internal/api/middleware/correlation.go

// Package middleware provides HTTP middleware components for the CLI Proxy API server.
// This file contains correlation ID middleware for request tracing.
package middleware

import (
	"github.com/gin-gonic/gin"
	"github.com/google/uuid"
)

const (
	// CorrelationIDHeader is the HTTP header name for correlation IDs
	CorrelationIDHeader = "X-Correlation-ID"
	// CorrelationIDContextKey is the context key for correlation IDs
	CorrelationIDContextKey = "correlation_id"
)

// CorrelationIDMiddleware creates a Gin middleware that ensures every request
// has a correlation ID for distributed tracing. It checks for an existing ID
// in the request headers and generates a new one if not present.
func CorrelationIDMiddleware() gin.HandlerFunc {
	return func(c *gin.Context) {
		// Check for existing correlation ID in header
		correlationID := c.GetHeader(CorrelationIDHeader)
		
		// Generate new ID if not present
		if correlationID == "" {
			correlationID = generateCorrelationID()
		}
		
		// Store in context
		c.Set(CorrelationIDContextKey, correlationID)
		
		// Add to response headers
		c.Header(CorrelationIDHeader, correlationID)
		
		c.Next()
	}
}

// GetCorrelationID retrieves the correlation ID from the Gin context.
// Returns empty string if no correlation ID is found.
func GetCorrelationID(c *gin.Context) string {
	if id, exists := c.Get(CorrelationIDContextKey); exists {
		if str, ok := id.(string); ok {
			return str
		}
	}
	return ""
}

// generateCorrelationID generates a new unique correlation ID.
func generateCorrelationID() string {
	return uuid.New().String()
}