Fixes a bug that made a copy of the changing vars within the verifier leading to an incorrect count (#8451)

Removes all the unneeded keyword (mutating) from verifier

Adds tests to verify depth

Author: mustiikhalil

swift/Sources/FlatBuffers/Verifier.swift

@@ -22,22 +22,29 @@ public struct Verifier {
 
   /// Flag to check for alignment if true
   fileprivate let _checkAlignment: Bool
-  /// Capacity of the current buffer
-  fileprivate var _capacity: Int
-  /// Current ApparentSize
-  fileprivate var _apparentSize: UOffset = 0
-  /// Amount of tables present within a buffer
-  fileprivate var _tableCount = 0
-
-  /// Capacity of the buffer
-  internal var capacity: Int { _capacity }
-  /// Current reached depth within the buffer
-  internal var _depth = 0
+  /// Storage for all changing values within the verifier
+  private let storage: Storage
   /// Current verifiable ByteBuffer
   internal var _buffer: ByteBuffer
   /// Options for verification
   internal let _options: VerifierOptions
 
+  /// Current stored capacity within the verifier
+  var capacity: Int {
+    storage.capacity
+  }
+
+  /// Current depth of verifier
+  var depth: Int {
+    storage.depth
+  }
+
+  /// Current table count
+  var tableCount: Int {
+    storage.tableCount
+  }
+
+
   /// Initializer for the verifier
   /// - Parameters:
   ///   - buffer: Bytebuffer that is required to be verified
@@ -54,23 +61,23 @@ public struct Verifier {
     }
 
     _buffer = buffer
-    _capacity = buffer.capacity
     _checkAlignment = checkAlignment
     _options = options
+    storage = Storage(capacity: buffer.capacity)
   }
 
   /// Resets the verifier to initial state
-  public mutating func reset() {
-    _depth = 0
-    _tableCount = 0
+  public func reset() {
+    storage.depth = 0
+    storage.tableCount = 0
   }
 
   /// Checks if the value of type `T` is aligned properly in the buffer
   /// - Parameters:
   ///   - position: Current position
   ///   - type: Type of value to check
   /// - Throws: `missAlignedPointer` if the pointer is not aligned properly
-  public mutating func isAligned<T>(position: Int, type: T.Type) throws {
+  public func isAligned<T>(position: Int, type: T.Type) throws {
 
     /// If check alignment is false this mutating function doesnt continue
     if !_checkAlignment { return }
@@ -94,13 +101,13 @@ public struct Verifier {
   /// - Throws: `outOfBounds` if the value is out of the bounds of the buffer
   /// and `apparentSizeTooLarge` if the apparent size is bigger than the one specified
   /// in `VerifierOptions`
-  public mutating func rangeInBuffer(position: Int, size: Int) throws {
+  public func rangeInBuffer(position: Int, size: Int) throws {
     let end = UInt(clamping: (position &+ size).magnitude)
     if end > _buffer.capacity {
-      throw FlatbuffersErrors.outOfBounds(position: end, end: capacity)
+      throw FlatbuffersErrors.outOfBounds(position: end, end: storage.capacity)
     }
-    _apparentSize = _apparentSize &+ UInt32(size)
-    if _apparentSize > _options._maxApparentSize {
+    storage.apparentSize = storage.apparentSize &+ UInt32(size)
+    if storage.apparentSize > _options._maxApparentSize {
       throw FlatbuffersErrors.apparentSizeTooLarge
     }
   }
@@ -111,7 +118,7 @@ public struct Verifier {
   ///   - position: Current readable position
   ///   - type: Type of value to check
   /// - Throws: FlatbuffersErrors
-  public mutating func inBuffer<T>(position: Int, of type: T.Type) throws {
+  public func inBuffer<T>(position: Int, of type: T.Type) throws {
     try isAligned(position: position, type: type)
     try rangeInBuffer(position: position, size: MemoryLayout<T>.size)
   }
@@ -131,15 +138,15 @@ public struct Verifier {
       type: VOffset.self)
     try rangeInBuffer(position: vtablePosition, size: length)
 
-    _tableCount += 1
+    storage.tableCount += 1
 
-    if _tableCount > _options._maxTableCount {
+    if storage.tableCount > _options._maxTableCount {
       throw FlatbuffersErrors.maximumTables
     }
 
-    _depth += 1
+    storage.depth += 1
 
-    if _depth > _options._maxDepth {
+    if storage.depth > _options._maxDepth {
       throw FlatbuffersErrors.maximumDepth
     }
 
@@ -154,7 +161,7 @@ public struct Verifier {
   /// - Parameter position: Current position to be read
   /// - Throws: `inBuffer` errors
   /// - Returns: a value of type `T` usually a `VTable` or a table offset
-  internal mutating func getValue<T>(at position: Int) throws -> T {
+  internal func getValue<T>(at position: Int) throws -> T {
     try inBuffer(position: position, of: T.self)
     return _buffer.read(def: T.self, position: position)
   }
@@ -165,7 +172,7 @@ public struct Verifier {
   /// - Throws: `inBuffer` errors & `signedOffsetOutOfBounds`
   /// - Returns: Current readable position for a field
   @inline(__always)
-  internal mutating func derefOffset(position: Int) throws -> Int {
+  internal func derefOffset(position: Int) throws -> Int {
     try inBuffer(position: position, of: Int32.self)
 
     let offset = _buffer.read(def: Int32.self, position: position)
@@ -197,14 +204,14 @@ public struct Verifier {
   }
 
   /// finishes the current iteration of verification on an object
-  internal mutating func finish() {
-    _depth -= 1
+  internal func finish() {
+    storage.depth -= 1
   }
 
   @inline(__always)
-  mutating func verify(id: String) throws {
+  func verify(id: String) throws {
     let size = MemoryLayout<Int32>.size
-    guard _capacity >= (size * 2) else {
+    guard storage.capacity >= (size * 2) else {
       throw FlatbuffersErrors.bufferDoesntContainID
     }
     let str = _buffer.readString(at: size, count: size)
@@ -214,4 +221,18 @@ public struct Verifier {
     throw FlatbuffersErrors.bufferIdDidntMatchPassedId
   }
 
+  final private class Storage {
+    /// Current ApparentSize
+    fileprivate var apparentSize: UOffset = 0
+    /// Amount of tables present within a buffer
+    fileprivate var tableCount = 0
+    /// Capacity of the current buffer
+    fileprivate let capacity: Int
+    /// Current reached depth within the buffer
+    fileprivate var depth = 0
+
+    init(capacity: Int) {
+      self.capacity = capacity
+    }
+  }
 }

tests/swift/tests/Tests/FlatBuffers.Test.SwiftTests/FlatBuffersVectorsTests.swift

@@ -65,9 +65,6 @@ final class FlatBuffersVectors: XCTestCase {
     var b = FlatBufferBuilder(initialSize: 100)
     let o = b.createVector(ofStructs: vector)
     b.finish(offset: o)
-    vector.withUnsafeBytes { pointer in
-      print(Array(pointer))
-    }
     // swiftformat:disable all
     XCTAssertEqual(b.sizedByteArray, [4, 0, 0, 0, 3, 0, 0, 0, 0, 0, 128, 63, 0, 0, 0, 64, 0, 0, 64, 64, 0, 0, 128, 64, 0, 0, 160, 64, 0, 0, 192, 64, 0, 0, 224, 64, 0, 0, 0, 65, 0, 0, 16, 65])
     // swiftformat:enable all

tests/swift/tests/Tests/FlatBuffers.Test.SwiftTests/FlatbuffersVerifierTests.swift

@@ -75,7 +75,7 @@ final class FlatbuffersVerifierTests: XCTestCase {
   }
 
   func testVerifierCheckAlignment() {
-    var verifier = try! Verifier(buffer: &buffer)
+    let verifier = try! Verifier(buffer: &buffer)
     do {
       try verifier.isAligned(position: 20, type: Int.self)
     } catch {
@@ -85,7 +85,7 @@ final class FlatbuffersVerifierTests: XCTestCase {
     }
     XCTAssertNoThrow(try verifier.isAligned(position: 16, type: Int.self))
 
-    var newVerifer = try! Verifier(buffer: &buffer, checkAlignment: false)
+    let newVerifer = try! Verifier(buffer: &buffer, checkAlignment: false)
     XCTAssertNoThrow(try newVerifer.isAligned(position: 16, type: Int.self))
   }
 
@@ -112,7 +112,7 @@ final class FlatbuffersVerifierTests: XCTestCase {
   }
 
   func testPositionInBuffer() {
-    var verifier = try! Verifier(buffer: &buffer)
+    let verifier = try! Verifier(buffer: &buffer)
     XCTAssertNoThrow(try verifier.inBuffer(position: 0, of: Int64.self))
     XCTAssertNoThrow(try verifier.inBuffer(position: 24, of: Int64.self))
     XCTAssertThrowsError(try verifier.inBuffer(position: -9, of: Int64.self))
@@ -134,6 +134,9 @@ final class FlatbuffersVerifierTests: XCTestCase {
     var verifier = try! Verifier(buffer: &validFlatbuffersObject)
 
     var tableVerifer = try! verifier.visitTable(at: 48)
+    XCTAssertEqual(verifier.depth, 1)
+    XCTAssertEqual(verifier.tableCount, 1)
+
     XCTAssertNoThrow(try tableVerifer.visit(
       field: 4,
       fieldName: "Vec",
@@ -210,6 +213,8 @@ final class FlatbuffersVerifierTests: XCTestCase {
         error as! FlatbuffersErrors,
         .missAlignedPointer(position: 25, type: "UInt16"))
     }
+    tableVerifer.finish()
+    XCTAssertEqual(verifier.depth, 0)
   }
 
   func testVerifyUnionVectors() {
@@ -291,7 +296,51 @@ final class FlatbuffersVerifierTests: XCTestCase {
     XCTAssertNoThrow(try getCheckedRoot(byteBuffer: &buf) as Movie)
   }
 
+  func testNestedTables() throws {
+    var builder = FlatBufferBuilder()
+    let name = builder.create(string: "Monster")
+
+    let enemy = MyGame_Example_Monster.createMonster(
+      &builder,
+      nameOffset: name)
+    let currentName = builder.create(string: "Main name")
+    let monster = MyGame_Example_Monster.createMonster(
+      &builder,
+      nameOffset: currentName,
+      enemyOffset: enemy)
+    builder.finish(offset: monster)
+
+    var sizedBuffer = builder.sizedBuffer
+    var verifier = try! Verifier(buffer: &sizedBuffer)
+    var tableVerifer = try! verifier.visitTable(
+      at: try getOffset(at: 0, within: verifier))
+    XCTAssertEqual(verifier.depth, 1)
+    XCTAssertEqual(verifier.tableCount, 1)
+
+    let position = try tableVerifer.dereference(28)!
+
+    var nestedTable = try verifier.visitTable(
+      at: try getOffset(at: position, within: verifier))
+
+    XCTAssertEqual(verifier.depth, 2)
+    XCTAssertEqual(verifier.tableCount, 2)
+    nestedTable.finish()
+    XCTAssertEqual(verifier.depth, 1)
+    XCTAssertEqual(verifier.tableCount, 2)
+    tableVerifer.finish()
+    XCTAssertEqual(verifier.depth, 0)
+    XCTAssertEqual(verifier.tableCount, 2)
+  }
+
   func add(buffer: inout ByteBuffer, v: Int32, p: Int) {
     buffer.write(value: v, index: p)
   }
+
+  private func getOffset(
+    at value: Int,
+    within verifier: Verifier) throws -> Int
+  {
+    let offset: UOffset = try verifier.getValue(at: value)
+    return Int(clamping: (Int(offset) &+ 0).magnitude)
+  }
 }