Menyusun aliran

Penyimpanan pencadangan adalah media penyimpanan, seperti disk atau memori. Setiap jenis penyimpanan backing mengimplementasikan alirannya sendiri sebagai implementasi kelas Stream .

Setiap jenis aliran membaca dan menulis byte dari dan ke penyimpanan pencadangan yang diberikan. Aliran yang terhubung ke penyimpanan pencadangan disebut aliran dasar. Aliran dasar memiliki konstruktor dengan parameter yang diperlukan untuk menghubungkan aliran ke penyimpanan pencadangan. Misalnya, FileStream memiliki konstruktor yang menentukan parameter mode akses, yang menentukan apakah file dibaca dari, ditulis ke, atau keduanya.

Desain kelas System.IO menyediakan komposisi aliran yang disederhanakan. Anda dapat melampirkan aliran dasar ke satu atau beberapa aliran pass-through yang menyediakan fungsionalitas yang Anda inginkan. Anda dapat melampirkan pembaca atau penulis ke ujung rantai, sehingga jenis yang disukai dapat dibaca atau ditulis dengan mudah.

Prasyarat

Contoh-contoh ini menggunakan file teks biasa bernama data.txt. File ini harus berisi beberapa teks.

Contoh: Mengenkripsi dan mendekripsi data aliran

Contoh berikut membaca data dari file, mengenkripsinya, lalu menulis data terenkripsi ke file lain. Komposisi aliran digunakan untuk mengubah data menggunakan cipher pergeseran dasar. Setiap byte yang melewati aliran memiliki nilainya berubah sebesar 80.

Membaca data sumber untuk enkripsi

Kode berikut membaca teks dari satu file, mengubahnya, lalu menulisnya ke file lain.

void WriteShiftedFile()
{
    // Create the base streams for the input and output files
    using FileStream inputBaseStream = File.OpenRead("data.txt");
    using CipherStream encryptStream = CipherStream.CreateForRead(inputBaseStream);
    using FileStream outputBaseStream = File.Open("shifted.txt", FileMode.Create, FileAccess.Write);

    int intValue;

    // Read byte from inputBaseStream through the encryptStream (normal bytes into shifted bytes)
    while ((intValue = encryptStream.ReadByte()) != -1)
    {
        outputBaseStream.WriteByte((byte)intValue);
    }

    // Process is:
    //  (inputBaseStream -> encryptStream) -> outputBaseStream
}

Sub WriteShiftedFile()

    'Create the base streams for the input and output files
    Using inputBaseStream As FileStream = File.OpenRead("data.txt")
        Using encryptStream As CipherStream = CipherStream.CreateForRead(inputBaseStream)
            Using outputBaseStream As FileStream = File.Open("shifted.txt", FileMode.Create, FileAccess.Write)


                'Read byte from inputBaseStream through the encryptStream (normal bytes into shifted bytes)
                Dim intValue As Integer = encryptStream.ReadByte()
                While intValue <> -1

                    outputBaseStream.WriteByte(Convert.ToByte(intValue))

                    intValue = encryptStream.ReadByte()

                End While

            End Using
        End Using
    End Using

    'Process is:
    '  (inputBaseStream -> encryptStream) -> outputBaseStream
End Sub

Pertimbangkan aspek-aspek berikut tentang kode sebelumnya:

• Ada dua FileStream objek:
  • Objek (inputBaseStream variabel) pertama FileStream membaca konten file data.txt. Ini adalah aliran data input .
  • Objek kedua FileStream (outputBaseStream variabel) menulis data masuk ke file shifted.txt . Ini adalah aliran data output .
• Objek CipherStream (encryptStream variabel) membungkus inputBaseStream, membuat inputBaseStream aliran dasar untuk encryptStream.

Aliran input dapat dibaca dari secara langsung, menulis data ke aliran output, tetapi itu tidak akan mengubah data. Sebagai gantinya, pembungkus encryptStream aliran input digunakan untuk membaca data. Saat data dibaca dari encryptStream, data akan menarik dari inputBaseStream aliran dasar, mengubahnya, dan mengembalikannya. Data yang dikembalikan ditulis ke outputBaseStream, yang menulis data ke file shifted.txt .

Membaca data yang diubah untuk dekripsi

Kode ini membalikkan enkripsi yang dilakukan oleh kode sebelumnya:

void ReadShiftedFile()
{
    int intValue;

    // Create the base streams for the input and output files
    using FileStream inputBaseStream = File.OpenRead("shifted.txt");
    using FileStream outputBaseStream = File.Open("unshifted.txt", FileMode.Create, FileAccess.Write);
    using CipherStream unencryptStream = CipherStream.CreateForWrite(outputBaseStream);

    // Read byte from inputBaseStream through the encryptStream (shifted bytes into normal bytes)
    while ((intValue = inputBaseStream.ReadByte()) != -1)
    {
        unencryptStream.WriteByte((byte)intValue);
    }

    // Process is:
    //  inputBaseStream -> (encryptStream -> outputBaseStream)
}

Sub ReadShiftedFile()

    'Create the base streams for the input and output files
    Using inputBaseStream As FileStream = File.OpenRead("shifted.txt")
        Using outputBaseStream As FileStream = File.Open("unshifted.txt", FileMode.Create, FileAccess.Write)
            Using unencryptStream As CipherStream = CipherStream.CreateForWrite(outputBaseStream)


                'Read byte from inputBaseStream through the encryptStream (shifted bytes into normal bytes)
                Dim intValue As Integer = inputBaseStream.ReadByte()
                While intValue <> -1

                    unencryptStream.WriteByte(Convert.ToByte(intValue))

                    intValue = inputBaseStream.ReadByte()

                End While

            End Using
        End Using
    End Using

End Sub

Pertimbangkan aspek-aspek berikut tentang kode sebelumnya:

• Ada dua FileStream objek:
  • Objek (inputBaseStream variabel) pertama FileStream membaca konten file shifted.txt. Ini adalah aliran data input .
  • Objek kedua FileStream (outputBaseStream variabel) menulis data masuk ke file unshifted.txt . Ini adalah aliran data output .
• Objek CipherStream (unencryptStream variabel) membungkus outputBaseStream, membuat outputBaseStream aliran dasar untuk unencryptStream.

Di sini, kode sedikit berbeda dari contoh sebelumnya. Alih-alih membungkus aliran input, unencryptStream membungkus aliran output. Saat data dibaca dari inputBaseStream aliran input, data dikirim ke pembungkus unencryptStream aliran output. Saat unencryptStream menerima data, data mengubahnya lalu menulis data ke outputBaseStream aliran dasar. Aliran outputBaseStream output menulis data ke file unshifted.txt .

Memvalidasi data yang diubah

Dua contoh sebelumnya melakukan dua operasi pada data. Pertama, konten file data.txt dienkripsi dan disimpan ke file shifted.txt . Dan kedua, konten terenkripsi dari file shifted.txt didekripsi dan disimpan ke file unshifted.txt . Oleh karena itu, file data.txt dan file unshifted.txt harus sama persis. Kode berikut membandingkan file-file tersebut untuk kesetaraan:

bool IsShiftedFileValid()
{
    // Read the shifted file
    string originalText = File.ReadAllText("data.txt");

    // Read the shifted file
    string shiftedText = File.ReadAllText("unshifted.txt");

    // Check if the decrypted file is valid
    return shiftedText == originalText;
}

Function IsShiftedFileValid() As Boolean

    'Read the shifted file
    Dim originalText As String = File.ReadAllText("data.txt")

    'Read the shifted file
    Dim shiftedText As String = File.ReadAllText("unshifted.txt")

    'Check if the decrypted file is valid
    Return shiftedText = originalText

End Function

Kode berikut menjalankan seluruh proses dekripsi enkripsi ini:

// Read the contents of data.txt, encrypt it, and write it to shifted.txt
WriteShiftedFile();

// Read the contents of shifted.txt, decrypt it, and write it to unshifted.txt
ReadShiftedFile();

// Check if the decrypted file is valid
Console.WriteLine(IsShiftedFileValid()
                    ? "Decrypted file is valid"     // True
                    : "Decrypted file is invalid"   // False
                 );

// Output:
//   Decrypted file is valid

Sub Main(args As String())
    'Read the contents of data.txt, encrypt it, And write it to shifted.txt
    WriteShiftedFile()

    'Read the contents of shifted.txt, decrypt it, And write it to unshifted.txt
    ReadShiftedFile()

    'Check if the decrypted file Is valid
    Console.WriteLine(IIf(IsShiftedFileValid(),
                            "Decrypted file is valid",  ' True
                            "Decrypted file is invalid" ' False
                     ))
End Sub

Kelas CipherStream

Cuplikan berikut menyediakan CipherStream kelas , yang menggunakan cipher shifting dasar untuk mengenkripsi dan mendekripsi byte. Kelas ini mewarisi dari Stream dan mendukung membaca atau menulis data.

using System.IO;

public class CipherStream : Stream
{
    // WARNING: This is a simple encoding algorithm and should not be used in production code

    const byte ENCODING_OFFSET = 80;

    private bool _readable;
    private bool _writable;

    private Stream _wrappedBaseStream;

    public override bool CanRead => _readable;
    public override bool CanSeek => false;
    public override bool CanWrite => _writable;
    public override long Length => _wrappedBaseStream.Length;
    public override long Position
    {
        get => _wrappedBaseStream.Position;
        set => _wrappedBaseStream.Position = value;
    }

    public static CipherStream CreateForRead(Stream baseStream)
    {
        return new CipherStream(baseStream)
        {
            _readable = true,
            _writable = false
        };
    }

    public static CipherStream CreateForWrite(Stream baseStream)
    {
        return new CipherStream(baseStream)
        {
            _readable = false,
            _writable = true
        };
    }

    private CipherStream(Stream baseStream) =>
        _wrappedBaseStream = baseStream;

    public override int Read(byte[] buffer, int offset, int count)
    {
        if (!_readable) throw new NotSupportedException();
        if (count == 0) return 0;

        int returnCounter = 0;

        for (int i = 0; i < count; i++)
        {
            int value = _wrappedBaseStream.ReadByte();

            if (value == -1)
                return returnCounter;

            value += ENCODING_OFFSET;
            if (value > byte.MaxValue)
                value -= byte.MaxValue;

            buffer[i + offset] = Convert.ToByte(value);
            returnCounter++;
        }

        return returnCounter;
    }

    public override void Write(byte[] buffer, int offset, int count)
    {
        if (!_writable) throw new NotSupportedException();

        byte[] newBuffer = new byte[count];
        buffer.CopyTo(newBuffer, offset);

        for (int i = 0; i < count; i++)
        {
            int value = newBuffer[i];

            value -= ENCODING_OFFSET;

            if (value < 0)
                value = byte.MaxValue - value;

            newBuffer[i] = Convert.ToByte(value);
        }

        _wrappedBaseStream.Write(newBuffer, 0, count);
    }

    public override void Flush() => _wrappedBaseStream.Flush();
    public override long Seek(long offset, SeekOrigin origin) => throw new NotSupportedException();
    public override void SetLength(long value) => throw new NotSupportedException();
}

Imports System.IO

Public Class CipherStream
    Inherits Stream

    Const ENCODING_OFFSET As Byte = 80

    Private _readable As Boolean = False
    Private _writable As Boolean = False

    Private _wrappedBaseStream As Stream

    Public Overrides ReadOnly Property CanRead As Boolean
        Get
            Return _readable
        End Get
    End Property

    Public Overrides ReadOnly Property CanSeek As Boolean
        Get
            Return False
        End Get
    End Property

    Public Overrides ReadOnly Property CanWrite As Boolean
        Get
            Return _writable
        End Get
    End Property

    Public Overrides ReadOnly Property Length As Long
        Get
            Return _wrappedBaseStream.Length
        End Get
    End Property

    Public Overrides Property Position As Long
        Get
            Return _wrappedBaseStream.Position
        End Get
        Set(value As Long)
            _wrappedBaseStream.Position = value
        End Set
    End Property

    Public Shared Function CreateForRead(baseStream As Stream) As CipherStream
        Return New CipherStream(baseStream) With
        {
            ._readable = True,
            ._writable = False
        }
    End Function

    Public Shared Function CreateForWrite(baseStream As Stream) As CipherStream
        Return New CipherStream(baseStream) With
        {
            ._readable = False,
            ._writable = True
        }
    End Function

    Private Sub New(baseStream As Stream)
        _wrappedBaseStream = baseStream
    End Sub

    Public Overrides Function Read(buffer() As Byte, offset As Integer, count As Integer) As Integer

        If Not _readable Then Throw New NotSupportedException()
        If count = 0 Then Return 0

        Dim returnCounter As Integer = 0

        For i = 0 To count - 1

            Dim value As Integer = _wrappedBaseStream.ReadByte()

            If (value = -1) Then Return returnCounter

            value += ENCODING_OFFSET
            If value > Byte.MaxValue Then
                value -= Byte.MaxValue
            End If

            buffer(i + offset) = Convert.ToByte(value)
            returnCounter += 1

        Next

        Return returnCounter

    End Function

    Public Overrides Sub Write(buffer() As Byte, offset As Integer, count As Integer)
        If Not _writable Then Throw New NotSupportedException()

        Dim newBuffer(count) As Byte
        buffer.CopyTo(newBuffer, offset)

        For i = 0 To count - 1

            Dim value As Integer = newBuffer(i)

            value -= ENCODING_OFFSET

            If value < 0 Then
                value = Byte.MaxValue - value
            End If

            newBuffer(i) = Convert.ToByte(value)

        Next

        _wrappedBaseStream.Write(newBuffer, 0, count)

    End Sub


    Public Overrides Sub Flush()
        _wrappedBaseStream.Flush()
    End Sub

    Public Overrides Function Seek(offset As Long, origin As SeekOrigin) As Long
        Throw New NotSupportedException()
    End Function

    Public Overrides Sub SetLength(value As Long)
        Throw New NotSupportedException()
    End Sub

End Class

Lihat juga

• StreamReader
• StreamReader.ReadLine
• StreamReader.Peek
• FileStream
• BinaryReader
• BinaryReader.ReadByte
• BinaryReader.PeekChar