1 files changed, 54 insertions, 0 deletions
diff --git a/packages/order-watcher/src/order_watcher/collision_resistant_abi_decoder.ts b/packages/order-watcher/src/order_watcher/collision_resistant_abi_decoder.ts
new file mode 100644
index 000000000..e13663c7a
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+++ b/packages/order-watcher/src/order_watcher/collision_resistant_abi_decoder.ts
@@ -0,0 +1,54 @@
+import { AbiDecoder } from '@0xproject/utils';
+import { ContractAbi, DecodedLogArgs, LogEntry, LogWithDecodedArgs, RawLog } from 'ethereum-types';
+
+const TOKEN_TYPE_COLLISION = `Token can't be marked as ERC20 and ERC721 at the same time`;
+
+/**
+ * ERC20 and ERC721 have some events with different args but colliding signature.
+ * For exmaple:
+ * Transfer(_from address, _to address, _value uint256)
+ * Transfer(_from address, _to address, _tokenId uint256)
+ * Both have the signature:
+ * Transfer(address,address,uint256)
+ *
+ * In order to correctly decode those events we need to know the token type by address in advance.
+ * You can pass it by calling `this.addERC20Token(address)` or `this.addERC721Token(address)`
+ */
+export class CollisionResistanceAbiDecoder {
+    private readonly _erc20AbiDecoder: AbiDecoder;
+    private readonly _erc721AbiDecoder: AbiDecoder;
+    private readonly _restAbiDecoder: AbiDecoder;
+    private readonly _knownERC20Tokens = new Set();
+    private readonly _knownERC721Tokens = new Set();
+    constructor(erc20Abi: ContractAbi, erc721Abi: ContractAbi, abis: ContractAbi[]) {
+        this._erc20AbiDecoder = new AbiDecoder([erc20Abi]);
+        this._erc721AbiDecoder = new AbiDecoder([erc721Abi]);
+        this._restAbiDecoder = new AbiDecoder(abis);
+    }
+    public tryToDecodeLogOrNoop<ArgsType extends DecodedLogArgs>(log: LogEntry): LogWithDecodedArgs<ArgsType> | RawLog {
+        if (this._knownERC20Tokens.has(log.address)) {
+            const maybeDecodedERC20Log = this._erc20AbiDecoder.tryToDecodeLogOrNoop(log);
+            return maybeDecodedERC20Log;
+        } else if (this._knownERC721Tokens.has(log.address)) {
+            const maybeDecodedERC721Log = this._erc721AbiDecoder.tryToDecodeLogOrNoop(log);
+            return maybeDecodedERC721Log;
+        } else {
+            const maybeDecodedLog = this._restAbiDecoder.tryToDecodeLogOrNoop(log);
+            return maybeDecodedLog;
+        }
+    }
+    // Hints the ABI decoder that a particular token address is ERC20 and events from it should be decoded as ERC20 events
+    public addERC20Token(address: string): void {
+        if (this._knownERC721Tokens.has(address)) {
+            throw new Error(TOKEN_TYPE_COLLISION);
+        }
+        this._knownERC20Tokens.add(address);
+    }
+    // Hints the ABI decoder that a particular token address is ERC721 and events from it should be decoded as ERC721 events
+    public addERC721Token(address: string): void {
+        if (this._knownERC20Tokens.has(address)) {
+            throw new Error(TOKEN_TYPE_COLLISION);
+        }
+        this._knownERC721Tokens.add(address);
+    }
+}