问题
I'm using the below sample code for writing and downloading a memory stream to a file in C#.
MemoryStream memoryStream = new MemoryStream();
TextWriter textWriter = new StreamWriter(memoryStream);
textWriter.WriteLine("Something");
byte[] bytesInStream = new byte[memoryStream.Length];
memoryStream.Write(bytesInStream, 0, bytesInStream.Length);
memoryStream.Close();
Response.Clear();
Response.ContentType = "application/force-download";
Response.AddHeader("content-disposition",
"attachment; filename=name_you_file.xls");
Response.BinaryWrite(bytesInStream);
Response.End();
I am getting the following error:
Specified argument was out of the range of valid values.
Parameter name: offset
What may be the cause?
回答1:
At the point in your code where you copy the data to an array, the TextWriter might not have flushed the data. This will happen when you Flush() or when you Close() it.
See if this works:
MemoryStream memoryStream = new MemoryStream();
TextWriter textWriter = new StreamWriter(memoryStream);
textWriter.WriteLine("Something");
textWriter.Flush(); // added this line
byte[] bytesInStream = memoryStream.ToArray(); // simpler way of converting to array
memoryStream.Close();
Response.Clear();
Response.ContentType = "application/force-download";
Response.AddHeader("content-disposition", "attachment; filename=name_you_file.xls");
Response.BinaryWrite(bytesInStream);
Response.End();
回答2:
You are doing something wrong logically here. First, you write some text to the MemoryStream and then you write an empty array to the same stream. I assume you are trying to copy the contents of the stream into the bytesInStream array. You can create this array by calling memoryStream.ToArray().
Alternatively, you can avoid the array copying by writing the stream directly to the response output stream using MemoryStream.CopyTo. Replace your BinaryWrite call with this:
memoryStream.Position = 0;
memoryStream.CopyTo(Response.OutputStream);
Note: explicitly position the stream at the start since CopyTo will copy from the current position.
回答3:
OK, since one obviously gets downvoted for providing just a working example, let me Elaborate:
First, you don't do
textWriter.Flush()
and expect the Content of textwriter to have been flushed to memorystream.
Then you don't do
memoryStream.Position = 0
And expect the memorystream to be "written" from Position 0.
Then you do
memoryStream.Write(bytesInStream, 0, bytesInStream.Length);
but what you actually mean is
memoryStream.Read(bytesInStream, 0, CInt(memoryStream.Length))
You also missed that length is Long, while read uses an integer, so you can get an exception there.
So this is your code minimally adapted to "work" (i copied it into a vb Project)
Imports System.Web
Imports System.Web.Services
Public Class TextHandler
Implements System.Web.IHttpHandler
Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
'context.Response.ContentType = "text/plain"
'context.Response.Write("Hello World!")
Dim memoryStream As New System.IO.MemoryStream()
Dim textWriter As System.IO.TextWriter = New System.IO.StreamWriter(memoryStream)
textWriter.WriteLine("Something")
textWriter.Flush()
memoryStream.Position = 0
Dim bytesInStream As Byte() = New Byte(memoryStream.Length - 1) {}
'memoryStream.Write(bytesInStream, 0, bytesInStream.Length)
memoryStream.Read(bytesInStream, 0, CInt(memoryStream.Length))
memoryStream.Close()
context.Response.Clear()
context.Response.ContentType = "application/force-download"
context.Response.AddHeader("content-disposition", "attachment; filename=name_you_file.txt")
context.Response.BinaryWrite(bytesInStream)
context.Response.End()
End Sub
ReadOnly Property IsReusable() As Boolean Implements IHttpHandler.IsReusable
Get
Return False
End Get
End Property
End Class
Then you use
Content-Type: application/force-download
which means
"I, the web server, am going to lie to you (the browser) about what this file is so that you will not treat it as a PDF/Word Document/MP3/whatever and prompt the user to save the mysterious file to disk instead". It is a dirty hack that breaks horribly when the client doesn't do "save to disk".
...
And finally, you don't encode the filename correctly, so if one uses non-ASCII characters for the filename, it will garble the filename, which is very funny if you happen to be Chinese or Russian and operate entirely outside the ASCII character set.
Original
Here a quick excerpt from one of my ajax handlers. It's VB.NET, when converting, take care on the length -1 things.
Sub ProcessRequest(ByVal context As HttpContext) Implements IHttpHandler.ProcessRequest
Dim strFileName As String = "Umzugsmitteilung.doc"
Dim strUID As String = context.Request.QueryString("ump_uid")
context.Response.Clear()
'If String.IsNullOrEmpty(strUID) Or fileData Is Nothing Then
' context.Response.Write("<script type=""text/javascript"">alert('File does not exist !')</script>")
' context.Response.End()
'End If
context.Response.ClearContent()
'context.Response.AddHeader("Content-Disposition", "attachment; filename=" + strFileName)
context.Response.AddHeader("Content-Disposition", GetContentDisposition(strFileName))
'context.Response.ContentType = "application/msword"
context.Response.ContentType = "application/octet-stream"
GetUmzugsMitteilung(strUID)
context.Response.End()
End Sub ' ProcessRequest
Public Shared Sub SaveWordDocumentToOutputStream(strUID As String, doc As Aspose.Words.Document)
Using ms As System.IO.MemoryStream = New System.IO.MemoryStream()
CreateWordDocumentFromTemplate(strUID, doc, ms)
ms.Position = 0
Dim bytes As Byte() = New Byte(ms.Length - 1) {}
ms.Read(bytes, 0, CInt(ms.Length))
System.Web.HttpContext.Current.Response.OutputStream.Write(bytes, 0, ms.Length)
ms.Close()
End Using ' ms
End Sub ' SaveWordDocumentToOutputStream
Public Shared Function StripInvalidPathChars(str As String) As String
If str Is Nothing Then
Return Nothing
End If
Dim strReturnValue As String = ""
Dim strInvalidPathChars As New String(System.IO.Path.GetInvalidPathChars())
Dim bIsValid As Boolean = True
For Each cThisChar As Char In str
bIsValid = True
For Each cInvalid As Char In strInvalidPathChars
If cThisChar = cInvalid Then
bIsValid = False
Exit For
End If
Next cInvalid
If bIsValid Then
strReturnValue += cThisChar
End If
Next cThisChar
Return strReturnValue
End Function ' StripInvalidPathChars
Public Shared Function GetContentDisposition(ByVal strFileName As String) As String
' http://stackoverflow.com/questions/93551/how-to-encode-the-filename-parameter-of-content-disposition-header-in-http
Dim contentDisposition As String
strFileName = StripInvalidPathChars(strFileName)
If System.Web.HttpContext.Current IsNot Nothing AndAlso System.Web.HttpContext.Current.Request.Browser IsNot Nothing Then
If (System.Web.HttpContext.Current.Request.Browser.Browser = "IE" And (System.Web.HttpContext.Current.Request.Browser.Version = "7.0" Or System.Web.HttpContext.Current.Request.Browser.Version = "8.0")) Then
contentDisposition = "attachment; filename=" + Uri.EscapeDataString(strFileName).Replace("'", Uri.HexEscape("'"c))
ElseIf (System.Web.HttpContext.Current.Request.Browser.Browser = "Safari") Then
contentDisposition = "attachment; filename=" + strFileName
Else
contentDisposition = "attachment; filename*=UTF-8''" + Uri.EscapeDataString(strFileName)
End If
Else
contentDisposition = "attachment; filename*=UTF-8''" + Uri.EscapeDataString(strFileName)
End If
Return contentDisposition
End Function ' GetContentDisposition
回答4:
You're using a very long way to convert string to bytes.
Are you sure, that you need any streams? Why just don't use encoding?
Response.BinaryWrite(Encoding.UTF8.GetBytes("Something"))
来源：https://stackoverflow.com/questions/16558317/how-to-download-memorystream-to-a-file