位置: IT常识 - 正文

6.824 Lab 1: A simple web proxy

编辑:rootadmin
6.824 Lab 1: A simple web proxy6.824 - Spring 20046.824 Lab 1: A simple web proxyDue: Tuesday, Febru

推荐整理分享6.824 Lab 1: A simple web proxy,希望有所帮助,仅作参考,欢迎阅读内容。

文章相关热门搜索词:,内容如对您有帮助,希望把文章链接给更多的朋友!

6.824 - Spring 20046.824 Lab 1: A simple web proxyDue: Tuesday, February 10th, 1:00pm.Introduction

Please read Getting started with 6.824 labs before starting this assignment. You will also need Using TCP through sockets at a later stage.

If you have questions, please first read Office hours and asking questions. After you have done that, you can send e-mail to 6.824-staff@pdos.lcs.mit.edu.

In this lab assignment you will write a simple web proxy. A web proxy is a program that reads a request from a browser, forwards that request to a web server, reads the reply from the web server, and forwards the reply back to the browser. People typically use web proxies to cache pages for better performance, to modify web pages in transit (e.g. to remove annoying advertisements), or for weak anonymity.

You'll be writing a web proxy to learn about how to structure servers. For this assignment you'll start simple; in particular your proxy need only handle a single connection at a time. It should accept a new connection from a browser, completely handle the request and response for that browser, and then start work on the next connection. (A real web proxy would be able to handle many connections concurrently.)

In this handout, we use client to mean an application program that establishes connections for the purpose of sending requests[3], typically a web browser (e.g., lynx or Netscape). We use server to mean an application program that accepts connections in order to service requests by sending back responses (e.g., the Apache web server)[1]. Note that a proxy acts as both a client and server. Moreover, a proxy could communicate with other proxies (e.g., a cache hierarchy).

Design Requirements

Your proxy will speak a subset of the HTTP/1.0 protocol, which is defined in RFC 1945. You're only responsible for a small subset of HTTP/1.0, so you can ignore most of the spec. You should make sure your proxy satisfies these requirements:

GET requests work.Images/Binary files are transferred correctly.Your webproxy should properly handle Full-Requests (RFC 1945, Section 4.1) up to, and including, 65535 bytes. You should close the connection if a Full-Request is larger than that.You must support URLs with a numerical IP address instead of the server name (e.g. http://18.181.0.31/).You are not allowed to use fork().You may not allocate more than 100MB of memory.You can not have more than 32 open file descriptors.Your proxy should correctly service each request if possible. If an error occurs, and it is possible for the proxy to continue with subsequent requests, it should close the connection and then proceed to the next request. If an error occurs from which the proxy cannot reasonably recover, the proxy should print an error message on the standard error and call exit(1). There are not many non-recoverable errors; perhaps the only ones are failure of the initial socket(), bind(), listen() calls, or a call to accept(). The proxy should never dump core except in situations beyond your control (e.g. a hardware or operating system failure).

You do not have to worry about correct implementation of any of the following features; just ignore them as best you can:

POST or HEAD requests. URLs of any type other than http. HTTP-headers (RFC 1945, Section 4.2).

If your browser can fetch pages and images through your proxy, and your proxy passes our tester (see below), you're done.

HTTP example without a web proxy

HTTP is a request/response protocol that runs over TCP. A client opens a connection to a web server and sends a request for a file; the server responds with some status information and the file contents, and then closes the connection.

You can try out HTTP yourself:

% telnet web.mit.edu 80

This connects to web.mit.edu on port 80, the default port for HTTP (web) servers.

Then type

GET / HTTP/1.0

followed by two carriage returns. This ends the header section of the request. The server locates the web page and sends it back. You should see it on your screen.

To form the path to the file to be retrieved on a server, the client takes everything after the machine name. For example, http://web.mit.edu/resources.html means we should ask for the file /resources.html. If you see a URL with nothing after the machine name and port, then / is assumed---the server figures out what page to return when just given /. Typically this default page is index.html or home.html.

On most servers, the HTTP server lives on port 80. However, one can specify a different port number in the URL. For example, typing http://web.mit.edu:2206 in your browser will tell it to find a web server on port 2206 on web.mit.edu. (No, this doesn't work for this address.)

HTTP (request) example with a web proxy

Before you can do this example, you need to tell your web browser to use a web proxy. This explanation assumes you are running Mozilla, but things should be remarkably similar for Netscape. Choose ``Edit'' ---> ``Preferences''. Then choose ``Advanced'' ---> ``Proxies''. Click on ``Manual proxy configuration''. Now set the ``HTTP proxy'' to speakeasy-mit-ron.lcs.mit.edu and port 3128. Mozilla will now send all HTTP request to this web proxy rather than directly to web servers.

Lynx---a poor man's browser---can be told to use this web proxy by setting the environment variable http_proxy to speakeasy-mit-ron.lcs.mit.edu:3128.

Now to the real stuff.

You can use nc to peek at HTTP requests that a browser sends to a web proxy. nc lets you read and write data across network connections using UDP or TCP[10]. The class machines have nc installed.

First we'll examine the requests that a browser sends to the proxy. We'll use nc to listen on a port and direct our web browser (Lynx) to use that host and port as a proxy. We're going to let nc listen on port 8888 and tell Lynx to use a web proxy on port 8888.

% nc -lp 8888

This tells nc to listen on port 8888. Chances are that you will have to choose a different port number than 8888 because someone else may be using that port. Choose a number greater than 1024, less than 65536. Now try, on the same machine, to retrieve a web page port 8888 as a proxy:

% env http_proxy=http://localhost:8888/ lynx -source http://www.yahoo.com

This tells Lynx to fetch http://www.yahoo.com using a web proxy on port 8888, which happens to be our spy friend nc.

Netcat neatly prints out the request headers that Lynx sent:

% nc -lp 8888GET http://www.yahoo.com/ HTTP/1.0Host: www.yahoo.comAccept: text/html, text/plain, application/vnd.rn-rn_music_package, application/x-freeamp-theme, audio/mp3, audio/mpeg, audio/mpegurl, audio/scpls, audio/x-mp3, audio/x-mpeg, audio/x-mpegurl, audio/x-scpls, audio/mod, image/*, video/mpeg, video/*Accept: application/pgp, application/pdf, application/postscript, message/partial, message/external-body, x-be2, application/andrew-inset, text/richtext, text/enriched, x-sun-attachment, audio-file, postscript-file, default, mail-fileAccept: sun-deskset-message, application/x-metamail-patch, application/msword, text/sgml, */*;q=0.01Accept-Encoding: gzip, compressAccept-Language: enUser-Agent: Lynx/2.8.4rel.1 libwww-FM/2.14 SSL-MM/1.4.1 OpenSSL/0.9.6b

The GET request on the first tells the proxy to get file http://www.yahoo.com using HTTP version 1.0. Notice how this request is quite different from the example without a web proxy! The protocol and machine name (http://www.yahoo.com) are now part of the request. In the previous example this part was omitted. Look in RFC 1945 for details on the remaining lines. (It's effective reading material if you really can't sleep and Dostoevsky didn't do the trick.)

HTTP (reply) example with a web proxy

The previous example shows the HTTP request. Now we'll try to see what a real web proxy (speakeasy-mit-ron.lcs.mit.edu port 3128) sends to a web server. To achieve this we use nc to be a fake web server. Start the ``fake server'' on anguish.lcs.mit.edu with the following command:

% nc -lp 88886.824 Lab 1: A simple web proxy

Again, you may have to choose a different number if 8888 turns out to be taken by someone else.

% env http_proxy=http://speakeasy-mit-ron.lcs.mit.edu:3128/ lynx -source http://anguish.lcs.mit.edu:8888

Needless to say, you should replace 8888 by whatever port you chose to run nc on. nc will show the following request:

% nc -lp 8888GET / HTTP/1.0Accept: text/html, text/plain, audio/x-pn-realaudio, audio/vnd.rn-realaudio, application/smil, text/vnd.rn-realtext, video/vnd.rn-realvideo, image/vnd.rn-realflash, application/x-shockwave-flash2-preview, application/sdp, application/x-sdpAccept: application/vnd.rn-realmedia, image/vnd.rn-realpix, audio/wav, audio/x-wav, audio/x-pn-wav, audio/x-pn-windows-acm, audio/basic, audio/x-pn-au, audio/aiff, audio/x-aiff, audio/x-pn-aiff, text/sgml, video/mpeg, image/jpeg, image/tiffAccept: image/x-rgb, image/png, image/x-xbitmap, image/x-xbm, image/gif, application/postscript, */*;q=0.01Accept-Encoding: gzip, compressAccept-Language: enUser-Agent: Lynx/2.8.4rel.1 libwww-FM/2.14Host: anguish.lcs.mit.edu:8888X-RAN-Loopstop: trueX-RAN-Loopstop: trueVia: 1.0 speakeasy.ron.lcs.mit.edu:3128 (squid/2.5.STABLE2), 1.0 speakeasy.ron.lcs.mit.edu:3148 (squid/2.5.STABLE4), 1.0 nyu.ron.lcs.mit.edu:3128 (squid/2.5.STABLE4)X-Forwarded-For: 18.26.4.9, 127.0.0.1, unknownCache-Control: max-age=259200Connection: keep-alive

Notice how the web proxy stripped away the http://anguish.lcs.mit.edu:8888 part from the request!

Your web proxy

Your web proxy will have to translate between requests that the client makes (the one that starts with ``GET http://machinename'') into requests that the server understands. So far for the bad news. The good news is that we provide you with some helpful code that will make this very easy to do.

Your web proxy will listen on a port other than port 80, so as to avoid conflicts with regular web servers.

Once the request line has been received, the web proxy should continue reading the input from the client until it encounters a blank line. The proxy should then fetch the URL from the appropriate server, forward the response back to the client, and close the connection. The proxy should forward response data as it arrives, rather than buffering the entire response; this allows the proxy to handle huge responses without running out of memory.

Your web proxy has to support the GET method only [3]. A GET method takes two arguments: the file to be retrieved and the HTTP version. Additional headers may follow the request.

Getting Started

We have provided a skeleton webproxy directory. It is available at http://pdos.lcs.mit.edu/6.824/labs/webproxy1.tar.gz. The following sequence of commands should yield a compiled version of the server you should extend to pass the tests.

% wget http://pdos.lcs.mit.edu/6.824/labs/webproxy1.tar.gz% tar xzvf webproxy1.tar.gz% cd webproxy1% gmake

The tarball contains http.C, http.h, Makefile, webproxy1.C and webproxy1-test.C. The first two files will help you parse HTTP requests. The Makefile is, as its meaningful name implies, a Makefile. Webproxy1.C is a pretty useless web server that, nonetheless, should help you on your way. webproxy1-test.C is our testing program which checks your program for correctness.

http.C and http.h : a HTTP parser

We have provided a parser for proxy-style HTTP requests. It is implemented in the files http.C and http.h that are included in the tarball.

http.h defines the class httpreq that inherits from the class httpparse (if you are unfamiliar with C++ inheritance, consult the Stroustrup C++ language guide referenced in the course information page. Don't drop this book on someone's face. It's a pretty hefty book.)

To parse a request, first create a httpreq object. Then, parse the (potentially incomplete) HTTP request by feeding it to int parse (char *buf, ssize_t len) until it returns 1, indicating that the headers are complete. buf should be the buffer that contains the (potentially incomplete) HTTP request. len is the length of the HTTP request fragment in buf. Notice that parse needs to see the whole request you have read so far.

parse returns 1 if the HTTP request is complete, 0 if it needs more data to complete, or -1 on a parse error. parse does not modify the contents of buf. Once parse returns 1, you can call---amongst others---the following methods on the calling httpreq.

char* method() The 'type' of request (POST, GET, HEAD)char* host() The destination hostshort port() The destination portchar* path() The filename part of the requested URLchar* url() The requested URL

Here's a simple program that illustrates the use of httpreq.

#include <stdio.h>#include "http.h"intmain(){ httpreq *r = new httpreq(); char buf[512]; int ret; // incomplete header strcpy(buf, "GET http://web.mit.edu/index.html"); ret = r->parse(buf, strlen(buf)); printf("ret %d file %s\n", ret, ret == 1 ? r->path() : "(none)"); // complete header strcat(buf, " HTTP/1.0\r\n\r\n"); ret = r->parse(buf, strlen(buf)); printf("ret %d file %s\n", ret, ret == 1 ? r->path() : "(none)"); delete r; exit(0);}Documentation

You may want to read Using TCP through sockets to learn about socket programming in C/C++. Also, take a look at the references at the bottom of this page.

Running and testing the proxy

Your proxy program should take exactly one argument, a port number on which to listen. For example, to run the proxy on port 2000:

% ./webproxy1 2000

As a first test of the proxy you should attempt to use it to browse the web. Set up your web browswer to use one of the class machines running your proxy as a proxy and experiment with a variety of different pages.

When you think your proxy is ready, you can run it against the test program webproxy1-test, our tester. Run the tester with your proxy as an argument:

% ./webproxy1-test ./webproxy1

Note that this may take several minutes to complete. The test program runs the following tests:

Ordinary fetch

This test is the "normal case". We send a normal HTTP 1.0 GET request and expect the correct web page.

Split request

This tests splits the HTTP request in two chunks. The first chunk contains a partial HTTP request. The second chunk completes the first after which the tester expects the correct web page contents to come back.

Large request

The tester does a request of exactly 65535 bytes.

Large response

The tester fetches a web page larger than the maximum amount of memory available to your web proxy.

Zero-size response

The tester fetches a web page without a body.

Recover after bad connect

The tester sends a request with a URL that specifies a false port. Your proxy will attempt to make a connection to a bogus port. Soon thereafter, the tester tries to fetch a valid page to see if your proxy is still doing ok.

Malformed request

The tester sends an HTTP request that is not syntactically correct. After that, it tries to fetch a valid page to see if it your proxy is still doing ok.

Premature client close()

The tester sends a partial HTTP request and then closes the connection. After that, it tries to fetch a valid page to see if it your proxy is still doing ok.

Infinitely long request

The tester swamps your proxy with a request larger than 65535 bytes. The tester expects your proxy to close the connection. After that, it tries to fetch a valid page to see if it your proxy is still doing ok.

Stress test

The tester stress tests your web proxy with a ruthless combination of ordinary fetches, split requests, malformed requests, and large responses. This may expose memory leaks, unclosed connections, and random other bugs.

Collaboration policy

You must write all the code you hand in for the programming assignments, except for code that we give you as part of the assigment. You are not allowed to look at anyone else's solution (and you're not allowed to look at solutions from previous years). You may discuss the assignments with other students, but you may not look at or copy each others' code.

Handin procedure

You should hand in a gzipped tarball webproxy1-handin.tgz produced by gmake dist. Copy this file to ~/handin/webproxy1-handin.tgz. Do not make this file world readable! We will use the first copy of the file that we can find after the deadline---we try every few minutes. Don't bother to copy a new version over the old one hoping that we will use it instead. We won't.

References1Apache Web Proxy, http://www.apache.org/docs/mod/mod_proxy.html.2T. Berners-Lee, et al. RFC 1945: Hypertext Transfer Protocol - HTTP/1.0, May 1996.3CERN Web Proxy, http://www.w3.org/Daemon/User/Proxies/Proxies.html.4Netcat. http://www.atstake.com/research/tools/nc110.txt.
本文链接地址:https://www.jiuchutong.com/zhishi/303719.html 转载请保留说明!

上一篇:CSS Houdini:用浏览器引擎实现高级CSS效果(css代码怎么在浏览器运行)

下一篇:帝国cms如何投稿(帝国cms怎么上传图片)

  • 城市维护建设税怎么做分录
  • 固定资产折旧会计处理
  • 固定资产装修费用计入房产税吗
  • 端午节福利计入什么科目
  • 其他应收款款项性质有哪几种
  • 其他应收款账龄怎么算
  • 偶然所得申报表
  • 短期借款的主要形式
  • 小规模纳税人企业所得税怎么申报
  • 会计中制造费用是什么意思
  • 销售公司车辆如何填报销项税
  • 不动产发票如何开具
  • 开发票与实际金额不符属于什么
  • 非基本人员单位部分
  • 罚没支出包括税收滞纳金吗
  • 申报预缴企业所得税
  • 外地培训产生的费用
  • 月末增值税进项和销项怎么结转
  • 员工娱乐活动比赛项目
  • 审计报告与汇缴报告
  • 加速折旧以后年度如何填报调减额
  • 预交土地增值税怎么计算的
  • 上个月多计提的费用怎么调整
  • linux命令df -h结果详解
  • php错误日志
  • dcs是什么文件夹可以删除吗
  • 有没有不需要网络的摄像头
  • 如何申请菜鸟驿站快递代理点
  • 微信小程序分成比例
  • ts基础类型
  • 固定资产折旧的计算方法
  • PHP 中TP5 Request 请求对象的实例详解
  • 教育经费地方出多少
  • 出口货物免抵退税额的计算方法
  • 收入支出如何算利润
  • 浅谈双减背景下的高效课堂
  • 小规模企业要交哪些税种
  • .net tpl
  • Php实现注解注入
  • 购买电脑做什么分录
  • 政府补助可以挂账吗
  • 买资产买负债
  • 工会组织机构需要备案吗
  • 免税的10万元是什么
  • 个体工商户纳税申抿
  • Sql Server中Substring函数的用法实例解析
  • 发行股份的原则
  • 应付账款的入账时间为
  • 自然人扣缴客户端恢复数据
  • 计提税费和实际缴纳的有差额怎么办
  • 国有独资企业是有限责任公司吗
  • 非居民企业股权转让特殊性税务处理
  • 注册资金没显示
  • 借贷不平衡是什么意思
  • 其他综合收益什么时候转留存收益什么时候转损益
  • 收到增值税发票后该如何处理啊?
  • 制造费用影响什么
  • 如何在sql server表中添加数据表格为什么没有显示
  • Mysql执行sql文件
  • mysql的随机函数
  • win19截屏快捷键
  • Xp系统的桌面文件在哪里
  • centos7网卡强制千兆
  • win7电脑连不上wifi怎么解决
  • ubuntu virtual box
  • mac怎么打开macintosh
  • Win10 Mobile首个RS2预览版14905快速版今日开始推送
  • win10系统如何设置锁屏壁纸图片
  • 关于月亮的诗句
  • shell 命令执行顺序
  • jquery设置文本字体样式
  • js数组操作方法
  • Android studio 打包apk后卡在首屏
  • unity mul函数
  • JavaScript为事件句柄绑定监听函数实例详解
  • 国税总局关于总局的文件
  • 21年小规模企业所得税税率
  • 收到免税的苗木发票怎么做账
  • 江苏灵活就业医保交多少年
  • 网上税务局网址
  • 免责声明:网站部分图片文字素材来源于网络,如有侵权,请及时告知,我们会第一时间删除,谢谢! 邮箱:opceo@qq.com

    鄂ICP备2023003026号

    网站地图: 企业信息 工商信息 财税知识 网络常识 编程技术

    友情链接: 武汉网站建设