HTTP的POST请求的详细构造[实现机器提交表单含上传文件及普通文本域]

最近用C#做测试网站的服务程序，由于有些接口需要真实的测试数据。比如提交表单中的文本域和文件域，但.Net中只提供了简单的单独提交文本或文件的方法，所以只能自己构造格式为

multipart/form-data

的HTTP请求，而让我更加了解了HTTP请求的格式。

下面是在Google搜索后的一个解决方案，原链接：http://stackoverflow.com/questions/566462/upload-files-with-httpwebrequest-multipart-form-data

方法1：上传文本域及一个文件[测试成功]

//发送对应表单文本域和一个文件[函数中的输出语句自己调节]
public static void HttpUploadFile(string url, string file, string paramName, string contentType, NameValueCollection nvc)
{
Console.WriteLine(string.Format("Uploading {0} to {1}", file, url));
string boundary = "---------------------------" + DateTime.Now.Ticks.ToString("x");
byte[] boundarybytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "\r\n");

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

Stream rs = wr.GetRequestStream();

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);
string formitem = string.Format(formdataTemplate, key, nvc[key]);
byte[] formitembytes = System.Text.Encoding.UTF8.GetBytes(formitem);
rs.Write(formitembytes, 0, formitembytes.Length);
}
rs.Write(boundarybytes, 0, boundarybytes.Length);

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

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

byte[] trailer = System.Text.Encoding.ASCII.GetBytes("\r\n--" + boundary + "--\r\n");
rs.Write(trailer, 0, trailer.Length);
rs.Close();

WebResponse wresp = null;
try
{
wresp = wr.GetResponse();
Stream stream2 = wresp.GetResponseStream();
StreamReader reader2 = new StreamReader(stream2);
Console.WriteLine(string.Format("File uploaded, server response is: {0}", reader2.ReadToEnd()));
}
catch (Exception ex)
{
//log.Error("Error uploading file", ex);
if (wresp != null)
{
wresp.Close();
wresp = null;
}
}
finally
{
wr = null;
}
}

//使用的例子
//nvc中存放表单文本域的键值对
//image/jpeg是上传文件的格式
NameValueCollection nvc = new NameValueCollection();
nvc.Add("id", "TTR");
nvc.Add("btn-submit-photo", "Upload");
HttpUploadFile("http://your.server.com/upload",
@"C:\test\test.jpg", "file", "image/jpeg", nvc);

方法2：上传表单文本域和多个文件[我没测试成功]

public static  void UploadFilesToRemoteUrl(string url, string[] files, string
logpath, NameValueCollection nvc)
{

long length = 0;
string boundary = "----------------------------" +
DateTime.Now.Ticks.ToString("x");

HttpWebRequest httpWebRequest2 = (HttpWebRequest)WebRequest.Create(url);
httpWebRequest2.ContentType = "multipart/form-data; boundary=" +
boundary;
httpWebRequest2.Method = "POST";
httpWebRequest2.KeepAlive = true;
httpWebRequest2.Credentials =
System.Net.CredentialCache.DefaultCredentials;

Stream memStream = new System.IO.MemoryStream();

byte[] boundarybytes = System.Text.Encoding.ASCII.GetBytes("\r\n--" +
boundary + "\r\n");

string formdataTemplate = "\r\n--" + boundary +
"\r\nContent-Disposition: form-data; name=\"{0}\";\r\n\r\n{1}";

foreach (string key in nvc.Keys)
{
string formitem = string.Format(formdataTemplate, key, nvc[key]);
byte[] formitembytes = System.Text.Encoding.UTF8.GetBytes(formitem);
memStream.Write(formitembytes, 0, formitembytes.Length);
}

memStream.Write(boundarybytes, 0, boundarybytes.Length);

string headerTemplate = "Content-Disposition: form-data; name=\"{0}\"; filename=\"{1}\"\r\n Content-Type: application/octet-stream\r\n\r\n";

for (int i = 0; i < files.Length; i++)
{

//string header = string.Format(headerTemplate, "file" + i, files[i]);
string header = string.Format(headerTemplate, "uplTheFile", files[i]);

byte[] headerbytes = System.Text.Encoding.UTF8.GetBytes(header);

memStream.Write(headerbytes, 0, headerbytes.Length);

FileStream fileStream = new FileStream(files[i], FileMode.Open,
FileAccess.Read);
byte[] buffer = new byte[1024];

int bytesRead = 0;

while ((bytesRead = fileStream.Read(buffer, 0, buffer.Length)) != 0)
{
memStream.Write(buffer, 0, bytesRead);

}

memStream.Write(boundarybytes, 0, boundarybytes.Length);

fileStream.Close();
}

httpWebRequest2.ContentLength = memStream.Length;

Stream requestStream = httpWebRequest2.GetRequestStream();

memStream.Position = 0;
byte[] tempBuffer = new byte[memStream.Length];
memStream.Read(tempBuffer, 0, tempBuffer.Length);
memStream.Close();
requestStream.Write(tempBuffer, 0, tempBuffer.Length);
requestStream.Close();

WebResponse webResponse2 = httpWebRequest2.GetResponse();

Stream stream2 = webResponse2.GetResponseStream();
StreamReader reader2 = new StreamReader(stream2);

MessageBox.Show(reader2.ReadToEnd());

webResponse2.Close();
httpWebRequest2 = null;
webResponse2 = null;
}

原理解释：

详细见链接。下面简单复制过来的。

I believe that you are not building the request body correctly. First, you need to include part boundary (random text) in content type header. For example,

Content-Type: multipart/form-data; boundary=----WebKitFormBoundarySkAQdHysJKel8YBM

Now format of request body will be something like

------WebKitFormBoundarySkAQdHysJKel8YBM
Content-Disposition: form-data;name="key"

KeyValueGoesHere
------WebKitFormBoundarySkAQdHysJKel8YBM
Content-Disposition: form-data;name="param2"

ValueHere
------WebKitFormBoundarySkAQdHysJKel8YBM
Content-Disposition: form-data;name="fileUpload"; filename="y1.jpg"
Content-Type: image/jpeg

[image data goes here]

I will suggest you to use tool such as Fiddler to understand how these requests are built.