Add preconditions to DataStream, tweak seek API (#3)

Author: MaxDesiatov

Sources/OLEKit/DataStream.swift

@@ -37,12 +37,19 @@ public final class DataReader: Reader {
     self.data = data
   }
 
-  public func seek(toOffset offset: UInt64) {
-    byteOffset = Int(offset)
+  public var totalBytes: Int {
+    data.count
+  }
+
+  public func seek(toOffset offset: Int) {
+    precondition(offset < data.count)
+
+    byteOffset = offset
   }
 
   /// Read a single byte from the stream and increment `byteOffset` by 1.
   public func read() -> UInt8 {
+    precondition(byteOffset + 1 <= data.count)
     defer { byteOffset += 1 }
 
     return data[byteOffset]
@@ -51,6 +58,7 @@ public final class DataReader: Reader {
   /// Read two bytes in little-endian order as a single `UInt16` value and
   /// increment `byteOffset` by 2.
   public func read() -> UInt16 {
+    precondition(byteOffset + 2 <= data.count)
     defer { byteOffset += 2 }
 
     return (UInt16(data[byteOffset + 1]) << 8) + UInt16(data[byteOffset])
@@ -59,6 +67,7 @@ public final class DataReader: Reader {
   /// Read four bytes in little-endian order as a single `UInt32` value and
   /// increment `byteOffset` by 4.
   public func read() -> UInt32 {
+    precondition(byteOffset + 4 <= data.count)
     defer { byteOffset += 4 }
 
     return (UInt32(data[byteOffset + 3]) << 24)
@@ -69,12 +78,15 @@ public final class DataReader: Reader {
 
   /// Read a given `count` of bytes as raw data and increment `byteOffset` by `count`.
   public func readData(ofLength length: Int) -> Data {
+    precondition(byteOffset + length <= data.count)
     defer { byteOffset += length }
 
     return data[byteOffset..<byteOffset + length]
   }
 
   public func readDataToEnd() -> Data {
+    guard data.count > 0 else { return data }
+
     defer { byteOffset = data.count - 1 }
 
     return data[byteOffset..<data.count]

Sources/OLEKit/OLEStream.swift

@@ -54,7 +54,7 @@ extension Reader {
       guard currentSectorID >= 0 && UInt64(currentSectorID) < fat.count
       else { throw OLEError.invalidOLEStreamSectorID(id: currentSectorID, total: fat.count) }
 
-      seek(toOffset: firstSectorOffset + UInt64(sectorSize) * UInt64(currentSectorID))
+      seek(toOffset: Int(firstSectorOffset) + Int(sectorSize) * Int(currentSectorID))
 
       // if sector is the last of the file, sometimes it is not a
       // complete sector (of 512 or 4K), so we may read less than

Sources/OLEKit/Reader.swift

@@ -2,12 +2,12 @@ import Foundation
 
 /// Helper protocol that presents a unified interface for both `FileHandle` and `DataReader`.
 protocol Reader: AnyObject {
-  func seek(toOffset: UInt64)
+  func seek(toOffset: Int)
   func readData(ofLength: Int) -> Data
   func readDataToEnd() -> Data
 }
 
 extension FileHandle: Reader {
-  func seek(toOffset offset: UInt64) { seek(toFileOffset: offset) }
+  func seek(toOffset offset: Int) { seek(toFileOffset: UInt64(offset)) }
   func readDataToEnd() -> Data { readDataToEndOfFile() }
 }