feat: auto capture fields for add and remove field

epoch/context_keys.go

@@ -0,0 +1,55 @@
+package epoch
+
+import (
+	"github.com/gin-gonic/gin"
+)
+
+// CapturedFieldsKey is the context key for storing captured request field values
+// These are used by response transformers to restore original values when
+// a field was removed from the request and needs to be added back to the response
+const CapturedFieldsKey = "epoch_captured_fields"
+
+// GetCapturedFields retrieves the captured fields map from a Gin context
+func GetCapturedFields(c *gin.Context) map[string]interface{} {
+	if c == nil {
+		return nil
+	}
+	if val, exists := c.Get(CapturedFieldsKey); exists {
+		if fields, ok := val.(map[string]interface{}); ok {
+			return fields
+		}
+	}
+	return nil
+}
+
+// SetCapturedField stores a captured field value in the Gin context
+// The field is keyed by field name only. Since the Gin context is request-scoped,
+// there's no risk of collision between different requests. This allows captured
+// values to flow from request types to response types with the same field name.
+func SetCapturedField(c *gin.Context, fieldName string, value interface{}) {
+	if c == nil {
+		return
+	}
+	fields := GetCapturedFields(c)
+	if fields == nil {
+		fields = make(map[string]interface{})
+		c.Set(CapturedFieldsKey, fields)
+	}
+	fields[fieldName] = value
+}
+
+// GetCapturedField retrieves a specific captured field value
+func GetCapturedField(c *gin.Context, fieldName string) (interface{}, bool) {
+	fields := GetCapturedFields(c)
+	if fields == nil {
+		return nil, false
+	}
+	val, exists := fields[fieldName]
+	return val, exists
+}
+
+// HasCapturedField checks if a field has been captured
+func HasCapturedField(c *gin.Context, fieldName string) bool {
+	_, exists := GetCapturedField(c, fieldName)
+	return exists
+}