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Value already read, or no value when trying to read from a Stream

I've been trying this for a long time but it keeps giving me an error. I have an array of bytes that should represent a nbt document. I would like to convert this into a c# object with a library: fNbt.
Here is my code:
byte[] buffer = Convert.FromBase64String(value);
byte[] decompressed;
using (var inputStream = new MemoryStream(buffer))
{
using var outputStream = new MemoryStream();
using (var gzip = new GZipStream(inputStream, CompressionMode.Decompress, leaveOpen: true))
{
gzip.CopyTo(outputStream);
}
fNbt.NbtReader reader = new fNbt.NbtReader(outputStream, true);
var output = reader.ReadValueAs<AuctionItem>(); //Error: Value already read, or no value to read.
return output;
}
When I try this, it works:
decompressed = outputStream.ToArray();
outputStream.Seek(0, SeekOrigin.Begin);
outputStream.Read(new byte[1000], 0, decompressed.Count() - 1);
But when I try this, it doesn't:
outputStream.Seek(0, SeekOrigin.Begin);
fNbt.NbtReader reader = new fNbt.NbtReader(outputStream, true);
reader.ReadValueAs<AuctionItem>();

NbtReader, like most stream readers, begins reading from the current position of whatever stream you give it. Since you're just done writing to outputStream, then that position is the stream's end. Which means at that point there's nothing to be read.
The solution is to seek the outputStream back to the beginning before reading from it:
outputStream.Seek(0, SeekOrigin.Begin); // <-- seek to the beginning
// Do the read
fNbt.NbtReader reader = new fNbt.NbtReader(outputStream, true);
var output = reader.ReadValueAs<AuctionItem>(); // No error anymore
return output;

The solution is as follows. NbtReader.ReadValueAs does not consider a nbtCompound or nbtList as value. I made this little reader but it is not done yet (I will update the code once it is done).
public static T ReadValueAs<T>(string value) where T: new()
{
byte[] buffer = Convert.FromBase64String(value);
using (var inputStream = new MemoryStream(buffer))
{
using var outputStream = new MemoryStream();
using (var gzip = new GZipStream(inputStream, CompressionMode.Decompress, leaveOpen: true))
{
gzip.CopyTo(outputStream);
}
outputStream.Seek(0, SeekOrigin.Begin);
return new EasyNbt.NbtReader(outputStream).ReadValueAs<T>();
}
}
This is the NbtReader:
private MemoryStream MemStream { get; set; }
public NbtReader(MemoryStream memStream)
{
MemStream = memStream;
}
public T ReadValueAs<T>() where T: new()
{
return ReadTagAs<T>(new fNbt.NbtReader(MemStream, true).ReadAsTag());
}
private T ReadTagAs<T>(fNbt.NbtTag nbtTag)
{
//Reads to the root and adds to T...
}

Avoid copying compressed data when using DeflateStream

Assume we have given an API function f(Stream s) to put binary data contained in a stream into a database. I want to put a file into the database using f but I want to compress the data in advance. Hence I thought I could do the following:
var fileStream= File.OpenRead(path);
using(var dstream = new DeflateStream(fileStream, CompressionLevel.Optimal))
f(dstream);
But it seems DeflateStream only writes into the stream fileStream but does not read from it when compressing. In all examples I found, the CopyTo method of the stream was used to compress or decompress. But this would mean that I have to keep a copy of the compressed data in memory before passing it to f for instance like this:
var memoryStream = new MemoryStream();
using(var fileStream= File.OpenRead(path))
using(var dstream = new DeflateStream(memoryStream, CompressionLevel.Optimal)) {
fileStream.CopyTo(dstream);
memoryStream.Seek(0, SeekOrigin.Begin);
f(memoryStream);
}
Is there any way to avoid using the MemoryStream?
Update
For the sake of the persistency of some commentators I add a complete example:
using System;
using System.IO;
using System.IO.Compression;
public class ThisWouldBeTheDatabaseClient {
public void f(Stream s) {
// some implementation I don't have access to
// The only thing I know is that it reads data from the stream in some way.
var buffer = new byte[10];
s.Read(buffer,0,10);
}
}
public class Program {
public static void Main() {
var dummyDatabaseClient = new ThisWouldBeTheDatabaseClient();
var dataBuffer = new byte[1000];
var fileStream= new MemoryStream( dataBuffer ); // would be "File.OpenRead(path)" in real case
using(var dstream = new DeflateStream(fileStream, CompressionLevel.Optimal))
dummyDatabaseClient.f(dstream);
}
}
The read operation in the dummy implementation of f throws an exception: InvalidOperationException: Reading from the compression stream is not supported. Concluding the discussion in the comments, I assume that the desired behaviour is not possible with DeflateStream but there are alternatives in third party libraries.

You can use SharpCompress for this. Its DeflateStream allows you to read the compressed data on the fly, which is exactly what you want.
Here's a complete example based on Sir Rufo's:
using System;
using System.IO;
using SharpCompress.Compressors;
using SharpCompress.Compressors.Deflate;
using System.Linq;
public class Program
{
public static void Main()
{
var dataBuffer = Enumerable.Range(1, 50000).Select(e => (byte)(e % 256)).ToArray();
using (var dataStream = new MemoryStream(dataBuffer))
{
// Note: this refers to SharpCompress.Compressors.Deflate.DeflateStream
using (var deflateStream = new DeflateStream(dataStream, CompressionMode.Compress))
{
ConsumeStream(deflateStream);
}
}
}
public static void ConsumeStream(Stream stream)
{
// Let's just prove we can reinflate to the original data...
byte[] data;
using (var decompressed = new MemoryStream())
{
using (var decompressor = new DeflateStream(stream, CompressionMode.Decompress))
{
decompressor.CopyTo(decompressed);
}
data = decompressed.ToArray();
}
Console.WriteLine("Reinflated size: " + data.Length);
int errors = 0;
for (int i = 0; i < data.Length; i++)
{
if (data[i] != (i + 1) % 256)
{
errors++;
}
}
Console.WriteLine("Total errors: " + errors);
}
}
Or using your sample code:
using System;
using System.IO;
using SharpCompress.Compressors;
using SharpCompress.Compressors.Deflate;
public class ThisWouldBeTheDatabaseClient {
public void f(Stream s) {
// some implementation I don't have access to
// The only thing I know is that it reads data from the stream in some way.
var buffer = new byte[10];
s.Read(buffer,0,10);
}
}
public class Program {
public static void Main() {
var dummyDatabaseClient = new ThisWouldBeTheDatabaseClient();
var dataBuffer = new byte[1000];
var fileStream= new MemoryStream( dataBuffer ); // would be "File.OpenRead(path)" in real case
using(var dstream = new DeflateStream(
fileStream, CompressionMode.Compress, CompressionLevel.BestCompression))
dummyDatabaseClient.f(dstream);
}
}
This now doesn't throw an exception, and will serve the compressed data.

The DeflateStream is just a wrapper and needs a stream for the compressed data. So you have to use two streams.
Is there any way to avoid using the MemoryStream?
Yes.
You need a stream to store temporary data without consuming (too much) memory. Instead using MemoryStream you can use a temporary file for that.
For the lazy people (like me in first place) let's create a class that will behave mostly like a MemoryStream
public class TempFileStream : FileStream
{
public TempFileStream() : base(
path: Path.GetTempFileName(),
mode: FileMode.Open,
access: FileAccess.ReadWrite,
share: FileShare.None,
bufferSize: 4096,
options: FileOptions.DeleteOnClose | FileOptions.Asynchronous | FileOptions.Encrypted | FileOptions.RandomAccess)
{
}
}
The important part here is FileOptions.DeleteOnClose which will remove the temporary file when you dispose the stream.
And then use it
using (var compressedStream = new TempFileStream())
{
using (var deflateStream = new DeflateStream(
stream: compressedStream,
compressionLevel: CompressionLevel.Optimal,
leaveOpen: true))
using (var fileStream = File.OpenRead(path))
{
fileStream.CopyTo(deflateStream);
}
f(compressedStream);
}

Writing a memory stream to a file

I have tried retrieving data in the json format as a string and writing it to a file and it worked great. Now I am trying to use MemoryStream to do the same thing but nothing gets written to a file - merely [{},{},{},{},{}] without any actual data.
My question is - how can I check if data indeed goes to memory stream correctly or if the problem occurs somewhere else. I do know that myList does contain data.
Here is my code:
MemoryStream ms = new MemoryStream();
DataContractJsonSerializer dcjs = new DataContractJsonSerializer(typeof(List<myClass>));
dcjs.WriteObject(ms, myList);
using (FileStream fs = new FileStream(Path.Combine(Application.StartupPath,"MyFile.json"), FileMode.OpenOrCreate))
{
ms.Position = 0;
ms.Read(ms.ToArray(), 0, (int)ms.Length);
fs.Write(ms.ToArray(), 0, ms.ToArray().Length);
ms.Close();
fs.Flush();
fs.Close();
}

There is a very handy method, Stream.CopyTo(Stream).
using (MemoryStream ms = new MemoryStream())
{
StreamWriter writer = new StreamWriter(ms);
writer.WriteLine("asdasdasasdfasdasd");
writer.Flush();
//You have to rewind the MemoryStream before copying
ms.Seek(0, SeekOrigin.Begin);
using (FileStream fs = new FileStream("output.txt", FileMode.OpenOrCreate))
{
ms.CopyTo(fs);
fs.Flush();
}
}
Also, you don't have to close fs since it's in a using statement and will be disposed at the end.

using (var memoryStream = new MemoryStream())
{
...
var fileName = $"FileName.xlsx";
string tempFilePath = Path.Combine(Path.GetTempPath() + fileName );
using (var fs = new FileStream(tempFilePath, FileMode.Create, FileAccess.Write))
{
memoryStream.WriteTo(fs);
}
}

//reset the position of the stream
ms.Position = 0;
//Then copy to filestream
ms.CopyTo(fileStream);

The issue is nothing to do with your file stream/ memory stream. The problem is that DataContractJsonSerializer is an OPT IN Serializer. You need to add [DataMemberAttribute] to all the properties that you need to serialize on myClass.
[DataContract]
public class myClass
{
[DataMember]
public string Foo { get; set; }
}

This line looks problematic:
ms.Read(ms.ToArray(), 0, (int)ms.Length);
You shouldn't need to read anything into the memory stream at this point, particularly when you're code is written to read ms into ms.
I'm pretty confident that simply removing this line will fix your problem.

DeflateStream doesnt work on MemoryStream?

I have the following piece of code:
MemoryStream resultStream = new MemoryStream();
string users = ""//Really long string goes here
BinaryFormatter bFormatter = new BinaryFormatter();
using (MemoryStream assignedUsersStream = new MemoryStream())
{
bFormatter.Serialize(assignedUsersStream, users);
assignedUsersStream.Position = 0;
using (var compressionStream =
new DeflateStream(resultStream, CompressionLevel.Optimal))
{
assignedUsersStream.CopyTo(compressionStream);
Console.WriteLine("Compressed from {0} to {1} bytes.",
assignedUsersStream.Length.ToString(),
resultStream.Length.ToString());
}
}
the thing is that resultStream is always empty!
What am I doing wrong here?

Put your verification WriteLine outside of the using. The buffers haven't been flushed yet.
using (DeflateStream compressionStream = new DeflateStream(resultStream, CompressionLevel.Optimal))
{
assignedUsersStream.CopyTo(compressionStream);
//Console.WriteLine("Compressed from {0} to {1} bytes.",
// assignedUsersStream.Length.ToString(), resultStream.Length.ToString());
}
Console.WriteLine("Compressed from {0} to {1} bytes.",
assignedUsersStream.Length, resultStream.ToArray().Length);
And aside, you don't need all those ToString()s in a writeline.
PS: All a BinaryFormatter does with a string is write the bytes with length prefix. If you don't need the prefix (my guess), it could become:
string users = "";//Really long string goes here
byte[] result;
using (MemoryStream resultStream = new MemoryStream())
{
using (DeflateStream compressionStream = new DeflateStream(resultStream,
CompressionLevel.Optimal))
{
byte[] inBuffer = Encoding.UTF8.GetBytes(users);
compressionStream.Write(inBuffer, 0, inBuffer.Length);
}
result = resultStream.ToArray();
}
The reverse is just as easy but you'll need an estimate of the maximum length to create the read-buffer:
string users2 = null;
using (MemoryStream resultStream = new MemoryStream(result))
{
using (DeflateStream compressionStream = new DeflateStream(resultStream,
CompressionMode.Decompress))
{
byte[] outBuffer = new byte[2048]; // need an estimate here
int length = compressionStream.Read(outBuffer, 0, outBuffer.Length);
users2 = Encoding.UTF8.GetString(outBuffer, 0, length);
}
}

That is because the DeflateStream doesn't flush the data to the underlying stream until it is closed. After it is closed, resultStream will contain the compressed data. Note that by default, DeflateStream closes the underlying stream when it's closed, but you don't want that, so you need to pass true for the leaveOpen parameter. Also, you don't need 2 memory streams, you can just serialize directly to the compressionStream:
string users = ""; //Really long string goes here
BinaryFormatter bFormatter = new BinaryFormatter();
using (MemoryStream resultStream = new MemoryStream())
{
using (DeflateStream compressionStream = new DeflateStream(resultStream, CompressionLevel.Optimal, true))
{
bFormatter.Serialize(compressionStream, users);
Console.WriteLine(resultStream.Length); // 0 at this point
}
Console.WriteLine(resultStream.Length); // now contains the actual length
}

From the original answer (I don't have enough credits to vote down)
Put your control WriteLine outside of the using
This is incomplete and IMO therefore misleading. DeflateStream's Dispose(bool) implementation Closes the underlying resultStream when the DeflateStream is being Finalized after it's been Garbage Collected. When this happens, resultStream.Length will throw:
Unhandled Exception: System.ObjectDisposedException: Cannot access a closed Stream.
In other words, Thomas Levesque's note is critical: also set leaveOpen to true.
An interesting question with some good points raised by HH and TL.

I've come in late to this as I ran into this same problem and reading the conflicting answers. The initial response works! as does this test (over simplified to highlight the answer):
var inStream = new MemoryStream(data);
var outStream = new MemoryStream();
using (var compressor = new DeflateStream(outStream, CompressionLevel.Optimal))
{
inStream.CopyTo(compressor);
}
return outStream;
where the using block needs to complete, triggering the compressor's Dispose, which internally Flush()es so that outStream will be guaranteed to contain the complete compressed data.

How do I use GZipStream with System.IO.MemoryStream?

I am having an issue with this test function where I take an in memory string, compress it, and decompress it. The compression works great, but I can't seem to get the decompression to work.
//Compress
System.IO.MemoryStream outStream = new System.IO.MemoryStream();
GZipStream tinyStream = new GZipStream(outStream, CompressionMode.Compress);
mStream.Position = 0;
mStream.CopyTo(tinyStream);
//Decompress
outStream.Position = 0;
GZipStream bigStream = new GZipStream(outStream, CompressionMode.Decompress);
System.IO.MemoryStream bigStreamOut = new System.IO.MemoryStream();
bigStream.CopyTo(bigStreamOut);
//Results:
//bigStreamOut.Length == 0
//outStream.Position == the end of the stream.
I believe that bigStream out should at least have data in it, especially if my source stream (outStream) is being read. is this a MSFT bug or mine?

What happens in your code is that you keep opening streams, but you never close them.
In line 2, you create a GZipStream. This stream will not write anything to the underlying stream until it feels it’s the right time. You can tell it to by closing it.
However, if you close it, it will close the underlying stream (outStream) too. Therefore you can’t use mStream.Position = 0 on it.
You should always use using to ensure that all your streams get closed. Here is a variation on your code that works.
var inputString = "“ ... ”";
byte[] compressed;
string output;
using (var outStream = new MemoryStream())
{
using (var tinyStream = new GZipStream(outStream, CompressionMode.Compress))
using (var mStream = new MemoryStream(Encoding.UTF8.GetBytes(inputString)))
mStream.CopyTo(tinyStream);
compressed = outStream.ToArray();
}
// “compressed” now contains the compressed string.
// Also, all the streams are closed and the above is a self-contained operation.
using (var inStream = new MemoryStream(compressed))
using (var bigStream = new GZipStream(inStream, CompressionMode.Decompress))
using (var bigStreamOut = new MemoryStream())
{
bigStream.CopyTo(bigStreamOut);
output = Encoding.UTF8.GetString(bigStreamOut.ToArray());
}
// “output” now contains the uncompressed string.
Console.WriteLine(output);

This is a known issue: http://blogs.msdn.com/b/bclteam/archive/2006/05/10/592551.aspx
I have changed your code a bit so this one works:
var mStream = new MemoryStream(new byte[100]);
var outStream = new System.IO.MemoryStream();
using (var tinyStream = new GZipStream(outStream, CompressionMode.Compress))
{
mStream.CopyTo(tinyStream);
}
byte[] bb = outStream.ToArray();
//Decompress
var bigStream = new GZipStream(new MemoryStream(bb), CompressionMode.Decompress);
var bigStreamOut = new System.IO.MemoryStream();
bigStream.CopyTo(bigStreamOut);

The way to compress and decompress to and from a MemoryStream is:
public static Stream Compress(
Stream decompressed,
CompressionLevel compressionLevel = CompressionLevel.Fastest)
{
var compressed = new MemoryStream();
using (var zip = new GZipStream(compressed, compressionLevel, true))
{
decompressed.CopyTo(zip);
}
compressed.Seek(0, SeekOrigin.Begin);
return compressed;
}
public static Stream Decompress(Stream compressed)
{
var decompressed = new MemoryStream();
using (var zip = new GZipStream(compressed, CompressionMode.Decompress, true))
{
zip.CopyTo(decompressed);
}
decompressed.Seek(0, SeekOrigin.Begin);
return decompressed;
}
This leaves the compressed / decompressed stream open and as such usable after creating it.

Another implementation, in VB.NET:
Imports System.Runtime.CompilerServices
Imports System.IO
Imports System.IO.Compression
Public Module Compressor
<Extension()> _
Function CompressASCII(str As String) As Byte()
Dim bytes As Byte() = Encoding.ASCII.GetBytes(str)
Using ms As New MemoryStream
Using gzStream As New GZipStream(ms, CompressionMode.Compress)
gzStream.Write(bytes, 0, bytes.Length)
End Using
Return ms.ToArray
End Using
End Function
<Extension()> _
Function DecompressASCII(compressedString As Byte()) As String
Using ms As New MemoryStream(compressedString)
Using gzStream As New GZipStream(ms, CompressionMode.Decompress)
Using sr As New StreamReader(gzStream, Encoding.ASCII)
Return sr.ReadToEnd
End Using
End Using
End Using
End Function
Sub TestCompression()
Dim input As String = "fh3o047gh"
Dim compressed As Byte() = input.CompressASCII()
Dim decompressed As String = compressed.DecompressASCII()
If input <> decompressed Then
Throw New ApplicationException("failure!")
End If
End Sub
End Module

public static byte[] compress(byte[] data)
{
using (MemoryStream outStream = new MemoryStream())
{
using (GZipStream gzipStream = new GZipStream(outStream, CompressionMode.Compress))
using (MemoryStream srcStream = new MemoryStream(data))
srcStream.CopyTo(gzipStream);
return outStream.ToArray();
}
}
public static byte[] decompress(byte[] compressed)
{
using (MemoryStream inStream = new MemoryStream(compressed))
using (GZipStream gzipStream = new GZipStream(inStream, CompressionMode.Decompress))
using (MemoryStream outStream = new MemoryStream())
{
gzipStream.CopyTo(outStream);
return outStream.ToArray();
}
}

If you are attempting to use the MemoryStream (e.g. passing it into another function) but receiving the Exception "Cannot access a closed Stream." then there is another GZipStream constructor you can use that will help you.
By passing in a true to the leaveOpen parameter, you can instruct GZipStream to leave the stream open after disposing of itself, by default it closes the target stream (which I didn't expect). https://msdn.microsoft.com/en-us/library/27ck2z1y(v=vs.110).aspx
using (FileStream fs = File.OpenRead(f))
using (var compressed = new MemoryStream())
{
//Instruct GZipStream to leave the stream open after performing the compression.
using (var gzipstream = new GZipStream(compressed, CompressionLevel.Optimal, true))
fs.CopyTo(gzipstream);
//Do something with the memorystream
compressed.Seek(0, SeekOrigin.Begin);
MyFunction(compressed);
}

I had an issue where *.CopyTo(stream)* would end up with a byte[0] result.
The solution was to add .Position=0 before calling .CopyTo(stream)
Answered here
I also use a BinaryFormatter that would throw an 'End of stream encountered before parsing was completed' exception if position was not set to 0 before deserialization.
Answered here
This is the code that worked for me.
public static byte[] SerializeAndCompressStateInformation(this IPluginWithStateInfo plugin, Dictionary<string, object> stateInfo)
{
byte[] retArr = new byte[] { byte.MinValue };
try
{
using (MemoryStream msCompressed = new MemoryStream())//what gzip writes to
{
using (GZipStream gZipStream = new GZipStream(msCompressed, CompressionMode.Compress))//setting up gzip
using (MemoryStream msToCompress = new MemoryStream())//what the settings will serialize to
{
BinaryFormatter formatter = new BinaryFormatter();
//serialize the info into bytes
formatter.Serialize(msToCompress, stateInfo);
//reset to 0 to read from beginning byte[0] fix.
msToCompress.Position = 0;
//this then does the compression
msToCompress.CopyTo(gZipStream);
}
//the compressed data as an array of bytes
retArr = msCompressed.ToArray();
}
}
catch (Exception ex)
{
Logger.Error(ex.Message, ex);
throw ex;
}
return retArr;
}
public static Dictionary<string, object> DeserializeAndDecompressStateInformation(this IPluginWithStateInfo plugin, byte[] stateInfo)
{
Dictionary<string, object> settings = new Dictionary<string, object>();
try
{
using (MemoryStream msDecompressed = new MemoryStream()) //the stream that will hold the decompressed data
{
using (MemoryStream msCompressed = new MemoryStream(stateInfo))//the compressed data
using (GZipStream gzDecomp = new GZipStream(msCompressed, CompressionMode.Decompress))//the gzip that will decompress
{
msCompressed.Position = 0;//fix for byte[0]
gzDecomp.CopyTo(msDecompressed);//decompress the data
}
BinaryFormatter formatter = new BinaryFormatter();
//prevents 'End of stream encountered' error
msDecompressed.Position = 0;
//change the decompressed data to the object
settings = formatter.Deserialize(msDecompressed) as Dictionary<string, object>;
}
}
catch (Exception ex)
{
Logger.Error(ex.Message, ex);
throw ex;
}
return settings;
}

I thought I would share this answer for anyone interested in reproducing this on PowerShell, the code is mostly inspired from Timwi's helpful answer, however unfortunately as of now there is no implementation for the using statement like on C# for PowerShell, hence the need to manually dispose the streams before output.
Functions below requires PowerShell 5.0+.
Required using statements and ArgumentCompleter for -Encoding Parameter.
Improved versions of these 2 functions as well as Compression From File Path and Expansion from File Path can be found in this repo as well as in the PowerShell Gallery.
using namespace System.Text
using namespace System.IO
using namespace System.IO.Compression
using namespace System.Collections
using namespace System.Management.Automation
using namespace System.Collections.Generic
using namespace System.Management.Automation.Language
Add-Type -AssemblyName System.IO.Compression
class EncodingCompleter : IArgumentCompleter {
[IEnumerable[CompletionResult]] CompleteArgument (
[string] $commandName,
[string] $parameterName,
[string] $wordToComplete,
[CommandAst] $commandAst,
[IDictionary] $fakeBoundParameters
) {
[CompletionResult[]] $arguments = foreach($enc in [Encoding]::GetEncodings().Name) {
if($enc.StartsWith($wordToComplete)) {
[CompletionResult]::new($enc)
}
}
return $arguments
}
}
Compression from string to Base64 GZip compressed string:
function Compress-GzipString {
[cmdletbinding()]
param(
[Parameter(Mandatory, ValueFromPipeline)]
[string] $String,
[Parameter()]
[ArgumentCompleter([EncodingCompleter])]
[string] $Encoding = 'utf-8',
[Parameter()]
[CompressionLevel] $CompressionLevel = 'Optimal'
)
try {
$enc = [Encoding]::GetEncoding($Encoding)
$outStream = [MemoryStream]::new()
$gzip = [GZipStream]::new($outStream, [CompressionMode]::Compress, $CompressionLevel)
$inStream = [MemoryStream]::new($enc.GetBytes($string))
$inStream.CopyTo($gzip)
}
catch {
$PSCmdlet.WriteError($_)
}
finally {
$gzip, $outStream, $inStream | ForEach-Object Dispose
}
try {
[Convert]::ToBase64String($outStream.ToArray())
}
catch {
$PSCmdlet.WriteError($_)
}
}
Expansion from Base64 GZip compressed string to string:
function Expand-GzipString {
[cmdletbinding()]
param(
[Parameter(Mandatory, ValueFromPipeline)]
[string] $String,
[Parameter()]
[ArgumentCompleter([EncodingCompleter])]
[string] $Encoding = 'utf-8'
)
try {
$enc = [Encoding]::GetEncoding($Encoding)
$bytes = [Convert]::FromBase64String($String)
$outStream = [MemoryStream]::new()
$inStream = [MemoryStream]::new($bytes)
$gzip = [GZipStream]::new($inStream, [CompressionMode]::Decompress)
$gzip.CopyTo($outStream)
$enc.GetString($outStream.ToArray())
}
catch {
$PSCmdlet.WriteError($_)
}
finally {
$gzip, $outStream, $inStream | ForEach-Object Dispose
}
}
And for the little Length comparison, querying the Loripsum API:
$loremIp = Invoke-RestMethod loripsum.net/api/10/long
$compressedLoremIp = Compress-GzipString $loremIp
$loremIp, $compressedLoremIp | Select-Object Length
Length
------
8353
4940
(Expand-GzipString $compressedLoremIp) -eq $loremIp # => Should be True

If you still need it, you can use GZipStream constructor wit boolean argument (there are two such constructors) and pass true value there:
tinyStream = new GZipStream(outStream, CompressionMode.Compress, true);
In that case, when you close your tynyStream, your out stream will be still opened. Don't forget to copy data:
mStream.CopyTo(tinyStream);
tinyStream.Close();
Now you've got memory stream outStream with zipped data
Bugs and kisses for U
Good luck

Please refer to below link, It is avoid to use double MemoryStream.
https://stackoverflow.com/a/53644256/1979406