Search
K

Retrieve Events of a Smart Contract

Given a smart contract address passed as a parameter, this module returns the logs attached to the contract.

Running the Substreams

First, generate the Protobuf modules and build the Rust code:
make protogen
make build
Now, you can run the Substreams. The logs retrieved correspond to the 0xbc4ca0eda7647a8ab7c2061c2e118a18a936f13d (BoredApeYachtClub smart contract). To avoid iterating over the full blockchain, the following command starts at block 17717995 and finished at block 17718004. Therefore, only the BoredApeYachtClub smart contract logs that happened within this block range are printed.
substreams run -e mainnet.eth.streamingfast.io:443 substreams.yaml map_contract_events --start-block 17717995 --stop-block +10
The output of the command should be similar to:
...output omitted...
----------- BLOCK #17,717,995 (bfecb26963a2cd77700754612185e0074fc9589d2d73abb90e362fe9e7969451) ---------------
----------- BLOCK #17,717,996 (7bf431a4f9df67e1d7e385d9a6cba41c658e66a77f0eb926163a7bbf6619ce20) ---------------
----------- BLOCK #17,717,997 (fa5a57231348f1f138cb71207f0cdcc4a0a267e2688aa63ebff14265b8dae275) ---------------
{
"@module": "map_contract_events",
"@block": 17717997,
"@type": "eth.event.v1.Events",
"@data": {
"events": [
{
"address": "bc4ca0eda7647a8ab7c2061c2e118a18a936f13d",
"topics": [
"8c5be1e5ebec7d5bd14f71427d1e84f3dd0314c0f7b2291e5b200ac8c7c3b925",
"000000000000000000000000e2a83b15fc300d8457eb9e176f98d92a8ff40a49",
"0000000000000000000000000000000000000000000000000000000000000000",
"00000000000000000000000000000000000000000000000000000000000026a7"
],
"txHash": "f18291982e955f3c2112de58c1d0a08b79449fb473e58b173de7e0e189d34939"
},
{
"address": "bc4ca0eda7647a8ab7c2061c2e118a18a936f13d",
"topics": [
"ddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef",
"000000000000000000000000e2a83b15fc300d8457eb9e176f98d92a8ff40a49",
"000000000000000000000000c67db0df922238979da0fd00d46016e8ae14cecb",
"00000000000000000000000000000000000000000000000000000000000026a7"
],
"txHash": "f18291982e955f3c2112de58c1d0a08b79449fb473e58b173de7e0e189d34939"
}
]
}
}
----------- BLOCK #17,717,998 (372ff635821a434c81759b3b23e8dac59393fc27a7ebb88b561c1e5da3c4643a) ---------------
----------- BLOCK #17,717,999 (43f0878e119836cc789ecaf12c3280b82dc49567600cc44f6a042149e2a03779) ---------------
----------- BLOCK #17,718,000 (439efaf9cc0059890a09d34b4cb5a3fe4b61e8ef96ee67673c060d58ff951d4f) ---------------
----------- BLOCK #17,718,001 (c97ca5fd26db28128b0ec2483645348bbfe998e9a6e19e3a442221198254c9ea) ---------------
----------- BLOCK #17,718,002 (9398569e46a954378b16e0e7ce95e49d0f21e6119ed0e3ab84f1c91f16c0c30e) ---------------
----------- BLOCK #17,718,003 (80bcd4c1131c35a413c32903ffa52a14f8c8fe712492a8f6a0feddbb03b10bba) ---------------
----------- BLOCK #17,718,004 (d27309ac29fe47f09fa4987a318818c325403863a53eec6a3676c2c2f8c069d9) ---------------
all done
The smart contract address is passed as a parameter defined in the Substreams manifest (substreams.yml):
params:
map_contract_events: "0xbc4ca0eda7647a8ab7c2061c2e118a18a936f13d"

Inspecting the Code

Declaration of the module in the manifest (substreams.yml):
- name: map_contract_events
kind: map
inputs:
- params: string
- source: sf.ethereum.type.v2.Block
output:
type: proto:eth.event.v1.Events
The module expects two inputs: the parameter as a string, and a raw Ethereum block. The output is the Events object defined in the Protobuf.
The corresponding Rust function declaration, which matches the name of the module, map_contract_events:
fn map_contract_events(contract_address: String, blk: Block) -> Result<Events, Error> {
verify_parameter(&contract_address)?; // Verify address
let events: Vec<Event> = blk
.logs() // 1.
.filter(|log| log.address().to_vec() == Hex::decode(&contract_address).expect("already validated")) // 2.
.map(|log| Event { // 3.
address: Hex::encode(log.address()),
topics: log.topics().into_iter().map(Hex::encode).collect(),
tx_hash: Hex::encode(&log.receipt.transaction.hash),
})
.collect(); // 4.
Ok(Events { events })
}
In this example, you do not need to parse the parameters, as contract_address is the only string passed and you can use it directly. However, it is necessary to verify that the parameter is a valid Ethereum; this verification is performed by the verify_parameter function.
Then, you iterate over the events of the contract:
  1. 1.
    The .logs() function iterates over the logs of successful transactions within the block.
  2. 2.
    For every log of a successful transaction, you verify if its address matches the smart contract address (i.e. you verify if the log was actually emitted by the smart contract). For the comparison, both log.address() and contract_address are converted to Vec<u8>.
  3. 3.
    Every filtered log (i.e. every log that belongs to the smart contract) is mapped to a pb::eth::event::v1::Event struct, which was specified in the Protobuf definition.
  4. 4.
    Finally, you collect all the events in a vector.