lwptut.3

视频监控网络部分的协议ddns,的模块的实现代码,请大家大胆指正.

Or if need be, you can go in disguise, like this:
.Sp
.Vb 1
\&  $browser\->agent( \*(AqMozilla/4.0 (compatible; MSIE 5.12; Mac_PowerPC)\*(Aq );
.Ve
.IP "\(bu" 4
\&\f(CW\*(C`push @{ $ua\->requests_redirectable }, \*(AqPOST\*(Aq;\*(C'\fR
.Sp
This tells this browser to obey redirection responses to \s-1POST\s0 requests
(like most modern interactive browsers), even though the \s-1HTTP\s0 \s-1RFC\s0 says
that should not normally be done.
.PP
For more options and information, see the full documentation for
LWP::UserAgent.
.Sh "Writing Polite Robots"
.IX Subsection "Writing Polite Robots"
If you want to make sure that your LWP-based program respects \fIrobots.txt\fR
files and doesn't make too many requests too fast, you can use the LWP::RobotUA
class instead of the LWP::UserAgent class.
.PP
LWP::RobotUA class is just like LWP::UserAgent, and you can use it like so:
.PP
.Vb 3
\&  use LWP::RobotUA;
\&  my $browser = LWP::RobotUA\->new(\*(AqYourSuperBot/1.34\*(Aq, \*([e-mail]\*(Aq);
\&    # Your bot\*(Aqs name and your email address
\&
\&  my $response = $browser\->get($url);
.Ve
.PP
But HTTP::RobotUA adds these features:
.IP "\(bu" 4
If the \fIrobots.txt\fR on \f(CW$url\fR's server forbids you from accessing
\&\f(CW$url\fR, then the \f(CW$browser\fR object (assuming it's of class LWP::RobotUA)
won't actually request it, but instead will give you back (in \f(CW$response\fR) a 403 error
with a message \*(L"Forbidden by robots.txt\*(R".  That is, if you have this line:
.Sp
.Vb 2
\&  die "$url \-\- ", $response\->status_line, "\enAborted"
\&   unless $response\->is_success;
.Ve
.Sp
then the program would die with an error message like this:
.Sp
.Vb 2
\&  http://whatever.site.int/pith/x.html \-\- 403 Forbidden by robots.txt
\&  Aborted at whateverprogram.pl line 1234
.Ve
.IP "\(bu" 4
If this \f(CW$browser\fR object sees that the last time it talked to
\&\f(CW$url\fR's server was too recently, then it will pause (via \f(CW\*(C`sleep\*(C'\fR) to
avoid making too many requests too often. How long it will pause for, is
by default one minute \*(-- but you can control it with the \f(CW\*(C`$browser\->delay( \f(CIminutes\f(CW )\*(C'\fR attribute.
.Sp
For example, this code:
.Sp
.Vb 1
\&  $browser\->delay( 7/60 );
.Ve
.Sp
\&...means that this browser will pause when it needs to avoid talking to
any given server more than once every 7 seconds.
.PP
For more options and information, see the full documentation for
LWP::RobotUA.
.Sh "Using Proxies"
.IX Subsection "Using Proxies"
In some cases, you will want to (or will have to) use proxies for
accessing certain sites and/or using certain protocols. This is most
commonly the case when your \s-1LWP\s0 program is running (or could be running)
on a machine that is behind a firewall.
.PP
To make a browser object use proxies that are defined in the usual
environment variables (\f(CW\*(C`HTTP_PROXY\*(C'\fR, etc.), just call the \f(CW\*(C`env_proxy\*(C'\fR
on a user-agent object before you go making any requests on it.
Specifically:
.PP
.Vb 2
\&  use LWP::UserAgent;
\&  my $browser = LWP::UserAgent\->new;
\&  
\&  # And before you go making any requests:
\&  $browser\->env_proxy;
.Ve
.PP
For more information on proxy parameters, see the LWP::UserAgent
documentation, specifically the \f(CW\*(C`proxy\*(C'\fR, \f(CW\*(C`env_proxy\*(C'\fR,
and \f(CW\*(C`no_proxy\*(C'\fR methods.
.Sh "\s-1HTTP\s0 Authentication"
.IX Subsection "HTTP Authentication"
Many web sites restrict access to documents by using \*(L"\s-1HTTP\s0
Authentication\*(R". This isn't just any form of \*(L"enter your password\*(R"
restriction, but is a specific mechanism where the \s-1HTTP\s0 server sends the
browser an \s-1HTTP\s0 code that says \*(L"That document is part of a protected
\&'realm', and you can access it only if you re-request it and add some
special authorization headers to your request\*(R".
.PP
For example, the Unicode.org admins stop email-harvesting bots from
harvesting the contents of their mailing list archives, by protecting
them with \s-1HTTP\s0 Authentication, and then publicly stating the username
and password (at \f(CW\*(C`http://www.unicode.org/mail\-arch/\*(C'\fR) \*(-- namely
username \*(L"unicode-ml\*(R" and password \*(L"unicode\*(R".
.PP
For example, consider this \s-1URL\s0, which is part of the protected
area of the web site:
.PP
.Vb 1
\&  http://www.unicode.org/mail\-arch/unicode\-ml/y2002\-m08/0067.html
.Ve
.PP
If you access that with a browser, you'll get a prompt
like 
\&\*(L"Enter username and password for 'Unicode\-MailList\-Archives' at server
\&'www.unicode.org'\*(R".
.PP
In \s-1LWP\s0, if you just request that \s-1URL\s0, like this:
.PP
.Vb 2
\&  use LWP;
\&  my $browser = LWP::UserAgent\->new;
\&
\&  my $url =
\&   \*(Aqhttp://www.unicode.org/mail\-arch/unicode\-ml/y2002\-m08/0067.html\*(Aq;
\&  my $response = $browser\->get($url);
\&
\&  die "Error: ", $response\->header(\*(AqWWW\-Authenticate\*(Aq) || \*(AqError accessing\*(Aq,
\&    #  (\*(AqWWW\-Authenticate\*(Aq is the realm\-name)
\&    "\en ", $response\->status_line, "\en at $url\en Aborting"
\&   unless $response\->is_success;
.Ve
.PP
Then you'll get this error:
.PP
.Vb 4
\&  Error: Basic realm="Unicode\-MailList\-Archives"
\&   401 Authorization Required
\&   at http://www.unicode.org/mail\-arch/unicode\-ml/y2002\-m08/0067.html
\&   Aborting at auth1.pl line 9.  [or wherever]
.Ve
.PP
\&...because the \f(CW$browser\fR doesn't know any the username and password
for that realm (\*(L"Unicode-MailList-Archives\*(R") at that host
(\*(L"www.unicode.org\*(R").  The simplest way to let the browser know about this
is to use the \f(CW\*(C`credentials\*(C'\fR method to let it know about a username and
password that it can try using for that realm at that host.  The syntax is:
.PP
.Vb 5
\&  $browser\->credentials(
\&    \*(Aqservername:portnumber\*(Aq,
\&    \*(Aqrealm\-name\*(Aq,
\&   \*(Aqusername\*(Aq => \*(Aqpassword\*(Aq
\&  );
.Ve
.PP
In most cases, the port number is 80, the default \s-1TCP/IP\s0 port for \s-1HTTP\s0; and
you usually call the \f(CW\*(C`credentials\*(C'\fR method before you make any requests.
For example:
.PP
.Vb 5
\&  $browser\->credentials(
\&    \*(Aqreports.mybazouki.com:80\*(Aq,
\&    \*(Aqweb_server_usage_reports\*(Aq,
\&    \*(Aqplinky\*(Aq => \*(Aqbanjo123\*(Aq
\&  );
.Ve
.PP
So if we add the following to the program above, right after the \f(CW\*(C`$browser = LWP::UserAgent\->new;\*(C'\fR line...
.PP
.Vb 5
\&  $browser\->credentials(  # add this to our $browser \*(Aqs "key ring"
\&    \*(Aqwww.unicode.org:80\*(Aq,
\&    \*(AqUnicode\-MailList\-Archives\*(Aq,
\&    \*(Aqunicode\-ml\*(Aq => \*(Aqunicode\*(Aq
\&  );
.Ve
.PP
\&...then when we run it, the request succeeds, instead of causing the
\&\f(CW\*(C`die\*(C'\fR to be called.
.Sh "Accessing \s-1HTTPS\s0 URLs"
.IX Subsection "Accessing HTTPS URLs"
When you access an \s-1HTTPS\s0 \s-1URL\s0, it'll work for you just like an \s-1HTTP\s0 \s-1URL\s0
would \*(-- if your \s-1LWP\s0 installation has \s-1HTTPS\s0 support (via an appropriate
Secure Sockets Layer library).  For example:
.PP
.Vb 8
\&  use LWP;
\&  my $url = \*(Aqhttps://www.paypal.com/\*(Aq;   # Yes, HTTPS!
\&  my $browser = LWP::UserAgent\->new;
\&  my $response = $browser\->get($url);
\&  die "Error at $url\en ", $response\->status_line, "\en Aborting"
\&   unless $response\->is_success;
\&  print "Whee, it worked!  I got that ",
\&   $response\->content_type, " document!\en";
.Ve
.PP
If your \s-1LWP\s0 installation doesn't have \s-1HTTPS\s0 support set up, then the
response will be unsuccessful, and you'll get this error message:
.PP
.Vb 3
\&  Error at https://www.paypal.com/
\&   501 Protocol scheme \*(Aqhttps\*(Aq is not supported
\&   Aborting at paypal.pl line 7.   [or whatever program and line]
.Ve
.PP
If your \s-1LWP\s0 installation \fIdoes\fR have \s-1HTTPS\s0 support installed, then the
response should be successful, and you should be able to consult
\&\f(CW$response\fR just like with any normal \s-1HTTP\s0 response.
.PP
For information about installing \s-1HTTPS\s0 support for your \s-1LWP\s0
installation, see the helpful \fI\s-1README\s0.SSL\fR file that comes in the
libwww-perl distribution.
.Sh "Getting Large Documents"
.IX Subsection "Getting Large Documents"
When you're requesting a large (or at least potentially large) document,
a problem with the normal way of using the request methods (like \f(CW\*(C`$response = $browser\->get($url)\*(C'\fR) is that the response object in
memory will have to hold the whole document \*(-- \fIin memory\fR. If the
response is a thirty megabyte file, this is likely to be quite an
imposition on this process's memory usage.
.PP
A notable alternative is to have \s-1LWP\s0 save the content to a file on disk,
instead of saving it up in memory.  This is the syntax to use:
.PP
.Vb 3
\&  $response = $ua\->get($url,
\&                         \*(Aq:content_file\*(Aq => $filespec,
\&                      );
.Ve
.PP
For example,
.PP
.Vb 3
\&  $response = $ua\->get(\*(Aqhttp://search.cpan.org/\*(Aq,
\&                         \*(Aq:content_file\*(Aq => \*(Aq/tmp/sco.html\*(Aq
\&                      );
.Ve
.PP
When you use this \f(CW\*(C`:content_file\*(C'\fR option, the \f(CW$response\fR will have
all the normal header lines, but \f(CW\*(C`$response\->content\*(C'\fR will be
empty.
.PP
Note that this \*(L":content_file\*(R" option isn't supported under older
versions of \s-1LWP\s0, so you should consider adding \f(CW\*(C`use LWP 5.66;\*(C'\fR to check
the \s-1LWP\s0 version, if you think your program might run on systems with
older versions.
.PP
If you need to be compatible with older \s-1LWP\s0 versions, then use
this syntax, which does the same thing:
.PP
.Vb 2
\&  use HTTP::Request::Common;
\&  $response = $ua\->request( GET($url), $filespec );
.Ve
.SH "SEE ALSO"
.IX Header "SEE ALSO"
Remember, this article is just the most rudimentary introduction to
\&\s-1LWP\s0 \*(-- to learn more about \s-1LWP\s0 and LWP-related tasks, you really
must read from the following:
.IP "\(bu" 4
LWP::Simple \*(-- simple functions for getting/heading/mirroring URLs
.IP "\(bu" 4
\&\s-1LWP\s0 \*(-- overview of the libwww-perl modules
.IP "\(bu" 4
LWP::UserAgent \*(-- the class for objects that represent \*(L"virtual browsers\*(R"
.IP "\(bu" 4
HTTP::Response \*(-- the class for objects that represent the response to
a \s-1LWP\s0 response, as in \f(CW\*(C`$response = $browser\->get(...)\*(C'\fR
.IP "\(bu" 4
HTTP::Message and HTTP::Headers \*(-- classes that provide more methods
to HTTP::Response.
.IP "\(bu" 4
\&\s-1URI\s0 \*(-- class for objects that represent absolute or relative URLs
.IP "\(bu" 4
URI::Escape \*(-- functions for URL-escaping and URL-unescaping strings
(like turning \*(L"this & that\*(R" to and from \*(L"this%20%26%20that\*(R").
.IP "\(bu" 4
HTML::Entities \*(-- functions for HTML-escaping and HTML-unescaping strings
(like turning \*(L"C. & E. Bronte\*:\*(R" to and from \*(L"C. & E. Brontë\*(R")
.IP "\(bu" 4
HTML::TokeParser and HTML::TreeBuilder \*(-- classes for parsing \s-1HTML\s0
.IP "\(bu" 4
HTML::LinkExtor \*(-- class for finding links in \s-1HTML\s0 documents
.IP "\(bu" 4
The book \fIPerl & \s-1LWP\s0\fR by Sean M. Burke.  O'Reilly & Associates, 2002.
\&\s-1ISBN:\s0 0\-596\-00178\-9.  \f(CW\*(C`http://www.oreilly.com/catalog/perllwp/\*(C'\fR
.SH "COPYRIGHT"
.IX Header "COPYRIGHT"
Copyright 2002, Sean M. Burke.  You can redistribute this document and/or
modify it, but only under the same terms as Perl itself.
.SH "AUTHOR"
.IX Header "AUTHOR"
Sean M. Burke \f(CW\*(C`[e-mail]\*(C'\fR