C# 解压缩SQL Blob内容并在PushStreamContent.NETCore中返回答案

我正在一个.NET核心服务中开发一个新的API，新的API应该从SQL表中读取一个BLOB，使用DeflateStream解压它。然后将其返回（流式传输）到客户端

为了不消耗太多内存。我将返回一个类型为的响应，这样我就可以直接将sql流复制到响应流中，而无需在内存中加载blob。所以我就这样结束了

return this.ResponseMessage(new HttpResponseMessage
        {
            Content = new PushStreamContent(async (outStream, httpContent, transportContext) =>
            {
                using (SqlConnection connection = new SqlConnection(connectionString))
                {
                    await connection.OpenAsync();
                    using (SqlCommand command = new SqlCommand(query, connection))
                    {

                        // The reader needs to be executed with the SequentialAccess behavior to enable network streaming
                        // Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions
                        using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess))
                        {
                            if (await reader.ReadAsync() && !(await reader.IsDBNullAsync(0)))
                            {
                                using (Stream streamToDecompress = reader.GetStream(0))
                                using (Stream decompressionStream = new DeflateStream(streamToDecompress, CompressionMode.Decompress))
                                {
                                    // This copyToAsync will take for ever
                                    await decompressionStream.CopyToAsync(outStream);
                                    outStream.close();

                                    return;
                                }
                            }

                            throw new Exception("Couldn't retrieve blob");
                        }
                    }
                }
            },
            "application/octet-stream")
        });

这里的问题是，将deflateStream复制到响应输出流的步骤将永远像代码中提到的那样进行。虽然我尝试了同样的方法，但将流写入一个文件，而不是复制到resp流，效果非常好

你们能帮我吗？？我使用PushStreamContent是不是错了？我应该使用不同的方法吗？问题是我不想在内存中加载整个Blob，我想读取它

---

并在飞行中解压。blobs，我想利用它。

这是PushStreamContent中的死锁，我并不假装理解。但我改变了它

await decompressionStream.CopyToAsync(outStream);

到

解决它

这是完整的报告：

public ResponseMessageResult Get()
{
    var data =  new string[] { "value1", "value2" };

    var jsonData = Newtonsoft.Json.JsonConvert.SerializeObject(data);

    var msSource = new MemoryStream(Encoding.UTF8.GetBytes(jsonData));
    var msDest = new MemoryStream();
    var compressionStream = new DeflateStream(msDest, CompressionMode.Compress);
    msSource.CopyTo(compressionStream);
    compressionStream.Close();

    var compressedBytes = msDest.ToArray();

    var query = "select @bytes buf";
    var connectionString = "server=localhost;database=tempdb;integrated security=true";

    
    return this.ResponseMessage(new HttpResponseMessage
    {
        Content = new PushStreamContent(async (outStream, httpContent, transportContext) =>
        {
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                await connection.OpenAsync();
                using (SqlCommand command = new SqlCommand(query, connection))
                {
                    command.Parameters.Add("@bytes", SqlDbType.VarBinary, -1).Value = compressedBytes;

                    // The reader needs to be executed with the SequentialAccess behavior to enable network streaming
                    // Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions
                    using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess))
                    {
                        if (await reader.ReadAsync() && !(await reader.IsDBNullAsync(0)))
                        {
                            using (Stream streamToDecompress = reader.GetStream(0))
                            {
                                //var buf = new MemoryStream();
                                //streamToDecompress.CopyTo(buf);
                                //buf.Position = 0;

                                using (Stream decompressionStream = new DeflateStream(streamToDecompress, CompressionMode.Decompress))
                                {
                                    
                                    // This copyToAsync will take for ever
                                    //await decompressionStream.CopyToAsync(outStream);
                                    decompressionStream.CopyTo(outStream);
                                    outStream.Close();

                                    return;
                                }
                            }
                        }

                        throw new Exception("Couldn't retrieve blob");
                    }
                }
            }
        },
    "application/octet-stream")
    });
}

---

“此copyToAsync将永远持续”是指无限期挂起吗？您确定客户端正在读取到响应流的末尾吗？@DavidBrowne Microsoft，感谢您的回答。是的，它确实无限期地悬挂着。我知道我可以从响应流中读取数据（一次来自SqlReader）。如果我注释掉deflate流，并将响应流复制到outStream，而不进行解压缩，那么它就会工作。但似乎放气流没有从响应中读取。

public ResponseMessageResult Get()
{
    var data =  new string[] { "value1", "value2" };

    var jsonData = Newtonsoft.Json.JsonConvert.SerializeObject(data);

    var msSource = new MemoryStream(Encoding.UTF8.GetBytes(jsonData));
    var msDest = new MemoryStream();
    var compressionStream = new DeflateStream(msDest, CompressionMode.Compress);
    msSource.CopyTo(compressionStream);
    compressionStream.Close();

    var compressedBytes = msDest.ToArray();

    var query = "select @bytes buf";
    var connectionString = "server=localhost;database=tempdb;integrated security=true";

    
    return this.ResponseMessage(new HttpResponseMessage
    {
        Content = new PushStreamContent(async (outStream, httpContent, transportContext) =>
        {
            using (SqlConnection connection = new SqlConnection(connectionString))
            {
                await connection.OpenAsync();
                using (SqlCommand command = new SqlCommand(query, connection))
                {
                    command.Parameters.Add("@bytes", SqlDbType.VarBinary, -1).Value = compressedBytes;

                    // The reader needs to be executed with the SequentialAccess behavior to enable network streaming
                    // Otherwise ReadAsync will buffer the entire BLOB into memory which can cause scalability issues or even OutOfMemoryExceptions
                    using (SqlDataReader reader = await command.ExecuteReaderAsync(CommandBehavior.SequentialAccess))
                    {
                        if (await reader.ReadAsync() && !(await reader.IsDBNullAsync(0)))
                        {
                            using (Stream streamToDecompress = reader.GetStream(0))
                            {
                                //var buf = new MemoryStream();
                                //streamToDecompress.CopyTo(buf);
                                //buf.Position = 0;

                                using (Stream decompressionStream = new DeflateStream(streamToDecompress, CompressionMode.Decompress))
                                {
                                    
                                    // This copyToAsync will take for ever
                                    //await decompressionStream.CopyToAsync(outStream);
                                    decompressionStream.CopyTo(outStream);
                                    outStream.Close();

                                    return;
                                }
                            }
                        }

                        throw new Exception("Couldn't retrieve blob");
                    }
                }
            }
        },
    "application/octet-stream")
    });
}