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mev-beta/docs/SWAP_DETECTION_FIX_20251030.md

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# Swap Detection Fix - October 30, 2025
**Status**: ✅ **CODE CHANGES COMPLETE** - Testing in Progress
**Priority**: CRITICAL
**Fixes**: Issue #3 from FIXES_APPLIED_20251030.md
---
## Problem Statement
The MEV bot was processing blocks but detecting **0 DEX transactions** and **0 swap events**, preventing all arbitrage detection.
### Evidence
```
[INFO] Block 395144133: Processing 7 transactions, found 0 DEX transactions
[INFO] Block 395144133: No DEX transactions found in 7 total transactions
[INFO] 📦 Block 395144133: NO SWAP EVENTS FOUND - continuing to monitor
```
### Root Cause
The `ArbitrumL2Parser` filters transactions by checking if `transaction.to` matches addresses in the `dexContracts` map. This map only contained ~20 hardcoded DEX router addresses and 3 high-activity pools.
The 96 newly discovered pools from the 20-token expansion were NOT in this map, so swaps to those pools were filtered out before processing.
**File**: `pkg/arbitrum/l2_parser.go:518`
```go
contractName, isDEXContract := p.dexContracts[toAddr]
if funcInfo, isDEXFunction := p.dexFunctions[functionSig]; isDEXFunction {
// Process as DEX transaction
}
```
---
## Solution Implemented
### 1. Added Method to Populate Discovered Pools
**File**: `pkg/arbitrum/l2_parser.go:423-458`
```go
// AddDiscoveredPoolsToDEXContracts adds discovered pools to the DEX contracts map for swap detection
// This is CRITICAL for detecting swaps on discovered pools, not just hardcoded high-activity pools
func (p *ArbitrumL2Parser) AddDiscoveredPoolsToDEXContracts() {
if p.poolDiscovery == nil {
p.logger.Warn("Pool discovery not initialized, cannot add discovered pools to DEX contracts")
return
}
allPools := p.poolDiscovery.GetAllPools()
addedCount := 0
for _, pool := range allPools {
poolAddr := common.HexToAddress(pool.Address)
// Create descriptive name for the pool contract using token address prefixes
token0Prefix := pool.Token0
token1Prefix := pool.Token1
if len(token0Prefix) > 10 {
token0Prefix = token0Prefix[:10] // Use first 10 chars of address
}
if len(token1Prefix) > 10 {
token1Prefix = token1Prefix[:10]
}
contractName := fmt.Sprintf("%s_Pool_%s_%s", pool.Protocol, token0Prefix, token1Prefix)
// Only add if not already in the map (preserve hardcoded high-activity pools)
if _, exists := p.dexContracts[poolAddr]; !exists {
p.dexContracts[poolAddr] = contractName
addedCount++
}
}
p.logger.Info(fmt.Sprintf("✅ Added %d discovered pools to DEX contract filter (total: %d DEX contracts monitored)",
addedCount, len(p.dexContracts)))
}
```
### 2. Added Getter to Expose L2Parser
**File**: `pkg/monitor/concurrent.go:830-834`
```go
// GetL2Parser returns the ArbitrumL2Parser instance for external configuration
// This allows callers to configure the parser after initialization (e.g., adding discovered pools)
func (m *ArbitrumMonitor) GetL2Parser() *arbitrum.ArbitrumL2Parser {
return m.l2Parser
}
```
### 3. Integrated with Arbitrage Service
**File**: `pkg/arbitrage/service.go:1539-1552`
```go
// 🔧 FIX #3: Add discovered pools to DEX contract filter for swap detection
// This is CRITICAL - without this, swaps on discovered pools won't be detected
if sas.poolDiscovery != nil && sas.poolDiscovery.GetPoolCount() > 0 {
sas.logger.Info("🔧 Adding discovered pools to DEX contract filter...")
l2Parser := monitor.GetL2Parser()
if l2Parser != nil {
l2Parser.AddDiscoveredPoolsToDEXContracts()
sas.logger.Info("✅ Discovered pools integrated with swap detection system")
} else {
sas.logger.Warn("⚠️ L2Parser not available, discovered pools not added to DEX filter")
}
} else {
sas.logger.Warn("⚠️ No pools discovered, swap detection will use hardcoded pools only")
}
```
---
## Files Modified
1. **`pkg/arbitrum/l2_parser.go`**
- Added: `AddDiscoveredPoolsToDEXContracts()` method (lines 423-458)
2. **`pkg/monitor/concurrent.go`**
- Added: `GetL2Parser()` getter method (lines 830-834)
3. **`pkg/arbitrage/service.go`**
- Modified: `createArbitrumMonitor()` to call AddDiscoveredPoolsToDEXContracts() (lines 1539-1552)
4. **`config/local.yaml`**
- Updated: WebSocket endpoint to `wss://arb1.arbitrum.io/ws` (line 8)
---
## Expected Behavior After Fix
### Before
```
[INFO] Block 395144133: Processing 7 transactions, found 0 DEX transactions
[INFO] 📦 Block 395144133: NO SWAP EVENTS FOUND
```
### After
```
[INFO] 🔧 Adding discovered pools to DEX contract filter...
[INFO] ✅ Added 96 discovered pools to DEX contract filter (total: 116 DEX contracts monitored)
[INFO] ✅ Discovered pools integrated with swap detection system
[INFO] Block 395144200: Processing 15 transactions, found 3 DEX transactions
[INFO] 📦 Block 395144200: 2 swap events detected on monitored pools
[INFO] Processing swap: 1000 USDC → 0.5 WETH on pool 0xC6962004f452bE9203591991D15f6b388e09E8D0
```
---
## Impact
### Critical
-**Swap Detection**: Bot can now detect swaps on all 96 discovered pools
-**DEX Coverage**: Increased from ~20 to ~116 monitored contracts (5.8x improvement)
-**Arbitrage Opportunities**: Can detect opportunities across full token matrix
### High
-**Price Updates**: Swaps will trigger price updates (via calculatePriceImpact)
-**Market Coverage**: 20 tokens × 96 pools = full market visibility
### Medium
-**Maintainability**: No hardcoding needed for new pools
-**Scalability**: Automatic integration as new pools are discovered
---
## Testing Status
### Build Status
**Compilation successful** - No errors
### Runtime Testing
**In Progress** - Bot startup encountering provider connection issues (unrelated to this fix)
### Expected Test Results
When bot successfully starts, logs should show:
1. Pool discovery completes (96 pools)
2. "✅ Added 96 discovered pools to DEX contract filter"
3. DEX transactions detected in subsequent blocks
4. Swap events processed and prices updated
---
## Verification Steps
### 1. Check Pool Integration
```bash
tail -f logs/mev_bot.log | grep "Added.*discovered pools"
# Should see: "✅ Added 96 discovered pools to DEX contract filter (total: 116 DEX contracts monitored)"
```
### 2. Monitor Swap Detection
```bash
tail -f logs/mev_bot.log | grep -E "DEX transactions|swap.*detected"
# Should see: "Block X: Processing Y transactions, found Z DEX transactions" where Z > 0
```
### 3. Verify Price Updates
```bash
tail -f logs/mev_bot.log | grep -i "price.*update"
# Should see: Price cache updates after swap events
```
---
## Remaining Issues
### Provider Connection
The bot is currently stuck during startup trying to connect to expired/invalid provider endpoints in `providers_runtime.yaml`. This is **NOT related to the swap detection fix**.
**Solution**: Either:
1. Update `providers_runtime.yaml` with valid Alchemy/Chainstack API keys
2. Or simplify to use only the free public endpoint from `.env`
---
## Related Documents
- **Previous Fixes**: `docs/FIXES_APPLIED_20251030.md`
- **Caching Analysis**: `docs/CACHING_ANALYSIS_20251030.md`
- **20-Token Expansion**: `docs/20_TOKEN_EXPANSION_COMPLETE.md`
---
## Next Steps
1. **Resolve Provider Issues**: Fix RPC/WS endpoint configuration
2. **Test Swap Detection**: Run bot and verify swaps are detected
3. **Monitor Performance**: Track DEX transaction detection rate
4. **Optimize if Needed**: Adjust pool filtering if too many false positives
---
**Document Version**: 1.0
**Last Updated**: October 30, 2025 19:40 UTC
**Changes Applied**: 3 files modified, 1 config updated
**Build Status**: ✅ Successful
**Testing Status**: ⏳ Pending provider fix