C# 如何在ASP.NET Core中提供文件，而它'；它还在写
我有一个由后台服务不断写入的日志文件。到目前为止，用户需要能够下载该文件。当我返回一个MVCC# 如何在ASP.NET Core中提供文件，而它'；它还在写,c#,asp.net-core,.net-core,asp.net-core-2.0,C#,Asp.net Core,.net Core,Asp.net Core 2.0,我有一个由后台服务不断写入的日志文件。到目前为止，用户需要能够下载该文件。当我返回一个MVCFileResult时，由于内容长度不匹配，我得到一个InvalidOperationException，这可能是因为某些内容在提供服务时已写入文件。提供了一个文件，基本上没有问题，但它通常有一个不完整的最后一行 后台服务基本上是这样做的： var stream = new FileStream(evidenceFilePath, FileMode.Append, FileAccess.Write, Fi
FileResultvar stream = new FileStream(evidenceFilePath, FileMode.Append, FileAccess.Write, FileShare.Read);
while (true) // obviously it isn't actually this, but it does happen a lot!
{
var content = "log content\r\n";
stream.Write(Encoding.UTF8.GetBytes(content);
}
我不太介意这个例外，但如果不发生的话，我宁愿这样。不过，我确实需要修复不完整的最后一行问题。对我来说，最明显的解决方案是跟踪已写入文件的字节数，并以某种方式只提供前n个字节。但是，我看不到任何简单的方法可以通过
FileResult其次，对于控制器，您可以查看MSDN示例，通过控制器提供文件服务。一般来说，您可能会遇到文件锁定问题，因此您需要对此进行规划和补偿。然而，你眼前的问题更容易解决。问题归结为返回一条流。在返回响应时写入该流，因此在创建响应主体时计算的内容长度是错误的 您需要做的是在某个时间点捕获日志，即将其读入
字节[]字节[]using (var stream = new FileStream("C:\\path\\to\\the\\file.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (var ms = new MemoryStream())
{
await stream.CopyToAsync(ms);
return File(ms.ToArray(), "text/plain");
}
最后，我编写了一个定制的ActionResult和IActionResultExecutor进行匹配，它们在很大程度上基于MVC和： 问题是——它根据当时的文件长度设置一次
内容长度StreamCopyOperation.CopyToAsyncFileStreamIActionResultExecutorusing (var stream = new FileStream("C:\\path\\to\\the\\file.txt", FileMode.Open, FileAccess.Read, FileShare.ReadWrite))
using (var ms = new MemoryStream())
{
await stream.CopyToAsync(ms);
return File(ms.ToArray(), "text/plain");
}
public class PartialFileStreamResult : FileResult
{
Stream stream;
long bytes;
/// <summary>
/// Creates a new <see cref="PartialFileStreamResult"/> instance with
/// the provided <paramref name="fileStream"/> and the
/// provided <paramref name="contentType"/>, which will download the first <paramref name="bytes"/>.
/// </summary>
/// <param name="stream">The stream representing the file</param>
/// <param name="contentType">The Content-Type header for the response</param>
/// <param name="bytes">The number of bytes to send from the start of the file</param>
public PartialFileStreamResult(Stream stream, string contentType, long bytes)
: base(contentType)
{
this.stream = stream ?? throw new ArgumentNullException(nameof(stream));
if (bytes == 0)
{
throw new ArgumentOutOfRangeException(nameof(bytes), "Invalid file length");
}
this.bytes = bytes;
}
/// <summary>
/// Gets or sets the stream representing the file to download.
/// </summary>
public Stream Stream
{
get => stream;
set => stream = value ?? throw new ArgumentNullException(nameof(stream));
}
/// <summary>
/// Gets or sets the number of bytes to send from the start of the file.
/// </summary>
public long Bytes
{
get => bytes;
set
{
if (value == 0)
{
throw new ArgumentOutOfRangeException(nameof(bytes), "Invalid file length");
}
bytes = value;
}
}
/// <inheritdoc />
public override Task ExecuteResultAsync(ActionContext context)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
var executor = context.HttpContext.RequestServices.GetRequiredService<IActionResultExecutor<PartialFileStreamResult>>();
return executor.ExecuteAsync(context, this);
}
}
public class PartialFileStreamResultExecutor : FileResultExecutorBase, IActionResultExecutor<PartialFileStreamResult>
{
public PartialFileStreamResultExecutor(ILoggerFactory loggerFactory)
: base(CreateLogger<PartialFileStreamResultExecutor>(loggerFactory))
{
}
public async Task ExecuteAsync(ActionContext context, PartialFileStreamResult result)
{
if (context == null)
{
throw new ArgumentNullException(nameof(context));
}
if (result == null)
{
throw new ArgumentNullException(nameof(result));
}
using (result.Stream)
{
long length = result.Bytes;
var (range, rangeLength, serveBody) = SetHeadersAndLog(context, result, length, result.EnableRangeProcessing);
if (!serveBody) return;
try
{
var outputStream = context.HttpContext.Response.Body;
if (range == null)
{
await StreamCopyOperation.CopyToAsync(result.Stream, outputStream, length, bufferSize: BufferSize, cancel: context.HttpContext.RequestAborted);
}
else
{
result.Stream.Seek(range.From.Value, SeekOrigin.Begin);
await StreamCopyOperation.CopyToAsync(result.Stream, outputStream, rangeLength, BufferSize, context.HttpContext.RequestAborted);
}
}
catch (OperationCanceledException)
{
// Don't throw this exception, it's most likely caused by the client disconnecting.
// However, if it was cancelled for any other reason we need to prevent empty responses.
context.HttpContext.Abort();
}
}
}
}
services.AddTransient<IActionResultExecutor<PartialFileStreamResult>, PartialFileStreamResultExecutor>();
[HttpGet]
public IActionResult DownloadLog()
{
var (path, bytes) = GetThePathAndTheNumberOfBytesIKnowHaveBeenFlushed();
var stream = new FileStream(path, FileMode.Open, FileAccess.Read, FileShare.ReadWrite); // this ensures that the file can be read while it's still being written
return new PartialFileStreamResult(stream, "text/plain", bytes);
}