How to Upload Files via HTTP POST using C#?

C# HTTP POST File Upload: A Comprehensive Guide

This guide details how to use C# to upload files to a remote server via an HTTP POST request.

1. Constructing the HTTP Request

First, create an HttpWebRequest object specifying the target URL. Set the Method property to "POST", and define the ContentType and ContentLength appropriately.

2. Authentication and Connection Parameters

Configure the request's Credentials property with the necessary user credentials. Enable pre-authentication by setting PreAuthenticate to true.

3. Building Multipart Form Data

For C# 4.5 and later, leverage the MultipartFormDataContent class to create multipart form data. Add both string and file data using StringContent and StreamContent respectively.

4. Sending the Request and Handling the Response

Send the request using req.GetResponse() and manage any potential exceptions. Process the server's response accordingly.

5. Code Example

The following code demonstrates the process:

HttpWebRequest req = WebRequest.Create(uri) as HttpWebRequest;
req.KeepAlive = false;
req.Method = "POST";
req.Credentials = new NetworkCredential(user.UserName, user.UserPassword);
req.PreAuthenticate = true;
req.ContentType = file.ContentType;
req.ContentLength = file.Length;

using (var formData = new MultipartFormDataContent())
{
    formData.Add(new StringContent(paramString), "param1", "param1");
    formData.Add(new StreamContent(paramFileStream), "file1", "file1");
    formData.Add(new ByteArrayContent(paramFileBytes), "file2", "file2");
    using (var client = new HttpClient())
    {
        var response = await client.PostAsync(uri, formData);
        // Process the response here...
    }
}

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