简介
本文用C#实现了一个最简单的HTTP服务器类，你可以将它嵌入到自己的项目中，或者也可以阅读代码来学习关于HTTP协议的知识。
背景
高性能的WEB应用一般都架设在强大的WEB服务器上，例如IIS, Apache, 和Tomcat。然而，HTML是非常灵活的UI标记语言，也就是说任何应用和后端服务都可以提供HTML的生成支持。在这个小小的例子中，像IIS,、Apache这样的服务器消耗的资源太大了，我们需要自己实现一个简单的HTTP服务器，将它嵌入到我们的应用中用来处理WEB请求。我们仅需要一个类就可以实现了，很简单。
代码实现
首先我们来回顾一下如何使用类，然后我们再来分析实现的具体细节。这里我们创建了一个继承于HttpServer的类，并实现了handleGETRequest 和handlePOSTRequest 这两个抽象方法：
public class MyHttpServer : HttpServer { public MyHttpServer(intport):base(port) { } public override void handleGETRequest(HttpProcessor p) { Console.WriteLine("request: {0}", p.http_url); p.writeSuccess(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("Current Time: " + DateTime.Now.ToString()); p.outputStream.WriteLine("url : {0}", p.http_url); p.outputStream.WriteLine("<form method=post action=/form>"); p.outputStream.WriteLine("<input type=text name=foo value=foovalue>"); p.outputStream.WriteLine("<input type=submit name=bar value=barvalue>"); p.outputStream.WriteLine("</form>"); } public override void handlePOSTRequest(HttpProcessor p, StreamReader inputData) { Console.WriteLine("POST request: {0}", p.http_url); stringdata = inputData.ReadToEnd(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("<a href=/test>return</a><p>"); p.outputStream.WriteLine("postbody: <pre>{0}</pre>", data); } }
当开始处理一个简单的请求时，我们就需要单独启动一个线程来监听一个端口，比如8080端口：
HttpServer httpServer = new MyHttpServer(8080); Thread thread = new Thread(newThreadStart(httpServer.listen)); thread.Start();
如果你编译运行这个项目，你会在浏览器http://localhost:8080地址下看到页面上生成的示例内容。让我们来简单看一下这个HTTP服务器引擎是怎么实现的。
这个WEB服务器由两个组件构成，一个是负责启动TcpListener来监听指定端口的HttpServer类，并且用AcceptTcpClient()方法循环处理TCP连接请求，这是处理TCP连接的第一步。然后请求到达“已指定“的端口，接着就会创建一对新的端口，用来初始化客户端到服务器端的TCP连接。这对端口便是TcpClient的session，这样就可以保持我们的主端口可以继续接收新的连接请求。从下面的代码中我们可以看到，每一次监听程序都会创建一个新的TcpClien，HttpServer类又会创建一个新的HttpProcessor，然后启动一个线程来操作。HttpServer类中还包含两个抽象方法，你必须实现这两个方法。
public abstract class HttpServer { protected int port; TcpListener listener; boolis_active = true; publicHttpServer(intport) { this.port = port; } public void listen() { listener = newTcpListener(port); listener.Start(); while(is_active) { TcpClient s = listener.AcceptTcpClient(); HttpProcessor processor = newHttpProcessor(s, this); Thread thread = newThread(newThreadStart(processor.process)); thread.Start(); Thread.Sleep(1); } } public abstract void handleGETRequest(HttpProcessor p); public abstract void handlePOSTRequest(HttpProcessor p, StreamReader inputData); }
这样，一个新的tcp连接就在自己的线程中被HttpProcessor处理了，HttpProcessor的工作就是正确解析HTTP头，并且控制正确实现的抽象方法。下面我们来看看HTTP头的处理过程，HTTP请求的第一行代码如下：
GET /myurl HTTP/1.0
在设置完process()的输入和输出后，HttpProcessor就会调用parseRequest()方法。
public void parseRequest() { String request = inputStream.ReadLine(); string[] tokens = request.Split(' '); if(tokens.Length != 3) { throw new Exception("invalid http request line"); } http_method = tokens[0].ToUpper(); http_url = tokens[1]; http_protocol_versionstring = tokens[2]; Console.WriteLine("starting: " + request); }
HTTP请求由3部分组成，所以我们只需要用string.Split()方法将它们分割成3部分即可，接下来就是接收和解析来自客户端的HTTP头信息，头信息中的每一行数据是以Key-Value（键-值）形式保存，空行表示HTTP头信息结束标志，我们代码中用readHeaders方法来读取HTTP头信息：
public void readHeaders() { Console.WriteLine("readHeaders()"); String line; while((line = inputStream.ReadLine()) != null) { if(line.Equals("")) { Console.WriteLine("got headers"); return; } intseparator = line.IndexOf(':'); if(separator == -1) { throw new Exception("invalid http header line: " + line); } String name = line.Substring(0, separator); intpos = separator + 1; while((pos < line.Length) && (line[pos] == ' ')) { pos++;// 过滤掉所有空格 } string value = line.Substring(pos, line.Length - pos); Console.WriteLine("header: {0}:{1}",name,value); httpHeaders[name] = value; } }
到这里，我们已经了解了如何处理简单的GET和POST请求，它们分别被分配给正确的handler处理程序。在本例中，发送数据的时候有一个棘手的问题需要处理，那就是请求头信息中包含发送数据的长度信息content-length，当我们希望子类HttpServer中的handlePOSTRequest方法能够正确处理数据时，我们需要将数据长度content-length信息一起放入数据流中，否则发送端会因为等待永远不可能到达的数据和阻塞等待。我们用了一种看起来不那么优雅但非常有效的方法来处理这种情况，即将数据发送给POST处理方法前先把数据读入到MemoryStream中。这种做法不太理想，原因如下：如果发送的数据很大，甚至是上传一个文件，那么我们将这些数据缓存在内存就不那么合适甚至是不可能的。理想的方法是限制post的长度，比如我们可以将数据长度限制为10MB。
这个简易版HTTP服务器另一个简化的地方就是content-type的返回值，在HTTP协议中，服务器总是会将数据的MIME-Type发送给客户端，告诉客户端自己需要接收什么类型的数据。在writeSuccess()方法中，我们看到，服务器总是发送text/html类型，如果你需要加入其他的类型，你可以扩展这个方法。
完整代码：
using System; using System.Collections; using System.IO; using System.Net; using System.Net.Sockets; using System.Threading; namespace Bend.Util { public class HttpProcessor { public TcpClient socket; public HttpServer srv; private Stream inputStream; public StreamWriter outputStream; public String http_method; public String http_url; public String http_protocol_versionstring; public Hashtable httpHeaders = new Hashtable(); private static int MAX_POST_SIZE = 10 * 1024 * 1024; // 10MB public HttpProcessor(TcpClient s, HttpServer srv) { this.socket = s; this.srv = srv; } private string streamReadLine(Stream inputStream) { int next_char; string data = ""; while (true) { next_char = inputStream.ReadByte(); if (next_char == ' ') { break; } if (next_char == ' ') { continue; } if (next_char == -1) { Thread.Sleep(1); continue; }; data += Convert.ToChar(next_char); } return data; } public void process() { // we can't use a StreamReader for input, because it buffers up extra data on us inside it's // "processed" view of the world, and we want the data raw after the headers inputStream = new BufferedStream(socket.GetStream()); // we probably shouldn't be using a streamwriter for all output from handlers either outputStream = new StreamWriter(new BufferedStream(socket.GetStream())); try { parseRequest(); readHeaders(); if (http_method.Equals("GET")) { handleGETRequest(); } else if (http_method.Equals("POST")) { handlePOSTRequest(); } } catch (Exception e) { Console.WriteLine("Exception: " + e.ToString()); writeFailure(); } outputStream.Flush(); // bs.Flush(); // flush any remaining output inputStream = null; outputStream = null; // bs = null; socket.Close(); } public void parseRequest() { String request = streamReadLine(inputStream); string[] tokens = request.Split(' '); if (tokens.Length != 3) { throw new Exception("invalid http request line"); } http_method = tokens[0].ToUpper(); http_url = tokens[1]; http_protocol_versionstring = tokens[2]; Console.WriteLine("starting: " + request); } public void readHeaders() { Console.WriteLine("readHeaders()"); String line; while ((line = streamReadLine(inputStream)) != null) { if (line.Equals("")) { Console.WriteLine("got headers"); return; } int separator = line.IndexOf(':'); if (separator == -1) { throw new Exception("invalid http header line: " + line); } String name = line.Substring(0, separator); int pos = separator + 1; while ((pos < line.Length) && (line[pos] == ' ')) { pos++; // strip any spaces } string value = line.Substring(pos, line.Length - pos); Console.WriteLine("header: {0}:{1}",name,value); httpHeaders[name] = value; } } public void handleGETRequest() { srv.handleGETRequest(this); } private const int BUF_SIZE = 4096; public void handlePOSTRequest() { // this post data processing just reads everything into a memory stream. // this is fine for smallish things, but for large stuff we should really // hand an input stream to the request processor. However, the input stream // we hand him needs to let him see the "end of the stream" at this content // length, because otherwise he won't know when he's seen it all! Console.WriteLine("get post data start"); int content_len = 0; MemoryStream ms = new MemoryStream(); if (this.httpHeaders.ContainsKey("Content-Length")) { content_len = Convert.ToInt32(this.httpHeaders["Content-Length"]); if (content_len > MAX_POST_SIZE) { throw new Exception( String.Format("POST Content-Length({0}) too big for this simple server", content_len)); } byte[] buf = new byte[BUF_SIZE]; int to_read = content_len; while (to_read > 0) { Console.WriteLine("starting Read, to_read={0}",to_read); int numread = this.inputStream.Read(buf, 0, Math.Min(BUF_SIZE, to_read)); Console.WriteLine("read finished, numread={0}", numread); if (numread == 0) { if (to_read == 0) { break; } else { throw new Exception("client disconnected during post"); } } to_read -= numread; ms.Write(buf, 0, numread); } ms.Seek(0, SeekOrigin.Begin); } Console.WriteLine("get post data end"); srv.handlePOSTRequest(this, new StreamReader(ms)); } public void writeSuccess() { outputStream.WriteLine("HTTP/1.0 200 OK"); outputStream.WriteLine("Content-Type: text/html;charset=utf-8"); outputStream.WriteLine("Connection: close"); outputStream.WriteLine(""); } public void writeFailure() { outputStream.WriteLine("HTTP/1.0 404 File not found"); outputStream.WriteLine("Connection: close"); outputStream.WriteLine(""); } } public abstract class HttpServer { protected int port; TcpListener listener; bool is_active = true; public HttpServer(int port) { this.port = port; } public void listen() { listener = new TcpListener(port); listener.Start(); while (is_active) { TcpClient s = listener.AcceptTcpClient(); HttpProcessor processor = new HttpProcessor(s, this); Thread thread = new Thread(new ThreadStart(processor.process)); thread.Start(); Thread.Sleep(1); } } public abstract void handleGETRequest(HttpProcessor p); public abstract void handlePOSTRequest(HttpProcessor p, StreamReader inputData); } public class MyHttpServer : HttpServer { public MyHttpServer(int port) : base(port) { } public override void handleGETRequest(HttpProcessor p) { Console.WriteLine("request: {0}", p.http_url); p.writeSuccess(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("Current Time: " + DateTime.Now.ToString()); p.outputStream.WriteLine("url : {0}", p.http_url); p.outputStream.WriteLine("<form method=post action=/form>"); p.outputStream.WriteLine("<input type=text name=foo value=foovalue>"); p.outputStream.WriteLine("<input type=submit name=bar value=barvalue>"); p.outputStream.WriteLine("</form>"); } public override void handlePOSTRequest(HttpProcessor p, StreamReader inputData) { Console.WriteLine("POST request: {0}", p.http_url); string data = inputData.ReadToEnd(); p.outputStream.WriteLine("<html><body><h1>test server</h1>"); p.outputStream.WriteLine("<a href=/test>return</a><p>"); p.outputStream.WriteLine("postbody: <pre>{0}</pre>", data); } } public class TestMain { public static int Main(String[] args) { HttpServer httpServer; if (args.GetLength(0) > 0) { httpServer = new MyHttpServer(Convert.ToInt16(args[0])); } else { httpServer = new MyHttpServer(8080); } Thread thread = new Thread(new ThreadStart(httpServer.listen)); thread.Start(); return 0; } } }