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.

.PP
For example, here's how to send some more Netscape-like headers, in case
you're dealing with a site that would otherwise reject your request:
.PP
.Vb 6
\&  my @ns_headers = (
\&   \*(AqUser\-Agent\*(Aq => \*(AqMozilla/4.76 [en] (Win98; U)\*(Aq,
\&   \*(AqAccept\*(Aq => \*(Aqimage/gif, image/x\-xbitmap, image/jpeg, image/pjpeg, image/png, */*\*(Aq,
\&   \*(AqAccept\-Charset\*(Aq => \*(Aqiso\-8859\-1,*,utf\-8\*(Aq,
\&   \*(AqAccept\-Language\*(Aq => \*(Aqen\-US\*(Aq,
\&  );
\&
\&  ...
\&  
\&  $response = $browser\->get($url, @ns_headers);
.Ve
.PP
If you weren't reusing that array, you could just go ahead and do this:
.PP
.Vb 6
\&  $response = $browser\->get($url,
\&   \*(AqUser\-Agent\*(Aq => \*(AqMozilla/4.76 [en] (Win98; U)\*(Aq,
\&   \*(AqAccept\*(Aq => \*(Aqimage/gif, image/x\-xbitmap, image/jpeg, image/pjpeg, image/png, */*\*(Aq,
\&   \*(AqAccept\-Charset\*(Aq => \*(Aqiso\-8859\-1,*,utf\-8\*(Aq,
\&   \*(AqAccept\-Language\*(Aq => \*(Aqen\-US\*(Aq,
\&  );
.Ve
.PP
If you were only ever changing the 'User\-Agent' line, you could just change
the \f(CW$browser\fR object's default line from \*(L"libwww\-perl/5.65\*(R" (or the like)
to whatever you like, using the LWP::UserAgent \f(CW\*(C`agent\*(C'\fR method:
.PP
.Vb 1
\&   $browser\->agent(\*(AqMozilla/4.76 [en] (Win98; U)\*(Aq);
.Ve
.Sh "Enabling Cookies"
.IX Subsection "Enabling Cookies"
A default LWP::UserAgent object acts like a browser with its cookies
support turned off. There are various ways of turning it on, by setting
its \f(CW\*(C`cookie_jar\*(C'\fR attribute. A \*(L"cookie jar\*(R" is an object representing
a little database of all
the \s-1HTTP\s0 cookies that a browser can know about. It can correspond to a
file on disk (the way Netscape uses its \fIcookies.txt\fR file), or it can
be just an in-memory object that starts out empty, and whose collection of
cookies will disappear once the program is finished running.
.PP
To give a browser an in-memory empty cookie jar, you set its \f(CW\*(C`cookie_jar\*(C'\fR
attribute like so:
.PP
.Vb 1
\&  $browser\->cookie_jar({});
.Ve
.PP
To give it a copy that will be read from a file on disk, and will be saved
to it when the program is finished running, set the \f(CW\*(C`cookie_jar\*(C'\fR attribute
like this:
.PP
.Vb 7
\&  use HTTP::Cookies;
\&  $browser\->cookie_jar( HTTP::Cookies\->new(
\&    \*(Aqfile\*(Aq => \*(Aq/some/where/cookies.lwp\*(Aq,
\&        # where to read/write cookies
\&    \*(Aqautosave\*(Aq => 1,
\&        # save it to disk when done
\&  ));
.Ve
.PP
That file will be an LWP-specific format. If you want to be access the
cookies in your Netscape cookies file, you can use the
HTTP::Cookies::Netscape class:
.PP
.Vb 2
\&  use HTTP::Cookies;
\&    # yes, loads HTTP::Cookies::Netscape too
\&  
\&  $browser\->cookie_jar( HTTP::Cookies::Netscape\->new(
\&    \*(Aqfile\*(Aq => \*(Aqc:/Program Files/Netscape/Users/DIR\-NAME\-HERE/cookies.txt\*(Aq,
\&        # where to read cookies
\&  ));
.Ve
.PP
You could add an \f(CW\*(C`\*(Aqautosave\*(Aq => 1\*(C'\fR line as further above, but at
time of writing, it's uncertain whether Netscape might discard some of
the cookies you could be writing back to disk.
.Sh "Posting Form Data"
.IX Subsection "Posting Form Data"
Many \s-1HTML\s0 forms send data to their server using an \s-1HTTP\s0 \s-1POST\s0 request, which
you can send with this syntax:
.PP
.Vb 7
\& $response = $browser\->post( $url,
\&   [
\&     formkey1 => value1, 
\&     formkey2 => value2, 
\&     ...
\&   ],
\& );
.Ve
.PP
Or if you need to send \s-1HTTP\s0 headers:
.PP
.Vb 9
\& $response = $browser\->post( $url,
\&   [
\&     formkey1 => value1, 
\&     formkey2 => value2, 
\&     ...
\&   ],
\&   headerkey1 => value1, 
\&   headerkey2 => value2, 
\& );
.Ve
.PP
For example, the following program makes a search request to AltaVista
(by sending some form data via an \s-1HTTP\s0 \s-1POST\s0 request), and extracts from
the \s-1HTML\s0 the report of the number of matches:
.PP
.Vb 4
\&  use strict;
\&  use warnings;
\&  use LWP 5.64;
\&  my $browser = LWP::UserAgent\->new;
\&  
\&  my $word = \*(Aqtarragon\*(Aq;
\&  
\&  my $url = \*(Aqhttp://www.altavista.com/sites/search/web\*(Aq;
\&  my $response = $browser\->post( $url,
\&    [ \*(Aqq\*(Aq => $word,  # the Altavista query string
\&      \*(Aqpg\*(Aq => \*(Aqq\*(Aq, \*(Aqavkw\*(Aq => \*(Aqtgz\*(Aq, \*(Aqkl\*(Aq => \*(AqXX\*(Aq,
\&    ]
\&  );
\&  die "$url error: ", $response\->status_line
\&   unless $response\->is_success;
\&  die "Weird content type at $url \-\- ", $response\->content_type
\&   unless $response\->content_type eq \*(Aqtext/html\*(Aq;
\&
\&  if( $response\->decoded_content =~ m{AltaVista found ([0\-9,]+) results} ) {
\&    # The substring will be like "AltaVista found 2,345 results"
\&    print "$word: $1\en";
\&  }
\&  else {
\&    print "Couldn\*(Aqt find the match\-string in the response\en";
\&  }
.Ve
.Sh "Sending \s-1GET\s0 Form Data"
.IX Subsection "Sending GET Form Data"
Some \s-1HTML\s0 forms convey their form data not by sending the data
in an \s-1HTTP\s0 \s-1POST\s0 request, but by making a normal \s-1GET\s0 request with
the data stuck on the end of the \s-1URL\s0.  For example, if you went to
\&\f(CW\*(C`imdb.com\*(C'\fR and ran a search on \*(L"Blade Runner\*(R", the \s-1URL\s0 you'd see
in your browser window would be:
.PP
.Vb 1
\&  http://us.imdb.com/Tsearch?title=Blade%20Runner&restrict=Movies+and+TV
.Ve
.PP
To run the same search with \s-1LWP\s0, you'd use this idiom, which involves
the \s-1URI\s0 class:
.PP
.Vb 3
\&  use URI;
\&  my $url = URI\->new( \*(Aqhttp://us.imdb.com/Tsearch\*(Aq );
\&    # makes an object representing the URL
\&  
\&  $url\->query_form(  # And here the form data pairs:
\&    \*(Aqtitle\*(Aq    => \*(AqBlade Runner\*(Aq,
\&    \*(Aqrestrict\*(Aq => \*(AqMovies and TV\*(Aq,
\&  );
\&  
\&  my $response = $browser\->get($url);
.Ve
.PP
See chapter 5 of \fIPerl & \s-1LWP\s0\fR for a longer discussion of \s-1HTML\s0 forms
and of form data, and chapters 6 through 9 for a longer discussion of
extracting data from \s-1HTML\s0.
.Sh "Absolutizing URLs"
.IX Subsection "Absolutizing URLs"
The \s-1URI\s0 class that we just mentioned above provides all sorts of methods
for accessing and modifying parts of URLs (such as asking sort of \s-1URL\s0 it
is with \f(CW\*(C`$url\->scheme\*(C'\fR, and asking what host it refers to with \f(CW\*(C`$url\->host\*(C'\fR, and so on, as described in the docs for the \s-1URI\s0
class.  However, the methods of most immediate interest
are the \f(CW\*(C`query_form\*(C'\fR method seen above, and now the \f(CW\*(C`new_abs\*(C'\fR method
for taking a probably-relative \s-1URL\s0 string (like \*(L"../foo.html\*(R") and getting
back an absolute \s-1URL\s0 (like \*(L"http://www.perl.com/stuff/foo.html\*(R"), as
shown here:
.PP
.Vb 2
\&  use URI;
\&  $abs = URI\->new_abs($maybe_relative, $base);
.Ve
.PP
For example, consider this program that matches URLs in the \s-1HTML\s0
list of new modules in \s-1CPAN:\s0
.PP
.Vb 4
\&  use strict;
\&  use warnings;
\&  use LWP;
\&  my $browser = LWP::UserAgent\->new;
\&  
\&  my $url = \*(Aqhttp://www.cpan.org/RECENT.html\*(Aq;
\&  my $response = $browser\->get($url);
\&  die "Can\*(Aqt get $url \-\- ", $response\->status_line
\&   unless $response\->is_success;
\&  
\&  my $html = $response\->decoded_content;
\&  while( $html =~ m/<A HREF=\e"(.*?)\e"/g ) {
\&    print "$1\en";
\&  }
.Ve
.PP
When run, it emits output that starts out something like this:
.PP
.Vb 7
\&  MIRRORING.FROM
\&  RECENT
\&  RECENT.html
\&  authors/00whois.html
\&  authors/01mailrc.txt.gz
\&  authors/id/A/AA/AASSAD/CHECKSUMS
\&  ...
.Ve
.PP
However, if you actually want to have those be absolute URLs, you
can use the \s-1URI\s0 module's \f(CW\*(C`new_abs\*(C'\fR method, by changing the \f(CW\*(C`while\*(C'\fR
loop to this:
.PP
.Vb 3
\&  while( $html =~ m/<A HREF=\e"(.*?)\e"/g ) {
\&    print URI\->new_abs( $1, $response\->base ) ,"\en";
\&  }
.Ve
.PP
(The \f(CW\*(C`$response\->base\*(C'\fR method from HTTP::Message
is for returning what \s-1URL\s0
should be used for resolving relative URLs \*(-- it's usually just
the same as the \s-1URL\s0 that you requested.)
.PP
That program then emits nicely absolute URLs:
.PP
.Vb 7
\&  http://www.cpan.org/MIRRORING.FROM
\&  http://www.cpan.org/RECENT
\&  http://www.cpan.org/RECENT.html
\&  http://www.cpan.org/authors/00whois.html
\&  http://www.cpan.org/authors/01mailrc.txt.gz
\&  http://www.cpan.org/authors/id/A/AA/AASSAD/CHECKSUMS
\&  ...
.Ve
.PP
See chapter 4 of \fIPerl & \s-1LWP\s0\fR for a longer discussion of \s-1URI\s0 objects.
.PP
Of course, using a regexp to match hrefs is a bit simplistic, and for
more robust programs, you'll probably want to use an HTML-parsing module
like HTML::LinkExtor or HTML::TokeParser or even maybe
HTML::TreeBuilder.
.Sh "Other Browser Attributes"
.IX Subsection "Other Browser Attributes"
LWP::UserAgent objects have many attributes for controlling how they
work.  Here are a few notable ones:
.IP "\(bu" 4
\&\f(CW\*(C`$browser\->timeout(15);\*(C'\fR
.Sp
This sets this browser object to give up on requests that don't answer
within 15 seconds.
.IP "\(bu" 4
\&\f(CW\*(C`$browser\->protocols_allowed( [ \*(Aqhttp\*(Aq, \*(Aqgopher\*(Aq] );\*(C'\fR
.Sp
This sets this browser object to not speak any protocols other than \s-1HTTP\s0
and gopher. If it tries accessing any other kind of \s-1URL\s0 (like an \*(L"ftp:\*(R"
or \*(L"mailto:\*(R" or \*(L"news:\*(R" \s-1URL\s0), then it won't actually try connecting, but
instead will immediately return an error code 500, with a message like
\&\*(L"Access to 'ftp' URIs has been disabled\*(R".
.IP "\(bu" 4
\&\f(CW\*(C`use LWP::ConnCache; $browser\->conn_cache(LWP::ConnCache\->new());\*(C'\fR
.Sp
This tells the browser object to try using the \s-1HTTP/1\s0.1 \*(L"Keep-Alive\*(R"
feature, which speeds up requests by reusing the same socket connection
for multiple requests to the same server.
.IP "\(bu" 4
\&\f(CW\*(C`$browser\->agent( \*(AqSomeName/1.23 (more info here maybe)\*(Aq )\*(C'\fR
.Sp
This changes how the browser object will identify itself in
the default \*(L"User-Agent\*(R" line is its \s-1HTTP\s0 requests.  By default,
it'll send "libwww\-perl/\fIversionnumber\fR\*(L", like
\&\*(R"libwww\-perl/5.65".  You can change that to something more descriptive
like this:
.Sp
.Vb 1
\&  $browser\->agent( \*(AqSomeName/3.14 ([e-mail])\*(Aq );
.Ve
.Sp