将字符串转换为内存流-内存流不可扩展

本文关键字：内存 可扩展 字符串 转换 | 更新日期: 2023-09-27 18:14:06

我试图将字符串写入内存流，但是失败了，显示错误信息:

Memory stream is not expandable.

产生这个问题的代码行:

context.Response.Filter = new System.IO.MemoryStream(System.Text.Encoding.UTF8.GetBytes(myPage));

有人有解决方法/修复吗?

异常堆栈

: 

[NotSupportedException: Memory stream is not expandable.]
   System.IO.MemoryStream.set_Capacity(Int32 value) +9385744
   System.IO.MemoryStream.EnsureCapacity(Int32 value) +50
   System.IO.MemoryStream.Write(Byte[] buffer, Int32 offset, Int32 count) +265
   System.Web.HttpWriter.FilterIntegrated(Boolean finalFiltering, IIS7WorkerRequest wr) +9155697
   System.Web.HttpResponse.FilterOutput() +159
   System.Web.CallFilterExecutionStep.System.Web.HttpApplication.IExecutionStep.Execute() +52
   System.Web.HttpApplication.ExecuteStep(IExecutionStep step, Boolean& completedSynchronously) +75

将字符串转换为内存流-内存流不可扩展

下面的代码可以正常运行

public class Foo
{
    public static void Main()
    {
        var myPage = "test string";
        var repo =  new System.IO.MemoryStream(System.Text.Encoding.UTF8.GetBytes(myPage));
    }
}
似乎正确的方法是使用默认构造函数 创建MemoryStream。
var repo = new System.IO.MemoryStream();

，然后写入

var stringBytes = System.Text.Encoding.UTF8.GetBytes(myPage);
repo.Write(stringBytes, 0, stringBytes.Length);

如果你想能够正常读取流(例如使用StreamReader)，那么你还需要调用:

repo.Seek(0, SeekOrigin.Begin);

添加数据的自定义流更合适。

最小测试。假设您希望在刷新流时写入文本，然后只写入一次。

public class AppendTextFilter : Stream
{
    private Stream Filter { get; set; }
    private string Text { get; set; }
    private bool TextWritten { get; set; }
    public AppendTextFilter( Stream filter, string text )
    {
        this.Filter = filter;
        this.Text = text;
    }
    public override bool CanRead { get { return Filter.CanRead; } }
    public override bool CanSeek { get { return Filter.CanSeek; } }
    public override bool CanWrite { get { return Filter.CanWrite; } }
    public override void Flush()
    {
        if (!TextWritten)
        {
            var bytes = Encoding.UTF7.GetBytes( Text );
            Filter.Write( bytes, 0, bytes.Length );
            TextWritten = true;
        }
        Filter.Flush();
    }
    public override long Length { get { return Filter.Length + Text.Length; } }
    public override long Position
    {
        get
        {
            return Filter.Position;
        }
        set
        {
            Filter.Position = value;
        }
    }
    public override int Read( byte[] buffer, int offset, int count )
    {
        return Filter.Read( buffer, offset, count );
    }
    public override long Seek( long offset, SeekOrigin origin )
    {
        return Filter.Seek( offset, origin );
    }
    public override void SetLength( long value )
    {
        Filter.SetLength( value );
    }
    public override void Write( byte[] buffer, int offset, int count )
    {
        Filter.Write( buffer, offset, count );
    }
}

从字节数组创建MemoryStream时，实际上是在该数组周围创建了一个包装器。这意味着流的缓冲区一旦达到容量就无法扩展。

然而，HttpResponse.Filter本质上是:过滤器。文档说明:

当你创建一个Stream对象并将Filter属性设置为Stream对象时，Write发送的所有HTTP输出都将通过该过滤器。

因此数据最终被写入MemoryStream。所以它会帮助你知道你想要实现什么，确切地说，因为MemoryStream不会成为一个有用的过滤器。

            byte[] buffer = File.ReadAllBytes("test.xml");
            XmlDocument doc = new XmlDocument();
            using (MemoryStream output = new MemoryStream())
            {
                using (MemoryStream ms = new MemoryStream(buffer ))
                {
                    doc.Load(ms);
                }
                // Make changes to your memory stream here
                doc.Save(output);//Output stream has the changes.
            }
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