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介绍

我们将学习如何写一个简单的web服务器，用于响应知名的HTTP请求（GET和POST)，用C#发送响应。然后，我们从网络访问这台服务器，这次我们会说“Hello world!”

背景

HTTP协议

HTTP是服务器和客户机之间的通信协议。它使用TCP/IP协议来发送/接收请求/响应。

有几个HTTP方法，我们将实现两个：GET和POST。

GET

当我们将一个地址输入到我们的Web浏览器的地址栏中，按下回车键时，会发生什么情况？（虽然我们使用TCP/IP，但我们不指定端口号，因为HTTP默认使用80端口，我们并不需要指定80）

GET / HTTP/1.1\r\n
Host: okbase.net\r\n
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:14.0) Gecko/20100101 Firefox/14.0.1\r\n
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n
Accept-Language: tr-tr,tr;q=0.8,en-us;q=0.5,en;q=0.3\r\n
Accept-Encoding: gzip, deflate\r\n
Connection: keep-alive\r\n\r\n

该GET请求使用TCP/IP通过浏览器向服务器发送，请求的是okbase.net的根目录下的内容。我们可以添加更多的头信息，最基本的信息如下：

GET / HTTP/1.1\r\n
Host: okbase.net\r\n\r\n

POST

POST请求和GET请求类似，在GET请求里，变量加到url的?下面，POST请求，变量加到两行回车的下面，并需要指定内容长度。

POST /index.html HTTP/1.1\r\n
Host: atasoyweb.net\r\n
User-Agent: Mozilla/5.0 (Windows NT 6.1; rv:15.0) Gecko/20100101 Firefox/15.0.1\r\n
Accept: text/html,application/xhtml+xml,application/xml;q=0.9,*/*;q=0.8\r\n
Accept-Language: tr-tr,tr;q=0.8,en-us;q=0.5,en;q=0.3\r\n
Accept-Encoding: gzip, deflate\r\n
Connection: keep-alive\r\n
Referer: http://okbase.net/\r\n
Content-Type: application/x-www-form-urlencoded\r\n
Content-Length: 35\r\n\r\n
variable1=value1&variable2=value2

简化版本如下：

POST /index.html HTTP/1.1\r\n
Host: okbase.net\r\n
Content-Length: 35\r\n\r\n
variable1=value1&variable2=value2

响应

当服务器接收到一个请求进行解析，并返回一个响应状态代码：

HTTP/1.1 200 OK\r\n
Server: Apache/1.3.3.7 (Unix) (Red-Hat/Linux)\r\n
Content-Length: {content_length}\r\n
Connection: close\r\n
Content-Type: text/html; charset=UTF-8\r\n\r\n
the content of which length is equal to {content_length}

这是一个响应头，"200 OK"便是一切OK，请求的内容将被返回。状态码有很多，我们经常使用200,501,404。

“501 Not Implemented”方法未实现。我们将只实现GET和POST。如果通过其它方法请求，我们将发送此代码。

“404 Not Found”：没有找到请求的内容。

内容类型

服务器必须指定它们的响应中的内容的类型。有许多内容类型，这些也被称为“MIME（多用途互联网邮件扩展）类型”（因为它们也可以用来识别非ASCII的电子邮件）。以下是在我们的实现中，我们将使用的内容类型：（您可以修改代码并添加更多）

text/html
text/xml
text/plain
text/css
image/png
image/gif
image/jpg
image/jpeg
application/zip

如果服务器指定了错误的内容类型的内容会被曲解。例如，如果一台服务器发送纯文本，使用“图像/ png”类型，客户端试图显示的文字图像。

多线程

如果我们使我们的服务器可以同时响应多个客户端，我们必须为每个请求创建新的线程。因此，每个线程处理一个请求，并退出完成它的使命。（多线程也加快了页面加载，因为如果我们请求一个页面，页面中使用了CSS和图像，每个图像和CSS文件会以GET方式发送请求）。

一个简单的Web服务器的实现

现在，我们准备实现一个简单的Web服务器。首先，让我们来定义变量，我们将使用：

public bool running = false; // Is it running?private int timeout = 8; // Time limit for data transfers.
private Encoding charEncoder = Encoding.UTF8; // To encode string
private Socket serverSocket; // Our server socket
private string contentPath; // Root path of our contents// Content types that are supported by our server
// You can add more...
// To see other types: http://www.webmaster-toolkit.com/mime-types.shtml
private Dictionary<string, string> extensions = new Dictionary<string, string>()
{ //{ "extension", "content type" }{ "htm", "text/html" },{ "html", "text/html" },{ "xml", "text/xml" },{ "txt", "text/plain" },{ "css", "text/css" },{ "png", "image/png" },{ "gif", "image/gif" },{ "jpg", "image/jpg" },{ "jpeg", "image/jpeg" },{ "zip", "application/zip"}
};

启动服务器的方法：

public bool start(IPAddress ipAddress, int port, int maxNOfCon, string contentPath)
{if (running) return false; // If it is already running, exit.try{// A tcp/ip socket (ipv4)serverSocket = new Socket(AddressFamily.InterNetwork, SocketType.Stream,ProtocolType.Tcp);serverSocket.Bind(new IPEndPoint(ipAddress, port));serverSocket.Listen(maxNOfCon);serverSocket.ReceiveTimeout = timeout;serverSocket.SendTimeout = timeout;running = true;this.contentPath = contentPath;}catch { return false; }// Our thread that will listen connection requests// and create new threads to handle them.Thread requestListenerT = new Thread(() =>{while (running){Socket clientSocket;try{clientSocket = serverSocket.Accept();// Create new thread to handle the request and continue to listen the socket.Thread requestHandler = new Thread(() =>{clientSocket.ReceiveTimeout = timeout;clientSocket.SendTimeout = timeout;try { handleTheRequest(clientSocket); }catch{try { clientSocket.Close(); } catch { }}});requestHandler.Start();}catch{}}});requestListenerT.Start();return true;
}

停止服务器的方法

public void stop()
{if (running){running = false;try { serverSocket.Close(); }catch { }serverSocket = null;}
}

最重要的部分代码：

private void handleTheRequest(Socket clientSocket)
{byte[] buffer = new byte[10240]; // 10 kb, just in caseint receivedBCount = clientSocket.Receive(buffer); // Receive the requeststring strReceived = charEncoder.GetString(buffer, 0, receivedBCount);// Parse method of the requeststring httpMethod = strReceived.Substring(0, strReceived.IndexOf(" "));int start = strReceived.IndexOf(httpMethod) + httpMethod.Length + 1;int length = strReceived.LastIndexOf("HTTP") - start - 1;string requestedUrl = strReceived.Substring(start, length);string requestedFile;if (httpMethod.Equals("GET") || httpMethod.Equals("POST"))requestedFile = requestedUrl.Split('?')[0];else // You can implement other methods...{notImplemented(clientSocket);return;}requestedFile = requestedFile.Replace("/", @"\").Replace("\\..", "");start = requestedFile.LastIndexOf('.') + 1;if (start > 0){length = requestedFile.Length - start;string extension = requestedFile.Substring(start, length);if (extensions.ContainsKey(extension)) // Do we support this extension?if (File.Exists(contentPath + requestedFile)) //If yes check existence of the file// Everything is OK, send requested file with correct content type:sendOkResponse(clientSocket,File.ReadAllBytes(contentPath + requestedFile), extensions[extension]);elsenotFound(clientSocket); // We don't support this extension.// We are assuming that it doesn't exist.}else{// If file is not specified try to send index.htm or index.html// You can add more (default.htm, default.html)if (requestedFile.Substring(length - 1, 1) != @"\")requestedFile += @"\";if (File.Exists(contentPath + requestedFile + "index.htm"))sendOkResponse(clientSocket,File.ReadAllBytes(contentPath + requestedFile + "\\index.htm"), "text/html");else if (File.Exists(contentPath + requestedFile + "index.html"))sendOkResponse(clientSocket,File.ReadAllBytes(contentPath + requestedFile + "\\index.html"), "text/html");elsenotFound(clientSocket);}
}

不同的状态代码的响应：

private void notFound(Socket clientSocket)
{sendResponse(clientSocket, "<html><head><meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\"></head><body><h2>Atasoy Simple Web Server</h2><div>404 - Not Found</div></body></html>", "404 Not Found", "text/html");
}private void sendOkResponse(Socket clientSocket, byte[] bContent, string contentType)
{sendResponse(clientSocket, bContent, "200 OK", contentType);
}private void notImplemented(Socket clientSocket)
{sendResponse(clientSocket, "<html><head><meta http-equiv=\"Content-Type\" content=\"text/html; charset=utf-8\"></head><body><h2>Atasoy Simple Web Server</h2><div>501 - Method Not Implemented</div></body></html>", "501 Not Implemented", "text/html");}

将响应发送到客户端的方法

// For strings
private void sendResponse(Socket clientSocket, string strContent, string responseCode,string contentType)
{byte[] bContent = charEncoder.GetBytes(strContent);sendResponse(clientSocket, bContent, responseCode, contentType);
}// For byte arrays
private void sendResponse(Socket clientSocket, byte[] bContent, string responseCode,string contentType)
{try{byte[] bHeader = charEncoder.GetBytes("HTTP/1.1 " + responseCode + "\r\n"+ "Server: Atasoy Simple Web Server\r\n"+ "Content-Length: " + bContent.Length.ToString() + "\r\n"+ "Connection: close\r\n"+ "Content-Type: " + contentType + "\r\n\r\n");clientSocket.Send(bHeader);clientSocket.Send(bContent);clientSocket.Close();}catch { }
}

用法

// to create new one:
Server server = new Server();
// to start it
server.start(ipAddress, port, maxconnections, contentpath);
// to stop it
server.stop();