使用 ServiceStack Rest-API 下载文件

Question

I'm quite new to REST-services in general and I'm playing around with ServiceStack (which is awesome!). I have some services running and now I want to be able to download files (zip) via the service.

My idea is to set a route (/download) to receive files and download them with the client to store them locally.

My current approach looks like this:

[Route("/download")]
public class DownloadRequest : IReturn<HttpResult>
{

}

public class FileDownloadService : Service
{
    public object Any(DownloadRequest request)
    {
        string fileFullPath = @"C:\Users\marcel\Downloads\test.zip";
        string mimeType = "application/zip";
        FileInfo fi = new FileInfo(fileFullPath);

        byte[] reportBytes = File.ReadAllBytes(fi.FullName);
        HttpResult result = new HttpResult(reportBytes, mimeType);

        result.Headers.Add("Content-Disposition", "attachment;filename=Download.zip;");

        return result;
    }
}

I'd like to change this implementation to send data as stream. I stumbled upon IStreamWriterAsync, but couldn't really find documentation on usage for this. I'd also like to be able to handle client-side download with the ServiceStack C#-Client.

What would be a good strategy do implement my plan?

Edit: Something like that?

[Route("/download")]
public class DownloadRequest : IReturn<Stream>
{

}

public class FileDownloadService : Service, IHasOptions
{
    public IDictionary<string, string> Options { get; private set; }

    public Stream Any(DownloadRequest request)
    {
        string fileFullPath = @"C:\Users\marcel\Downloads\test.zip";
        FileInfo fi = new FileInfo(fileFullPath);

        Options = new Dictionary<string, string>
        {
            {"Content-Type","application/zip" },
            {"Content-Disposition", "attachment;filename=Download.zip;" }
        };

        return fi.OpenRead();
    }
}

Answer 1

An easy way to download a file is to return the fileInfo in a HttpResult, eg:

return new HttpResult(new FileInfo(fileFullPath), asAttachment:true);

Or by using the Virtual File System

return new HttpResult(
    VirtualFileSources.GetFile(virtualPath), asAttachment:true);

Both of these APIs already write the file bytes as a Stream so there's no need to try manually doing it yourself.

Note: HttpResult is just a server wrapper object not the response body itself so it should never be used in an IReturn<T> interface whose purpose is to tell clients what Response Type the Service returns.

The IReturn<T> should specify what the Response Body is, in this case since it's not a Response DTO it can be either:

IReturn<byte[]> or IReturn<Stream> 

Or you can just leave it unspecified as you'll still be able to download it using the ServiceClient's raw data APIs :

With IReturn<Stream> interface:

using (Stream stream = client.Get(new DownloadRequest())) {
   ...
}

Or you can just easily download the response as a Stream without the IReturn<T> by specifying how you want to access the raw data on the call-site, eg:

Stream stream = client.Get<Stream>(new DownloadRequest());
byte[] bytes = client.Get<byte[]>("/download");

If you want to also access the Response HTTP Headers you can also request the raw HttpWebResponse to be returned which will let you access the Response HTTP Headers:

using (var webRes = client.Get<HttpWebResponse>(new DownloadRequest()))
using (var stream = webRes.GetResponseStream())
{
    var contentDisposition = webRes.Headers[HttpHeaders.ContentDisposition];
}

Alternatively you can also use HTTP Utils to download arbitrary files, eg:

 string info = null;
 var bytes = baseUrl.CombineWith("download").GetBytesFromUrl(
     responseFilter: res => info = res.Headers[HttpHeaders.ContentDisposition]);

Answer 2

Have a look at this article. Basically, just return a Stream . You can use fi.OpenRead and return that stream.

To combine headers and stream, an option is a custom return type instead, something like this

public class DownloadFileResult : IStreamWriterAsync, IHasOptions
{
    private readonly Stream _stream;
    public IDictionary<string, string> Options { get; }

    public DownloadFileResult(Stream responseStream, string mime, string filename)
    {
        _stream = responseStream;

        Options = new Dictionary<string, string>()
        {
            {"Content-Disposition", $"attachment; filename=\"{filename}\";"},
            {"Content-Type", mime}
        };
    }

    public async Task WriteToAsync(Stream responseStream, CancellationToken token)
    {
        if (_stream == null) { 
            return;
        }

        await _stream.CopyToAsync(responseStream);
        responseStream.Flush();
    }
}