How to Correctly Upload Files to a Server using HTTP POST Multipart/Form-Data in Windows Phone 8?

Correctly upload files to server in Windows Phone 8 using HTTP POST Multipart/Form-Data

In web development, uploading files to the server using HTTP POST with multipart/form-data is a common task. This article will resolve issues encountered when using HTTPWebRequest to upload files in Windows Phone 8 apps and provide an improved solution.

Original code in Windows Phone 8

The original implementation uses HttpWebRequest to send multipart/form-data POST requests. However, the code incorrectly attempts to send the entire file without accompanying metadata. Multipart/form-data requests need to specify file boundaries and the necessary form data headers.

Improved solutions for Windows Phone 8

To solve this problem, the following is the modified code:

async void MainPage_Loaded(object sender, RoutedEventArgs e)
{
    var file = await Windows.ApplicationModel.Package.Current.InstalledLocation.GetFileAsync(DBNAME);
    byte[] fileBytes = null;
    using (var stream = await file.OpenReadAsync())
    {
        fileBytes = new byte[stream.Size];
        using (var reader = new DataReader(stream))
        {
            await reader.LoadAsync((uint)stream.Size);
            reader.ReadBytes(fileBytes);
        }
    }

    string boundary = Guid.NewGuid().ToString();
    HttpWebRequest httpWebRequest = (HttpWebRequest)WebRequest.Create("http://www.myserver.com/upload.php");
    httpWebRequest.ContentType = "multipart/form-data; boundary=" + boundary;
    httpWebRequest.Method = "POST";

    httpWebRequest.BeginGetRequestStream(GetRequestStreamCallback, new object[] { fileBytes, boundary });
}

private void GetRequestStreamCallback(IAsyncResult asynchronousResult, object state)
{
    object[] stateData = (object[])state;
    byte[] postData = (byte[])stateData[0];
    string boundary = (string)stateData[1];
    HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
    Stream postStream = request.EndGetRequestStream(asynchronousResult);

    //写入起始边界
    byte[] boundaryBytes = System.Text.Encoding.UTF8.GetBytes("--" + boundary + "\r\n");
    postStream.Write(boundaryBytes, 0, boundaryBytes.Length);

    //写入文件数据
    string filename = DBNAME;
    byte[] fileData = System.Text.Encoding.UTF8.GetBytes($"Content-Disposition: form-data; name=\"file\"; filename=\"{filename}\"\r\nContent-Type: application/octet-stream\r\n\r\n");
    postStream.Write(fileData, 0, fileData.Length);
    postStream.Write(postData, 0, postData.Length);

    //写入结束边界
    boundaryBytes = System.Text.Encoding.UTF8.GetBytes("\r\n--" + boundary + "--\r\n");
    postStream.Write(boundaryBytes, 0, boundaryBytes.Length);

    postStream.Close();
    request.BeginGetResponse(GetResponseCallback, request);
}

private void GetResponseCallback(IAsyncResult asynchronousResult)
{
    HttpWebRequest request = (HttpWebRequest)asynchronousResult.AsyncState;
    using (HttpWebResponse response = (HttpWebResponse)request.EndGetResponse(asynchronousResult))
    using (Stream streamResponse = response.GetResponseStream())
    using (StreamReader streamRead = new StreamReader(streamResponse))
    {
        string responseString = streamRead.ReadToEnd();
        // 处理服务器响应
    }
}

Conclusion

This modified code should resolve file upload issues in Windows Phone 8 apps. Remember, when using multipart/form-data requests, be sure to specify the boundaries correctly and provide the necessary headers for the file and accompanying metadata. A clearer Content-Disposition header has been added to the code, and using statements are used to ensure correct release of resources.

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