#
Events

Explain how topics and such work

##
Solidity Topics

How to compute the topic...

##
Logs and Filtering

Example hog logs are used.

Link to provider.getLogs and contract.on

###
Filters

Filter are used as a way to query ... efficient, explain bloom filters lightly

A filter may have up to 4 topic-sets, where each topic-set refers to a condition that must match the log topic in that position (i.e. each condition is `AND`-ed together).

If a topic-set is `null`, a log topic in that position is not filtered at all and any value matches.

If a topic-set is a single topic, a log topic in that position must match that topic.

If a topic-set is an array of topics, a log topic in that position must match any one of topics (i.e. the topic in thie position are `OR`-ed).

Topic-Sets | Matching Logs |
[ A ] | topic[0] = A |
[ A, null ] |
[ null, B ] | topic[1] = B |
[ null, [ B ] ] |
[ null, [ B ], null ] |
[ A, B ] | (topic[0] = A) AND (topic[1] = B) |
[ A, [ B ] ] |
[ A, [ B ], null ] |
[ [ A, B ] ] | (topic[0] = A) OR (topic[0] = B) |
[ [ A, B ], null ] |
[ [ A, B ], [ C, D ] ] | [ (topic[0] = A) OR (topic[0] = B) ] AND [ (topic[1] = C) OR (topic[1] = D) ] |
Example Log Matching |

ERC-20 Transfer Filter Examples
// Short example of manually creating filters for an ERC-20 // Transfer event. // // Most users should generally use the Contract API to // compute filters, as it is much simpler, but this is // provided as an illustration for those curious. See // below for examples of the equivalent Contract API. // ERC-20: // Transfer(address indexed src, address indexed dst, uint val) // // -------------------^ // ----------------------------------------^ // // Notice that only *src* and *dst* are *indexed*, so ONLY they // qualify for filtering. // // Also, note that in Solidity an Event uses the first topic to // identify the Event name; for Transfer this will be: // id("Transfer(address,address,uint256)") // // Other Notes: // - A topic must be 32 bytes; so shorter types must be padded // List all token transfers *from* myAddress filter = { address: tokenAddress, topics: [ id("Transfer(address,address,uint256)"), hexZeroPad(myAddress, 32) ] } // List all token transfers *to* myAddress: filter = { address: tokenAddress, topics: [ id("Transfer(address,address,uint256)"), null, hexZeroPad(myAddress, 32) ] } // List all token transfers *to* myAddress or myOtherAddress: filter = { address: tokenAddress, topics: [ id("Transfer(address,address,uint256)"), null, [ hexZeroPad(myAddress, 32), hexZeroPad(myOtherAddress, 32), ] ] }

To simplify life, ..., explain here, the contract API

ERC-20 Contract Filter Examples
const abi = [ "event Transfer(address indexed src, address indexed dst, uint val)" ]; const contract = new Contract(tokenAddress, abi, provider); // List all token transfers *from* myAddress contract.filters.Transfer(myAddress) // { // address: '0x6B175474E89094C44Da98b954EedeAC495271d0F', // topics: [ // '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef', // '0x0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72' // ] // } // List all token transfers *to* myAddress: contract.filters.Transfer(null, myAddress) // { // address: '0x6B175474E89094C44Da98b954EedeAC495271d0F', // topics: [ // '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef', // null, // '0x0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72' // ] // } // List all token transfers *from* myAddress *to* otherAddress: contract.filters.Transfer(myAddress, otherAddress) // { // address: '0x6B175474E89094C44Da98b954EedeAC495271d0F', // topics: [ // '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef', // '0x0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72', // '0x000000000000000000000000ea517d5a070e6705cc5467858681ed953d285eb9' // ] // } // List all token transfers *to* myAddress OR otherAddress: contract.filters.Transfer(null, [ myAddress, otherAddress ]) // { // address: '0x6B175474E89094C44Da98b954EedeAC495271d0F', // topics: [ // '0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef', // null, // [ // '0x0000000000000000000000008ba1f109551bd432803012645ac136ddd64dba72', // '0x000000000000000000000000ea517d5a070e6705cc5467858681ed953d285eb9' // ] // ] // }

###
Other Things? TODO

Explain what happens to strings and bytes, how to filter and retain the value

The content of this site is licensed under the Creative Commons License. Last modified on June 12, 2020, 7:17pm.