正在附加到MemoryStream

Question

我正试图将一些数据附加到流中。这对于FileStream来说效果很好，但对于MemoryStream来说效果不佳，因为缓冲区大小固定。

将数据写入流的方法与创建流的方法是分开的（我在下面的示例中对其进行了极大的简化）。创建流的方法不知道要写入流的数据的长度。

public void Foo(){
    byte[] existingData = System.Text.Encoding.UTF8.GetBytes("foo");
    Stream s1 = new FileStream("someFile.txt", FileMode.Append, FileAccess.Write, FileShare.Read);
    s1.Write(existingData, 0, existingData.Length);

    Stream s2 = new MemoryStream(existingData, 0, existingData.Length, true);
    s2.Seek(0, SeekOrigin.End); //move to end of the stream for appending
    WriteUnknownDataToStream(s1);
    WriteUnknownDataToStream(s2); // NotSupportedException is thrown as the MemoryStream is not expandable
}
public static void WriteUnknownDataToStream(Stream s)
{
   // this is some example data for this SO query - the real data is generated elsewhere and is of a variable, and often large, size.
   byte[] newBytesToWrite = System.Text.Encoding.UTF8.GetBytes("bar"); // the length of this is not known before the stream is created.
   s.Write(newBytesToWrite, 0, newBytesToWrite.Length);
}

我的一个想法是向函数发送一个可扩展的MemoryStream，然后将返回的数据附加到现有数据中。

public void ModifiedFoo()
{
   byte[] existingData = System.Text.Encoding.UTF8.GetBytes("foo");
   Stream s2 = new MemoryStream(); // expandable capacity memory stream
   WriteUnknownDataToStream(s2);
   // append the data which has been written into s2 to the existingData
   byte[] buffer = new byte[existingData.Length + s2.Length];
   Buffer.BlockCopy(existingData, 0, buffer, 0, existingData.Length);
   Stream merger = new MemoryStream(buffer, true);
   merger.Seek(existingData.Length, SeekOrigin.Begin);
   s2.CopyTo(merger);
}

有更好（更高效）的解决方案吗？

Answer 1

一个可能的解决方案是首先不限制MemoryStream的容量。如果您事先不知道需要写入的字节总数，请创建一个容量未指定的MemoryStream，并将其用于两次写入。

byte[] existingData = System.Text.Encoding.UTF8.GetBytes("foo");
MemoryStream ms = new MemoryStream();
ms.Write(existingData, 0, existingData.Length); 
WriteUnknownData(ms);

毫无疑问，这将比从byte[]初始化MemoryStream的性能差，但如果您需要继续写入流，我相信这是您唯一的选择。