8. Describe the process that reads from Ethereum blockchain (RPC calls)

Introduction to Ethereum RPC¶

Remote Procedure Calls (RPC) in Ethereum are crucial for reading data from the blockchain. These calls allow applications to query Ethereum nodes, enabling them to access transaction histories, block information, and smart contract states.

The Essence of RPC in Ethereum¶

RPC in Ethereum facilitates direct communication between a client (such as a dApp or wallet) and the Ethereum network. Through RPC, these clients can request specific information from nodes without needing to host the entire blockchain locally.

Ethereum RPC Mechanism¶

How RPC Works¶

Client Request: The client sends a structured RPC request, specifying the method and parameters required.
Node Processing: The Ethereum node receives the request, interprets it, and accesses the relevant blockchain data.
Data Retrieval: The node extracts the requested data from its blockchain database.
Response Delivery: The node sends the data back to the client in a structured format, typically as a JSON object.

Technical Aspects¶

JSON-RPC Protocol: Ethereum uses JSON-RPC, a stateless protocol that communicates via JSON-formatted messages.
Transport Layers: RPC calls can be made over various transport layers, including HTTP, WebSocket, and IPC (Inter-Process Communication).

Key RPC Methods for Reading Blockchain Data¶

`eth_getBlockByNumber`¶

Retrieves comprehensive details of a specified block.
Parameters: Block number (in hexadecimal) and a boolean to indicate if the full transaction details are needed.

`eth_getTransactionByHash`¶

Provides information about a specific transaction identified by its hash.
Parameters: Transaction hash.

Smart Contract Calls (SSCs)¶

SSCs involve RPC calls that read from smart contract storage and return its content. These are simple to execute, often done using tools like Geth.

No Gas Cost: SSCs do not require any gas since they don't alter the blockchain state.
Immediate Response: Clients receive immediate responses from nodes.
Non-Transactional Nature: Calls are read-only and don't change the network state.

Example of SSC: Reading Contract State¶

{
  "jsonrpc": "2.0",
  "method": "eth_call",
  "params": [{
    "to": "0xContractAddress",
    "data": "0xFunctionSelector"
  }, "latest"],
  "id": 1
}

This call reads the state of a smart contract, immediately returning the result without any gas cost.

`eth_getLogs`¶

Fetches logs related to smart contracts, useful for extracting event data.
Parameters: Filter parameters like address, topics, and block range.

`eth_getTransactionCount`¶

Returns the number of transactions sent from an address, useful for nonce management.
Parameters: Address and block number.

Response Handling and Data Interpretation¶

JSON Responses: Ethereum nodes return data in JSON format, which clients need to parse for usable information.
Error Management: Clients must be prepared to handle possible errors in responses, such as invalid parameters or unavailable data.

Best Practices for Efficient RPC Calls¶

Optimized Querying: Minimize the load on nodes by requesting only necessary data.
Caching Mechanisms: Implement caching to reduce redundant queries for frequently accessed data.
Rate Limiting and Node Health: Be aware of rate limits and maintain node health for uninterrupted access.