如何开发自己的HttpServer-NanoHttpd源码解读

标签：http协议   源码   服务器   

现在作为一个开发人员，http server相关的内容已经是无论如何都要了解的知识了。用curl发一个请求，配置一下apache，部署一个web server对我们来说都不是很难，但要想搞清楚这些背后都发生了什么技术细节还真不是很简单的。所以新的系列将是分享我学习Http Server的过程。

NanoHttpd是Github上的一个开源项目，号称只用一个java文件就能创建一个http server，我将通过分析NanoHttpd的源码解析如何开发自己的HttpServer。Github 地址：https://github.com/NanoHttpd/nanohttpd

在开始前首先简单说明HttpServer的基本要素：

1.能接受HttpRequest并返回HttpResponse

2.满足一个Server的基本特征，能够长时间运行

关于Http协议一般HttpServer都会声明支持Http协议的哪些特性，nanohttpd作为一个轻量级的httpserver只实现了最简单、最常用的功能，不过我们依然可以从中学习很多。

首先看下NanoHttpd类的start函数

public void start() throws IOException {
        myServerSocket = new ServerSocket();
        myServerSocket.bind((hostname != null) ? new InetSocketAddress(hostname, myPort) : new InetSocketAddress(myPort));

        myThread = new Thread(new Runnable() {
            @Override
            public void run() {
                do {
                    try {
                        final Socket finalAccept = myServerSocket.accept();
                        registerConnection(finalAccept);
                        finalAccept.setSoTimeout(SOCKET_READ_TIMEOUT);
                        final InputStream inputStream = finalAccept.getInputStream();
                        asyncRunner.exec(new Runnable() {
                            @Override
                            public void run() {
                                OutputStream outputStream = null;
                                try {
                                    outputStream = finalAccept.getOutputStream();
                                    TempFileManager tempFileManager = tempFileManagerFactory.create();
                                    HTTPSession session = new HTTPSession(tempFileManager, inputStream, outputStream, finalAccept.getInetAddress());
                                    while (!finalAccept.isClosed()) {
                                        session.execute();
                                    }
                                } catch (Exception e) {
                                    // When the socket is closed by the client, we throw our own SocketException
                                    // to break the  "keep alive" loop above.
                                    if (!(e instanceof SocketException && "NanoHttpd Shutdown".equals(e.getMessage()))) {
                                        e.printStackTrace();
                                    }
                                } finally {
                                    safeClose(outputStream);
                                    safeClose(inputStream);
                                    safeClose(finalAccept);
                                    unRegisterConnection(finalAccept);
                                }
                            }
                        });
                    } catch (IOException e) {
                    }
                } while (!myServerSocket.isClosed());
            }
        });
        myThread.setDaemon(true);
        myThread.setName("NanoHttpd Main Listener");
        myThread.start();
    }

2.创建主线程，主线程负责和client建立连接

3.建立连接后会生成一个runnable对象放入asyncRunner中，asyncRunner.exec会创建一个线程来处理新生成的连接。

4.新线程首先创建了一个HttpSession，然后while(true)的执行httpSession.exec。

这里介绍下HttpSession的概念，HttpSession是java里Session概念的实现，简单来说一个Session就是一次httpClient->httpServer的连接，当连接close后session就结束了，如果没结束则session会一直存在。这点从这里的代码也能看到：如果socket不close或者exec没有抛出异常（异常有可能是client段断开连接）session会一直执行exec方法。

一个HttpSession中存储了一次网络连接中server应该保存的信息，比如：URI，METHOD，PARAMS，HEADERS，COOKIES等。

5.这里accept一个client的socket就创建一个独立线程的server模型是ThreadServer模型，特点是一个connection就会创建一个thread，是比较简单、常见的socket server实现。缺点是在同时处理大量连接时线程切换需要消耗大量的资源，如果有兴趣可以了解更加高效的NIO实现方式。

当获得client的socket后自然要开始处理client发送的httprequest。

Http Request Header的parse：

// Read the first 8192 bytes.
// The full header should fit in here.
                // Apache's default header limit is 8KB.
                // Do NOT assume that a single read will get the entire header at once!
                byte[] buf = new byte[BUFSIZE];
                splitbyte = 0;
                rlen = 0;
                {
                    int read = -1;
                    try {
                        read = inputStream.read(buf, 0, BUFSIZE);
                    } catch (Exception e) {
                        safeClose(inputStream);
                        safeClose(outputStream);
                        throw new SocketException("NanoHttpd Shutdown");
                    }
                    if (read == -1) {
                        // socket was been closed
                        safeClose(inputStream);
                        safeClose(outputStream);
                        throw new SocketException("NanoHttpd Shutdown");
                    }
                    while (read > 0) {
                        rlen += read;
                        splitbyte = findHeaderEnd(buf, rlen);
                        if (splitbyte > 0)
                            break;
                        read = inputStream.read(buf, rlen, BUFSIZE - rlen);
                    }
                }

2.通过findHeaderEnd函数找到header数据的截止位置，并把位置保存到splitbyte内。

if (splitbyte < rlen) {
                    inputStream.unread(buf, splitbyte, rlen - splitbyte);
                }

                parms = new HashMap<String, String>();
                if(null == headers) {
                    headers = new HashMap<String, String>();
                }

                // Create a BufferedReader for parsing the header.
                BufferedReader hin = new BufferedReader(new InputStreamReader(new ByteArrayInputStream(buf, 0, rlen)));

                // Decode the header into parms and header java properties
                Map<String, String> pre = new HashMap<String, String>();
                decodeHeader(hin, pre, parms, headers);

1.使用unread函数将之前读出来的body pushback回去，这里使用了pushbackstream，用法比较巧妙，因为一旦读到了header的尾部就需要进入下面的逻辑来判断是否需要再读下去了，而不应该一直读，读到没有数据为止

2.decodeHeader，将byte的header转换为java对象

private int findHeaderEnd(final byte[] buf, int rlen) {
            int splitbyte = 0;
            while (splitbyte + 3 < rlen) {
                if (buf[splitbyte] == '\r' && buf[splitbyte + 1] == '\n' && buf[splitbyte + 2] == '\r' && buf[splitbyte + 3] == '\n') {
                    return splitbyte + 4;
                }
                splitbyte++;
            }
            return 0;
        }

private void decodeHeader(BufferedReader in, Map<String, String> pre, Map<String, String> parms, Map<String, String> headers)
            throws ResponseException {
            try {
                // Read the request line
                String inLine = in.readLine();
                if (inLine == null) {
                    return;
                }

                StringTokenizer st = new StringTokenizer(inLine);
                if (!st.hasMoreTokens()) {
                    throw new ResponseException(Response.Status.BAD_REQUEST, "BAD REQUEST: Syntax error. Usage: GET /example/file.html");
                }

                pre.put("method", st.nextToken());

                if (!st.hasMoreTokens()) {
                    throw new ResponseException(Response.Status.BAD_REQUEST, "BAD REQUEST: Missing URI. Usage: GET /example/file.html");
                }

                String uri = st.nextToken();

                // Decode parameters from the URI
                int qmi = uri.indexOf('?');
                if (qmi >= 0) {
                    decodeParms(uri.substring(qmi + 1), parms);
                    uri = decodePercent(uri.substring(0, qmi));
                } else {
                    uri = decodePercent(uri);
                }

                // If there's another token, it's protocol version,
                // followed by HTTP headers. Ignore version but parse headers.
                // NOTE: this now forces header names lowercase since they are
                // case insensitive and vary by client.
                if (st.hasMoreTokens()) {
                    String line = in.readLine();
                    while (line != null && line.trim().length() > 0) {
                        int p = line.indexOf(':');
                        if (p >= 0)
                            headers.put(line.substring(0, p).trim().toLowerCase(Locale.US), line.substring(p + 1).trim());
                        line = in.readLine();
                    }
                }

                pre.put("uri", uri);
            } catch (IOException ioe) {
                throw new ResponseException(Response.Status.INTERNAL_ERROR, "SERVER INTERNAL ERROR: IOException: " + ioe.getMessage(), ioe);
            }
        }

2.后面每行都是KEY:VALUE格式的header

3.uri需要经过URIDecode处理后才能使用

4.uri中如果包含？则表示有param，httprequest的param一般表现为:/index.jsp?username=xiaoming&id=2

下面是处理cookie，不过这里cookie的实现较为简单，所以跳过。之后是serve方法，serve方法提供了用户自己实现httpserver具体逻辑的很好接口。在NanoHttpd中的serve方法实现了一个默认的简单处理功能。

/**
     * Override this to customize the server.
     * <p/>
     * <p/>
     * (By default, this delegates to serveFile() and allows directory listing.)
     *
     * @param session The HTTP session
     * @return HTTP response, see class Response for details
     */
    public Response serve(IHTTPSession session) {
        Map<String, String> files = new HashMap<String, String>();
        Method method = session.getMethod();
        if (Method.PUT.equals(method) || Method.POST.equals(method)) {
            try {
                session.parseBody(files);
            } catch (IOException ioe) {
                return new Response(Response.Status.INTERNAL_ERROR, MIME_PLAINTEXT, "SERVER INTERNAL ERROR: IOException: " + ioe.getMessage());
            } catch (ResponseException re) {
                return new Response(re.getStatus(), MIME_PLAINTEXT, re.getMessage());
            }
        }

        Map<String, String> parms = session.getParms();
        parms.put(QUERY_STRING_PARAMETER, session.getQueryParameterString());
        return serve(session.getUri(), method, session.getHeaders(), parms, files);
    }

parseBody方法中使用了tmpFile的方法保存httpRequest的content信息，然后处理，具体逻辑就不细说了，不是一个典型的实现。

最后看一下发response的逻辑：

/**
         * Sends given response to the socket.
         */
        protected void send(OutputStream outputStream) {
            String mime = mimeType;
            SimpleDateFormat gmtFrmt = new SimpleDateFormat("E, d MMM yyyy HH:mm:ss 'GMT'", Locale.US);
            gmtFrmt.setTimeZone(TimeZone.getTimeZone("GMT"));

            try {
                if (status == null) {
                    throw new Error("sendResponse(): Status can't be null.");
                }
                PrintWriter pw = new PrintWriter(outputStream);
                pw.print("HTTP/1.1 " + status.getDescription() + " \r\n");

                if (mime != null) {
                    pw.print("Content-Type: " + mime + "\r\n");
                }

                if (header == null || header.get("Date") == null) {
                    pw.print("Date: " + gmtFrmt.format(new Date()) + "\r\n");
                }

                if (header != null) {
                    for (String key : header.keySet()) {
                        String value = header.get(key);
                        pw.print(key + ": " + value + "\r\n");
                    }
                }

                sendConnectionHeaderIfNotAlreadyPresent(pw, header);

                if (requestMethod != Method.HEAD && chunkedTransfer) {
                    sendAsChunked(outputStream, pw);
                } else {
                    int pending = data != null ? data.available() : 0;
                    sendContentLengthHeaderIfNotAlreadyPresent(pw, header, pending);
                    pw.print("\r\n");
                    pw.flush();
                    sendAsFixedLength(outputStream, pending);
                }
                outputStream.flush();
                safeClose(data);
            } catch (IOException ioe) {
                // Couldn't write? No can do.
            }
        }

1.设置mimeType和Time等内容。

2.创建一个PrintWriter，按照HTTP协议依次开始写入内容

3.第一行是HTTP的返回码

4.然后是content-Type

5.然后是Date时间

6.之后是其他的HTTP Header

7.设置Keep-Alive的Header，Keep-Alive是Http1.1的新特性，作用是让客户端和服务器端之间保持一个长链接。

8.如果客户端指定了ChunkedEncoding则分块发送response，Chunked Encoding是Http1.1的又一新特性。一般在response的body比较大的时候使用，server端会首先发送response的HEADER，然后分块发送response的body，每个分块都由chunk length\r\n和chunk data\r\n组成，最后由一个0\r\n结束。

private void sendAsChunked(OutputStream outputStream, PrintWriter pw) throws IOException {
            pw.print("Transfer-Encoding: chunked\r\n");
            pw.print("\r\n");
            pw.flush();
            int BUFFER_SIZE = 16 * 1024;
            byte[] CRLF = "\r\n".getBytes();
            byte[] buff = new byte[BUFFER_SIZE];
            int read;
            while ((read = data.read(buff)) > 0) {
                outputStream.write(String.format("%x\r\n", read).getBytes());
                outputStream.write(buff, 0, read);
                outputStream.write(CRLF);
            }
            outputStream.write(String.format("0\r\n\r\n").getBytes());
        }

9.如果没指定ChunkedEncoding则需要指定Content-Length来让客户端指定response的body的size，然后再一直写body直到写完为止。

private void sendAsFixedLength(OutputStream outputStream, int pending) throws IOException {
            if (requestMethod != Method.HEAD && data != null) {
                int BUFFER_SIZE = 16 * 1024;
                byte[] buff = new byte[BUFFER_SIZE];
                while (pending > 0) {
                    int read = data.read(buff, 0, ((pending > BUFFER_SIZE) ? BUFFER_SIZE : pending));
                    if (read <= 0) {
                        break;
                    }
                    outputStream.write(buff, 0, read);
                    pending -= read;
                }
            }
        }

最后总结下实现HttpServer最重要的几个部分：

1.能够accept tcp连接并从socket中读取request数据

2.把request的比特流转换成request对象中的对象数据

3.根据http协议的规范处理http request

4.产生http response再写回到socket中传给client。

如何开发自己的HttpServer-NanoHttpd源码解读

标签：http协议   源码   服务器   

原文地址：http://blog.csdn.net/mrtitan/article/details/24332429