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Node

The Node Implementation

A node is ran as a REST API using the FastAPI web framework, and is attributed a UUID at startup.

Each node stores a full blockchain, the current transactions (to be written in the next block), and the list of other nodes registered in the network. Each node's blockchain is a BlockChain object from the toychain.blockchain module.

A node can:

  • Add a transaction to the list of current transactions,
  • Add a new block to its chain,
  • Run the proof of work algorithm,
  • Validate the proof of a block,
  • Register other nodes on the network,
  • Infer an arbitrary node's blockchain's validity,
  • Resolve conflict through a consensus algorithm, checking all nodes' chains in the network and adopting the longest valid one.
What endpoints are available for those actions?
  • GET endpoint /mine to trigger the addition of a new block to the chain,
  • POST endpoint /transactions/new to add a transaction to the node's list,
  • GET endpoint /chain to pull the full chain,
  • POST endpoint /nodes/register to register other nodes' addresses as part of the network,
  • GET endpoint /nodes/resolve: to trigger a run of the consensus algorithm and resolve conflicts: the longest valid chain of all nodes in the network is used as reference, replacing the local one, and is returned.
How do I remember these?

Once the server is running, FastAPI serves an automated documentation at the /docs and /redoc endpoints. So if your node is running at localhost:5000, head over to localhost:5000/docs for instance. If you simply head to localhost:5000, you'll get a hint on where to go ;)

Interacting with a Node

Let's consider our node is running at localhost:5000. Here's how to POST a transaction to the node's transactions/new endpoint with either cURL, HTTPie or Wget:

curl --request POST \
  --url http://localhost:5000/transactions/new \
  --header 'content-type: application/json' \
  --data '{
 "sender": "d4ee26eee15148ee92c6cd394edd974e",
 "recipient": "someone-other-address",
 "amount": 5
}'

echo '{
  "sender": "d4ee26eee15148ee92c6cd394edd974e",
  "recipient": "someone-other-address",
  "amount": 5
}' | http POST http://localhost:5000/transactions/new

wget -qSO- \
--header='Content-Type: application/json' \
--post-data='{
  "sender": "d4ee26eee15148ee92c6cd394edd974e",
  "recipient": "someone-other-address",
  "amount": 5
}' http://localhost:5000/transactions/new

Let's now consider that we have started a second node at localhost:5001. POSTing a payload to register this new node to the first one's network would be done as follows:

curl --request POST \
  --url http://localhost:5000/nodes/register \
  --header 'content-type: application/json' \
  --data '{
 "nodes": ["http://127.0.0.1:5001"]
}'

echo '{
  "nodes": ["http://127.0.0.1:5001"]
}' | http POST http://localhost:5000/nodes/register

wget -qSO- \
--header='Content-Type: application/json' \
--post-data='{
  "nodes": ["http://127.0.0.1:5001"]
}' http://localhost:5000/nodes/register