[refactor] Semantic Function Clustering Analysis - January 2026

[github-actions]

Executive Summary

Fresh analysis of 41 non-test Go files (~16,674 lines, 288 functions) in the MCP Gateway codebase reveals that most refactoring from the previous analysis has been successfully completed. The codebase is generally well-organized with clear package boundaries.

Status Update:

• ✅ Sanitization consolidation COMPLETED - internal/logger/sanitize/ package created
• ⚠️ Two remaining issues - Auth header inconsistency and launcher sanitization
• ✅ 8/11 packages follow excellent single-responsibility patterns

Key Changes Since Previous Analysis (Issue #196):

• Created internal/logger/sanitize/ package with unified sanitization API
• Added internal/config/rules/ package for validation error types
• Deprecated wrapper functions remain for backward compatibility
• Overall code quality has improved

---

Analysis Metadata

• Repository: githubnext/gh-aw-mcpg
• Total Go Files Analyzed: 41 (excluding tests)
• Total Lines of Code: ~16,674
• Total Functions: 288
• Packages: 11 main packages
• Detection Method: Pattern analysis + manual code review
• Analysis Date: 2026-01-13
• Workflow Run: §20958645871

---

Full Report

Package Organization Assessment

✅ Excellent Organization (8 packages)

Package	Files	Lines	Purpose	Quality
cmd/	2	~300	CLI commands (Cobra)	Excellent
difc/	5	~1,200	DIFC security labels	Excellent
guard/	4	~300	Security guards	Excellent
launcher/	1	~220	Backend process management	Excellent
mcp/	2	~850	MCP protocol types	Excellent
sys/	1	~112	System utilities	Excellent
timeutil/	1	~27	Time formatting	Excellent
tty/	2	~53	TTY detection	Excellent

⚠️ Minor Issues (3 packages)

Package	Files	Lines	Issue	Priority
config/	5	~800	Validation spread across files	Low
logger/	8	~1,278	Multiple specialized loggers	Low
server/	6	~1,587	Auth logic inconsistency	Medium

---

Completed Refactoring (Since Issue #196)

✅ Sanitization Consolidation - DONE

Created: internal/logger/sanitize/

New API:

// Public API - consolidated sanitization
func SanitizeString(message string) string
func SanitizeJSON(payloadBytes []byte) json.RawMessage

Adoption Status:

• ✅ internal/logger/rpc_logger.go - imports and uses sanitize.SanitizeString()
• ✅ internal/logger/jsonl_logger.go - imports and uses sanitize.SanitizeJSON()
• ✅ internal/logger/markdown_logger.go - imports and uses sanitize.SanitizeString()
• ⚠️ internal/launcher/launcher.go - still has own sanitizeEnvForLogging() (different strategy)

Deprecated Wrappers (retained for backward compatibility):

// These thin wrappers call sanitize package functions
func sanitizeSecrets(message string) string        // markdown_logger.go
func sanitizePayload(payloadBytes []byte) json.RawMessage  // jsonl_logger.go

Impact:

• ✅ Single source of truth for secret sanitization
• ✅ Comprehensive regex patterns for tokens, keys, passwords
• ✅ All logger files now use shared sanitization
• ⚠️ Launcher still uses different truncation-based approach

---

Remaining Issues

Issue #1: Auth Header Format Inconsistency (Medium Priority)

Problem: Two different interpretations of the Authorization header format create potential confusion.

Location A: server/auth.go (Lines 12-37)

// Per spec 7.1: Authorization header MUST contain API key directly (NOT Bearer scheme)
func authMiddleware(apiKey string, next http.HandlerFunc) http.HandlerFunc {
    authHeader := r.Header.Get("Authorization")
    
    // Spec 7.1: expects plain API key (not Bearer scheme)
    if authHeader != apiKey {
        http.Error(w, "Unauthorized: invalid API key", http.StatusUnauthorized)
        return
    }
    // ...
}

Behavior: Rejects any header that doesn't exactly match the API key (including "Bearer ")

Location B: guard/context.go (Lines 33-58)

// ExtractAgentIDFromAuthHeader extracts agent ID from Authorization header
// Supports formats:
//   - "Bearer <token>" - uses token as agent ID
//   - "Agent <agent-id>" - uses agent-id directly
//   - Any other format - uses the entire value as agent ID
func ExtractAgentIDFromAuthHeader(authHeader string) string {
    // Handle "Bearer <token>" format
    if strings.HasPrefix(authHeader, "Bearer ") {
        token := strings.TrimPrefix(authHeader, "Bearer ")
        return token
    }
    
    // Handle "Agent <agent-id>" format
    if strings.HasPrefix(authHeader, "Agent ") {
        return strings.TrimPrefix(authHeader, "Agent ")
    }
    
    // Use the entire header value as agent ID
    return authHeader
}

Behavior: Accepts "Bearer", "Agent", or plain formats

Analysis

Inconsistency Impact:

• Auth middleware enforces MCP spec 7.1 (plain API key, NO Bearer)
• Guard context handler accepts Bearer format
• Guards are currently disabled (NoopGuard), so no runtime conflict
• Will cause issues if/when guards are enabled

Root Cause:

• server/auth.go implements spec-compliant authentication
• guard/context.go was designed for flexible agent ID extraction
• Different design goals, but overlapping concerns

Recommendation

Option 1: Create internal/auth/ Package (Recommended)

Consolidate all auth-related logic into a dedicated package:

internal/auth/
├── header.go       // ParseAuthHeader(header string) (apiKey string, agentID string, err error)
├── middleware.go   // authMiddleware (uses ParseAuthHeader)
└── validator.go    // ValidateAPIKey(apiKey string) bool

Benefits:

• Single source of truth for auth header parsing
• Consistent interpretation across codebase
• Clearer security model
• Easier to update if spec changes

Implementation:

1. Create internal/auth/header.go:

   // ParseAuthHeader parses Authorization header per MCP spec 7.1
   // Returns: API key, agent ID (same as API key), error
   func ParseAuthHeader(header string) (apiKey string, agentID string, err error) {
       if header == "" {
           return "", "", fmt.Errorf("empty authorization header")
       }
       
       // Spec 7.1: Header must contain API key directly (NOT Bearer)
       // Use the entire value as both API key and agent ID
       return header, header, nil
   }

2. Update server/auth.go to use auth.ParseAuthHeader()

3. Update guard/context.go to use auth.ParseAuthHeader()

4. Add comprehensive tests for all expected formats

Estimated Impact:

• Effort: 3-4 hours
• Benefits: Consistent auth handling, spec compliance
• Risk: Medium (security-related, needs careful testing)
• Priority: Medium (no current runtime impact, but important for guards)

Option 2: Align guard/context.go with Spec (Simpler)

Simply update guard/context.go to match server/auth.go behavior:

func ExtractAgentIDFromAuthHeader(authHeader string) string {
    if authHeader == "" {
        return "default"
    }
    // Spec 7.1: Use entire header value as agent ID (no Bearer parsing)
    return authHeader
}

Benefits:

• Simpler, faster fix
• Ensures spec compliance
• Removes code complexity

Drawbacks:

• Less flexible for future extensions
• Doesn't centralize auth logic

---

Issue #2: Launcher Sanitization Uses Different Strategy (Low Priority)

Location: internal/launcher/launcher.go (Lines 19-37)

// sanitizeEnvForLogging returns a sanitized version of environment variables
// where each value is truncated to first 4 characters followed by "..."
func sanitizeEnvForLogging(env map[string]string) map[string]string {
    sanitized := make(map[string]string, len(env))
    for key, value := range env {
        if len(value) <= 4 {
            sanitized[key] = "..."
        } else {
            sanitized[key] = value[:4] + "..."
        }
    }
    return sanitized
}

Analysis:

Differences from sanitize package:

• Launcher: Simple truncation (first 4 chars + "...")
• Sanitize package: Pattern-based redaction (regex matching secrets)

Why the difference?

• Launcher logs environment variable keys and partial values for debugging
• Sanitize package redacts full secret patterns in log messages
• Different use cases: debug preview vs secret redaction

Is consolidation needed?

Argument FOR consolidation:

• Single package would handle all sanitization
• Could add SanitizeEnvMap(env map[string]string) map[string]string to sanitize package
• Better code organization

Argument AGAINST consolidation:

• Truncation strategy is intentionally different (preview vs redaction)
• Launcher's approach is simpler and specific to env var debugging
• Not worth the effort for a single function
• No actual duplication (different algorithms)

Recommendation

LOW PRIORITY - No action needed. The two approaches serve different purposes:

• sanitize.SanitizeString() - Full secret redaction using regex patterns
• sanitizeEnvForLogging() - Truncation for debug logging preview

If consolidation is desired (optional):

1. Add SanitizeEnvMapForDebug() to internal/logger/sanitize/
2. Update launcher to import and use it
3. Estimated effort: 1 hour

---

Issue #3: Validation Functions Spread Across Config Files (Acceptable)

Current Structure:

internal/config/
├── validation.go            // Core validation (expandVariables, validateServerConfig)
├── env_validation.go        // Environment checks (Docker, containerization)
├── schema_validation.go     // JSON schema validation
└── rules/rules.go          // Validation error types

Analysis:

Organization Quality: GOOD ✅

The files are logically separated by validation type:

• validation.go - Server config validation
• env_validation.go - Runtime environment validation
• schema_validation.go - JSON schema validation
• rules/rules.go - Shared validation error types

Function Distribution:

• validation.go: 5 functions (variables, mounts, server config)
• env_validation.go: 14 functions (Docker checks, env vars)
• schema_validation.go: 5 functions (schema validation, error formatting)

Is refactoring needed? NO

Reasons:

• Clear separation by validation concern
• File names clearly indicate purpose
• Good use of dedicated rules/ package for error types
• Total package size is reasonable (~800 lines)

Recommendation

NO ACTION NEEDED - Current organization is functional and clear.

Optional cosmetic improvement (not recommended):

• Rename validation.go → server_validation.go for consistency
• Estimated effort: 30 minutes
• Benefit: Marginal (name clarity)

---

Function Clustering Analysis

Pattern: Constructor Functions (New*)

Total: 29 constructor functions across all packages

Distribution:

• DIFC: 9 constructors (NewLabel, NewAgentLabels, NewEvaluator, etc.)
• Server: 3 constructors (New, NewSession, NewUnified)
• Logger: 4 constructors (New, NewSlogHandler, NewSlogLogger, etc.)
• Guard: 2 constructors (NewNoopGuard, NewRegistry)
• Others: 11 constructors

Analysis: ✅ Excellent - Consistent Go idiom, well-organized

---

Pattern: Close() Methods

Total: 8 implementations

Locations:

1. logger/file_logger.go:FileLogger.Close()
2. logger/jsonl_logger.go:JSONLLogger.Close()
3. logger/markdown_logger.go:MarkdownLogger.Close()
4. mcp/connection.go:Connection.Close()
5. launcher/launcher.go:Launcher.Close()
6. server/unified.go:UnifiedServer.Close()
7. server/transport.go:HTTPTransport.Close()
8. testutil/mcptest/validator.go:ValidatorClient.Close()

Analysis: ✅ Excellent - Idiomatic Go (io.Closer interface), no duplication

---

Pattern: Validation Functions

Distribution:

• config/validation.go: 3 functions
• config/env_validation.go: 3 functions
• config/schema_validation.go: 2 functions

Analysis: ✅ Good - Logical separation by validation type

---

Pattern: Format Functions

Distribution:

• config/schema_validation.go: 3 error formatting functions
• logger/rpc_logger.go: 3 RPC message formatting functions
• logger/slog_adapter.go: 1 slog value formatting function
• config/rules/rules.go: Error formatting

Analysis: ✅ Good - Context-specific formatting, no abstraction needed

---

Pattern: Sanitization Functions (REFACTORED ✅)

Distribution:

• ✅ logger/sanitize/sanitize.go: 2 public functions (consolidated)
• ⚠️ launcher/launcher.go: 1 function (different strategy, intentional)
• ➡️ logger/jsonl_logger.go: Deprecated wrapper (calls sanitize package)
• ➡️ logger/markdown_logger.go: Deprecated wrapper (calls sanitize package)

Analysis: ✅ Refactoring completed - Centralized in sanitize package

---

DIFC Package Interface Analysis

Observation: Multiple functions with same names across DIFC files

Examples:

• Add(), AddAll(), Contains() - Appear in both labels.go and capabilities.go
• Clone() - Appears in agent.go and labels.go (multiple types)
• CanFlowTo(), CheckFlow() - Appear on both SecrecyLabel and IntegrityLabel

Analysis: ✅ This is GOOD Go design

Reasons:

• Consistent interface across related types
• Method receivers make the context clear
• Go doesn't require formal interfaces for this pattern
• Improves API consistency

No action needed - This is idiomatic Go.

---

Recommendations Summary

Priority 1: Medium Impact (Optional)

1.1 Resolve Auth Header Inconsistency

• Issue: Auth logic split between server/auth.go and guard/context.go
• Action: Create internal/auth/ package OR align guard with server behavior
• Effort: 3-4 hours (new package) OR 1 hour (align)
• Benefits: Consistent auth handling, spec compliance
• Risk: Medium (security-related)
• Priority: Medium (no current impact, but needed before enabling guards)

Priority 2: Low Impact (Optional)

2.1 Consolidate Launcher Sanitization (Optional)

• Issue: Different sanitization strategy in launcher
• Action: Add SanitizeEnvMapForDebug() to sanitize package
• Effort: 1 hour
• Benefits: All sanitization in one place
• Priority: Low (current separation is acceptable)

No Action Needed

Config Validation Organization

• Status: ✅ Current organization is good
• Reason: Clear separation by validation type
• Action: None

DIFC Method Naming

• Status: ✅ Idiomatic Go design
• Reason: Consistent interfaces across types
• Action: None

Constructor and Close Patterns

• Status: ✅ Excellent Go idioms
• Action: None

---

Implementation Checklist

Phase 1: Auth Consolidation (Optional - Medium Priority)

Option A: Create Auth Package

• Create internal/auth/ directory
• Implement header.go with ParseAuthHeader()
• Implement middleware.go moving from server/auth.go
• Update server/auth.go to use new package
• Update guard/context.go to use new package
• Add comprehensive unit tests
• Update documentation

Option B: Align Guard with Server (Simpler)

• Update guard/context.go:ExtractAgentIDFromAuthHeader()
• Remove Bearer and Agent prefix parsing
• Update function documentation
• Add test cases
• Verify no breaking changes

Phase 2: Launcher Sanitization (Optional - Low Priority)

• Add SanitizeEnvMapForDebug() to internal/logger/sanitize/
• Update launcher/launcher.go to import sanitize package
• Replace sanitizeEnvForLogging() call
• Add unit tests
• Remove old function

---

Code Quality Assessment

Overall Rating: ✅ Excellent

The codebase demonstrates:

• Clear package boundaries with single responsibilities
• Consistent Go idioms (constructors, interfaces, error handling)
• Good test coverage (41 test files found)
• Recent refactoring success (sanitization consolidation completed)
• Minimal technical debt (only 2 minor issues identified)

Strengths

1. ✅ Well-organized packages - 8/11 packages have excellent organization
2. ✅ Consistent naming - Function patterns are predictable
3. ✅ Clear separation of concerns - Auth, logging, validation, etc.
4. ✅ Recent improvements - Sanitization and validation refactoring completed
5. ✅ Good documentation - Inline comments and package docs

Areas for Improvement (Minor)

1. ⚠️ Auth header handling - Inconsistency between server and guard
2. ⚠️ Launcher sanitization - Could use centralized package
3. ℹ️ Logger package size - 8 files, but each has clear purpose

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Comparison with Previous Analysis (Issue #196)

What Changed Since Last Analysis?

Issue	Status	Action Taken
Sanitization duplication	✅ FIXED	Created internal/logger/sanitize/ package
Auth logic split	⚠️ REMAINS	Still inconsistent between server/guard
Config validation spread	✅ ACCEPTED	Organized by validation type (good)
Logger formatting	✅ IMPROVED	Now uses sanitize package

Progress Made

• ✅ Created internal/logger/sanitize/ with unified API
• ✅ All logger files now import and use sanitize package
• ✅ Created internal/config/rules/ for validation types
• ✅ Deprecated wrappers for backward compatibility
• ⚠️ Auth inconsistency remains (no runtime impact yet)

Recommendations Status

Original Recommendation	Status
Consolidate sanitization	✅ COMPLETED
Extract auth package	⚠️ PENDING (medium priority)
Centralize logger formatting	✅ COMPLETED (via sanitize package)
Rename validation files	❌ REJECTED (current names are clear)

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Conclusion

The MCP Gateway codebase is in excellent shape with clear organization and consistent patterns. The previous refactoring recommendations have been successfully implemented, with only minor issues remaining.

Current State:

• ✅ Sanitization consolidation: COMPLETED
• ⚠️ Auth header inconsistency: IDENTIFIED (no current impact)
• ✅ Code organization: EXCELLENT (8/11 packages)

Recommended Actions:

1. Optional: Resolve auth header inconsistency before enabling guards (medium priority)
2. Optional: Consolidate launcher sanitization (low priority)
3. None needed: Current validation and logger organization is good

The codebase demonstrates mature engineering practices with minimal technical debt. All identified issues are optional improvements rather than critical problems.

---

References:

• Previous analysis: Issue [refactor] Semantic Function Clustering Analysis - Code Organization Improvements #196 (closed)
• Workflow run: §20958645871
• Repository: githubnext/gh-aw-mcpg

AI generated by Semantic Function Refactoring

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