Create FileStream.md

FileStream.md

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+# File Input Stream
+
+`FileInputStream` is used for reading data from a file. It can be added to a ciphers chain
+```swift
+let inputFileStream = FileInputStream(with: try! FileHandle(forReadingFrom: originalFileURL))
+try inputFileStream.open()
+```
+```swift
+guard let inputFileStream = FileInputStream(with: originalFileURL) else {
+  // file not exist
+  return
+}
+try inputFileStream.open()
+```
+```swift
+let tmpBufferLen = 1<<16 // 65KB buffer
+var tmpBuffer = Array<UInt8>(repeating: 0, count: tmpBufferLen)
+while inputFileStream.hasBytesAvailable {
+  let readLen = inputFileStream.read(&tmpBuffer, maxLength: tmpBufferLen)
+  try compressingStream.write(tmpBuffer, length: readLen)
+}
+```