Event Decoding Functions
Mirror provides two custom functions which can be in used within transforms to decode raw contract events during processing: _gs_fetch_abi
and _gs_evm_decode
_gs_evm_decode
This function can decode data given a json string representing the ABI string. Since it is stateless, and will scale very well across different pipeline sizes.
It will automatically use the matching event in the ABI, but partial ABIs that only contain the target event will also work.
_gs_evm_decode(string abi, string topics, string data)
Params
A string representing a json array of events and functions
Name of the column the dataset which contains a string containing the topics, comma separated.
Name of the column the dataset which contains a string containing the payload of the event.
Return
The function will output a nested ROW type with event_param::TEXT[]
and event_signature::TEXT
. If you’re planning on using a sink that doesn’t support nested ROWs, you may want to do a further transformation to unnest the result.
Examples
If you were using the Raw Logs source dataset, you would call this function passing your ABI and using the ‘topics’ and ‘data’ columns. For example:
SELECT
_gs_evm_decode('[
{
"anonymous": false,
"inputs": [
{
"indexed": true,
"name": "src",
"type": "address"
},
{
"indexed": true,
"name": "dst",
"type": "address"
},
{
"indexed": false,
"name": "wad",
"type": "uint256"
}
],
"name": "Transfer",
"type": "event"
}
]', `topics`, `data`) as decoded
from base.raw_logs
You would then able to access both topics and data from the decoded column as decoded.event_params
and decoded.event_signature
in a second transform. See below for a complete example pipeline.
_gs_fetch_abi
We provide a convenient function for fetching ABIs, as often they are too big to copy and paste into the yaml definition.
_gs_fetch_abi(string url, string type)
Params
The URL from where the ABI will be fetched
The type of url. Two types of value are accepted:
etherscan
for etherscan or etherscan-compatible APIsraw
for json array ABIs.
If you use etherscan-compatible APIs it’s highly recommended to include your own API key if you are using this function with a large pipeline. The amount of workers may result in the API limits being surpassed.
Examples
Following up on the previous example, we can replace the raw ABI definition by a call to basescan using the _gs_evm_decode function:
select
# Call the EVM decoding function
_gs_evm_decode(
# This fetches the ABI from basescan, a `etherscan` compatible site.
_gs_fetch_abi('https://api.basescan.org/api?module=contract&action=getabi&address=0xcf205808ed36593aa40a44f10c7f7c2f67d4a4d4', 'etherscan'),
`topics`,
`data`
) as `decoded`,
from base.raw_logs
In some cases, you may prefer to host the ABI yourself and retrieve it from your a separate server such as Github Gist:
select
# Call the EVM decoding function
_gs_evm_decode(
# This fetches the ABI from Github Gist
_gs_fetch_abi('https://gist.github.com/JavierTrujilloG/bde43d5079ea5d03edcc68b4516fd297', 'raw'),
`topics`,
`data`
) as `decoded`,
from base.raw_logs
Pipeline Example
Below is an example pipeline definition for decoding events for Friendtech contract in Base, make sure to visit this guide for a more in-depth explanation of this pipeline:
sources:
- type: dataset
referenceName: base.raw_logs
version: 1.0.0
transforms:
- referenceName: friendtech_decoded
type: sql
primaryKey: id
# Fetch the ABI from basescan, then use it to decode from the friendtech address.
sql: >
select
`id`,
_gs_evm_decode(
_gs_fetch_abi('https://api.basescan.org/api?module=contract&action=getabi&address=0xcf205808ed36593aa40a44f10c7f7c2f67d4a4d4', 'etherscan'),
`topics`,
`data`
) as `decoded`,
block_number,
transaction_hash
from base.raw_logs
where address='0xcf205808ed36593aa40a44f10c7f7c2f67d4a4d4'
- referenceName: friendtech_clean
primaryKey: id
type: sql
# Clean up the previous transform, unnest the values from the `decoded` object.
sql: >
select
`id`,
decoded.event_params as `event_params`,
decoded.event_signature as `event_signature`,
block_number,
transaction_hash
from friendtech_decoded
where decoded is not null
sinks:
- referenceName: friendtech_events
secretName: EXAMPLE_SECRET
type: postgres
sourceStreamName: friendtech_clean
schema: decoded_events
table: friendtech
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