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client帮助文档

client帮助文档

前言超文本传输协议（HTTP）也许是当今互联网上使用的最重要的协议了。

Web服务，有网络功能的设备和网络计算的发展，都持续扩展了HTTP协议的角色，超越了用户使用的Web 浏览器范畴，同时，也增加了需要HTTP协议支持的应用程序的数量。

尽管包提供了基本通过HTTP访问资源的功能，但它没有提供全面的灵活性和其它很多应用程序需要的功能。

HttpClient就是寻求弥补这项空白的组件，通过提供一个有效的，保持更新的，功能丰富的软件包来实现客户端最新的HTTP标准和建议。

为扩展而设计，同时为基本的HTTP协议提供强大的支持，HttpClient组件也许就是构建HTTP客户端应用程序，比如web浏览器，web服务端，利用或扩展HTTP协议进行分布式通信的系统的开发人员的关注点。

1. HttpClient的范围基于HttpCore[/httpcomponents-core/index.html]的客户端HTTP运输实现库基于经典（阻塞）I/O内容无关2. 什么是HttpClient不能做的HttpClient 不是一个浏览器。

它是一个客户端的HTTP通信实现库。

HttpClient的目标是发送和接收HTTP报文。

HttpClient不会去缓存内容，执行嵌入在HTML页面中的javascript 代码，猜测内容类型，重新格式化请求/重定向URI，或者其它和HTTP运输无关的功能。

第一章基础1.1 执行请求HttpClient 最重要的功能是执行HTTP方法。

一个HTTP方法的执行包含一个或多个HTTP 请求/HTTP响应交换，通常由HttpClient的内部来处理。

而期望用户提供一个要执行的请求对象，而HttpClient期望传输请求到目标服务器并返回对应的响应对象，或者当执行不成功时抛出异常。

很自然地，HttpClient API的主要切入点就是定义描述上述规约的HttpClient接口。

这里有一个很简单的请求执行过程的示例：HttpClient httpclient = new DefaultHttpClient();HttpGet httpget = new HttpGet("http://localhost/");HttpResponse response = httpclient.execute(httpget);HttpEntity entity = response.getEntity();if (entity != null) {InputStream instream = entity.getContent();int l;byte[] tmp = new byte[2048];while ((l = instream.read(tmp)) != -1) {}}1.1.1 HTTP请求所有HTTP请求有一个组合了方法名，请求URI和HTTP协议版本的请求行。

client用法

client用法

client用法
Client是一个通用的术语，用于描述在计算机领域中的客户端应用程序或者设备。

在软件开发中，Client通常是指使用某种协议与服务器进行通信的应用程序。

Client用法包含了以下几个重要方面：
1. 网络通信：Client用于与服务器进行网络通信，客户端应用程序通过与服务器建立连接来发送请求并接收响应。

这种通信可以基于不同的协议，如HTTP、FTP、SMTP等。

2. 用户界面：Client提供了一个用户界面，使用户能够与应用程序进行交互。

这可能是一个图形界面(GUI)、命令行界面(CLI)或者移动设备应用的UI。

客户端的设计应该考虑易用性和用户体验。

3. 数据管理：Client用于管理应用程序的数据。

客户端应该能够存储、读取和管理相关数据，以便在需要的时候进行操作和显示。

这可以通过本地数据库、缓存或者远程服务器实现。

4. 安全性：Client应该具备必要的安全性，以保护用户的数据和隐私。

这可以通过使用加密保护传输数据、身份验证和访问控制来实现。

客户端还应该定期更新以修复安全漏洞和保持系统的安全性。

5. 跨平台兼容性：Client应该能够在不同的操作系统和设备上运行。

这意味着开发人员需要确保客户端应用程序在不同的环境中保持稳定并具有一致的功能。

总之，Client用法涵盖了与服务器进行通信、提供用户界面、管理数据、确保安全性和实现跨平台兼容性等方面。

开发人员在设计和开发Client应用程序时应该考虑到这些重要方面，以提供优秀的用户体验和功能性。

client认证过程

client认证过程

4) AP以EAP Over RADIUS的报文格式将EAP-Response/Identity发送给认证服务器Radius,并且带上相关的RADIUS的属性。
5) Radius收到客户端发来的EAP-Response/Identity，根据配置确定使用EAP-PEAP认证，并向AP发送RADIUS-Access-Challenge报文，里面含有Radius发送给客户端的EAP-Request/Peap/Start的报文，表示希望开始进行EAP-PEAP的认证。
27) 在AP和客户端的数据传输过程中，为了保证数据的安全WPA要求定时或定量（包的数目）进行更新组播密钥，当更新的时间或者数据传输的数目到了，AP会发起密钥更新。
11 实时计费
28) 在用户上网过程中，为了保护用户计费信息，每隔一段时间AP就向Radius报一个实时计费信息，包括当前用户上网总时长，以及用户总流量信息。
19) 组播密钥安装（GTK）:AP和Client使用单播密钥安装中生成key（128～255bit）的保护下进行组播密钥安装.(2步握手),详细过程请参阅引用[5]
7 地址分配
20) 密钥安装成功后，客户端和AP间的空中数据报文进行加密传送，与AC进行DHCP流程交互，直至Client获取IP地址
9 强制Portal
23) 用户打开IE，访问某个网站，发起HTTP请求
24) AC截获用户的HTTP请求，强制到Portal服务器，并在强制Portal URL中加入相关参数。
25) Portal服务器返回门户页面
10 密钥更新
26) 在AP和客户端的数据传输过程中，为了保证数据的安全WPA要求定时或定量（包的数目）进行更新单播密钥，当更新的时间或者数据传输的数目到了，AP会发起密钥更新]。

client专业术语的含义

client专业术语的含义

client专业术语的含义Client（客户）是指在商业活动中接受产品或服务，并支付相应费用的个人、组织或企业。

在不同的领域和专业中，Client可能具有不同的含义和含义。

以下是一些常见领域和专业中的Client术语及其含义。

1.项目管理：在项目管理中，Client是指要求项目交付的个体、组织或企业。

Client通常向项目团队提出需求和目标，并向他们提供资金和支持。

项目经理和项目团队与Client合作，确保项目按时完成，并满足其期望和要求。

2.法律行业：在法律领域中，Client指的是律师为其提供法律咨询和代理服务的个人或企业。

律师必须遵守法律道德规范，保护Client的权益，并为其提供专业的法律建议和服务。

3.市场营销：在市场营销中，Client是指购买产品或服务的个人或组织。

市场营销人员通过开展市场调研、制定营销策略、推广和销售，吸引和留住Client，并满足其需求和期望。

4.咨询服务：在咨询服务领域，Client是指聘请咨询公司或咨询专家提供专业咨询的个人、组织或企业。

咨询师与Client合作，分析问题、制定解决方案，并提供战略指导和建议，帮助Client改善业务绩效和取得成功。

5.信息技术：在信息技术领域，Client是指使用计算机系统或应用程序的个人或组织。

Client可以采取各种形式，如个人电脑、移动设备、网络浏览器等。

信息技术专业人员负责开发、维护和支持Client所使用的软件和硬件系统。

6.银行和金融：在银行和金融领域中，Client是指使用银行服务的个人或企业。

银行为Client提供各种金融产品和服务，如存款、贷款、投资等。

银行员工与Client进行交流和协商，确保其金融需求得到满足。

7.广告和公关：在广告和公关领域，Client是指聘请广告代理公司或公关机构提供广告和公关服务的个人、组织或企业。

广告和公关专业人员与Client合作，制定营销和公关策略，设计和实施广告活动，提高品牌知名度和形象。

cas单点登录系统：客户端（client）详细配置

cas单点登录系统：客户端（client）详细配置

cas单点登录系统：客户端（client）详细配置最近⼀直在研究cas登录中⼼这⼀块的应⽤，分享⼀下记录的⼀些笔记和⼼得。

后⾯会把cas-server端的配置和重构，另外还有这⼏天再搞nginx+cas的https反向代理配置，以及cas的证书相关的知识分享出来。

Cas由两部分组成，Cas Server和Cas Client。

Cas Server是Cas⾃⼰的服务端，⽽Cas Client是Cas客户端，往往客户端需要和我们具体的业务系统进⾏集成，这⾥我们主要详述cas 客户端的配置以及实例第⼀步：我们得有⼀个现成的web项⽬，然后我们要加⼊cas-client-core-xxx.jar到classpath；maven项⽬⽤这个：<dependency><groupId>org.jasig.cas.client</groupId><artifactId>cas-client-core</artifactId><version>3.3.3</version></dependency>第⼆步：配置Filter我们需要在应⽤的web.xml⽂件中配置四个Filter，这四个Filter必须按照固定的顺序来进⾏配置，⽽且它们必须配置在应⽤的其它Filter之前。

它们的先后顺序要求如下：1、AuthenticationFilter2、TicketValidationFilter3、HttpServletRequestWrapperFilter4、AssertionThreadLocalFilter1.1、 配置AuthenticationFilter1.1.1、AuthenticationFilter有两个必须指定的参数：casServerLoginUrl⽤来指定Cas Server登录地址，serverName或service⽤来指定认证成功后需要跳转地址。

client

client

#include<Winsock2.h>#include<stdio.h>//服务器端口号为5050#define DEFAULT_PORT 5050#define DATA_BUFFER 1024void main(int argc,char *argv[ ]){WSADA TA wsaData;SOCKET sClient;int iPort= DEFAULT_PORT;//从服务器端接收的数据长度int iLen;//接收数据的缓冲char buf[DATA_BUFFER];//服务器端地址struct sockaddr_in ser;//判断输入的参数是否正确if(argc<2){//提示在命令行中输入服务器IP地址printf("Usage:client [server IP address]\n");return;}//接收数据的缓冲区初始化memset(buf,0,sizeof(buf));if(WSAStartup(MAKEWORD(2,2),&wsaData)!=0){printf("Failed to load Winsock.\n");return;}//填写要连接的服务器地址信息ser.sin_family=AF_INET;ser.sin_port=htons(iPort);//inet_addr( )函数将命令行的点分IP地址转化为用二进制表示的网络字节顺序的IP 地址ser.sin_addr.s_addr=inet_addr(argv[1]);//建立客户端流式套接口sClient=socket(AF_INET,SOCK_STREAM,0);if(sClient==INV ALID_SOCKET){printf("socket( ) Failed:%d\n", WSAGetLastError( ));return;}//请求与服务器端建立TCP连接if(connect(sClient,(struct sockaddr*)&ser,sizeof(ser))==INV ALID_SOCKET){printf("connect( ) Failed:%d\n", WSAGetLastError( ));return;}else{//从服务器端接收数据iLen=recv(sClient,buf,sizeof(buf),0);if(iLen==0)return;else if(iLen==SOCKET_ERROR){printf("recv( ) Failed:%d\n", WSAGetLastError( ));return;}printf("recv( ) data from server:%s\n",buf);}closesocket(sClient);WSACleanup( );}。

OPCClient工具使用说明

OPCClient工具使用说明OPC（OLE for Process Control）是一种用于实时数据通信的标准协议，它可以实现不同厂家、不同设备之间的数据交互和通信。

OPC Client工具是一种用于连接和监控OPC服务器的软件应用程序，它能够读取和写入OPC服务器中的数据，实现数据采集、传输和处理等功能。

以下是关于OPC Client工具的使用说明。

第一步：安装和配置OPC Client工具2. 打开OPC Client工具，进入配置页面，填写OPC服务器的IP地址和端口号等信息，并选择连接类型（如：TCP/IP）。

3.保存配置信息并进行连接测试，确保能够成功连接到OPC服务器。

第二步：浏览和选择OPC服务器中的项目2.可以通过过滤器或功能来快速定位和选择特定的项目。

3.选择需要监控和操作的项目，并将其添加到监控列表或操作列表中。

第三步：读取和显示OPC服务器中的数据1.在监控列表中选择需要读取的项目，并启动数据读取功能。

2. OPC Client工具会自动从OPC服务器中读取数据，并将其显示在监控列表中。

3.可以设置读取间隔和刷新频率，以实现实时数据显示。

第四步：写入和更新OPC服务器中的数据1.在操作列表中选择需要写入的项目，并在相应的输入框中输入新值。

2. 启动数据写入功能，OPC Client工具会将新值发送给OPC服务器，并更新相应的数据。

3.可以设置写入确认和错误处理功能，以确保数据的有效性和安全性。

第五步：设置和配置自动化任务和报警功能1. OPC Client工具通常支持自动化任务和报警功能。

可以设置定时任务，自动读取和写入OPC服务器中的数据。

2.可以设置报警条件和阈值，当满足条件时触发报警，并进行相应的处理和通知。

3.可以配置邮件、短信或声音等方式来实现报警通知。

第六步：导出和保存数据1. OPC Client工具通常支持数据的导出和保存功能，可以将监控列表中的数据导出为Excel、CSV或其他格式的文件。

AP+CLIENT设置详细说明图解和真正的万能中继设置详细说明图解(一看就会)

1.首先在运作模式里选择AP+CLIENT2.确定以后，无线网路模式中会出现AP+CLIENT选项，点击进入3.在ssid处填入将要进行连接的AP4.Security Type处选择被连接AP的加密方式，OPEN:开放式，不进行加密Shared：共享密匙WPAPSK:WPA个人版WPA2SPK：WPA2个人版4.1如果是选择WPA或者WPA2加密，则会进入以下页面SECURITY MODE里选择WPA或者WPA2 ENCRYPTION TYPE里选择相应的密码格式：TKIP或者AES 在PASS PHRASE里填入设定好的密码4.2如果加密类型为WEP，则按下图进行设置SECURITY MODE里选择OPEN或者shared，开放式加密或者共享加密ENCRYPTION TYPE里选择none或者wep，无密码或者wep密码如果选择WEP密码的话则在下面wep Default Key里选择一个KEY并在对应的wep key里输入密码最后点击最下方的APPLY应用设置如果连接成功的话，在客户端列表里可以看到连接状态真正的万能中继－DLINK2100AP这几天搬新家，没有网络，只能偷无线上，但家里只有厕所的马桶上和厨房的顶上有一个不加密的信号，但是很弱。

而且很容易断。

于是就想办法想扩展信号范围。

查了几个有中继功能的路由器，看上linksys WRE54G和dlink2100AP，觉得2100AP 功能多一些（我在英国，两个价钱差不多），看上去是高端产品，虽然样子不怎么样。

于是就去弄了一个回来2100AP，自带WDS功能，可以工作在5种模式下分别是1.AP2.wds with ap3.wds4.repeater5AP client.研究了半天总算大致搞清楚都是怎么回事，但是我最关心的就是repeater功能。

刚拿来就兴冲冲的拆包装，马上放厕所里，连上那个微弱的不加密信号。

设置倒是很简单，可以自动搜索无线信号，（接受能力比我的T40强一点点）。

client.read()的用法

一、client.read()的概述client.read()是一个在编程语言中常见的函数，主要用于读取客户端接收的数据流。

这条语句的作用是从客户端接收数据并存入缓冲区，以便后续的处理和分析。

在网络编程中，client.read()通常与socket或者其他网络通信库中的接收函数配合使用，用于接收来自服务端的数据。

二、client.read()的基本语法在C++语言中，client.read()的基本语法通常为：int client.read(char *buffer, int length);其中，client是指客户端的连接对象，read()是读取数据的函数。

参数buffer用于存储接收到的数据，而length表示要读取的数据的长度。

在Python语言中，client.read()的基本语法为：client.read(size)其中，client是指客户端的连接对象，read()是读取数据的函数。

参数size表示要读取的数据的长度。

三、client.read()的工作原理client.read()的工作原理与所使用的编程语言和网络通信库有关。

一般来说，当调用client.read()函数时，它会尝试从客户端接收数据，并将其存储到指定的缓冲区中。

具体的实现方式可能涉及到底层的网络通信协议、数据包的处理等内容。

四、使用client.read()接收数据的示例以下是一个使用client.read()函数接收数据的示例：C++示例：```cppchar buffer[1024];int bytesRead = client.read(buffer, 1024);```Python示例：```pythondata = client.read(1024)在这个示例中，我们通过client.read()函数从客户端接收了最多1024个字节的数据，并将其存储到了buffer或data中。

五、client.read()的注意事项在使用client.read()函数时，有一些需要注意的事项：1. 数据长度：在调用client.read()时，需要注意要读取的数据的长度，以免造成数据丢失或者缓冲区溢出的问题。

Client与Server

Client与Server Client与Server1、Clientpublic class Client {//⽤于与服务器端连接的Socketprivate Socket socket;//⽆参构造器public Client(){try{/*** 实例化Socket，⽤于连接服务端的ServerSocket* 参数1：服务端的ip地址 localhost表⽰本机* 参数2：服务端打开的端⼝号**///打开本机的对应端⼝号socket = new Socket("localhost",8088);}catch(Exception e){}}public void start(){try{//创建新线程实例GetServerInfoHandler handler = new GetServerInfoHandler();Thread t = new Thread(handler);t.setDaemon(true);t.start();//扫描器扫描是否有键盘输⼊Scanner scanner = new Scanner(System.in);//创建输出字节流，输出到服务端OutputStream out = socket.getOutputStream();//输出字符流，编码gbkOutputStreamWriter osw = new OutputStreamWriter(out,"gbk");//输出流，输出PrintWriter writer = new PrintWriter(osw,true);while (true) {//从键盘读取⼀⾏内容，发送到服务端去writer.println(scanner.nextLine());}}catch(Exception e){e.printStackTrace();}}private class GetServerInfoHandler implements Runnable{public void run(){try{//读取服务端传回的数据BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream(),"gbk")); while(true){String info = reader.readLine();if(info == null){break;}System.out.println(info);}}catch(Exception e){e.printStackTrace();}}}public static void main(String[] args) {//实例化⼀个客户端Client client = new Client();//启动客户端client.start();}}2、Serverpublic class Server {// 服务端的ServerSocketprivate ServerSocket server;// 线程池private ExecutorService threadPool;// 存放所有客户端输出流的集合private Vector<PrintWriter> allOut;// 创建⼀个消息队列，保存所有待转发的信息private BlockingDeque<String> msgQueue;public Server() {try {System.out.println("启动服务器");// 初始化消息队列msgQueue = new LinkedBlockingDeque<String>();// 启动做消息转发的线程SendMsgToAllClientHandler sendHandler = new SendMsgToAllClientHandler();Thread t = new Thread(sendHandler);t.start();// 初始化存放所有客户端输出流的集合allOut = new Vector<PrintWriter>();// 初始化线程池threadPool = Executors.newCachedThreadPool();//服务端端⼝server = new ServerSocket(8088);System.out.println("服务器启动完毕");} catch (Exception e) {e.printStackTrace();}}public synchronized void addClientOut(PrintWriter writer) {allOut.add(writer);}public synchronized void removeClientOut(PrintWriter writer) {allOut.remove(writer);}public synchronized void sendMsgToAllClient(String msg) {for (PrintWriter writer : allOut) {writer.println(msg);}}public void start() {try {while (true) {/** 若想让⽅法服务器端可以同时连接上不同的客户端那么我们就需要重复的调⽤accept()* 这样服务端才能发现其他客户端的连接。

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The Design and Implementation of a Distributed Hash Table for a Peer-to-Peer NetworkDHT–Distributed Hash TableHelsinki27th May2004Software Engineering ProjectUNIVERSITY OF HELSINKIDepartment of Computer ScienceCourse581260Software Engineering Project(6cr)Project GroupMarko RäihäRisto SaarelmaAntti SalonenTuomas ToivonenTomi TukiainenSimo ViitanenClientJussi LindgrenProject MastersJuha TainaTurjo TuohiniemiHomepagehttp://www.cs.helsinki.fi/group/dht/ Change LogVersion Date Modificationsi Contents1Introduction12Architecture22.1Environment (2)2.1.1GNUnet (2)2.1.2Kademlia (2)2.2Modules (2)2.2.1DHT API (2)2.2.2Client-server communications (2)2.2.3Kademlia (2)2.2.4Datalayer (3)2.2.5Tools (3)2.2.6RPC (3)3Implementation43.1Modules (4)3.1.1DHT API (4)3.1.2Client-server (4)3.1.3Kademlia (5)3.1.4Datalayer (6)3.1.5RPC (7)3.2Compilation (8)4Suggestions94.1Bugs (9)4.2Wishlist (9)4.2.1DHT API (9)4.2.2Client-server communications (10)4.2.3Kademlia (10)4.2.4Datalayer (10)5Conclusion11References121IntroductionIn this white paper we describe the design and implementation of a distributed hash table using a peer-to-peer networking approach.We used the GNUnet framework for core peer-to-peer networking functionality.As the distributed hash table algorithm we used Kademlia.The work was performed as part of the Software Engineering Project1course at the depart-ment of computer science2,University of Helsinki,Finland.The project team consisted of six students.Each participant worked on the project for approximately one and half man months during the spring2004term.In addition to the program source code and this white paper in English,the team produced a set of project and specification documents in Finnish.An archive of all the materials is available on the project’s web site[RSS+04]. In chapter two we describe the overall architecture of the distributed hash table imple-mentation.Rationale for using GNUnet and Kademlia as basic building blocks is given as is an overview of each implemented component.In chapter three we provide compon-ent by component implementation details.The chapter is intended as a gentle introduction to the actual source code.In the fourth chapter we describe for example missing features and suggestions for future improvements.The project team would like to acknowledge the input of Marianne Korpela and Jussi Lindgren.As the project instructor Marianne helped our at times unruly group stay fo-cused.Jussi,as the project customer,was responsive and knowledgeable,a fact we could have taken more advantage of.2Architecture2.1Environment2.1.1GNUnetGNUnet is described at the GNUnet development team’s website[GNU04].2.1.2KademliaKademlia is described by Maymounkov and Mazières[MM02].2.2Modules2.2.1DHT APITo access the distributed hash table(DHT)a client application uses an application pro-gramming interface(API)implemented in C.The API provides a set of synchronous func-tions.Each function will invoke the API library and communicate with the local GNUnet daemon resident DHT module over a TCP socket.The standard GNUnet client/server protocol is used in communicating with the daemon.The DHT API offersfive primitives for applications:create Used to create a new hash table.The creating node automatically joins the new hash table.join Used to join an existing hash table.After a node has joined to a hash table,it will be possible for the node to perform searches on the table and store new data to the table.leave Used to leave a hash table that the node has previously joined.insert Used to store a new<key,value>-pair to a joined hash table.list Used to retrieve a list of all hash tables the node is joined to.fetch Used to retrieve a<value>using a<key>from a joined hash table.2.2.2Client-server communicationsStandard GNUnet client-server communication framework is used.2.2.3KademliaTBD.2.2.4DatalayerDatalayer is the module representing storage and lookups for locally stored data.Data is stored as a mapping from a hash to a value.Datalayer supports multiple tables and in addition to storing nodes it supports four differ-ent lookups.These include:by key All data stored to a mapping from a single key.by ownflag All data stored by the local node.by expiration All data with expiration time exceeding.by xor metric distance All data units that are closer to another unit in xor metric topo-logy.In addition datalayer supports persistence module for the data.2.2.5ToolsFor testing and demonstration purposes a set of command line tools have been developed. Each tool invokes one of the DHT API functions.If the tools are used in a sequence, the output of one tool can be used as the parameters for other tools.For example,the output of dht-join tool is a hash table handle which can then be used as a parameter to eg. dht-create or dht-leave.2.2.6RPCThe RPC module is a generic Remote Procedure Call(RPC)mechanism on top of GNUnet’s message-based communication.By generic it is meant that it is not specific to the DHT application.Any node may either register a callback function in order to receive RPC’s, or node may make an RPC to a remote node.RPC’s take a set of request and response parameters,whose values may be of arbitrary length.The RPC module serializes the request(or response)parameters into a data packet which is then divided into segments that can be transmitted as GNUnet messages to another node.On top of GNUnet’s unreliable communication semantics,the RPC module attemps to provide reliable communication,so the messages sent are acknowledged by the receiver and if necessary,retransmitted by the sender.Directory Descriptiongtkui A(partially implemented)GTK+user interface to the DHT API.include The DHT API headers for use by client applications.module Implementation of the DHT as a GNUnet module.tools Command line tools for testing the DHT module and API.util Utility functions used by the DHT module.Table1:Subdirectories containing the DHT source code.3ImplementationThe DHT module has been implemented to form part of the GNUnet source tree.All DHT related code can be found in the directory.../src/applications/dht/(relative to the root of the GNUnet source tree).Table1presents an overview of the subdirectories containing the DHT source code.3.1Modules3.1.1DHT APIInterface dht_api.h,api_errorcodes.h,api_structs.h,client-server.hImplementation dht-api.cThe DHT API provides a C language application programming interface to client applic-ations that wish to use the distributed hash table.The API is synchronous.Each function only returns after a definitive set of return values have been prepared(eg.all values have been fetched).The API uses the GNUnet client-server-protocol to communicate with the GNUnet daemon resident DHT implementation.It is thus possible to connect over TCP to remote GNUnet daemons as well.Full documentation(in Doxygen compatible comments)of the API is given in the dht_api.h header.As an example the source code of testing tools in directory.../tools/can be per-used.Also.../tools/Makefile.am can be used as a example on how to incorporate new client applications to the GNU autoconf framework for compilation.3.1.2Client-serverInterface client-server.hImplementation client-server.cUndocumented.See Doxygen comments in code.3.1.3KademliaInterface dht.hImplementation dht.c,kademlia.h,kademlia.cKademlia is the module that implements the actual distributed hash table functionality. The interface in dht.h provides functions for joining and leaving tables in the network, creating new tables,inserting<key,value>pairs and fetching<key,value>pairs from the dht network based on key.Thefile kademlia.c contains the internal implementation of the dht system using the Kademlia algorithm.The Kademlia implementation stores local information using the datalayer module and queries for and receives remote information using the rpc module. The Kademlia implementation maintains afixed-size local routing table in each node. Routing information is updated when the implementation communicates with other nodes. Using the routing tables,the implementation should be able tofind a specific dht node in O(log n)time.The most important functions in the interface are the following:•create(tableConfig,metaData,tableId)-creates a new table and writes its identifier into tableId•join(nodeAddress,tableId)-joins the table with a given identifier that is hosted in the given node•leave(tableId)-leaves the table with the given identifier•insert(tableId,key,value)-inserts a<key,value>pair in a table•fetch(tableId,key,result)-searches for<key,value>pairs with the given key and writes them in the result set•tables(nodeAddress,tableSet)-lists all tables a given node has joinedNodes cannot join the dht network by themselves because they are not initially aware of any nodes which are running the dht service.To have the node join the dht network,the user must be aware of at least one other node already on the network.The node will then be able to join the network by joining into one or more tables in the other node. After the node has joined some tables,the Kademlia implementation will take over and begin routing queries,updating its routing information and storing<key,value>pairs as necessary.3.1.4DatalayerInterface datalayer.h,datalayer_persistance.hImplementation datalayer.c,datalayer_persistance.hDatalayer is the module representing all local lookups for<key,value>-pairs.Interface of the datalayer is presented in thefile datalayer.h.It also presents the structs needed by the datalayer.These structs include DHT_DataStoreUnit,DHT_LocalStoreResultSet, DHT_LocalTableSet and DHT_TableDef.DHT_DataStoreUnit is the basic entity for storing units.It contains hash,data,creation-and expiration time andflags.So datastore stores only mapping between a hash and a data.How these are constructed is not datalayer’s concern.DHT_TableDef is the struct which defines all that datalayer needs to know about one table.This includes table id,metadata and config information.Table id is the TableId identifier of the table.Metadata is strictly for user interfaces and config information is stored because it needs to be copied to new nodes joining the table.DHT_LocalStoreResultSet and DHT_LocalTableSet are structs representing results.They both present an abstract iteration pattern for the search results with an abstract typedef for both:LocalStoreTableIter and LocalStoreResultIter.Implementation of these iterators is not visible for the user of the datastore.The implementations are defined infile data-store.c.Datalayer is split in two layers:search layer and persistence layer.Search layer,as the name indicates,is responsible for implementing searches for the data.It implements four different searches:•localStoreGet(tableId,key)-searches all<key,value>-pairs stored to the specified table with the specified key•localStoreGetOwnData(tableId)-searches all<key,value>-pairs stored to the spe-cified table with theflag myData on•localStoreGetExpired(tableId,TIME_T now)-searches all<key,value>-pairs stored to the specified table with the expiration time older than the now parameter•localStoreGetCloserTo(tableId,myID,newID)-searches all<key,value>-pairs stored to the specified table with the key hash closer to the new id than my id.Closeness of the hashes is implemented in Kademlia’s XOR metric.Persistence layer is responsible for persisting the datastore.At the moment it is not imple-mented and the datastore only stores the data units to the search data structures of search layer.3.1.5RPCInterface module/rpc.hImplementation module/rpc.cThe RPC module provides an generic RPC mechanism on top of GNUnet’s message-based communication primitives.Unlike GNUnet’s unreliable communication semantics,the RPC module attempts to provide a reliable communication mechanism through ac-knowledgement and retransmission of messages in case they get lost.The interface is very straight-forward:•RPC_init-Registers peer-to-peer message handlers,etc.•RPC_register-Registers an RPC locally,identified by a string name and implemen-ted by a callback function•RPC_execute-Executes an RPC on another node(possibly itself)In addition,the interface includes the type RPC_Param,which represents a set of para-meters.The parameter names are strings and their values arbitrary data.No limit has been implemented for the size of a parameter’s value.A set of functions is provided to access parameter sets and the same type is used for passing both request and response paramet-ers.The parameter sets are accessed in an indexed fashion,and perhaps unconventionally, there can be several parameters with the same name in a set.Every successful RPC call in a GNUnet network includes the caller sending a request which is acknowledged by the receiver,and after the receiver has executed the RPC loc-ally it returns a response which is again acknowledged by the caller.The RPC module serializes the request(or response)and its parameters into a data packet,which is then di-vided into numbered segments which are eventually transmitted with GNUnet messages.The RPC module defines three new GNUnet message types for transmitting request data (REQ),response data(RES)and acknowledgements(ACK).Every REQ or RES message is acknowlegded by the receiver and if an acknowledgementis not received,retransmitted by the sender.The RPC module was designed to use a slid-ing window mechanism similar to TCP,with the send window’s size being increased until problems arise.However,with the current implementation the size remains1,althoughthe module has otherwise been implemented so that the send window could be of arbitrary size.In order to utilize the bandwidth of the network between the sender and the receiver, some sort of slow-start mechanism should be implemented.The RPC module is inherently multi-threaded.In addition to the interface function RPC_execute, control can be returned to the RPC module from GNUnet core with several callbacks.As GNUnet may call the callbacks concurrently,the callback functions and RPC_execute usea mutex to control access to shared data structures.The following callback functions are registered with GNUnet.•handleRPCMessageReq-Called when a REQ message is received•handleRPCMessageRes-Called when a RES message is received•handleRPCMessageAck-Called when an ACK message is received•retransmitTimerExpire-Called when the retransmission timer of sent message ex-pires•ackTimerExpire-Called when the acknowledgement timer of a received message expires3.2CompilationThe DHT module is implemented as part of the GNUnet source tree and is integrated with the GNU autoconf based compilation framework used by GNUnet.See autoconf documentation and Makefile.amfiles in the various DHT source code directories for more information.Operation Single node Multiple nodesdht-create OK??dht-fetch OK ERRORdht-insert ERROR ERRORdht-join OK OKdht-leave OK??dht-list OK ERRORdht-inserted-drop??ERRORdht-inserted-list ERROR N/ATable2:Summary of test results for each DHT API operation.OK signifies successful test case,ERROR a failure.N/A means that the operation doesn’t apply to the single or multiple nodes case.Question marks point to cases that haven’t been tested.4Suggestions4.1BugsSome of the bugs and missing features identified at the time of project closure are listed in the GNUnet bug tracking system,Mantis3.Table2summarises test results for each of the DHT API functions.The tests were per-formed using the command line tools.Success or failure indication was derived from debug logs and output of the tools.A more complete report of test cases and their results is available in Finnish at the project site[RSS+04].4.2Wishlist4.2.1DHT API•Add support for multiple threads;ie.make the API asynchronous.•The DHT implementation inside the GNUnet daemon doesn’t differentiate between clients.For example,two unrelated users can connect to tha same daemon and issue er A can join a table,but before executing fetches or inserts,user B could have unsubscribed(leave)the node from the previously joined table.There would appear to be no easy workaround to this.The decision to implement all DHT functionality inside GNUnet daemon instead of using an end-to-end model is inherent in the design.Perhaps from the perspective of the Kademlia algorithm we should have modelled each client application as a node of the peer-to-peer network.Functionality could thus have been pushed to the edge.4.2.2Client-server communications•Implement better checks for incoming messages.•Limit size of reply messages.•Implement process status queries(csStatus-function).4.2.3Kademlia•Joining a table—Joining could be improved with at least following:–Receiver:∗Send the DHT_TableConfig to the sender.∗Send information about n random nodes in the same table.–Sender∗Send join to multiple nodes(the Byzantine General Problem).•Timed tasks(crons)—All cron jobs maintaining the dht.These include:–Republishing own data(every24hours).–Dropping expired data(every now and then).–Distibuting data to the closest nodes in table(newly joined nodes)(everyhour).4.2.4Datalayer•Enhanced data structures:–Hashtable for mapping.–Use the general Vector data structure(used also by RPC and Kademlia).•Implement the persistence layer properly:–Onefile per table.–A daemon thread that writes the units tofile.5ConclusionAs a whole the project can be considered a moderate success.Almost all of the designed functionality was implemented.However,not all of the implementation was adequately tested and several critical bugs have been identified.Also,the design centralises function-ality in the DHT module instead of pushing it to the client applications on the network edges.This may not be the most opportune design charasteristic.ReferencesGNU04GNUnet,Website of the GNUnet project.URL http://www.ovmj.org/GNUnet/.2004.MM02Maymounkov,P.and Mazières,D.,Kademlia:A peer-to-peer information system based on the xor metric.Proceedings of the1st International Work-shop on Peer-to-Peer Systems(IPTPS).RSS+04Räihä,M.,Saarelma,R.,Salonen,A.,Toivonen,T.,Tukiainen,T.and Viitanen,S.,The Distributed Hash Table project:Archive of project doc-umentation and source code.URL http://www.cs.helsinki.fi/group/dht/.2004.。