add swift flatbuffers

flatbuffers/TableVerifier.swift

@@ -0,0 +1,207 @@
+/*
+ * Copyright 2023 Google Inc. All rights reserved.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+
+#if !os(WASI)
+import Foundation
+#else
+import SwiftOverlayShims
+#endif
+
+/// `TableVerifier` verifies a table object is within a provided memory.
+/// It checks if all the objects for a specific generated table, are within
+/// the bounds of the buffer, aligned.
+public struct TableVerifier {
+
+  /// position of current table in `ByteBuffer`
+  fileprivate var _position: Int
+
+  /// Current VTable position
+  fileprivate var _vtable: Int
+
+  /// Length of current VTable
+  fileprivate var _vtableLength: Int
+
+  /// `Verifier` object created in the base verifable call.
+  fileprivate var _verifier: Verifier
+
+  /// Creates a `TableVerifier` verifier that allows the Flatbuffer object
+  /// to verify the buffer before accessing any of the data.
+  ///
+  /// - Parameters:
+  ///   - position: Current table Position
+  ///   - vtable: Current `VTable` position
+  ///   - vtableLength: Current `VTable` length
+  ///   - verifier: `Verifier` Object  that caches the data of the verifiable object
+  internal init(
+    position: Int,
+    vtable: Int,
+    vtableLength: Int,
+    verifier: inout Verifier)
+  {
+    _position = position
+    _vtable = vtable
+    _vtableLength = vtableLength
+    _verifier = verifier
+  }
+
+  /// Dereference the current object position from the `VTable`
+  /// - Parameter field: Current VTable refrence to  position.
+  /// - Throws: A `FlatbuffersErrors` incase the voffset is not aligned/outOfBounds/apparentSizeTooLarge
+  /// - Returns: An optional position for current field
+  internal mutating func dereference(_ field: VOffset) throws -> Int? {
+    if field >= _vtableLength {
+      return nil
+    }
+
+    /// Reading the offset for the field needs to be read.
+    let offset: VOffset = try _verifier.getValue(
+      at: Int(clamping: _vtable &+ Int(field)))
+
+    if offset > 0 {
+      return Int(clamping: _position &+ Int(offset))
+    }
+    return nil
+  }
+
+  /// Visits all the fields within the table to validate the integrity
+  /// of the data
+  /// - Parameters:
+  ///   - field: voffset of the current field to be read
+  ///   - fieldName: fieldname to report data Errors.
+  ///   - required: If the field has to be available in the buffer
+  ///   - type: Type of field to be read
+  /// - Throws: A `FlatbuffersErrors` where the field is corrupt
+  public mutating func visit<T>(
+    field: VOffset,
+    fieldName: String,
+    required: Bool,
+    type: T.Type) throws where T: Verifiable
+  {
+    let derefValue = try dereference(field)
+
+    if let value = derefValue {
+      try T.verify(&_verifier, at: value, of: T.self)
+      return
+    }
+    if required {
+      throw FlatbuffersErrors.requiredFieldDoesntExist(
+        position: field,
+        name: fieldName)
+    }
+  }
+
+  /// Visits all the fields for a union object within the table to
+  /// validate the integrity of the data
+  /// - Parameters:
+  ///   - key: Current Key Voffset
+  ///   - field: Current field Voffset
+  ///   - unionKeyName: Union key name
+  ///   - fieldName: Field key name
+  ///   - required: indicates if an object is required to be present
+  ///   - completion: Completion is a handler that WILL be called in the generated
+  /// - Throws: A `FlatbuffersErrors` where the field is corrupt
+  public mutating func visit<T>(
+    unionKey key: VOffset,
+    unionField field: VOffset,
+    unionKeyName: String,
+    fieldName: String,
+    required: Bool,
+    completion: @escaping (inout Verifier, T, Int) throws -> Void) throws
+    where T: UnionEnum
+  {
+    let keyPos = try dereference(key)
+    let valPos = try dereference(field)
+
+    if keyPos == nil && valPos == nil {
+      if required {
+        throw FlatbuffersErrors.requiredFieldDoesntExist(
+          position: key,
+          name: unionKeyName)
+      }
+      return
+    }
+
+    if let _key = keyPos,
+       let _val = valPos
+    {
+      /// verifiying that the key is within the buffer
+      try T.T.verify(&_verifier, at: _key, of: T.T.self)
+      guard let _enum = try T.init(value: _verifier._buffer.read(
+        def: T.T.self,
+        position: _key)) else
+      {
+        throw FlatbuffersErrors.unknownUnionCase
+      }
+      /// we are assuming that Unions will always be of type Uint8
+      try completion(
+        &_verifier,
+        _enum,
+        _val)
+      return
+    }
+    throw FlatbuffersErrors.valueNotFound(
+      key: keyPos,
+      keyName: unionKeyName,
+      field: valPos,
+      fieldName: fieldName)
+  }
+
+  /// Visits and validates all the objects within a union vector
+  /// - Parameters:
+  ///   - key: Current Key Voffset
+  ///   - field: Current field Voffset
+  ///   - unionKeyName: Union key name
+  ///   - fieldName: Field key name
+  ///   - required: indicates if an object is required to be present
+  ///   - completion: Completion is a handler that WILL be called in the generated
+  /// - Throws: A `FlatbuffersErrors` where the field is corrupt
+  public mutating func visitUnionVector<T>(
+    unionKey key: VOffset,
+    unionField field: VOffset,
+    unionKeyName: String,
+    fieldName: String,
+    required: Bool,
+    completion: @escaping (inout Verifier, T, Int) throws -> Void) throws
+    where T: UnionEnum
+  {
+    let keyVectorPosition = try dereference(key)
+    let offsetVectorPosition = try dereference(field)
+
+    if let keyPos = keyVectorPosition,
+       let valPos = offsetVectorPosition
+    {
+      try UnionVector<T>.verify(
+        &_verifier,
+        keyPosition: keyPos,
+        fieldPosition: valPos,
+        unionKeyName: unionKeyName,
+        fieldName: fieldName,
+        completion: completion)
+      return
+    }
+    if required {
+      throw FlatbuffersErrors.requiredFieldDoesntExist(
+        position: field,
+        name: fieldName)
+    }
+  }
+
+  /// Finishs the current Table verifier, and subtracts the current
+  /// table from the incremented depth.
+  public mutating func finish() {
+    _verifier.finish()
+  }
+}