网页的response header信息:
LWP :Library for WWW access in Perl
LWP(3) User Contributed Perl Documentation LWP(3)
NAME
LWP - The World-Wide Web library for Perl
L
SYNOPSIS
use LWP;
print "This is libwww-perl-$LWP::VERSION\n";
DESCRIPTION
The libwww-perl collection is a set of Perl modules which provides a simple and consistent application programming interface (API) to the World-Wide Web. The main focus of the library is to provide classes and
functions that allow you to write WWW clients. The library also contain modules that are of more general use and even classes that help you implement simple HTTP servers.
lib www-perl 收集了一组Perl模块,提供了一个简单的一致的应用接口(api).库函数主要的目的是提供了classes和functions 允许你写www客户端,
标准库 也包含了更加通用的类和帮你实现简单的HTTP servers 的模块。
Most modules in this library provide an object oriented API. The user agent, requests sent and responses received from the WWW server are all represented by objects. This makes a simple and powerful interface
to these services. The interface is easy to extend and customize for your own needs.
这个库中的大多数模块提供了一个面向对象的接口, user agent，请求send 和responsed 从WWW server通过objects 体现。
这使得一个强大的对那些服务的接口, 该接口很容易扩展和自定义您自己的需求。
The main features of the library are:
1· Contains various reusable components (modules) that can be used separately or together.
2· Provides an object oriented model of HTTP-style communication. Within this framework we currently support access to http, https, gopher, ftp, news, file, and mailto resources.
3· Provides a full object oriented interface or a very simple procedural interface.
4· Supports the basic and digest authorization schemes.
5 Supports transparent redirect handling.
6· Supports access through proxy servers.
7· Provides parser for robots.txt files and a framework for constructing robots.
8· Supports parsing of HTML forms.
9· Implements HTTP content negotiation algorithm that can be used both in protocol modules and in server scripts (like CGI scripts).
10· Supports HTTP cookies.
11· Some simple command line clients, for instance "lwp-request" and "lwp-download".
这个库主要的功能:
1.包含可单独使用或一起使用的各种可重用组件（模块）。
2.提供一个面向对象的HTTP通信方式, 在这个框架内,我们当前支持的访问HTTP，HTTPS，FTP，Gopher，消息，文件，和站长资源
3.提供一个完整的面向对象的接口 或者一个简单的程序接口。
4.支持基本和文摘授权计划。
5.支持透明重定向处理
6.通过代理服务器访问访问
7.提供 robots.txt的解析和 构建机器人框架解析
8.支持HTML形式解析
9.实现了HTTP内容协商算法既可以用于协议模块和服务器脚本（如CGI脚本）。
10.Supports HTTP cookies.
11 一些简单的命令客户端, 用于 instance "lwp-request" and "lwp-download"
HTTP STYLE COMMUNICATION
HTTP通信方式
The libwww-perl library is based on HTTP style communication. This section tries to describe what that means.
lib www-perl library 基于HTTP通信方式,本节试图说明这是什么意思
Let us start with this quote from the HTTP specification document <URL:http://www.w3.org/pub/WWW/Protocols/>:
· The HTTP protocol is based on a request/response paradigm. A client establishes a connection with a server and sends a request to the server in the form of a request method, URI, and protocol version, followed
by a MIME-like message containing request modifiers, client information, and possible body content. The server responds with a status line, including the message’s protocol version and a success or error code,
followed by a MIME-like message containing server information, entity meta-information, and possible body content.
HTTP 协议是基于请求/响应模式,客户端与服务器建立连接，并在请求方法的形式中向服务器发送请求，URI,和协议版本,
跟着一个类似MINE的消息包含 请求符,客户端信息,和可能的主体信息。 服务器响应状态行,包括消息的协议和成功或者错误代码
跟着一个类似消息包含服务器信息,实体的元消息,和可能的主体信息。
What this means to libwww-perl is that communication always take place through these steps: First a request object is created and configured. This object is then passed to a server and we get a response object in
return that we can examine. A request is always independent of any previous requests, i.e. the service is stateless. The same simple model is used for any kind of service we want to access.
这意味着 lib www-perl 沟通总是通过这些步骤进行:
第一步 一个请求对象是被创建和配置。 这个对象传递到server，我们得到一个响应对象返回 我们可以检查,请求总是独立于任何先前的请求,
即服务是无状态的,简单的模型被用于任何类似的服务。
For example, if we want to fetch a document from a remote file server, then we send it a request that contains a name for that document and the response will contain the document itself. If we access a search
engine, then the content of the request will contain the query parameters and the response will contain the query result. If we want to send a mail message to somebody then we send a request object which
contains our message to the mail server and the response object will contain an acknowledgment that tells us that the message has been accepted and will be forwarded to the recipient(s).
比如, 如果我们需要 从远端的文件服务器取文档,然后,我们将发送一个请求.该请求抱哈了该文档的名称和响应将包含文本本身的内容。
如果我们访问搜索引擎, 请求的内容将包含查询的参数和响应将包含查询结果。如果我们要给某人发送一份邮件,那么我们发送一个请求对象
包含我们的邮件来发送到邮件服务器和响应对象会包含一个确认告诉我们该消息被接收,并将被转发到收件人。
It is as simple as that!
这和那一样简单！
The Request Object
The libwww-perl request object has the class name "HTTP::Request". The fact that the class name uses "HTTP::" as a prefix only implies that we use the HTTP model of communication. It does not limit the kind of
services we can try to pass this request to. For instance, we will send "HTTP::Request"s both to ftp and gopher servers, as well as to the local file system.
请求的对象:
lib www-perl 请求对象有类的名字 "HTTP::Request". 事实上 ,类的名字中使用"HTTP::" 作为前缀意味着我们使用HTTP通信模型。
它不限制服务的种类,我们可以尝试通过这个来请求 例如,我们将发送 "HTTP::Request"的请求 到ftp和gopher服务器, 以前本地的文件系统。
The main attributes of the request objects are:
· The method is a short string that tells what kind of request this is. The most common methods are GET, PUT, POST and HEAD.
· The uri is a string denoting the protocol, server and the name of the "document" we want to access. The uri might also encode various other parameters.
· The headers contain additional information about the request and can also used to describe the content. The headers are a set of keyword/value pairs.
· The content is an arbitrary amount of data.
请求对象的主要属性是:
1.该方法是一个简单的字符串,告诉请求是什么类型, 最常见的方法是GET, PUT, POST and HEAD
2.URL 是一个字符串表示的协议, server和文档的名字(我们要访问的), URI有各种编码参数
3.header 包含了额外的信息关于 请求和描述内容, header 是一组键值对
4.内容是任意数量的数据
The Response Object
The libwww-perl response object has the class name "HTTP::Response". The main attributes of objects of this class are:
· The code is a numerical value that indicates the overall outcome of the request.
· The message is a short, human readable string that corresponds to the code.
· The headers contain additional information about the response and describe the content.
· The content is an arbitrary amount of data.
响应对象:
lib www-perl 响应对象的类名是"HTTP 响应"，主要的属性是:
1. 代码是一个数值,说明请求的总体数量
2.消息是简短的, 人可读的字符串
4.headers 包含了额外的信息关于响应内容描述
5.内容是任意的数据
Since we don’t want to handle all possible code values directly in our programs, a libwww-perl response object has methods that can be used to query what kind of response this is. The most commonly used response
classification methods are:
因为我们不想处理所有的可能的返回值在程序中, 一个lib www-perl 响应对象的方法可以用来查询响应的响应 最常用的响应方法是:
is_success()
The request was was successfully received, understood or accepted.
请求是成功接收
is_error()
The request failed. The server or the resource might not be available, access to the resource might be denied or other things might have failed for some reason.
请求失败
The User Agent
Let us assume that we have created a request object. What do we actually do with it in order to receive a response?
让我们假设我们已经建立了一个对象请求, 我们实际上对它做了什么来接收响应呢？
The answer is that you pass it to a user agent object and this object takes care of all the things that need to be done (like low-level communication and error handling) and returns a response object. The user
agent represents your application on the network and provides you with an interface that can accept requests and return responses.
The user agent is an interface layer between your application code and the network. Through this interface you are able to access the various servers on the network.
答案是你传递给它一个user agent 对象,这个对象照顾所有你需要做的事情(像低级别的通信和错误处理)
返回一个响应的对象, user agent 说明了你的网络上的应用程序,为你提供了接收请求和返回响应的接口。
user agent 是你的应用程序代码和网络之间的接口,通过这个接口,你可以访问网络上的各种服务器。
The class name for the user agent is "LWP::UserAgent". Every libwww-perl application that wants to communicate should create at least one object of this class. The main method provided by this object is
request(). This method takes an "HTTP::Request" object as argument and (eventually) returns a "HTTP::Response" object.
The user agent has many other attributes that let you configure how it will interact with the network and with your application.
对于 user agent的类 是"LWP::UserAgent",每个lib www-perl 应用来通信需要创建至少一个类的对象,主要的方法是request().
这个方法以 "HTTP::Request" 对象作为参数并返回一个 "HTTP::Response" 对象。
· The timeout specifies how much time we give remote servers to respond before the library disconnects and creates an internal timeout response.
· The agent specifies the name that your application should use when it presents itself on the network.
· The from attribute can be set to the e-mail address of the person responsible for running the application. If this is set, then the address will be sent to the servers with every request.
· The parse_head specifies whether we should initialize response headers from the <head> section of HTML documents.
· The proxy and no_proxy attributes specify if and when to go through a proxy server. <URL:http://www.w3.org/pub/WWW/Proxies/>
· The credentials provide a way to set up user names and passwords needed to access certain services.
Many applications want even more control over how they interact with the network and they get this by sub-classing "LWP::UserAgent". The library includes a sub-class, "LWP::RobotUA", for robot applications.
1.超时指定了 我们给远程服务器的响应时间在 libarary 断开连接和创建一个内部超时响应
2.agent 指定你的应用使用的名字 当它出现在网络上的时候
3.从属性可以设置 e-mail的地址,如果这只了这个, 那么该地址将被请求发送到服务器。
4. parse_head 指定了是否要初始化响应头并从HTML 的head章节
5.代理和no_proxy属性指定是否以及何时去通过代理服务器。
6.凭据提供了一种方法来设置访问特定服务所需的用户名和密码
An Example
This example shows how the user agent, a request and a response are represented in actual perl code:
# Create a user agent object
use LWP::UserAgent;
my $ua = LWP::UserAgent->new;
$ua->agent("MyApp/0.1 ");
# Create a request
my $req = HTTP::Request->new(POST => 'http://search.cpan.org/search');
$req->content_type('application/x-www-form-urlencoded');
$req->content('query=libwww-perl&mode=dist');
# Pass request to the user agent and get a response back
my $res = $ua->request($req);
# Check the outcome of the response
if ($res->is_success) {
print $res->content;
}
else {
print $res->status_line, "\n";
}
The $ua is created once when the application starts up. New request objects should normally created for each request sent.
$ua 一旦被创建,当应用程序启动的时候,通常为每个新的请求创建新的对象
NETWORK SUPPORT
This section discusses the various protocol schemes and the HTTP style methods that headers may be used for each.
For all requests, a "User-Agent" header is added and initialized from the $ua->agent attribute before the request is handed to the network layer. In the same way, a "From" header is initialized from the
$ua->from attribute.
For all responses, the library adds a header called "Client-Date". This header holds the time when the response was received by your application. The format and semantics of the header are the same as the
server created "Date" header. You may also encounter other "Client-XXX" headers. They are all generated by the library internally and are not received from the servers.
网络支持:这个章节讨论了各种协议体系和HTTP 类型方法
对于所有的请求, 一个"User-Agent" header 是添加到header 和初始化从 $ua->agent 属性 在请求处理到网络层之前,用同样的方式, 一个 “form" header 被初始化从
$ua->from attribute.
对于所有的响应,该library 添加一个header 叫做 "Client-Date", 这个header 保存从应用程序接收响应的时间。 head的格式和语义是相同的,服务器创建"Date" header的时间。
你可能回遇到其他的 "Client-XXX" headers, 他们都是有内部库生成的,而不是从服务器接收的。
HTTP Requests
HTTP requests are just handed off to an HTTP server and it decides what happens. Few servers implement methods beside the usual "GET", "HEAD", "POST" and "PUT", but CGI-scripts may implement any method they
like.
If the server is not available then the library will generate an internal error response.
The library automatically adds a "Host" and a "Content-Length" header to the HTTP request before it is sent over the network.
For a GET request you might want to add a "If-Modified-Since" or "If-None-Match" header to make the request conditional.
For a POST request you should add the "Content-Type" header. When you try to emulate HTML <FORM> handling you should usually let the value of the "Content-Type" header be "application/x-www-form-urlencoded".
See lwpcook for examples of this.
The libwww-perl HTTP implementation currently support the HTTP/1.1 and HTTP/1.0 protocol.
The library allows you to access proxy server through HTTP. This means that you can set up the library to forward all types of request through the HTTP protocol module. See LWP::UserAgent for documentation of
this.
HTTP 请求被移交给HTTP server ,一些服务器的实现方法,除了通常的 GET,HEAD,POST 和PUT ，但CGI脚本可以实现任意的方法
如果服务器不可用,则库将产生内部错误响应
library 自动的增加一个 ”Host" 和一个 “Content-Length" header 到HTTP 请求在他发送到网络前
对于一个GET请求 你需要增加一个 "If-Modified-Since" or "If-None-Match" header 使请求有条件。
对于一个POST 请求 你需要增加 "Content-Type" header。
HTTPS Requests
HTTPS requests are HTTP requests over an encrypted network connection using the SSL protocol developed by Netscape. Everything about HTTP requests above also apply to HTTPS requests. In addition the library
will add the headers "Client-SSL-Cipher", "Client-SSL-Cert-Subject" and "Client-SSL-Cert-Issuer" to the response. These headers denote the encryption method used and the name of the server owner.
The request can contain the header "If-SSL-Cert-Subject" in order to make the request conditional on the content of the server certificate. If the certificate subject does not match, no request is sent to the
server and an internally generated error response is returned. The value of the "If-SSL-Cert-Subject" header is interpreted as a Perl regular expression.
FTP Requests
The library currently supports GET, HEAD and PUT requests. GET retrieves a file or a directory listing from an FTP server. PUT stores a file on a ftp server.
You can specify a ftp account for servers that want this in addition to user name and password. This is specified by including an "Account" header in the request.
User name/password can be specified using basic authorization or be encoded in the URL. Failed logins return an UNAUTHORIZED response with "WWW-Authenticate: Basic" and can be treated like basic authorization
for HTTP.
The library supports ftp ASCII transfer mode by specifying the "type=a" parameter in the URL. It also supports transfer of ranges for FTP transfers using the "Range" header.
Directory listings are by default returned unprocessed (as returned from the ftp server) with the content media type reported to be "text/ftp-dir-listing". The "File::Listing" module provides methods for parsing
of these directory listing.
The ftp module is also able to convert directory listings to HTML and this can be requested via the standard HTTP content negotiation mechanisms (add an "Accept: text/html" header in the request if you want
this).
For normal file retrievals, the "Content-Type" is guessed based on the file name suffix. See LWP::MediaTypes.
The "If-Modified-Since" request header works for servers that implement the MDTM command. It will probably not work for directory listings though.
Example:
$req = HTTP::Request->new(GET => 'ftp://me:[email protected]/');
$req->header(Accept => "text/html, */*;q=0.1");
News Requests
Access to the USENET News system is implemented through the NNTP protocol. The name of the news server is obtained from the NNTP_SERVER environment variable and defaults to "news". It is not possible to specify
the hostname of the NNTP server in news: URLs.
The library supports GET and HEAD to retrieve news articles through the NNTP protocol. You can also post articles to newsgroups by using (surprise!) the POST method.
GET on newsgroups is not implemented yet.
Examples:
$req = HTTP::Request->new(GET => 'news:[email protected]');
$req = HTTP::Request->new(POST => 'news:comp.lang.perl.test');
$req->header(Subject => 'This is a test',
From => '[email protected]');
$req->content(<<EOT);
This is the content of the message that we are sending to
the world.
EOT
Gopher Request
The library supports the GET and HEAD methods for gopher requests. All request header values are ignored. HEAD cheats and returns a response without even talking to server.
Gopher menus are always converted to HTML.
The response "Content-Type" is generated from the document type encoded (as the first letter) in the request URL path itself.
Example:
$req = HTTP::Request->new(GET => 'gopher://gopher.sn.no/');
File Request
The library supports GET and HEAD methods for file requests. The "If-Modified-Since" header is supported. All other headers are ignored. The host component of the file URL must be empty or set to "localhost".
Any other host value will be treated as an error.
Directories are always converted to an HTML document. For normal files, the "Content-Type" and "Content-Encoding" in the response are guessed based on the file suffix.
Example:
$req = HTTP::Request->new(GET => 'file:/etc/passwd');
Mailto Request
You can send (aka "POST") mail messages using the library. All headers specified for the request are passed on to the mail system. The "To" header is initialized from the mail address in the URL.
Example:
$req = HTTP::Request->new(POST => 'mailto:[email protected]');
$req->header(Subject => "subscribe");
$req->content("Please subscribe me to the libwww-perl mailing list!\n");
CPAN Requests
URLs with scheme "cpan:" are redirected to the a suitable CPAN mirror. If you have your own local mirror of CPAN you might tell LWP to use it for "cpan:" URLs by an assignment like this:
$LWP::Protocol::cpan::CPAN = "file:/local/CPAN/";
Suitable CPAN mirrors are also picked up from the configuration for the CPAN.pm, so if you have used that module a suitable mirror should be picked automatically. If neither of these apply, then a redirect to
the generic CPAN http location is issued.
Example request to download the newest perl:
$req = HTTP::Request->new(GET => "cpan:src/latest.tar.gz");
OVERVIEW OF CLASSES AND PACKAGES
This table should give you a quick overview of the classes provided by the library. Indentation shows class inheritance.
LWP::MemberMixin -- Access to member variables of Perl5 classes
LWP::UserAgent -- WWW user agent class
LWP::RobotUA -- When developing a robot applications
LWP::Protocol -- Interface to various protocol schemes
LWP::Protocol::http -- http:// access
LWP::Protocol::file -- file:// access
LWP::Protocol::ftp -- ftp:// access
...
LWP::Authen::Basic -- Handle 401 and 407 responses
LWP::Authen::Digest
HTTP::Headers -- MIME/RFC822 style header (used by HTTP::Message)
HTTP::Message -- HTTP style message
HTTP::Request -- HTTP request
HTTP::Response -- HTTP response
HTTP::Daemon -- A HTTP server class
WWW::RobotRules -- Parse robots.txt files
WWW::RobotRules::AnyDBM_File -- Persistent RobotRules
Net::HTTP -- Low level HTTP client
The following modules provide various functions and definitions.
LWP -- This file. Library version number and documentation.
LWP::MediaTypes -- MIME types configuration (text/html etc.)
LWP::Simple -- Simplified procedural interface for common functions
HTTP::Status -- HTTP status code (200 OK etc)
HTTP::Date -- Date parsing module for HTTP date formats
HTTP::Negotiate -- HTTP content negotiation calculation
File::Listing -- Parse directory listings
HTML::Form -- Processing for <form>s in HTML documents
MORE DOCUMENTATION
All modules contain detailed information on the interfaces they provide. The lwpcook manpage is the libwww-perl cookbook that contain examples of typical usage of the library. You might want to take a look at
how the scripts "lwp-request", "lwp-rget" and "lwp-mirror" are implemented.
ENVIRONMENT
The following environment variables are used by LWP:
HOME
The "LWP::MediaTypes" functions will look for the .media.types and .mime.types files relative to you home directory.
http_proxy
ftp_proxy
xxx_proxy
no_proxy
These environment variables can be set to enable communication through a proxy server. See the description of the "env_proxy" method in LWP::UserAgent.
PERL_LWP_USE_HTTP_10
Enable the old HTTP/1.0 protocol driver instead of the new HTTP/1.1 driver. You might want to set this to a TRUE value if you discover that your old LWP applications fails after you installed LWP-5.60 or
better.
PERL_HTTP_URI_CLASS
Used to decide what URI objects to instantiate. The default is "URI". You might want to set it to "URI::URL" for compatibility with old times.
AUTHORS
LWP was made possible by contributions from Adam Newby, Albert Dvornik, Alexandre Duret-Lutz, Andreas Gustafsson, Andreas KA~Xnig, Andrew Pimlott, Andy Lester, Ben Coleman, Benjamin Low, Ben Low, Ben Tilly, Blair
Zajac, Bob Dalgleish, BooK, Brad Hughes, Brian J. Murrell, Brian McCauley, Charles C. Fu, Charles Lane, Chris Nandor, Christian Gilmore, Chris W. Unger, Craig Macdonald, Dale Couch, Dan Kubb, Dave Dunkin, Dave W.
Smith, David Coppit, David Dick, David D. Kilzer, Doug MacEachern, Edward Avis, erik, Gary Shea, Gisle Aas, Graham Barr, Gurusamy Sarathy, Hans de Graaff, Harald Joerg, Harry Bochner, Hugo, Ilya Zakharevich,
INOUE Yoshinari, Ivan Panchenko, Jack Shirazi, James Tillman, Jan Dubois, Jared Rhine, Jim Stern, Joao Lopes, John Klar, Johnny Lee, Josh Kronengold, Josh Rai, Joshua Chamas, Joshua Hoblitt, Kartik Subbarao,
Keiichiro Nagano, Ken Williams, KONISHI Katsuhiro, Lee T Lindley, Liam Quinn, Marc Hedlund, Marc Langheinrich, Mark D. Anderson, Marko Asplund, Mark Stosberg, Markus B KrA~Xger, Markus Laker, Martijn Koster,
Martin Thurn, Matthew Eldridge, Matthew.van.Eerde, Matt Sergeant, Michael A. Chase, Michael Quaranta, Michael Thompson, Mike Schilli, Moshe Kaminsky, Nathan Torkington, Nicolai Langfeldt, Norton Allen, Olly
Betts, Paul J. Schinder, peterm, Philip GuentherDaniel Buenzli, Pon Hwa Lin, Radoslaw Zielinski, Radu Greab, Randal L. Schwartz, Richard Chen, Robin Barker, Roy Fielding, Sander van Zoest, Sean M. Burke,
shildreth, Slaven Rezic, Steve A Fink, Steve Hay, Steven Butler, Steve_Kilbane, Takanori Ugai, Thomas Lotterer, Tim Bunce, Tom Hughes, Tony Finch, Ville SkyttA~X, Ward Vandewege, William York, Yale Huang, and
Yitzchak Scott-Thoennes.
LWP owes a lot in motivation, design, and code, to the libwww-perl library for Perl4 by Roy Fielding, which included work from Alberto Accomazzi, James Casey, Brooks Cutter, Martijn Koster, Oscar Nierstrasz, Mel
Melchner, Gertjan van Oosten, Jared Rhine, Jack Shirazi, Gene Spafford, Marc VanHeyningen, Steven E. Brenner, Marion Hakanson, Waldemar Kebsch, Tony Sanders, and Larry Wall; see the libwww-perl-0.40 library for
details.
COPYRIGHT
Copyright 1995-2009, Gisle Aas
Copyright 1995, Martijn Koster
This library is free software; you can redistribute it and/or modify it under the same terms as Perl itself.
AVAILABILITY
The latest version of this library is likely to be available from CPAN as well as:
http://gitorious.org/projects/libwww-perl
The best place to discuss this code is on the <[email protected]> mailing list.
perl v5.10.1 2009-10-07 LWP(3)
