)
   • previous_hash: SHA-256 of the string representation of the preceding block
   • proof: has to be valid -> see: is_proof_of_work_valid()
   • timestamp: higher than the timestamp of of preceding block

Parameters:chain (list) – Optional chain if None internal representation is used. Returns:True if chain is valid, False otherwise. Return type:bool

_is_data_processed(data: blockchain.blockchain.data.Data) → bool

Checks if data is already in local chain.

Parameters:data (Data) – Data object to check if it exists in the actual chain. Returns:True if unprocessed. Return type:bool

static _is_proof_of_work_valid(last_proof: int, proof: int, difficulty: int) → bool

Checks if the proof of work was correct. The hash value of last_proof concatenated with proof has to be difficulty trailing 0s.

Parameters:

• last_proof (int) – Value of the proof of the preceding block.
• proof (int) – proof of the actual block.
• difficulty (int) – Amount of trailing 0s.

Returns:

True if proof of work is correct, False otherwise.

Return type:

bool

Raises:

ValueError – Will be raised if difficulty is not a positive integer value.

_mine() → None

Blocking Mining loop.

If not_processed_messages are available it uses a random message an mines a new block.

_new_message(message: str) → None

Adds the new message to its local cache.

Parameters:message (str) –

_proof_of_work(last_proof: int, difficulty: int) → int

Simple proof of work:

Find a number p that when hashed with the previous block’s solution a hash with difficulty trailing 0s is produced.

Parameters:

• last_proof (int) – Solution of the last blocks’ proof of work
• difficulty (int) – Amount of trailing 0s for a valid proof of work.

Returns:

Solution for this proof of work quiz.

Return type:

int

Raises:

ValueError – Will be raised if difficulty is not a positive integer value.

_update_neighbours() → None

Periodical thread to update neighbours if limit is not exceeded.

blockchain

difficulty

jobs

neighbours

port

queue

server_process

start() → None

Starts some background Job s for the Gossip Protocol, Chain syncing, Data syncing, communication thread as well as the server functionalities as process. Starts the blocking function mine().

stop() → None

Function that gets called when Python was killed. Takes care to shutting down all threads/process and saves the chain to disc.

unprocessed_data

blockchain.client.server module

blockchain.client.server.start_server(queue: multiprocessing.context.BaseContext.Queue, port: int)

Module contents

blockchain.ui package

Submodules

blockchain.ui.forms module

blockchain.ui.routes module

Module contents

blockchain.utils package

Submodules

blockchain.utils.constants module

blockchain.utils.errors module

exception blockchain.utils.errors.ChainNotFoundError

Bases: Exception

Error if no local chain could be found.

exception blockchain.utils.errors.ChainNotValidError

Bases: Exception

Error if loaded chain is not valid.

exception blockchain.utils.errors.PortValueError

Bases: ValueError

Error if given port is out af valid range (1 - 65535).

exception blockchain.utils.errors.ProgramKilledError

Bases: Exception

Error if process get killed.

blockchain.utils.utils module

class blockchain.utils.utils.Job(interval: datetime.timedelta, execute, *args, **kwargs)

Bases: threading.Thread

run() → None

Runs the background Job

stop() → None

Stops the background Job.

blockchain.utils.utils.colorize(text: str, color: str) → str

blockchain.utils.utils.create_proper_url_string(host_port: (<class 'str'>, <class 'int'>), path: str) → str

Takes the internal representation of neighbours and a endpoint path to create a proper URL string for requests.

Parameters:

• host_port (str, int) – Internal representation of IP address/hostname and port combination.
• path (str) – The endpoint of the API.

Returns:

Correct URL string for address and path.

Return type:

str

blockchain.utils.utils.encode_file_path_properly(file_path: str) → str

Encode each and every input filepath as absolute pathes.

Parameters:file_path (str) – Path to encode properly Returns:Absolute and properly encoded file_path Return type:str

blockchain.utils.utils.signal_handler(signum, frame)

Signal handler used to raise special ProgramKilledError.

Raises:ProgramKilledError – To intercept for graceful shutdown.

blockchain.utils.utils.split_url_string(host_port: str) -> (<class 'str'>, <class 'int'>)

Parses the given URL string and returns the IP address/hostname and the port/default port.

Parameters:

host_port (str) – Representation of the miner as URL string, e.g.: 127.0.0.1:12345, miner1:8888, miner, http://localhost, …

Returns:

Tuple of IPv4 Address or hostname string and port number.

Return type:

(str, int)

Raises:

• PortValueError – Will be raised if given port is out of range.
• AddressValueError – Will be raised if given address is not a valid IPv4 address or “localhost”.

Module contents

Module contents

Indices and tables

• Index
• Module Index
• Search Page