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| 1 | +//! ERC-20 / ERC-721 Transfer event decoder. |
| 2 | +//! |
| 3 | +//! Sentrix indexer-handlers crate is still a placeholder (Phase 0), so the |
| 4 | +//! `token_transfers` table sat empty even though raw logs were captured. |
| 5 | +//! Until the declarative-handler framework lands, decode the well-known |
| 6 | +//! Transfer signatures inline here so scan UIs can resolve token balances. |
| 7 | +//! |
| 8 | +//! ERC-1155 has a different topic0 (`TransferSingle` / `TransferBatch`) and |
| 9 | +//! a richer encoding; out of scope for this pass. |
| 10 | +
|
| 11 | +use alloy_primitives::U256; |
| 12 | +use indexer_domain::{Log, TokenStandard, TokenTransfer, Wei}; |
| 13 | + |
| 14 | +/// `keccak256("Transfer(address,address,uint256)")` — same selector for |
| 15 | +/// ERC-20 amount transfers and ERC-721 token-id transfers. The two are |
| 16 | +/// distinguished by topic count + data shape. |
| 17 | +const TRANSFER_TOPIC0: &str = "0xddf252ad1be2c89b69c2b068fc378daa952ba7f163c4a11628f55a4df523b3ef"; |
| 18 | + |
| 19 | +/// Try to decode a log as an ERC-20 or ERC-721 Transfer event. Returns |
| 20 | +/// `None` for anything else — caller drops it. |
| 21 | +/// |
| 22 | +/// Decoding rules: |
| 23 | +/// - topic0 must equal the canonical Transfer selector. |
| 24 | +/// - topic1, topic2 are 32-byte-padded from/to addresses (indexed). |
| 25 | +/// - ERC-20: topic3 absent, data = 32-byte amount. |
| 26 | +/// - ERC-721: topic3 present (indexed token_id), data empty, amount = 1. |
| 27 | +pub fn decode_transfer(log: &Log) -> Option<TokenTransfer> { |
| 28 | + if log.topic0.as_deref() != Some(TRANSFER_TOPIC0) { |
| 29 | + return None; |
| 30 | + } |
| 31 | + let from_topic = log.topic1.as_deref()?; |
| 32 | + let to_topic = log.topic2.as_deref()?; |
| 33 | + let from_addr = topic_to_address(from_topic)?; |
| 34 | + let to_addr = topic_to_address(to_topic)?; |
| 35 | + |
| 36 | + let (standard, token_id, amount) = match log.topic3.as_deref() { |
| 37 | + Some(id_topic) => { |
| 38 | + // ERC-721: token_id in topic3, data empty (or padding only). |
| 39 | + let token_id = topic_to_u256(id_topic)?; |
| 40 | + ( |
| 41 | + TokenStandard::Erc721, |
| 42 | + Some(Wei(token_id)), |
| 43 | + Wei(U256::from(1u64)), |
| 44 | + ) |
| 45 | + } |
| 46 | + None => { |
| 47 | + // ERC-20: amount in data (must be exactly 32 bytes). |
| 48 | + let data_str = log.data.as_deref()?; |
| 49 | + let amount = data_to_u256(data_str)?; |
| 50 | + (TokenStandard::Erc20, None, Wei(amount)) |
| 51 | + } |
| 52 | + }; |
| 53 | + |
| 54 | + Some(TokenTransfer { |
| 55 | + id: None, |
| 56 | + block_height: log.block_height, |
| 57 | + tx_hash: log.tx_hash.clone(), |
| 58 | + log_index: log.log_index, |
| 59 | + contract: log.address.clone(), |
| 60 | + standard, |
| 61 | + from_addr, |
| 62 | + to_addr, |
| 63 | + token_id, |
| 64 | + amount, |
| 65 | + }) |
| 66 | +} |
| 67 | + |
| 68 | +/// Last 20 bytes of a 32-byte topic → `0x`-prefixed lowercase address. |
| 69 | +fn topic_to_address(topic: &str) -> Option<String> { |
| 70 | + let hex = topic.trim_start_matches("0x"); |
| 71 | + if hex.len() != 64 { |
| 72 | + return None; |
| 73 | + } |
| 74 | + Some(format!("0x{}", &hex[24..])) |
| 75 | +} |
| 76 | + |
| 77 | +/// 32-byte topic → U256. |
| 78 | +fn topic_to_u256(topic: &str) -> Option<U256> { |
| 79 | + let hex = topic.trim_start_matches("0x"); |
| 80 | + if hex.len() != 64 { |
| 81 | + return None; |
| 82 | + } |
| 83 | + let bytes = hex::decode(hex).ok()?; |
| 84 | + Some(U256::from_be_slice(&bytes)) |
| 85 | +} |
| 86 | + |
| 87 | +/// 32-byte data field → U256. ERC-20 Transfer always has data length 32. |
| 88 | +fn data_to_u256(data: &str) -> Option<U256> { |
| 89 | + let hex = data.trim_start_matches("0x"); |
| 90 | + if hex.len() != 64 { |
| 91 | + return None; |
| 92 | + } |
| 93 | + let bytes = hex::decode(hex).ok()?; |
| 94 | + Some(U256::from_be_slice(&bytes)) |
| 95 | +} |
| 96 | + |
| 97 | +#[cfg(test)] |
| 98 | +mod tests { |
| 99 | + use super::*; |
| 100 | + use indexer_domain::{BlockHeight, LogIndex}; |
| 101 | + |
| 102 | + fn base_log() -> Log { |
| 103 | + Log { |
| 104 | + block_height: BlockHeight(1), |
| 105 | + tx_hash: "0xabc".into(), |
| 106 | + log_index: LogIndex(0), |
| 107 | + address: "0xcontract".into(), |
| 108 | + topic0: Some(TRANSFER_TOPIC0.into()), |
| 109 | + topic1: Some( |
| 110 | + "0x000000000000000000000000aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa".into(), |
| 111 | + ), |
| 112 | + topic2: Some( |
| 113 | + "0x000000000000000000000000bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb".into(), |
| 114 | + ), |
| 115 | + topic3: None, |
| 116 | + data: Some("0x0000000000000000000000000000000000000000000000000000000000000064".into()), |
| 117 | + } |
| 118 | + } |
| 119 | + |
| 120 | + #[test] |
| 121 | + fn decodes_erc20_transfer() { |
| 122 | + let t = decode_transfer(&base_log()).expect("erc20 should decode"); |
| 123 | + assert_eq!(t.standard, TokenStandard::Erc20); |
| 124 | + assert_eq!(t.from_addr, "0xaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"); |
| 125 | + assert_eq!(t.to_addr, "0xbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb"); |
| 126 | + assert_eq!(t.amount.0, U256::from(100u64)); |
| 127 | + assert!(t.token_id.is_none()); |
| 128 | + } |
| 129 | + |
| 130 | + #[test] |
| 131 | + fn decodes_erc721_transfer() { |
| 132 | + let mut log = base_log(); |
| 133 | + log.topic3 = |
| 134 | + Some("0x0000000000000000000000000000000000000000000000000000000000000007".into()); |
| 135 | + log.data = Some("0x".into()); |
| 136 | + let t = decode_transfer(&log).expect("erc721 should decode"); |
| 137 | + assert_eq!(t.standard, TokenStandard::Erc721); |
| 138 | + assert_eq!(t.token_id.unwrap().0, U256::from(7u64)); |
| 139 | + assert_eq!(t.amount.0, U256::from(1u64)); |
| 140 | + } |
| 141 | + |
| 142 | + #[test] |
| 143 | + fn skips_non_transfer() { |
| 144 | + let mut log = base_log(); |
| 145 | + log.topic0 = Some("0xdeadbeef".into()); |
| 146 | + assert!(decode_transfer(&log).is_none()); |
| 147 | + } |
| 148 | + |
| 149 | + #[test] |
| 150 | + fn skips_malformed_topic() { |
| 151 | + let mut log = base_log(); |
| 152 | + log.topic1 = Some("0xshort".into()); |
| 153 | + assert!(decode_transfer(&log).is_none()); |
| 154 | + } |
| 155 | +} |
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