Blockchain + MongoDB = BlockchainDB, aka blockchain-db

blockchain-db is Blockchain's implementation. It uses MongoDB as a database management system to store blocks' metadata. Other interesting technical details such as merkle tree, nonce, difficulty, and transactions are also implemented and documented in the source code.

It is done for the most part. Below are ideas for future implementations.

• Model Bitcoin's blockchain structure
• Implement Proof of Work, nonce, difficulty
• Enable transactions
• Implement Merkle Tree
• Introduce mining mechanics
• Introduce block reward
• Remember elapsed time and hash power metrics for later analytics
• Expose RESTful APIs, with simple UI
• Store the full chain in mongodb

• Dockerize the project
• Introduce networking with multiple nodes. For now, it only works with one node, which is the local host
• Introduce Wallet
• Introduce Attack

• Files and structure
  • blockchain_db.py
    • Block structure
    • Methods
    • GET methods
  • blockchain_db_server.py
    • APIs
• Usage
  • With networking
  • Without networking

This file contains the main BlockchainDB logic. I am using pymongo to connect with mongodb database named blockchain and the block collection. Whenever a new bock is mined, it will write to the database.

block = {
    "previous_block": <str>,
    'height': <int>,
    'timestamp': <unix time>,
    'transactions': <list>,
    "merkle_root": <str>,
    'number_of_transaction': <int>,
    'nonce': <int>,
    'previous_hash': <str>,
    'block_reward': <int>,
    'difficulty_bits': <int>,
    'difficulty': <int>,
    'elapsed_time': <int>,
    'hash_power': <int>
}

Here are the main methods. Details are well documented in doctrings.

• generate_genesis_block()
• generate_next_block(nonce, previous_hash=None)
• add_transaction(sender, recipient, amount)
• find_merkle_root(transaction_ids)
• mine_for_next_block()
• calculate_nonce(last_block, number_of_bits)
• calculate_block_reward()
• calculate_difficulty_bits()
• calculate_difficulty()
• hash_json_object(json_object)
• hash_string_pair(string_1, string_2)

• get_length()
• get_last_n_blocks(number)
• get_top_blocks(state, number)
• get_last_block()
• get_genesis_block()
• get_block(height)
• get_all_blocks()
• get_transaction_ids()

This file uses Flask to serve as a web page.

• In src, start blockchain_db_server.py and visit localhost:5000
• Hit /reset endpoint to create a genesis block. This endpoints can also be used to drop the database and start over whenever you want to.
• Mine some number of blocks at /mine/<int:number>
• Use available /view endpoints as mentioned above for more details.

• Use blockchain_db_test.py to create an instance of BlockchainDB to mine some blocks.
• Execute reset() only once when you start to drop the old database and create a genesis block.
• Comment it out after the second run and try to mine some blocks with the provided testing script.
• Similar to the first option, start blockchain_db_server.py in src to serve as a web page and view the result on the web or just print it using the console.