Temp File Stream

Makes using disk-backed temporary storage almost as simple as using a MemoryStream. Implements IDisposable. Geared towards net core services using DI (IServiceProvider).

Why?

Disk-based temporary storage is often under-utilized. Consider that some cloud providers provide fast ephemeral storage for little if any cost!

Commonly used Interfaces

To create a temp file, use ITempFileFactory's CreateTempFile method. This provides an instance of ITempFile, with its WriteStream property available for immediate use. Write information to the WriteStream, then dispose the WriteStream. To re-open the same temp file for reading, call CreateReadStream on the ITempFile. When done working with the temp file, dispose the read stream, and then dispose the ITempFile instance.

Temp File naming

Temp file names incorporate a cryptograhpically sound unique identifier, when the default namer (TempFileNamer) is used. This default namer is registered as part of the call to services.AddTempFileStream.

Temp File deletion

The default temp file disposer (BackgroundTempFileDisposer) launches a task (using Task.Run) when an ITempFile is disposed, deleting the file in the background. If deletion fails, several more attempts are made. The default implementation usually does the job, but does not attempt to offer a strong guarantee of temp file deletion. In particular, temp files created towards the end of the app lifetime might fail to be deleted. This strategy is geared towards apps running in a container (with a writeable temp folder!).

Configuration

The root folder where temp files are placed, file name prefix, and stream behaviors may be configured using TempFileStreamConfig. By default, Path.GetTempPath is used, and temp file names bear no particular prefix. The default configuration is suitable for many use cases.

Interfaces controlling implementation details

A suite of interfaces, in the TempFileStream.Abstractions namespace, can be used to control various facets of temporary file operations. The default implementations, as registered by services.AddTempFileStream, are suitable for most use cases. Note that custom implementations of some of the interfaces could in theory choose to not honor TempFileStreamConfig.

DI Registration

// without any particular configuration (suitable for many use cases)
services.AddDiskBasedTempFileStream(); // if writeable disk not available, use AddMemoryBasedTempFileStream as a drop-in fallback

// with custom configuration
services.AddTempFileStream().Configure<TempFileStreamConfig>(cfg =>
              {
                  cfg.Prefix = "someunit_";
              });

Example Usage

var tempFileFactory = serviceProvider.GetRequiredService<ITempFileFactory>();
using (var tempFile = tempFileFactory.CreateTempFile())
{
    // writeout data to temp file's write stream, and dispose the write stream
    using (var ws = tempFile.WriteStream)
    {
        ws.Write(buf, 0, buf.Length);
    }

    // now re-open it for reading etc.
    using (var readStream = tempFile.CreateReadStream())
    {
        // ...
    }
}

Security

The default implementation does incorporate a cryptographically sound random value in temp file names, but other than that, makes no further attempt to deter enumeration of temp files, access to their contents, or tampering with the contents. For some applications, it would be a good idea to use a generated in-memory symmetric key to encrypt temp file contents, effectively providing a confidentiality guarantee as good as straight in-memory storage of temporary data. Future versions of the library may offer such functionality.

bartpio/TempFileStream