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fix: off by one error during log topic decoding #296

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May 24, 2021
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fix: off by one error during log topic decoding #296

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2 changes: 1 addition & 1 deletion ethers-contract/ethers-contract-derive/src/lib.rs
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Original file line number Diff line number Diff line change
Expand Up @@ -432,7 +432,7 @@ fn derive_decode_from_log_impl(
let flat_topics = topics.iter().skip(1).flat_map(|t| t.as_ref().to_vec()).collect::<Vec<u8>>();
},
quote! {
if topic_tokens.is_empty() || topic_tokens.len() != topics.len() - 1 {
if topic_tokens.len() != topics.len() - 1 {
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@prestwich prestwich May 23, 2021 •
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can't this subtraction underflow if the LOG0 opcode is used? I'm not super familiar with these codepaths 🤔

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The macro generates different code for anonymous events:

ethers-rs/ethers-contract/ethers-contract-derive/src/lib.rs

Lines 411 to 440 in 94797f5

let (signature_check, flat_topics_init, topic_tokens_len_check) = if event.anonymous {
(
quote! {},
quote! {
let flat_topics = topics.iter().flat_map(|t| t.as_ref().to_vec()).collect::<Vec<u8>>();
},
quote! {
if topic_tokens.len() != topics.len() {
return Err(ethers_core::abi::Error::InvalidData);
}
},
)
} else {
(
quote! {
let event_signature = topics.get(0).ok_or(ethers_core::abi::Error::InvalidData)?;
if event_signature != &Self::signature() {
return Err(ethers_core::abi::Error::InvalidData);
}
},
quote! {
let flat_topics = topics.iter().skip(1).flat_map(|t| t.as_ref().to_vec()).collect::<Vec<u8>>();
},
quote! {
if topic_tokens.len() != topics.len() - 1 {
return Err(ethers_core::abi::Error::InvalidData);
}
},
)
};

only for non anonymous it makes sure that the signature is the first entry in topics

ethers-rs/ethers-contract/ethers-contract-derive/src/lib.rs

Line 426 in 94797f5

let event_signature = topics.get(0).ok_or(ethers_core::abi::Error::InvalidData)?;

so topics.len() - 1 can't underflow.

Most of this is adapted from:
https://github.com/rust-ethereum/ethabi/blob/970d47018e0f457440851752a7b46a4dbf793a0b/ethabi/src/event.rs#L122-L173

return Err(ethers_core::abi::Error::InvalidData);
}
},
Expand Down
36 changes: 34 additions & 2 deletions ethers-contract/tests/common/derive.rs
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Original file line number Diff line number Diff line change
@@ -1,6 +1,6 @@
use ethers::core::types::{H160, H256, I256, U128, U256};
use ethers_contract::{abigen, EthAbiType, EthEvent};
use ethers_core::abi::Tokenizable;
use ethers_contract::{abigen, EthAbiType, EthEvent, EthLogDecode};
use ethers_core::abi::{RawLog, Tokenizable};
use ethers_core::types::Address;

#[derive(Debug, Clone, PartialEq, EthAbiType)]
Expand Down Expand Up @@ -236,3 +236,35 @@ fn can_generate_ethevent_from_json() {
CreatedFilter::signature()
);
}

#[test]
fn can_decode_event_with_no_topics() {
#[derive(Debug, PartialEq, EthEvent)]
pub struct LiquidateBorrow {
liquidator: Address,
borrower: Address,
repay_amount: U256,
c_token_collateral: Address,
seize_tokens: U256,
}
// https://etherscan.io/tx/0xb7ba825294f757f8b8b6303b2aef542bcaebc9cc0217ddfaf822200a00594ed9#eventlog index 141
let log = RawLog {
topics: vec![
"298637f684da70674f26509b10f07ec2fbc77a335ab1e7d6215a4b2484d8bb52"
.parse()
.unwrap(),
],
data: vec![
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 188, 205, 0, 29, 173, 151, 238, 5, 127, 91, 31,
197, 154, 221, 40, 175, 143, 32, 26, 201, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 133, 129,
195, 136, 163, 5, 24, 136, 69, 34, 251, 23, 122, 146, 252, 33, 147, 81, 8, 20, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 9, 18, 195, 162, 210,
38, 128, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 77, 220, 45, 25, 57, 72, 146, 109, 2,
249, 177, 254, 158, 29, 170, 7, 24, 39, 14, 213, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0,
0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 0, 80, 30, 88,
],
};
let event = <LiquidateBorrow as EthLogDecode>::decode_log(&log).unwrap();
assert_eq!(event.seize_tokens, 5250648u64.into());
assert_eq!(event.repay_amount, 653800000000000000u64.into());
}