Simple Substreams Example

The BlockStats Susbtreams is a very basic Substreams, extracting data from the Injective blockchain.

Tip: This tutorial teaches you how to build a Substreams from scratch.

Remember that you can auto-generate your Substreams module by usig the code-generation tools.

Before You Begin

• Install the Substreams CLI

• Get an authentication token

• Learn about the basics of the Substreams

Clone the BlockStats Substreams GitHub repository and open it in an IDE of your choice (for example, VSCode).

Inspect the Project

Every Substreams project contains three main pieces:

• The Protobuf definitions: the outputs of your Substreams, which you define through Protobuf schemas.

• The source code: the Rust functions that extract the actual data from the blockchain.

• The Substreams manifest: the substreams.yaml file contains the configuration of your Substreams.

1. The proto folder contains the Protobuf definitions for the output of your Substreams. In this example, only a BlockStats Protobuf is defined as the output of the Substreams.

2. The src folder contains the source code of the Substreams transformations. Specifically, the lib.rs contains the Rust functions.

3. The substreams.yml is the Substreams manifest, which defines relevant information, such as the inputs/outputs of every module or the Protobuf files.

Take a look at the substreams.yaml file:

network: cosmos # 1.

imports:
  cosmos: https://github.com/streamingfast/substreams-cosmos/releases/download/v0.1.1/cosmos-v0.1.0.spkg # 2.

protobuf:
  files:
    - cosmos/v1/stats/stats.proto # 3.
  importPaths:
    - ./proto

binaries:
  default:
    type: wasm/rust-v1
    file: target/wasm32-unknown-unknown/release/cosmos_block_stats.wasm

modules:
  - name: block_to_stats # 4.
    kind: map
    initialBlock: 64987400
    inputs:
      - source: sf.cosmos.type.v2.Block # 5.
    output:
      type: proto:cosmos.v1.BlockStats # 6.

1. The network field specifies which network is the Substreams going to be executed on.

2. Import the Cosmos Block Protobuf, which gives you access to the blockchain data.

3. Import the user-defined Protobuf schemas (i.e. the outputs of your Substreams).

4. Define a module. block_to_stats, which will be mapped to the block_to_stats Rust function in the source code.

5. Define the inputs of the module. In this case, the Block Cosmos Protobuf.

6. Define the outputs of the module. In this case, the BlockStats Protobuf, which you imported in #3.

Run the Substreams

1. Build the Rust code:

make build

1. Run the Substreams using the substreams run command of the CLI:

substreams run substreams.yaml block_to_stats \
 -e mainnet.injective.streamingfast.io:443 \
 --start-block=64987400 --stop-block=+1000

• substreams.yaml is the Substreams manifest with the configurations.

• block_to_stats is the name of the module that you want to run (in this Substreams, there only one module).

• -e mainnet.injective.streamingfast.io:443 is the StreamingFast (Substreams provider) endpoint that will read execute the Substreams and stream back the data.

• --start-block=64987400 --stop-block=+1000 defines the start and stop block (start at block 64987400 and finish at block 64987500, 100 blocks later).

1. The substreams run displays the data extract at every block linearly, so it might be difficult to properly read the data if your execution happens through thousands of blocks. The substreams gui allows you to jump between blocks and search content.

substreams gui substreams.yaml block_to_stats \
 -e mainnet.injective.streamingfast.io:443 \
 --start-block=64987400 --stop-block=+1000

Review the GUI Reference to get more information on how to use this utility.

Inspect the Code

The lib.rs file contains the only module defined in this Substreams, block_to_stats.

mod pb;
use crate::pb::sf::cosmos::r#type::v2::Block; // 1.
use crate::pb::cosmos::v1::BlockStats; // 2.
use substreams::errors::Error;

#[substreams::handlers::map]
pub fn block_to_stats(block: Block) -> Result<BlockStats, Error> { // 3.
    let mut stats = BlockStats::default(); // 4.
    let header =  block.header.as_ref().unwrap();
    let last_block_id = header.last_block_id.as_ref().unwrap();

    stats.block_height = block.height as u64; // 5,
    stats.block_hash = hex::encode(block.hash);
    stats.block_time = block.time;
    stats.block_proposer = hex::encode(&header.proposer_address);
    stats.parent_hash = hex::encode(&last_block_id.hash);
    stats.parent_height = block.height - 1i64;

    stats.num_txs = block.txs.len() as u64; // 6.

    Ok(stats) // 7.
}

1. Import the Cosmos Block Protobuf object, which is passed as a parameter.

2. Import the BlockStats Protobuf object, which is the return type of the function. This Rust object is automatically generated from the Protobuf defined in the proto folder.

3. Declaration of the Rust function. Input: Injective block. Output: BlockStats object, which is defined by the user and is consumable from the outside world.

4. Creation of the BlockStats object.

5. Add data from the Block Injective object to user-defined BlockStats object. In this case, the height of the block.

6. Add more data. In this case, the number of transactions contained in the block.