GZipStream to compress/extract 2 files

Question

Hello

Here's an excellent sample to zip and unzip a single file using GZip:

https://learn.microsoft.com/en-us/dotnet/api/system.io.compression.gzipstream?view=netframework-4.0

Any idea how to include 2 files to compress and how to extract them back? Possible?

Thanks.

• .Net 4.0 full profile, so no Zip class, can't use 3rd party dlls, so need to stay with GZipStream :(

Answer 1

Hi @StewartBW ,

You can first create a temporary directory, then compress each file individually into that directory, and finally compress the directory itself into a single .gz file.

And to ensure that the extracted files retain their original names and content, you need to store that information during compression and restore it during extraction.

Private Sub Button3_Click(sender As Object, e As EventArgs) Handles Button3.Click
        Dim file1 As String = "C:\Users\Administrator\Desktop\file1.txt"
        Dim file2 As String = "C:\Users\Administrator\Desktop\file2.txt"
        Dim compressedFile As String = "C:\Users\Administrator\Desktop\compressed_files.gz"

        CompressFilesIntoGZip({file1, file2}, compressedFile)

    End Sub

    Private Sub Button4_Click(sender As Object, e As EventArgs) Handles Button4.Click
        Dim compressedFile As String = "C:\Users\Administrator\Desktop\compressed_files.gz"

        Dim outputDirectory As String = "C:\Users\Administrator\Desktop\extracted_files"

        ExtractFilesFromGZip(compressedFile, outputDirectory)
    End Sub

    Private Sub CompressFilesIntoGZip(files As String(), compressedFile As String)
        Using outputStream As FileStream = File.Create(compressedFile)
            Using gzipStream As New GZipStream(outputStream, CompressionMode.Compress)
                For Each f In files
                    Dim fileInfo As New FileInfo(f)
                    Dim fileSizeBytes As Long = fileInfo.Length

                    ' Write file name and size to the compressed stream
                    Dim fileNameBytes() As Byte = Encoding.UTF8.GetBytes(fileInfo.Name)
                    gzipStream.Write(BitConverter.GetBytes(fileNameBytes.Length), 0, 4)
                    gzipStream.Write(fileNameBytes, 0, fileNameBytes.Length)
                    gzipStream.Write(BitConverter.GetBytes(fileSizeBytes), 0, 8)

                    ' Write file content to the compressed stream
                    Using inputFileStream As FileStream = File.OpenRead(f)
                        inputFileStream.CopyTo(gzipStream)
                    End Using
                Next
            End Using
        End Using

        Console.WriteLine($"Files {String.Join(", ", files)} compressed into {compressedFile}")
    End Sub

    Private Sub ExtractFilesFromGZip(compressedFile As String, outputDirectory As String)
        ' Create a directory to extract files into
        Directory.CreateDirectory(outputDirectory)

        Using inputStream As FileStream = File.OpenRead(compressedFile)
            Using gzipStream As New GZipStream(inputStream, CompressionMode.Decompress)
                While True
                    ' Read file name length
                    Dim fileNameLengthBuffer(3) As Byte
                    Dim bytesRead As Integer = gzipStream.Read(fileNameLengthBuffer, 0, 4)
                    If bytesRead = 0 Then Exit While

                    ' Read file name
                    Dim fileNameLength As Integer = BitConverter.ToInt32(fileNameLengthBuffer, 0)
                    Dim fileNameBytes(fileNameLength - 1) As Byte
                    gzipStream.Read(fileNameBytes, 0, fileNameLength)
                    Dim fileName As String = Encoding.UTF8.GetString(fileNameBytes)

                    ' Read file size
                    Dim fileSizeBuffer(7) As Byte
                    gzipStream.Read(fileSizeBuffer, 0, 8)
                    Dim fileSize As Long = BitConverter.ToInt64(fileSizeBuffer, 0)

                    ' Create the output file path
                    Dim extractedFilePath As String = Path.Combine(outputDirectory, fileName)

                    ' Write file content to the output file
                    Using outputFileStream As New FileStream(extractedFilePath, FileMode.Create, FileAccess.Write)
                        Dim buffer(4096) As Byte
                        Dim totalBytesRead As Integer = 0
                        While totalBytesRead < fileSize
                            Dim bytesToRead As Integer = Math.Min(buffer.Length, CInt(fileSize - totalBytesRead))
                            Dim bytesReadThisTime As Integer = gzipStream.Read(buffer, 0, bytesToRead)
                            If bytesReadThisTime = 0 Then Exit While
                            outputFileStream.Write(buffer, 0, bytesReadThisTime)
                            totalBytesRead += bytesReadThisTime
                        End While
                    End Using
                End While
            End Using
        End Using

        Console.WriteLine($"Files extracted from {compressedFile} to {outputDirectory}")
    End Sub

Best Regards.

Jiachen Li

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