Question

Hy Guys, so after you help me to properly convert the “Compress” function ,i tryed to convert the Decompress function too

now im here
(decompress function by me)

let DecompressString (detext : string) =
    let buffer = Convert.FromBase64String detext
    using (new MemoryStream ()) <| fun memoryStream ->
            using (new GZipStream(memoryStream, CompressionMode.Decompress, true)) <| fun gzipStream ->
            memoryStream.Position <- 0L
            memoryStream.Read(buffer, 0, Array.length buffer)
            Encoding.UTF8.GetString(buffer)

the original Compressfunction is

let compressString (text : string) =
let buffer = Encoding.UTF8.GetBytes text
using (new MemoryStream ()) <| fun memoryStream ->
    using (new GZipStream(memoryStream, CompressionMode.Compress, true)) <| fun gzipStream ->
        gzipStream.Write (buffer, 0, Array.length buffer)
    memoryStream.Position <- 0L
    let compressedData = Array.zeroCreate (int memoryStream.Length)
    memoryStream.Read (compressedData, 0, compressedData.Length)
    let gzipBuffer = Array.zeroCreate (compressedData.Length + 4)
    Buffer.BlockCopy (compressedData, 0, gzipBuffer, 4, compressedData.Length)
    Buffer.BlockCopy (BitConverter.GetBytes buffer.Length, 0, gzipBuffer, 0, 4)
    Convert.ToBase64String gzipBuffer

if i compress a string like this

File.WriteAllText("test",compressString("bla"))

(I save the file named “test” in this file is the compressed string from “bla”)

“AwAAAB+LCAAAAAAABADtvQdgHEmWJSYvbcp7f0r1StfgdKEIgGATJNiQQBDswYjN5pLsHWlHIymrKoHKZVZlXWYWQMztnbz33nvvvffee++997o7nU4n99//P1xmZAFs9s5K2smeIYCqyB8/fnwfPyImZfb/ADmz70cDAAAA” < seems for me bigger then before? 😀

ok now i try to decompress it again like:

File.WriteAllText("test2",DecompressString(File.ReadAllText("test")))

but in the new “test2” file is only unreadable text like:

“?"&e�ï¿“

so i think my dcompress function dont work properly.

Maybe your my heroes can help me out a second and last time ? 🙂
Anyway thanks in advance

Answer 1

Firstly, the memory stream you’re reading from is empty, so nothing will be written to the destination buffer.

Secondly, you’re re-using buffer and this contains the bytes of the base 64 string argument.

You can’t get the Length of a GZipStream so you’ll have to copy it to another memory stream:

let DecompressString (detext : string) =
    let buffer = Convert.FromBase64String detext
    using (new MemoryStream ()) <| fun memoryStream ->
        memoryStream.Write(buffer, 0, Array.length buffer)
        memoryStream.Seek(0L, SeekOrigin.Begin) |> ignore
        using (new GZipStream(memoryStream, CompressionMode.Decompress, true)) <| fun gzipStream ->
            using(new MemoryStream()) <| outStream ->
                gzipStream.CopyTo(outStream)
                Encoding.UTF8.GetString(outStream.ToArray())