假设我们给了API函数F(流S)将流中包含的二进制数据放入数据库中。我想使用F将文件放入数据库中,但我想提前压缩数据。因此,我认为我可以做以下操作:
var fileStream= File.OpenRead(path);
using(var dstream = new DeflateStream(fileStream, CompressionLevel.Optimal))
f(dstream);
但似乎DeflateStream
仅写入流fileStream
中,但在压缩时不会从中读取。在我发现的所有示例中,流的CopyTo
方法用于压缩或解压缩。但这意味着我必须将压缩数据的副本保存在内存中,然后再将其传递给f
:
var memoryStream = new MemoryStream();
using(var fileStream= File.OpenRead(path))
using(var dstream = new DeflateStream(memoryStream, CompressionLevel.Optimal)) {
fileStream.CopyTo(dstream);
memoryStream.Seek(0, SeekOrigin.Begin);
f(memoryStream);
}
有什么方法可以避免使用Memorystream?
更新为了某些评论员的持久性,我添加了一个完整的示例:
using System;
using System.IO;
using System.IO.Compression;
public class ThisWouldBeTheDatabaseClient {
public void f(Stream s) {
// some implementation I don't have access to
// The only thing I know is that it reads data from the stream in some way.
var buffer = new byte[10];
s.Read(buffer,0,10);
}
}
public class Program {
public static void Main() {
var dummyDatabaseClient = new ThisWouldBeTheDatabaseClient();
var dataBuffer = new byte[1000];
var fileStream= new MemoryStream( dataBuffer ); // would be "File.OpenRead(path)" in real case
using(var dstream = new DeflateStream(fileStream, CompressionLevel.Optimal))
dummyDatabaseClient.f(dstream);
}
}
f
的虚拟实现中的读取操作抛出一个例外: invalidoperationException:不支持从压缩流中读取。在评论中结束讨论,我认为无法进行所需的行为使用DeflateStream
,但第三方库中有其他选择。
DeflateStream
只是一个包装器,需要压缩数据的流。因此,您必须使用两个流。
有什么方法可以避免使用Memorystream?
是。
您需要流来存储临时数据而不会消耗(太多)内存。而是使用MemoryStream
您可以使用临时文件为此。
对于懒惰的人(就像我一样),让我们创建一个类似于MemoryStream
public class TempFileStream : FileStream
{
public TempFileStream() : base(
path: Path.Combine(Path.GetTempPath(), Path.GetRandomFileName()),
mode: FileMode.OpenOrCreate,
access: FileAccess.ReadWrite,
share: FileShare.None,
bufferSize: 4096,
options: FileOptions.DeleteOnClose | FileOptions.Asynchronous | FileOptions.Encrypted | FileOptions.RandomAccess)
{
}
}
这里重要的部分是FileOptions.DeleteOnClose
,当您处置流时将删除临时文件。
然后使用它
using (var compressedStream = new TempFileStream())
{
using (var deflateStream = new DeflateStream(
stream: compressedStream,
compressionLevel: CompressionLevel.Optimal,
leaveOpen: true))
using (var fileStream = File.OpenRead(path))
{
fileStream.CopyTo(deflateStream);
}
f(compressedStream);
}
您可以使用SharpCompress
。它的DeflateStream
允许您即时阅读压缩数据,这正是您想要的。
这是基于Rufo爵士的完整示例:
using System;
using System.IO;
using SharpCompress.Compressors;
using SharpCompress.Compressors.Deflate;
using System.Linq;
public class Program
{
public static void Main()
{
var dataBuffer = Enumerable.Range(1, 50000).Select(e => (byte)(e % 256)).ToArray();
using (var dataStream = new MemoryStream(dataBuffer))
{
// Note: this refers to SharpCompress.Compressors.Deflate.DeflateStream
using (var deflateStream = new DeflateStream(dataStream, CompressionMode.Compress))
{
ConsumeStream(deflateStream);
}
}
}
public static void ConsumeStream(Stream stream)
{
// Let's just prove we can reinflate to the original data...
byte[] data;
using (var decompressed = new MemoryStream())
{
using (var decompressor = new DeflateStream(stream, CompressionMode.Decompress))
{
decompressor.CopyTo(decompressed);
}
data = decompressed.ToArray();
}
Console.WriteLine("Reinflated size: " + data.Length);
int errors = 0;
for (int i = 0; i < data.Length; i++)
{
if (data[i] != (i + 1) % 256)
{
errors++;
}
}
Console.WriteLine("Total errors: " + errors);
}
}
或使用您的示例代码:
using System;
using System.IO;
using SharpCompress.Compressors;
using SharpCompress.Compressors.Deflate;
public class ThisWouldBeTheDatabaseClient {
public void f(Stream s) {
// some implementation I don't have access to
// The only thing I know is that it reads data from the stream in some way.
var buffer = new byte[10];
s.Read(buffer,0,10);
}
}
public class Program {
public static void Main() {
var dummyDatabaseClient = new ThisWouldBeTheDatabaseClient();
var dataBuffer = new byte[1000];
var fileStream= new MemoryStream( dataBuffer ); // would be "File.OpenRead(path)" in real case
using(var dstream = new DeflateStream(
fileStream, CompressionMode.Compress, CompressionLevel.BestCompression))
dummyDatabaseClient.f(dstream);
}
}
现在,这不会引发异常,并且将提供压缩数据。