Validate public JSON-like inputs

json_copy.go

@@ -0,0 +1,218 @@
+package scriptorium
+
+import (
+	"encoding/json"
+	"fmt"
+	"math"
+	"reflect"
+	"strconv"
+)
+
+const maxSafeJSONInteger = 1<<53 - 1
+
+type jsonVisit struct {
+	typ reflect.Type
+	ptr uintptr
+}
+
+func copyPublicJSONMap(src map[string]any) (map[string]any, error) {
+	if src == nil {
+		return nil, nil
+	}
+	copied, err := copyPublicJSONValue(reflect.ValueOf(src), "extra_params", make(map[jsonVisit]struct{}))
+	if err != nil {
+		return nil, err
+	}
+	out, ok := copied.(map[string]any)
+	if !ok {
+		return nil, fmt.Errorf("extra_params: expected object")
+	}
+	return out, nil
+}
+
+func copyPublicJSONValue(value reflect.Value, path string, seen map[jsonVisit]struct{}) (any, error) {
+	if !value.IsValid() {
+		return nil, nil
+	}
+	if value.Kind() == reflect.Interface {
+		if value.IsNil() {
+			return nil, nil
+		}
+		return copyPublicJSONValue(value.Elem(), path, seen)
+	}
+	if !value.CanInterface() {
+		return nil, fmt.Errorf("%s: value cannot be copied", path)
+	}
+	if number, ok := value.Interface().(json.Number); ok {
+		f, err := strconv.ParseFloat(number.String(), 64)
+		if err != nil || math.IsNaN(f) || math.IsInf(f, 0) {
+			return nil, fmt.Errorf("%s: invalid JSON number", path)
+		}
+		return number, nil
+	}
+
+	switch value.Kind() {
+	case reflect.Bool, reflect.String:
+		return value.Interface(), nil
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		if value.Int() < -maxSafeJSONInteger || value.Int() > maxSafeJSONInteger {
+			return nil, fmt.Errorf("%s: integer is outside the JSON-safe range", path)
+		}
+		return value.Interface(), nil
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
+		if value.Uint() > maxSafeJSONInteger {
+			return nil, fmt.Errorf("%s: integer is outside the JSON-safe range", path)
+		}
+		return value.Interface(), nil
+	case reflect.Float32, reflect.Float64:
+		f := value.Convert(reflect.TypeOf(float64(0))).Float()
+		if math.IsNaN(f) || math.IsInf(f, 0) {
+			return nil, fmt.Errorf("%s: floating-point value must be finite", path)
+		}
+		return value.Interface(), nil
+	case reflect.Pointer:
+		if value.IsNil() {
+			return nil, nil
+		}
+		visit := jsonVisit{typ: value.Type(), ptr: value.Pointer()}
+		if _, ok := seen[visit]; ok {
+			return nil, fmt.Errorf("%s: cyclic value is not supported", path)
+		}
+		seen[visit] = struct{}{}
+		defer delete(seen, visit)
+		return copyPublicJSONValue(value.Elem(), path, seen)
+	case reflect.Map:
+		return copyPublicJSONMapValue(value, path, seen)
+	case reflect.Slice:
+		if value.IsNil() {
+			return nil, nil
+		}
+		return copyPublicJSONSequenceValue(value, path, seen)
+	case reflect.Array:
+		return copyPublicJSONSequenceValue(value, path, seen)
+	default:
+		return nil, fmt.Errorf("%s: unsupported JSON value type %s", path, value.Type())
+	}
+}
+
+func copyPublicJSONMapValue(value reflect.Value, path string, seen map[jsonVisit]struct{}) (any, error) {
+	if value.IsNil() {
+		return nil, nil
+	}
+	if value.Type().Key().Kind() != reflect.String {
+		return nil, fmt.Errorf("%s: map key type %s is not supported", path, value.Type().Key())
+	}
+
+	visit := jsonVisit{typ: value.Type(), ptr: value.Pointer()}
+	if _, ok := seen[visit]; ok {
+		return nil, fmt.Errorf("%s: cyclic value is not supported", path)
+	}
+	seen[visit] = struct{}{}
+	defer delete(seen, visit)
+
+	type entry struct {
+		key   reflect.Value
+		name  string
+		value any
+	}
+	entries := make([]entry, 0, value.Len())
+	preserveType := true
+	elemType := value.Type().Elem()
+	iter := value.MapRange()
+	for iter.Next() {
+		key := iter.Key()
+		name := key.String()
+		copied, err := copyPublicJSONValue(iter.Value(), path+"."+name, seen)
+		if err != nil {
+			return nil, err
+		}
+		entries = append(entries, entry{key: key, name: name, value: copied})
+		if copied == nil {
+			if !canAssignNil(elemType) {
+				preserveType = false
+			}
+			continue
+		}
+		if !reflect.TypeOf(copied).AssignableTo(elemType) {
+			preserveType = false
+		}
+	}
+
+	if preserveType {
+		out := reflect.MakeMapWithSize(value.Type(), len(entries))
+		for _, entry := range entries {
+			if entry.value == nil {
+				out.SetMapIndex(entry.key, reflect.Zero(elemType))
+				continue
+			}
+			out.SetMapIndex(entry.key, reflect.ValueOf(entry.value))
+		}
+		return out.Interface(), nil
+	}
+
+	out := make(map[string]any, len(entries))
+	for _, entry := range entries {
+		out[entry.name] = entry.value
+	}
+	return out, nil
+}
+
+func copyPublicJSONSequenceValue(value reflect.Value, path string, seen map[jsonVisit]struct{}) (any, error) {
+	var visit jsonVisit
+	if value.Kind() == reflect.Slice {
+		visit = jsonVisit{typ: value.Type(), ptr: value.Pointer()}
+		if _, ok := seen[visit]; ok {
+			return nil, fmt.Errorf("%s: cyclic value is not supported", path)
+		}
+		seen[visit] = struct{}{}
+		defer delete(seen, visit)
+	}
+
+	values := make([]any, value.Len())
+	preserveType := true
+	elemType := value.Type().Elem()
+	for i := 0; i < value.Len(); i++ {
+		copied, err := copyPublicJSONValue(value.Index(i), fmt.Sprintf("%s[%d]", path, i), seen)
+		if err != nil {
+			return nil, err
+		}
+		values[i] = copied
+		if copied == nil {
+			if !canAssignNil(elemType) {
+				preserveType = false
+			}
+			continue
+		}
+		if !reflect.TypeOf(copied).AssignableTo(elemType) {
+			preserveType = false
+		}
+	}
+
+	if preserveType {
+		out := reflect.New(value.Type()).Elem()
+		if value.Kind() == reflect.Slice {
+			out = reflect.MakeSlice(value.Type(), value.Len(), value.Len())
+		}
+		for i, copied := range values {
+			if copied == nil {
+				out.Index(i).Set(reflect.Zero(elemType))
+				continue
+			}
+			out.Index(i).Set(reflect.ValueOf(copied))
+		}
+		return out.Interface(), nil
+	}
+
+	out := make([]any, len(values))
+	copy(out, values)
+	return out, nil
+}
+
+func canAssignNil(typ reflect.Type) bool {
+	switch typ.Kind() {
+	case reflect.Chan, reflect.Func, reflect.Interface, reflect.Map, reflect.Pointer, reflect.Slice:
+		return true
+	default:
+		return false
+	}
+}