C# 使用HttpWebRequest上载文件（多部分/表单数据）

我试图通过API将文件上传到web服务器，但出现了错误 “远程服务器返回错误：（403）禁止。”我还尝试通过邮递员上载文件，但成功。下面是我的代码上载文件和邮递员预览

   public static void HttpUploadFile(string url, string file, string paramName, string contentType, NameValueCollection nvc)
    {
        MessageBox.Show(string.Format("Uploading {0} to {1}", file, url));
        var boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");
        var boundarybytes = Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");

        var wr = (HttpWebRequest)WebRequest.Create(url);
        wr.ContentType = "multipart/form-data; boundary=" + boundary;
        wr.Method = "POST";
        wr.KeepAlive = true;
        wr.Credentials = CredentialCache.DefaultCredentials;

        var rs = wr.GetRequestStream();

        const string formdataTemplate = "Content-Disposition: form-data; name=\"{0}\"\r\n\r\n{1}";
        foreach (string key in nvc.Keys)
        {
            rs.Write(boundarybytes, 0, boundarybytes.Length);
            var formitem = string.Format(formdataTemplate, key, nvc[key]);
            byte[] formitembytes = Encoding.UTF8.GetBytes(formitem);
            rs.Write(formitembytes, 0, formitembytes.Length);
        }
        rs.Write(boundarybytes, 0, boundarybytes.Length);

        const string headerTemplate = "Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\nContent-Type: {2}\r\n\r\n";
        var header = string.Format(headerTemplate, paramName, file, contentType);
        var headerbytes = Encoding.UTF8.GetBytes(header);
        rs.Write(headerbytes, 0, headerbytes.Length);

        var fileStream = new FileStream(file, FileMode.Open, FileAccess.Read);
        var buffer = new byte[4096];
        var bytesRead = 0;
        while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
        {
            rs.Write(buffer, 0, bytesRead);
        }
        fileStream.Close();

        var trailer = Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
        rs.Write(trailer, 0, trailer.Length);
        rs.Close();

        WebResponse wresp = null;
        try
        {
            wresp = wr.GetResponse();
            var stream2 = wresp.GetResponseStream();
            var reader2 = new StreamReader(stream2);
            MessageBox.Show(string.Format("Response is: {0}", reader2.ReadToEnd()));
        }
        catch (Exception ex)
        {
            MessageBox.Show("Error uploading file" + ex);
            if (wresp != null)
            {
                wresp.Close();
                wresp = null;
            }
        }
        finally
        {
            wr = null;
        }
    }

这是邮递员预览

POST / HTTP/1.1
Host: buckname.s3.amazonaws.com
Cache-Control: no-cache

----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="key"

2014/6b9830b098c9871c6356a5e55af91bfd/${filename}
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="AWSAccessKeyId"

AKIAJNXK6LUBUSZBXJIQ
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="acl"

public-read
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="policy"

eyJleHBpcmF0aW9uIjoiMjAxNC0wOC0yMlQxMDo1MTow
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="signature"

ezYsOF/P6bGcOqQdyJeE7iApu2A=
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="success_action_status"

201
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="secure"

true
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="x-amz-storage-class"

REDUCED_REDUNDANCY
----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="file"; filename="exp.png"
Content-Type: image/png


----WebKitFormBoundaryE19zNvXGzXaLvS5C
Content-Disposition: form-data; name="Content-Type"

image/jpeg
----WebKitFormBoundaryE19zNvXGzXaLvS5C

编辑（代码发送）

谢谢大家!

我的错误是

<?xml version="1.0" encoding="UTF-8"?> <Error><Code>AccessDenied</Code><Message>Invalid              according to Policy: Policy Condition failed: ["eq", "$Secure", "true"]</Message>

---

问题是字段的值（在我的例子中为：secure）case sensitive我试图发布True，但它必须是True

您的代码生成了什么？（您是否尝试过区分有效内容和无效内容？AccessDenied根据策略无效：策略条件失败：[“eq”、“$Secure”、“true”]@RichardNo，您的代码发送的是什么（即在POST请求中发送的输出是什么）。建议使用Fiddler或其他HTTP调试器。对不起，我添加了代码发送，我尝试使用类似postman（chrome扩展）的HTTP调试器@Richard您需要捕获代码发送的内容（标题和正文），并与有效的帖子进行比较。您的编码代码可能有缺陷。总体方法：修复代码，使之与有效的代码相匹配（然后使用类似的请求进行迭代）。因此，建议使用Fiddler来查看您的代码到底发送了什么。

<?xml version="1.0" encoding="UTF-8"?> <Error><Code>AccessDenied</Code><Message>Invalid              according to Policy: Policy Condition failed: ["eq", "$Secure", "true"]</Message>