perlfaq9.1

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.

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.\" ========================================================================
.\"
.IX Title "PERLFAQ9 1"
.TH PERLFAQ9 1 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
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.SH "NAME"
perlfaq9 \- Networking ($Revision: 8539 $)
.SH "DESCRIPTION"
.IX Header "DESCRIPTION"
This section deals with questions related to networking, the internet,
and a few on the web.
.Sh "What is the correct form of response from a \s-1CGI\s0 script?"
.IX Subsection "What is the correct form of response from a CGI script?"
(Alan Flavell <[e-mail]> answers...)
.PP
The Common Gateway Interface (\s-1CGI\s0) specifies a software interface between
a program (\*(L"\s-1CGI\s0 script\*(R") and a web server (\s-1HTTPD\s0). It is not specific
to Perl, and has its own FAQs and tutorials, and usenet group,
comp.infosystems.www.authoring.cgi
.PP
The \s-1CGI\s0 specification is outlined in an informational \s-1RFC:\s0
http://www.ietf.org/rfc/rfc3875
.PP
Other relevant documentation listed in: http://www.perl.org/CGI_MetaFAQ.html
.PP
These Perl FAQs very selectively cover some \s-1CGI\s0 issues. However, Perl
programmers are strongly advised to use the \s-1CGI\s0.pm module, to take care
of the details for them.
.PP
The similarity between \s-1CGI\s0 response headers (defined in the \s-1CGI\s0
specification) and \s-1HTTP\s0 response headers (defined in the \s-1HTTP\s0
specification, \s-1RFC2616\s0) is intentional, but can sometimes be confusing.
.PP
The \s-1CGI\s0 specification defines two kinds of script: the \*(L"Parsed Header\*(R"
script, and the \*(L"Non Parsed Header\*(R" (\s-1NPH\s0) script. Check your server
documentation to see what it supports. \*(L"Parsed Header\*(R" scripts are
simpler in various respects. The \s-1CGI\s0 specification allows any of the
usual newline representations in the \s-1CGI\s0 response (it's the server's
job to create an accurate \s-1HTTP\s0 response based on it). So \*(L"\en\*(R" written in
text mode is technically correct, and recommended. \s-1NPH\s0 scripts are more
tricky: they must put out a complete and accurate set of \s-1HTTP\s0
transaction response headers; the \s-1HTTP\s0 specification calls for records
to be terminated with carriage-return and line-feed, i.e \s-1ASCII\s0 \e015\e012
written in binary mode.
.PP
Using \s-1CGI\s0.pm gives excellent platform independence, including \s-1EBCDIC\s0
systems. \s-1CGI\s0.pm selects an appropriate newline representation
($CGI::CRLF) and sets binmode as appropriate.
.Sh "My \s-1CGI\s0 script runs from the command line but not the browser.  (500 Server Error)"
.IX Subsection "My CGI script runs from the command line but not the browser.  (500 Server Error)"
Several things could be wrong.  You can go through the \*(L"Troubleshooting
Perl \s-1CGI\s0 scripts\*(R" guide at
.PP
.Vb 1
\&        http://www.perl.org/troubleshooting_CGI.html
.Ve
.PP
If, after that, you can demonstrate that you've read the FAQs and that
your problem isn't something simple that can be easily answered, you'll
probably receive a courteous and useful reply to your question if you
post it on comp.infosystems.www.authoring.cgi (if it's something to do
with \s-1HTTP\s0 or the \s-1CGI\s0 protocols).  Questions that appear to be Perl
questions but are really \s-1CGI\s0 ones that are posted to comp.lang.perl.misc
are not so well received.
.PP
The useful FAQs, related documents, and troubleshooting guides are
listed in the \s-1CGI\s0 Meta \s-1FAQ:\s0
.PP
.Vb 1
\&        http://www.perl.org/CGI_MetaFAQ.html
.Ve
.Sh "How can I get better error messages from a \s-1CGI\s0 program?"
.IX Subsection "How can I get better error messages from a CGI program?"
Use the CGI::Carp module.  It replaces \f(CW\*(C`warn\*(C'\fR and \f(CW\*(C`die\*(C'\fR, plus the
normal Carp modules \f(CW\*(C`carp\*(C'\fR, \f(CW\*(C`croak\*(C'\fR, and \f(CW\*(C`confess\*(C'\fR functions with
more verbose and safer versions.  It still sends them to the normal
server error log.
.PP
.Vb 3
\&    use CGI::Carp;
\&    warn "This is a complaint";
\&    die "But this one is serious";
.Ve
.PP
The following use of CGI::Carp also redirects errors to a file of your choice,
placed in a \s-1BEGIN\s0 block to catch compile-time warnings as well:
.PP
.Vb 6
\&    BEGIN {
\&        use CGI::Carp qw(carpout);
\&        open(LOG, ">>/var/local/cgi\-logs/mycgi\-log")
\&            or die "Unable to append to mycgi\-log: $!\en";
\&        carpout(*LOG);
\&    }
.Ve
.PP
You can even arrange for fatal errors to go back to the client browser,
which is nice for your own debugging, but might confuse the end user.
.PP
.Vb 2
\&    use CGI::Carp qw(fatalsToBrowser);
\&    die "Bad error here";
.Ve
.PP
Even if the error happens before you get the \s-1HTTP\s0 header out, the module
will try to take care of this to avoid the dreaded server 500 errors.
Normal warnings still go out to the server error log (or wherever
you've sent them with \f(CW\*(C`carpout\*(C'\fR) with the application name and date
stamp prepended.
.Sh "How do I remove \s-1HTML\s0 from a string?"
.IX Subsection "How do I remove HTML from a string?"
The most correct way (albeit not the fastest) is to use HTML::Parser
from \s-1CPAN\s0.  Another mostly correct
way is to use HTML::FormatText which not only removes \s-1HTML\s0 but also
attempts to do a little simple formatting of the resulting plain text.
.PP
Many folks attempt a simple-minded regular expression approach, like
\&\f(CW\*(C`s/<.*?>//g\*(C'\fR, but that fails in many cases because the tags
may continue over line breaks, they may contain quoted angle-brackets,
or \s-1HTML\s0 comment may be present.  Plus, folks forget to convert
entities\*(--like \f(CW\*(C`&lt;\*(C'\fR for example.
.PP
Here's one \*(L"simple-minded\*(R" approach, that works for most files:
.PP
.Vb 2
\&    #!/usr/bin/perl \-p0777
\&    s/<(?:[^>\*(Aq"]*|([\*(Aq"]).*?\e1)*>//gs
.Ve
.PP
If you want a more complete solution, see the 3\-stage striphtml
program in
http://www.cpan.org/authors/Tom_Christiansen/scripts/striphtml.gz
\&.
.PP
Here are some tricky cases that you should think about when picking
a solution:
.PP
.Vb 1
\&    <IMG SRC = "foo.gif" ALT = "A > B">
\&
\&    <IMG SRC = "foo.gif"
\&         ALT = "A > B">
\&
\&    <!\-\- <A comment> \-\->
\&
\&    <script>if (a<b && a>c)</script>
\&
\&    <# Just data #>
\&
\&    <![INCLUDE CDATA [ >>>>>>>>>>>> ]]>
.Ve
.PP
If \s-1HTML\s0 comments include other tags, those solutions would also break
on text like this: