Adds a way to verify/exposes Entities ids (#7221)

swift/Sources/FlatBuffers/ByteBuffer.swift

@@ -400,10 +400,13 @@ public struct ByteBuffer {
   /// SkipPrefix Skips the first 4 bytes in case one of the following
   /// functions are called `getPrefixedSizeCheckedRoot` & `getPrefixedSizeRoot`
   /// which allows us to skip the first 4 bytes instead of recreating the buffer
+  @discardableResult
   @usableFromInline
-  mutating func skipPrefix() {
+  mutating func skipPrefix() -> Int32 {
     _writerSize = _writerSize &- MemoryLayout<Int32>.size
+    return read(def: Int32.self, position: 0)
   }
+
 }
 
 extension ByteBuffer: CustomDebugStringConvertible {

swift/Sources/FlatBuffers/FlatbuffersErrors.swift

@@ -19,6 +19,10 @@ import Foundation
 /// Collection of thrown from the Flatbuffer verifier
 public enum FlatbuffersErrors: Error, Equatable {
 
+  /// Thrown when verifying a file id that doesnt match buffer id
+  case bufferIdDidntMatchPassedId
+  /// Prefixed size doesnt match the current (readable) buffer size
+  case prefixedSizeNotEqualToBufferSize
   /// Thrown when buffer is bigger than the allowed 2GiB
   case exceedsMaxSizeAllowed
   /// Thrown when there is an missaligned pointer at position

swift/Sources/FlatBuffers/Root.swift

@@ -28,10 +28,39 @@ import Foundation
 /// the ``ByteBuffer`` and verifies the buffer by calling ``getCheckedRoot(byteBuffer:options:)``
 public func getPrefixedSizeCheckedRoot<T: FlatBufferObject & Verifiable>(
   byteBuffer: inout ByteBuffer,
+  fileId: String? = nil,
   options: VerifierOptions = .init()) throws -> T
 {
   byteBuffer.skipPrefix()
-  return try getCheckedRoot(byteBuffer: &byteBuffer, options: options)
+  return try getCheckedRoot(
+    byteBuffer: &byteBuffer,
+    fileId: fileId,
+    options: options)
+}
+
+/// Takes in a prefixed sized buffer, where we check if the sized buffer is equal to prefix size.
+/// And would verify that the buffer passed is a valid `Flatbuffers` Object.
+/// - Parameters:
+///   - byteBuffer: Buffer that needs to be checked and read
+///   - options: Verifier options
+/// - Throws: FlatbuffersErrors
+/// - Returns: Returns a valid, checked Flatbuffers object
+///
+/// ``getPrefixedSizeCheckedRoot(byteBuffer:options:)`` would skip the first Bytes in
+/// the ``ByteBuffer`` and verifies the buffer by calling ``getCheckedRoot(byteBuffer:options:)``
+public func getCheckedPrefixedSizeRoot<T: FlatBufferObject & Verifiable>(
+  byteBuffer: inout ByteBuffer,
+  fileId: String? = nil,
+  options: VerifierOptions = .init()) throws -> T
+{
+  let prefix = byteBuffer.skipPrefix()
+  if prefix != byteBuffer.size {
+    throw FlatbuffersErrors.prefixedSizeNotEqualToBufferSize
+  }
+  return try getCheckedRoot(
+    byteBuffer: &byteBuffer,
+    fileId: fileId,
+    options: options)
 }
 
 /// Takes in a prefixed sized buffer, where the prefixed size would be skipped.
@@ -61,9 +90,13 @@ public func getPrefixedSizeRoot<T: FlatBufferObject>(byteBuffer: inout ByteBuffe
 /// and within the ``ByteBuffer`` range.
 public func getCheckedRoot<T: FlatBufferObject & Verifiable>(
   byteBuffer: inout ByteBuffer,
+  fileId: String? = nil,
   options: VerifierOptions = .init()) throws -> T
 {
   var verifier = try Verifier(buffer: &byteBuffer, options: options)
+  if let fileId = fileId {
+    try verifier.verify(id: fileId)
+  }
   try ForwardOffset<T>.verify(&verifier, at: 0, of: T.self)
   return T.init(
     byteBuffer,

swift/Sources/FlatBuffers/Verifier.swift

@@ -200,4 +200,14 @@ public struct Verifier {
   internal mutating func finish() {
     _depth -= 1
   }
+
+  mutating func verify(id: String) throws {
+    let size = MemoryLayout<Int32>.size
+    let str = _buffer.readString(at: size, count: size)
+    if id == str {
+      return
+    }
+    throw FlatbuffersErrors.bufferIdDidntMatchPassedId
+  }
+
 }