chore: move to go folder

go/internal/core/utils.go

@@ -0,0 +1,129 @@
+package core
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"io"
+	"reflect"
+	"strings"
+
+	"github.com/gin-gonic/gin/binding"
+	"github.com/go-playground/validator/v10"
+)
+
+type FieldError struct {
+	Field   string `json:"field"`
+	Tag     string `json:"tag"`
+	Param   string `json:"param,omitempty"`
+	Message string `json:"message"`
+}
+
+type ValidationError struct {
+	Errors []FieldError `json:"errors"`
+}
+
+func (e *ValidationError) Error() string {
+	return fmt.Sprintf("validation failed (%d errors)", len(e.Errors))
+}
+
+// DecodeStrict decodes a JSON object from raw, rejects unknown fields, and
+// validates struct tags (binding:"..."). Returns a ValidationError for
+// semantic issues so callers can map it to HTTP 422.
+func DecodeStrict[T any](raw json.RawMessage) (T, error) {
+	var out T
+
+	trimmed := bytes.TrimSpace(raw)
+	if len(trimmed) == 0 || bytes.Equal(trimmed, []byte("null")) {
+		return out, &ValidationError{
+			Errors: []FieldError{{
+				Field:   "",
+				Tag:     "required",
+				Message: "config is required",
+			}},
+		}
+	}
+	if trimmed[0] != '{' {
+		return out, fmt.Errorf("config must be a JSON object")
+	}
+
+	dec := json.NewDecoder(bytes.NewReader(raw))
+	dec.DisallowUnknownFields()
+	if err := dec.Decode(&out); err != nil {
+		return out, fmt.Errorf("invalid JSON: %w", err)
+	}
+	// Ensure no trailing junk after the object
+	if err := dec.Decode(&struct{}{}); err != io.EOF {
+		if err == nil {
+			return out, errors.New("unexpected trailing data after JSON object")
+		}
+		return out, fmt.Errorf("invalid JSON: %w", err)
+	}
+
+	if binding.Validator == nil {
+		return out, errors.New("validator not initialized")
+	}
+	if err := binding.Validator.ValidateStruct(out); err != nil {
+		if verrs, ok := err.(validator.ValidationErrors); ok {
+			return out, toValidationError[T](verrs)
+		}
+		return out, err
+	}
+
+	return out, nil
+}
+
+func toValidationError[T any](verrs validator.ValidationErrors) *ValidationError {
+	errs := make([]FieldError, 0, len(verrs))
+	t := reflect.TypeOf((*T)(nil)).Elem()
+	if t.Kind() == reflect.Pointer {
+		t = t.Elem()
+	}
+
+	for _, fe := range verrs {
+		name := fe.Field()
+		if t.Kind() == reflect.Struct {
+			if sf, ok := t.FieldByName(fe.StructField()); ok {
+				if tag := sf.Tag.Get("json"); tag != "" && tag != "-" {
+					name = strings.Split(tag, ",")[0]
+				} else {
+					// fallback to lower-camel for nicer output
+					name = lowerCamel(name)
+				}
+			}
+		}
+		errs = append(errs, FieldError{
+			Field:   name,
+			Tag:     fe.Tag(),
+			Param:   fe.Param(),
+			Message: defaultMsg(fe),
+		})
+	}
+	return &ValidationError{Errors: errs}
+}
+
+func defaultMsg(fe validator.FieldError) string {
+	switch fe.Tag() {
+	case "required":
+		return ""
+	case "min":
+		return fmt.Sprintf("must be at least %s", fe.Param())
+	case "max":
+		return fmt.Sprintf("must be at most %s", fe.Param())
+	case "oneof":
+		return "must be one of: " + fe.Param()
+	case "hostname", "ip":
+		return "must be a valid " + fe.Tag()
+	}
+	return fe.Error()
+}
+
+func lowerCamel(s string) string {
+	if s == "" {
+		return s
+	}
+	r := []rune(s)
+	r[0] = []rune(strings.ToLower(string(r[0])))[0]
+	return string(r)
+}