Progress bar with HttpClient

问题:

i have a file downloader function:

        HttpClientHandler aHandler = new HttpClientHandler();
        aHandler.ClientCertificateOptions = ClientCertificateOption.Automatic;
        HttpClient aClient = new HttpClient(aHandler);
        aClient.DefaultRequestHeaders.ExpectContinue = false;
        HttpResponseMessage response = await aClient.GetAsync(url);
        InMemoryRandomAccessStream randomAccessStream = new InMemoryRandomAccessStream();

        // To save downloaded image to local storage
        var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
        filename, CreationCollisionOption.ReplaceExisting);
        var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);
        DataWriter writer = new DataWriter(fs.GetOutputStreamAt(0));

        writer.WriteBytes(await response.Content.ReadAsByteArrayAsync());

        await writer.StoreAsync();
        //current.image.SetSource(randomAccessStream);
        writer.DetachStream();
        await fs.FlushAsync();

How can i realize progress bar functionality? Maybe i can get the writers bytes written so far? Or something?

P.S. I cant use DownloadOperation(Background transferring) because data from server requests certificate - and this functionality doesn't exist in DownloadOperations.

回答1:

The best way to go is using Windows.Web.Http.HttpClient instead of System.Net.Http.HttpClient. The first one supports progress.

But if for some reason you want to stick to the System.Net one, you will need to implement your own progress.

Remove the DataWriter, remove the InMemoryRandomAccessStream and add HttpCompletionOption.ResponseHeadersRead to GetAsync call so it returns as soon as headers are received, not when the whole response is received. I.e.:

// Your original code.
HttpClientHandler aHandler = new HttpClientHandler();
aHandler.ClientCertificateOptions = ClientCertificateOption.Automatic;
HttpClient aClient = new HttpClient(aHandler);
aClient.DefaultRequestHeaders.ExpectContinue = false;
HttpResponseMessage response = await aClient.GetAsync(
    url,
    HttpCompletionOption.ResponseHeadersRead); // Important! ResponseHeadersRead.

// To save downloaded image to local storage
var imageFile = await ApplicationData.Current.LocalFolder.CreateFileAsync(
    filename,
    CreationCollisionOption.ReplaceExisting);
var fs = await imageFile.OpenAsync(FileAccessMode.ReadWrite);

// New code.
Stream stream = await response.Content.ReadAsStreamAsync();
IInputStream inputStream = stream.AsInputStream();
ulong totalBytesRead = 0;
while (true)
{
    // Read from the web.
    IBuffer buffer = new Windows.Storage.Streams.Buffer(1024);
    buffer = await inputStream.ReadAsync(
        buffer,
        buffer.Capacity,
        InputStreamOptions.None);

    if (buffer.Length == 0)
    {
        // There is nothing else to read.
        break;
    }

    // Report progress.
    totalBytesRead += buffer.Length;
    System.Diagnostics.Debug.WriteLine("Bytes read: {0}", totalBytesRead);

    // Write to file.
    await fs.WriteAsync(buffer);
}
inputStream.Dispose();
fs.Dispose();

回答2:

Here's a self-contained class that'll do the download, and report back the progress percentage, based on code from TheBlueSky on this SO answer, and eriksendc on this GitHub comment.

public class HttpClientDownloadWithProgress : IDisposable
{
    private readonly string _downloadUrl;
    private readonly string _destinationFilePath;

    private HttpClient _httpClient;

    public delegate void ProgressChangedHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);

    public event ProgressChangedHandler ProgressChanged;

    public HttpClientDownloadWithProgress(string downloadUrl, string destinationFilePath)
    {
        _downloadUrl = downloadUrl;
        _destinationFilePath = destinationFilePath;
    }

    public async Task StartDownload()
    {
        _httpClient = new HttpClient { Timeout = TimeSpan.FromDays(1) };

        using (var response = await _httpClient.GetAsync(_downloadUrl, HttpCompletionOption.ResponseHeadersRead))
            await DownloadFileFromHttpResponseMessage(response);
    }

    private async Task DownloadFileFromHttpResponseMessage(HttpResponseMessage response)
    {
        response.EnsureSuccessStatusCode();

        var totalBytes = response.Content.Headers.ContentLength;

        using (var contentStream = await response.Content.ReadAsStreamAsync())
            await ProcessContentStream(totalBytes, contentStream);
    }

    private async Task ProcessContentStream(long? totalDownloadSize, Stream contentStream)
    {
        var totalBytesRead = 0L;
        var readCount = 0L;
        var buffer = new byte[8192];
        var isMoreToRead = true;

        using (var fileStream = new FileStream(_destinationFilePath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
        {
            do
            {
                var bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);
                if (bytesRead == 0)
                {
                    isMoreToRead = false;
                    TriggerProgressChanged(totalDownloadSize, totalBytesRead);
                    continue;
                }

                await fileStream.WriteAsync(buffer, 0, bytesRead);

                totalBytesRead += bytesRead;
                readCount += 1;

                if (readCount % 100 == 0)
                    TriggerProgressChanged(totalDownloadSize, totalBytesRead);
            }
            while (isMoreToRead);
        }
    }

    private void TriggerProgressChanged(long? totalDownloadSize, long totalBytesRead)
    {
        if (ProgressChanged == null)
            return;

        double? progressPercentage = null;
        if (totalDownloadSize.HasValue)
            progressPercentage = Math.Round((double)totalBytesRead / totalDownloadSize.Value * 100, 2);

        ProgressChanged(totalDownloadSize, totalBytesRead, progressPercentage);
    }

    public void Dispose()
    {
        _httpClient?.Dispose();
    }
}

Usage:

var downloadFileUrl = "http://example.com/file.zip";
var destinationFilePath = Path.GetFullPath("file.zip");

using (var client = new HttpClientDownloadWithProgress(downloadFileUrl, destinationFilePath))
{
    client.ProgressChanged += (totalFileSize, totalBytesDownloaded, progressPercentage) => {
        Console.WriteLine($"{progressPercentage}% ({totalBytesDownloaded}/{totalFileSize})");
    };

    await client.StartDownload();
}

Result:

7.81% (26722304/342028776)
8.05% (27535016/342028776)
8.28% (28307984/342028776)
8.5% (29086548/342028776)
8.74% (29898692/342028776)
8.98% (30704184/342028776)
9.22% (31522816/342028776)

回答3:

From .Net 4.5 onwards: Use IProgress<T>

Since .Net 4.5 you can handle asynchronus progress reporting with the IProgress<T> interface. You can write an extension method for downloading files using the HttpClient that can be called like this where progress is the implementation of IProgress<float> for your porgress bar or other UI stuff:

// Seting up the http client used to download the data
using (var client = new HttpClient()) {
    client.Timeout = TimeSpan.FromMinutes(5);

    // Create a file stream to store the downloaded data.
    // This really can be any type of writeable stream.
    using (var file = new FileStream(filePath, FileMode.Create, FileAccess.Write, FileShare.None)) {

        // Use the custom extension method below to download the data.
        // The passed progress-instance will receive the download status updates.
        await client.DownloadAsync(DownloadUrl, file, progress, cancellationToken);
    }
}

Implementation

The code for this extension method looks like this. Note that this extension depends on another extension for handling asynchronous stream copying with progress reporting.

public static class HttpClientExtensions
{
    public static async Task DownloadAsync(this HttpClient client, string requestUri, Stream destination, IProgress<float> progress = null, CancellationToken cancellationToken = default) {
        // Get the http headers first to examine the content length
        using (var response = await client.GetAsync(requestUri, HttpCompletionOption.ResponseHeadersRead)) {
            var contentLength = response.Content.Headers.ContentLength;

            using (var download = await response.Content.ReadAsStreamAsync()) {

                // Ignore progress reporting when no progress reporter was 
                // passed or when the content length is unknown
                if (progress == null || !contentLength.HasValue) {
                    await download.CopyToAsync(destination);
                    return;
                }

                // Convert absolute progress (bytes downloaded) into relative progress (0% - 100%)
                var relativeProgress = new Progress<long>(totalBytes => progress.Report((float)totalBytes / contentLength.Value));
                // Use extension method to report progress while downloading
                await download.CopyToAsync(destination, 81920, relativeProgress, cancellationToken);
                progress.Report(1);
            }
        }
    }
}

With stream extension for the real progress reporting:

public static class StreamExtensions
{
    public static async Task CopyToAsync(this Stream source, Stream destination, int bufferSize, IProgress<long> progress = null, CancellationToken cancellationToken = default) {
        if (source == null)
            throw new ArgumentNullException(nameof(source));
        if (!source.CanRead)
            throw new ArgumentException("Has to be readable", nameof(source));
        if (destination == null)
            throw new ArgumentNullException(nameof(destination));
        if (!destination.CanWrite)
            throw new ArgumentException("Has to be writable", nameof(destination));
        if (bufferSize < 0)
            throw new ArgumentOutOfRangeException(nameof(bufferSize));

        var buffer = new byte[bufferSize];
        long totalBytesRead = 0;
        int bytesRead;
        while ((bytesRead = await source.ReadAsync(buffer, 0, buffer.Length, cancellationToken).ConfigureAwait(false)) != 0) {
            await destination.WriteAsync(buffer, 0, bytesRead, cancellationToken).ConfigureAwait(false);
            totalBytesRead += bytesRead;
            progress?.Report(totalBytesRead);
        }
    }
}

回答4:

The following code shows a minimal example of what must be done against the HttpClient api to get download progress.

HttpClient client = //...

// Must use ResponseHeadersRead to avoid buffering of the content
using (var response = await client.GetAsync(uri, HttpCompletionOption.ResponseHeadersRead)){
    // You must use as stream to have control over buffering and number of bytes read/received
    using (var stream = await response.Content.ReadAsStreamAsync())
    {
        // Read/process bytes from stream as appropriate

        // Calculated by you based on how many bytes you have read.  Likely incremented within a loop.
        long bytesRecieved = //...

        long? totalBytes = response.Content.Headers.ContentLength;
        double? percentComplete = (double)bytesRecieved / totalBytes;

        // Do what you want with `percentComplete`
    }
}

The above does not tell you how to process the stream, how to report the process, or try to provide a direct solution to the code in the original question. However, this answer may be more accessible to future readers who wish to apply having progress to in their code.

回答5:

same as @René Sackers solution above, but added the ability to cancel the download

class HttpClientDownloadWithProgress : IDisposable
{
    private readonly string _downloadUrl;
    private readonly string _destinationFilePath;
    private readonly CancellationToken? _cancellationToken;

    private HttpClient _httpClient;

    public delegate void ProgressChangedHandler(long? totalFileSize, long totalBytesDownloaded, double? progressPercentage);

    public event ProgressChangedHandler ProgressChanged;

    public HttpClientDownloadWithProgress(string downloadUrl, string destinationFilePath, CancellationToken? cancellationToken = null)
    {
        _downloadUrl = downloadUrl;
        _destinationFilePath = destinationFilePath;
        _cancellationToken = cancellationToken;
    }

    public async Task StartDownload()
    {
        _httpClient = new HttpClient { Timeout = TimeSpan.FromDays(1) };

        using (var response = await _httpClient.GetAsync(_downloadUrl, HttpCompletionOption.ResponseHeadersRead))
            await DownloadFileFromHttpResponseMessage(response);
    }

    private async Task DownloadFileFromHttpResponseMessage(HttpResponseMessage response)
    {
        response.EnsureSuccessStatusCode();

        var totalBytes = response.Content.Headers.ContentLength;

        using (var contentStream = await response.Content.ReadAsStreamAsync())
            await ProcessContentStream(totalBytes, contentStream);
    }

    private async Task ProcessContentStream(long? totalDownloadSize, Stream contentStream)
    {
        var totalBytesRead = 0L;
        var readCount = 0L;
        var buffer = new byte[8192];
        var isMoreToRead = true;

        using (var fileStream = new FileStream(_destinationFilePath, FileMode.Create, FileAccess.Write, FileShare.None, 8192, true))
        {
            do
            {
                int bytesRead;
                if (_cancellationToken.HasValue)
                {
                    bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length, _cancellationToken.Value);
                }
                else
                {
                    bytesRead = await contentStream.ReadAsync(buffer, 0, buffer.Length);
                }

                if (bytesRead == 0)
                {
                    isMoreToRead = false;
                    continue;
                }

                await fileStream.WriteAsync(buffer, 0, bytesRead);

                totalBytesRead += bytesRead;
                readCount += 1;

                if (readCount % 10 == 0)
                    TriggerProgressChanged(totalDownloadSize, totalBytesRead);
            }
            while (isMoreToRead);

        }

        //the last progress trigger should occur after the file handle has been released or you may get file locked error
        TriggerProgressChanged(totalDownloadSize, totalBytesRead);
    }

    private void TriggerProgressChanged(long? totalDownloadSize, long totalBytesRead)
    {
        if (ProgressChanged == null)
            return;

        double? progressPercentage = null;
        if (totalDownloadSize.HasValue)
            progressPercentage = Math.Round((double)totalBytesRead / totalDownloadSize.Value * 100, 2);

        ProgressChanged(totalDownloadSize, totalBytesRead, progressPercentage);
    }

    public void Dispose()
    {
        _httpClient?.Dispose();
    }
}

回答6:

Hm, you could have another thread check the current size of the stream being written (you'd also pass the expected file size to it) and then update the progress bar accordingly.