壓縮並編碼掉最後兩個字節的字符串

Question

我有一個VB.NET應用程序，它生成一個需要發佈到Web應用程序的XML文檔。在發佈XML之前，我需要壓縮XML和base64對其進行編碼。在下面，我有一個代碼片段，我使用一個XML字符串，使用gzip進行壓縮，然後使用base64編碼。爲了確保我所做的是正確的，我正在解碼base64，然後解壓gzip。解壓縮後，原始XML比我測試的XML長2個字節。我正在放棄最後2個字節。他們去了哪裏？

Dim xml As String = ds.ToXMLString() 

    ' compress and encode 
    Dim ceb() As Byte = System.Text.Encoding.UTF8.GetBytes(xml) 
    Dim cems As New System.IO.MemoryStream() 
    Dim cegz As New System.IO.Compression.GZipStream(cems, IO.Compression.CompressionMode.Compress) 
    cegz.Write(ceb, 0, ceb.Length) 
    Dim cees As String = System.Convert.ToBase64String(cems.ToArray()) 

    ' i want to make sure everything is working, 
    ' decode and decompress and make sure it matches 
    Dim ddb() As Byte = System.Convert.FromBase64String(cees) 
    Dim ddms As New System.IO.MemoryStream(ddb) 
    Dim ddgz As New System.IO.Compression.GZipStream(ddms, IO.Compression.CompressionMode.Decompress) 
    Dim ddms2 As New System.IO.MemoryStream() 
    ddgz.CopyTo(ddms2) 

    Dim xmlRestored As String = System.Text.Encoding.UTF8.GetString(ddms2.ToArray()) 

    Assert.AreEqual(xml.Substring(0, xmlRestored.Length), xmlRestored) ' <-- SUCCESS 
    Assert.AreEqual(xml.Length, xmlRestored.Length) ' <-- FAILS; xml.length=147802; xmlRestored.length=147800; 

Answer 1

沒關係。我沒有關閉壓縮流。應該是這樣的：

Dim xml As String = ds.ToXMLString() 

' compress and encode 
Dim ceb() As Byte = System.Text.Encoding.UTF8.GetBytes(xml) 
Dim cems As New System.IO.MemoryStream() 
Dim cegz As New System.IO.Compression.GZipStream(cems, IO.Compression.CompressionMode.Compress) 
cegz.Write(ceb, 0, ceb.Length) 

' i was missing the closing of the gzip stream 
cegz.Close() 

Dim cees As String = System.Convert.ToBase64String(cems.ToArray()) 

' i want to make sure everything is working, 
' decode and decompress and make sure it matches 
Dim ddb() As Byte = System.Convert.FromBase64String(cees) 
Dim ddms As New System.IO.MemoryStream(ddb) 
Dim ddgz As New System.IO.Compression.GZipStream(ddms, IO.Compression.CompressionMode.Decompress) 
Dim ddms2 As New System.IO.MemoryStream() 
ddgz.CopyTo(ddms2) 

Dim xmlRestored As String = System.Text.Encoding.UTF8.GetString(ddms2.ToArray()) 

Assert.AreEqual(xml, xmlRestored) ' <-- SUCCESS 
Assert.AreEqual(xml.Length, xmlRestored.Length) ' <-- SUCCESS