如何读取已加载到内存中的 txt 文件的内容

我有一个函数应该提取.gz文件并将其加载到内存中，我的问题是，一旦文件加载到内存中，我如何读取文件的内容而无需先将其保存到磁盘？

public static void Decompress2(FileInfo fileToDecompress)
{
    using (FileStream fileStream = fileToDecompress.OpenRead())
    {
        using (var memStream = new MemoryStream())
        {
            string currentFileName = fileToDecompress.FullName;
            string newFileName = currentFileName.Remove(currentFileName.Length - fileToDecompress.Extension.Length);
            using (FileStream decompressedFileStream = File.Create(newFileName))
            {
                using (GZipStream decompressionStream = new GZipStream(fileStream, CompressionMode.Decompress))
                {
                    byte[] bytes = new byte[4096];
                    int n;
                    while ((n = decompressionStream.Read(bytes, 0, bytes.Length)) != 0)
                    {
                        memStream.Write(bytes, 0, n);
                    }
                }
            }
        }
    }
}

private int _bufferSize = 16384; 
private void ReadFile(string filename) 
{
StringBuilder stringBuilder = new StringBuilder();     
FileStream fileStream = new FileStream(filename, FileMode.Open, FileAccess.Read);  
using (StreamReader streamReader = new StreamReader(fileStream))     
{        
    char[] fileContents = new char[_bufferSize];         
    int charsRead = streamReader.Read(fileContents, 0, _bufferSize); 
    // Can't do much with 0 bytes        
    if (charsRead == 0)             
        throw new Exception("File is 0 bytes"); 
    while (charsRead > 0)         
    {             
        stringBuilder.Append(fileContents);             
        charsRead = streamReader.Read(fileContents, 0, _bufferSize); 
    }     
}