updated as per the review comments

pkg/plugin/implementation/reqpreprocessor/reqpreprocessor.go

@@ -0,0 +1,108 @@
+package reqpreprocessor
+
+import (
+	"bytes"
+	"context"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"net/http"
+
+	"github.com/beckn/beckn-onix/pkg/log"
+	"github.com/google/uuid"
+)
+
+type Config struct {
+	ContextKeys []string
+	Role        string
+}
+
+type becknRequest struct {
+	Context map[string]any `json:"context"`
+}
+
+const contextKey = "context"
+const subscriberIDKey = "subscriber_id"
+
+func NewPreProcessor(cfg *Config) (func(http.Handler) http.Handler, error) {
+	if err := validateConfig(cfg); err != nil {
+		return nil, err
+	}
+	return func(next http.Handler) http.Handler {
+		return http.HandlerFunc(func(w http.ResponseWriter, r *http.Request) {
+			body, _ := io.ReadAll(r.Body)
+			var req becknRequest
+			ctx := r.Context()
+			if err := json.Unmarshal(body, &req); err != nil {
+				http.Error(w, "Failed to decode request body", http.StatusBadRequest)
+				return
+			}
+			if req.Context == nil {
+				http.Error(w, fmt.Sprintf("%s field not found.", contextKey), http.StatusBadRequest)
+				return
+			}
+			var subID any
+			switch cfg.Role {
+			case "bap":
+				subID = req.Context["bap_id"]
+			case "bpp":
+				subID = req.Context["bpp_id"]
+			}
+			if subID != nil {
+				log.Debugf(ctx, "adding subscriberId to request:%s, %v", subscriberIDKey, subID)
+				ctx = context.WithValue(ctx, subscriberIDKey, subID)
+			}
+			for _, key := range cfg.ContextKeys {
+				value := uuid.NewString()
+				updatedValue := update(req.Context, key, value)
+				ctx = context.WithValue(ctx, key, updatedValue)
+			}
+			reqData := map[string]any{"context": req.Context}
+			updatedBody, _ := json.Marshal(reqData)
+			r.Body = io.NopCloser(bytes.NewBuffer(updatedBody))
+			r.ContentLength = int64(len(updatedBody))
+			r = r.WithContext(ctx)
+			next.ServeHTTP(w, r)
+		})
+	}, nil
+}
+
+func update(wrapper map[string]any, key string, value any) any {
+	field, exists := wrapper[key]
+	if !exists || isEmpty(field) {
+		wrapper[key] = value
+		return value
+	}
+
+	return field
+}
+func isEmpty(v any) bool {
+	switch v := v.(type) {
+	case string:
+		return v == ""
+	case nil:
+		return true
+	default:
+		return false
+	}
+}
+
+func validateConfig(cfg *Config) error {
+	if cfg == nil {
+		return errors.New("config cannot be nil")
+	}
+
+	// Check if ContextKeys is empty.
+	if len(cfg.ContextKeys) == 0 {
+		return errors.New("ContextKeys cannot be empty")
+	}
+
+	// Validate that ContextKeys does not contain empty strings.
+	for _, key := range cfg.ContextKeys {
+		if key == "" {
+			return errors.New("ContextKeys cannot contain empty strings")
+		}
+	}
+	return nil
+}