[duplicate-code] Duplicate Code Pattern: Systemic Dual-Logging Across Server Package

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Part of duplicate code analysis: #2711

Summary

Across the internal/server package, there is a recurring pattern where typed debug loggers (e.g., logRouted, logUnified) were added alongside existing log.Printf calls for the same event, rather than replacing them. This pattern exists in at least 3 files and represents an ongoing maintenance risk as new debug loggers are added.

Duplication Details

Pattern: Typed debug logger + stdlib log.Printf for same event

• Severity: Medium
• Occurrences: 5+ dual-log pairs across 3 files
• Locations: internal/server/routed.go, internal/server/unified.go

routed.go — createFilteredServer (lines 132–133)

log.Printf("Creating filtered server for %s with %d tools", backendID, len(tools))
logRouted.Printf("Backend %s has %d tools available", backendID, len(tools))

Both lines describe the same event (a filtered server being created with N tools) but with slightly different wording. Neither is clearly superior.

unified.go — callBackendTool (lines 268–269)

log.Printf("Calling tool on %s: %s with DIFC enforcement", serverID, toolName)
logUnified.Printf("callBackendTool: serverID=%s, toolName=%s, args=%+v", serverID, toolName, args)

Same event (tool invocation), logged to both loggers. The debug logger adds args which is valuable; the stdlib logger provides a summary message.

unified.go — NewUnifiedServer (lines 176, 181)

logUnified.Printf("Auto-enabled DIFC: non-noop guard, global policy, or per-server guard policies detected")
log.Printf("Guards enforcement enabled with mode: %s", cfg.DIFCMode)

Same initialization event (DIFC/guards enabled), split across two nearby log calls.

Impact Analysis

• Maintainability: When updating log messages, developers must check both logger types; message divergence has already begun (different wording for same event)
• Log Verbosity: Production deployments receive double log entries for hot paths like callBackendTool, which is called for every MCP tool invocation
• Inconsistency: Some files have migrated to typed debug loggers (e.g., auth.go, health.go, response_writer.go) while others retain the dual pattern, making the logging strategy unclear
• Pattern Propagation: PR [log] Add debug logging to server/session.go #2673 followed this same pattern when adding logSession, suggesting no team-wide convention has been established

Refactoring Recommendations

1. Establish a clear convention: Debug loggers (logXxx.Printf) should replace not supplement log.Printf for the same event. The debug logger (when DEBUG=* is active) replaces verbosity; the file logger handles persistence.

2. Consolidate routed.go lines 132–133:

   // Before (two lines, same event):
   log.Printf("Creating filtered server for %s with %d tools", backendID, len(tools))
   logRouted.Printf("Backend %s has %d tools available", backendID, len(tools))
   
   // After (one debug log, one operational log if needed):
   logRouted.Printf("Creating filtered server: backend=%s, tools=%d", backendID, len(tools))

3. Consolidate unified.go lines 268–269:

   // Before:
   log.Printf("Calling tool on %s: %s with DIFC enforcement", serverID, toolName)
   logUnified.Printf("callBackendTool: serverID=%s, toolName=%s, args=%+v", serverID, toolName, args)
   
   // After (keep richer debug log, remove redundant stdlib log):
   logUnified.Printf("callBackendTool: serverID=%s, toolName=%s, args=%+v", serverID, toolName, args)

4. Update AGENTS.md to document the convention: debug loggers replace log.Printf for the same events; logger.LogInfo/Warn/Error is used for operational/persistent logging.

5. Estimated effort: ~1 hour for targeted cleanup of the identified dual-log pairs; longer if the full server package is audited

Implementation Checklist

• Decide on authoritative logging convention (debug logger replaces stdlib log for same event)
• Consolidate routed.go lines 132–133 into single logRouted.Printf
• Consolidate unified.go lines 268–269 into single logUnified.Printf
• Review and consolidate unified.go lines 176/181
• Audit remaining log.Printf calls in internal/server/*.go for additional dual-log pairs
• Document convention in AGENTS.md or a logging guide
• Run make agent-finished to verify no regressions

Parent Issue

See parent analysis report: #2711
Related to #2711

Generated by Duplicate Code Detector · ◷

• expires on Apr 4, 2026, 5:49 AM UTC