Add structured logging with request ID middleware

internal/middleware/requestid.go

@@ -0,0 +1,30 @@
+package middleware
+
+import (
+	"github.com/gin-gonic/gin"
+	"github.com/google/uuid"
+
+	mygolog "github.com/dhao2001/mygo/internal/log"
+)
+
+// RequestID returns a Gin middleware that ensures every request has a
+// request ID. If the client sends X-Request-ID, it is reused; otherwise a
+// new UUID v4 is generated. The ID is injected into both the Go
+// context.Context (for slog) and the Gin context (for handler access).
+func RequestID() gin.HandlerFunc {
+	return func(c *gin.Context) {
+		reqID := c.GetHeader("X-Request-ID")
+		if reqID == "" {
+			reqID = uuid.NewString()
+		}
+
+		// Inject into Go context for slog.*Context calls.
+		c.Request = c.Request.WithContext(mygolog.WithRequestID(c.Request.Context(), reqID))
+
+		// Also set in Gin context for direct access.
+		c.Set("req_id", reqID)
+		c.Header("X-Request-ID", reqID)
+
+		c.Next()
+	}
+}