C#：HttpClient，将多个文件作为MultipartFormDataContent上传时的文件上传进度

Posted 2023-03-31

【中文标题】C#：HttpClient，将多个文件作为MultipartFormDataContent上传时的文件上传进度

【英文标题】：C#: HttpClient, File upload progress when uploading multiple file as MultipartFormDataContent

【发布时间】：2016-12-29 11:07:02

【问题描述】：

我正在使用此代码上传多个文件，并且运行良好。它使用现代的httpclient库。

public async Task<string> PostImages (int platform, string url, List<byte []> imageList)

    try 
        int count = 1;
        var requestContent = new MultipartFormDataContent ();

        foreach (var image in imageList) 
            var imageContent = new ByteArrayContent (image);
            imageContent.Headers.ContentType = MediaTypeHeaderValue.Parse ("image/jpeg");
            requestContent.Add (imageContent, "image" + count, "image.jpg");
            count++;
        
        var cookieHandler = new NativeCookieHandler ();
        var messageHandler = new NativeMessageHandler (false, false, cookieHandler);
        cookieHandler.SetCookies (cookies);
        using (var client = new HttpClient (messageHandler)) 
            client.DefaultRequestHeaders.TryAddWithoutValidation ("User-Agent", GetUserAgent (platform));
            using (var r = await client.PostAsync (url, requestContent)) 
                string result = await r.Content.ReadAsStringAsync ();
                System.Diagnostics.Debug.WriteLine ("PostAsync: " + result);
                return result;
            
        
     catch (Exception e) 
        System.Diagnostics.Debug.WriteLine (e.Message);
        return null;
    

现在我需要上传文件时的进度。我在谷歌搜索，发现我需要使用 ProgressStreamContent

https://github.com/paulcbetts/ModernHttpClient/issues/80

由于 ProgressStreamContent 包含一个接受流的构造函数，因此我将 MultipartFormDataContent 转换为流并在其构造函数中使用它。但是，它不起作用。上传失败。我认为这是因为它是所有文件的流，这不是我的后端所期望的。

public async Task<string> PostImages (int platform, string url, List<byte []> imageList)

    try 
        int count = 1;
        var requestContent = new MultipartFormDataContent ();
            //    here you can specify boundary if you need---^
        foreach (var image in imageList) 
            var imageContent = new ByteArrayContent (image);
            imageContent.Headers.ContentType = MediaTypeHeaderValue.Parse ("image/jpeg");
            requestContent.Add (imageContent, "image" + count, "image.jpg");
            count++;
        
        var cookieHandler = new NativeCookieHandler ();
        var messageHandler = new NativeMessageHandler (false, false, cookieHandler);
        cookieHandler.SetCookies (RestApiPaths.cookies);


        var stream = await requestContent.ReadAsStreamAsync ();

        var client = new HttpClient (messageHandler);
        client.DefaultRequestHeaders.TryAddWithoutValidation ("User-Agent", RestApiPaths.GetUserAgent (platform));

        var request = new HttpRequestMessage (HttpMethod.Post, url);

        var progressContent = new ProgressStreamContent (stream, 4096);
        progressContent.Progress = (bytes, totalBytes, totalBytesExpected) => 
            Console.WriteLine ("Uploading 0/1", totalBytes, totalBytesExpected);
        ;

        request.Content = progressContent;

        var response = await client.SendAsync (request);
        string result = await response.Content.ReadAsStringAsync ();

        System.Diagnostics.Debug.WriteLine ("PostAsync: " + result);

        return result;

     catch (Exception e) 
        System.Diagnostics.Debug.WriteLine (e.Message);
        return null;
    

我应该怎么做才能让它工作？任何帮助表示赞赏

【问题讨论】：

你必须使用 MultiPartContent，而不是 ByteArrayContent

我将文件作为字节数组。

服务器不接受字节数组，http服务器大多需要多部分形式编码的内容，这是服务器期望数据的方式，而不是您发送的方式

我将每个 ByteArrayContent 添加到 MultipartFormDataContent。请查看代码，它就像我在文章开头所说的那样工作。

【参考方案1】：

我有一个 ProgressableStreamContent 的工作版本。请注意，我在构造函数中添加了标题，这是原始 ProgressStreamContent 中的一个错误，它没有添加标题！

internal class ProgressableStreamContent : HttpContent


    /// <summary>
    /// Lets keep buffer of 20kb
    /// </summary>
    private const int defaultBufferSize = 5*4096;

    private HttpContent content;
    private int bufferSize;
    //private bool contentConsumed;
    private Action<long,long> progress;

    public ProgressableStreamContent(HttpContent content, Action<long,long> progress) : this(content, defaultBufferSize, progress)  

    public ProgressableStreamContent(HttpContent content, int bufferSize, Action<long,long> progress)
    
        if (content == null)
        
            throw new ArgumentNullException("content");
        
        if (bufferSize <= 0)
        
            throw new ArgumentOutOfRangeException("bufferSize");
        

        this.content = content;
        this.bufferSize = bufferSize;
        this.progress = progress;

        foreach (var h in content.Headers) 
            this.Headers.Add(h.Key,h.Value);
        
    

    protected override Task SerializeToStreamAsync(Stream stream, TransportContext context)
    

        return Task.Run(async () =>
        
            var buffer = new Byte[this.bufferSize];
            long size;
            TryComputeLength(out size);
            var uploaded = 0;


            using (var sinput = await content.ReadAsStreamAsync())
            
                while (true)
                
                    var length = sinput.Read(buffer, 0, buffer.Length);
                    if (length <= 0) break;

                    //downloader.Uploaded = uploaded += length;
                    uploaded += length;
                    progress?.Invoke(uploaded, size);

                    //System.Diagnostics.Debug.WriteLine($"Bytes sent uploaded of size");

                    stream.Write(buffer, 0, length);
                    stream.Flush();
                
            
            stream.Flush();
        );
    

    protected override bool TryComputeLength(out long length)
    
        length = content.Headers.ContentLength.GetValueOrDefault();
        return true;
    

    protected override void Dispose(bool disposing)
    
        if (disposing)
        
            content.Dispose();
        
        base.Dispose(disposing);
    

另请注意，它需要 HttpContent，而不是流。

这就是你可以使用它的方式。

 var progressContent = new ProgressableStreamContent (
     requestContent, 
     4096,
     (sent,total) => 
        Console.WriteLine ("Uploading 0/1", sent, total);
    );

【讨论】：

这不起作用（不再）。它将通过“SerializeToStreamAsync”中的整个请求，然后才开始使用带宽并实际上传它。至少在 Xamarin 中。

可能是，但是在底层的http客户端实现中，你使用的是哪个实现？

对不起，我正在度假。我正在使用 Xamarin Forms (Mono) System.Net.Http

我在 Xamarin android 上使用基于 OkHttp 的 HttpClient，它运行良好。

好的。 ios 呢？

【参考方案2】：

最简单的方法

您可以通过跟踪您要上传的文件的 FileStream 的Position 来获得准确的进度。

FileStream fileToUpload = File.OpenRead(@"C:\test.mp3");

HttpContent content = new StreamContent(fileToUpload);
HttpRequestMessage msg = new HttpRequestMessage
    Content=content,
    RequestUri = new Uri(--yourUploadURL--)


bool keepTracking = true; //to start and stop the tracking thread
new Task(new Action(() =>  progressTracker(fileToUpload, ref keepTracking); )).Start();
var result = httpClient.SendAsync(msg).Result;
keepTracking = false; //stops the tracking thread

而progressTracker()函数定义为

void progressTracker(FileStream streamToTrack, ref bool keepTracking)

    int prevPos = -1;
    while (keepTracking)
    
        int pos = (int)Math.Round(100 * (streamToTrack.Position / (double)streamToTrack.Length));
        if (pos != prevPos)
        
            Console.WriteLine(pos + "%");

        
        prevPos = pos;

        Thread.Sleep(100);