HTTP protocol (v) proxy

Original: http://www.cnblogs.com/TankXiao/archive/2012/12/12/2794160.html

What is a proxy server

The Web Proxy server is the intermediary entity of the network. The agent sits between the Web client and the Web server, playing the role of "middleman".

The proxy server for HTTP is the Web server and the Web client.

Fiddler is a typical agent.

Fiddler is working as a proxy Web server, which uses proxy addresses: 127.0.0.1, Port: 8888. When Fiddler exits, it automatically unregisters the agent, so that it does not affect other programs.

The role of the agent one, FQ

Many people like to use Facebook and watch YouTube.  But we in the celestial, Celestial has the Great of Wall (Great Wall Firewall), blocked these good website.   What to do? Through the agent to jumps over, you can access the.

To find a proxy server is very troublesome, usually using FQ software to automatically discover the proxy server.

Role of Agent two, anonymous access

Often listen to the news, said, "xxx" posted on the Internet post, was cross-province hunting. If he uses an anonymous proxy server, it's not easy to reveal his identity.

The anonymity of the HTTP proxy server means that the HTTP proxy server hides the original user's IP address and other details from the remote server by removing the identity attribute in the HTTP message (such as the client's IP address, or the cookie, or the session ID of the URI). the log of the original user's access record is not recorded on the HTTP proxy server as well (otherwise it will be found).

Agent of the role of three, through the agent online

For example, LAN can not access the Internet, only through a proxy server in the LAN network.

Agent role four, through proxy cache, speed up the internet speed

Most proxy servers have the ability to cache, like a large cache, which has a lot of storage space, it constantly stores the new acquired data to its local storage, if the browser requested data on its native memory already exists and is up to date, then it does not re-fetch data from the Web server, The data on the memory is transmitted directly to the user's browser, which can significantly improve the browsing speed.

Role of the agent five: child filter

Many educational institutions use filter proxies to prevent students from accessing adult content.

IE proxy settings: Manually set up the agent

IE can be manually set up the agent, very simple, specify an IP address and port on it. Such as.

Tools-> Internet Options, connections-LAN settings (shortcut keys)

If the IP address of the proxy server has changed, or the port number has changed. Do you want hundreds of client browsers to modify the browser settings?  Impossable This is too difficult to maintain. There is also a more advanced approach to this point.

IE proxy settings: Using automatic configuration script (PAC)

Manually configuring the agent is simple, but not flexible. Only one proxy server can be specified, and failover is not supported.

In large companies, PAC files are generally used for configuration. You only need to specify the URL of the PAC file.

A PAC (Proxy Auto Config) file is a text file of a small JavaScript program, with a suffix of. dat.

When the browser accesses the network, the appropriate proxy server is selected based on the JavaScript functions in the PAC file.

Contents of the Sample_pac.dat file

functionFindProxyForURL (URL, host) {if (url.substring (0, 5) = = "http:") {//The specified proxy should be usedReturn "PROXY proxy:80"; }Elseif (url.substring (0, 4) = = "ftp:" return "PROXY fproxy:80" ;} else if (url.substring (0, 7) = = "Gopher:" return "PROXY gproxy" ;} else if (url.substring (0, 6) = = "https:" return "PROXY secproxy:8080" ;} else {// straight, without any agent Span style= "color: #0000ff;" >return "DIRECT"           

IE proxy settings: Auto detect settings (WPAD)

The browser can use the WPAD protocol by simply checking "Automatically detect settings", and WPAD will automatically find the URL of the PAC file. WPAD will use a series of resource discovery techniques (DHCP,DNS, etc.) to find PAC files.

Agent authentication, and 407 status codes

Proxy servers can also require permission authentication, and HTTP defines a mechanism called proxy authentication. This mechanism can block requests for content.

When a browser accesses a proxy that requires authentication, the proxy server returns 407 Authorization Required, telling the browser to enter a user name and password.

Proxy authentication and HTTP Basic authentication is the same mechanism, if you need to understand the mechanism of proxy authentication, see [HTTP protocol Basic authentication]

Security issues using a proxy server

The proxy server and the packet Capture tool (such as fiddler) can see the data in the HTTP request. If we send a request with sensitive data, such as username, password, credit card number. This information will be seen by the proxy server. So very dangerous.  So we usually use HTTPS to encrypt the HTTP request. This way the proxy server will not see the data inside.

How to build a proxy server

You can use Ccproxy, and squid to build a proxy server.

HTTP protocol (v) proxy