How to Effectively Upload Files to a Server Using HTTP POST Multipart/Form-Data in Windows Phone 8 and Windows 8?

Uploading Files to a Server with HTTP POST Multipart/Form-Data

Uploading files to a server is a common task when developing web applications. HTTP POST multipart/form-data is a MIME type used to transmit files along with other form data. This article will provide a comprehensive guide to uploading files using HTTP POST multipart/form-data in Windows Phone 8 and Windows 8, addressing the common issue of the code not uploading the file or providing errors.

Windows Phone 8 Implementation

The first code block in the question attempts to upload an SQLite database using HTTP POST multipart/form-data in Windows Phone 8. However, the provided code encounters an issue where the fileBytes array is empty. This could be because the correct method for reading the file from IsolatedStorageFile is not used.

To resolve this issue, consider using the following code to read the file:

var file = await ApplicationData.Current.LocalFolder.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);
    }
}

Another issue is passing additional data, such as "userid=SOME_ID," along with the file. In the provided code, there is no mechanism to pass this data. To include additional data, the HttpWebRequest object can be used as follows:

NameValueCollection postData = new NameValueCollection();
postData.Add("userid", "SOME_ID");
byte[] postDataBytes = Encoding.UTF8.GetBytes(postData.ToString());
postStream.Write(postDataBytes, 0, postDataBytes.Length);

Windows 8 Implementation

The second code block in the question uses a newer API, HttpClient, to upload files. However, the code assumes that a MultipartFormDataContent object is used to encapsulate both the file and the additional data. This assumption is incorrect, as HttpClient supports sending multipart/form-data requests directly, eliminating the need for an intermediate MultipartFormDataContent object.

The following code demonstrates how to upload a file using HttpClient in Windows 8:

HttpClient httpClient = new HttpClient();
ByteArrayContent fileContent = new ByteArrayContent(fileBytes);
fileContent.Headers.ContentType = new MediaTypeHeaderValue("application/octet-stream");
MultipartFormDataContent multiPartContent = new MultipartFormDataContent();
multiPartContent.Add(fileContent, "file", "file.ext");
HttpResponseMessage response = await httpClient.PostAsync("http://www.myserver.com/upload.php", multiPartContent);

In this example, the fileContent object is created and assigned the file bytes. The MediaTypeHeaderValue is used to specify the content type of the file. The file is added to the MultipartFormDataContent object along with the file name and extension. The response from the server can be accessed by checking the HttpResponseMessage object.

Conclusion

This article has explored the process of uploading files to a server using HTTP POST multipart/form-data in Windows Phone 8 and Windows 8. By addressing the issue of empty fileBytes and providing alternative implementations, this guide empowers developers with the knowledge to efficiently handle file uploads in their applications.

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