1LWP::Online(3) User Contributed Perl Documentation LWP::Online(3)
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6 LWP::Online - Does your process have access to the web
7
9 use LWP::Online 'online';
10 # "Is the internet working?"
12 die "NO INTARWWEB!!!" unless online();
13 # The above means something like this
15 unless ( online('http') ) {
16 die "No basic http access to the web";
17 }
18 # Special syntax for use in test scripts that need
20 # "real" access to the internet. Scripts will automatically
21 # skip if connection fails.
22 use LWP::Online ':skip_all';
23 use Test::More tests => 4; #after LWP::Online
24
26 This module attempts to answer, as accurately as it can, one of the
27 nastiest technical questions there is.
28 Am I on the internet?
30 The answer is useful in a wide range of decisions. For example...
32 Should my test scripts run the online portion of the tests or just skip
34 them?
35 Do I try to fetch fresh data from the server?
37 If my request to the server breaks, is it because I'm offline, or
39 because the server is offline?
40 And so on, and so forth.
42 But a host of networking and security issues make this problem very
44 difficult. There are firewalls, proxies (both well behaved and badly
45 behaved). We might not have DNS. We might not have a network card at
46 all!
47 You might have network access, but only to a for-money wireless network
49 that responds to ever HTTP request with a page asking you to enter your
50 credit card details for paid access. Which means you don't "REALLY"
51 have access.
52 The mere nature of the question makes it practically unsolvable.
54 But with the answer being so useful, and the only other alternative
56 being to ask the user "duh... are you online?" (when you might not have
57 a user at all) it's my gut feeling that it is worthwhile at least
58 making an attempt to solve the problem, if only in a limited way.
59 Why LWP::Online? Why not Net::Online?
61 The nice thing about LWP::Online is that LWP deals with a whole range
62 of different transports, and is very commonly installed. HTTP, HTTPS,
63 FTP, and so on and so forth.
64 Attempting to do a more generalised Net::Online that might also check
66 for SSH and so on would end up most likely having to install a whole
67 bunch of modules that you most likely will never use.
68 So LWP forms a nice base on which to write a module that covers most of
70 the situations in which you might care, while keeping the dependency
71 overhead down to a minimum.
72 Scope
74 "Am I online?" is inherently an Open Problem.
75 That is, it's a problem that had no clean permanent solution, and for
77 which you could just keep writing more and more functionality
78 indefinitely, asymtopically approaching 100% correctness but never
79 reaching it.
80 And so this module is intended to do as good a job as possible, without
82 having to resort to asking any human questions (who may well get it
83 wrong anyway), and limiting itself to a finite amount of programming
84 work and a reasonable level of memory overhead to load the code.
85 It is thus understood the module will never be perfect, and that if any
87 new functionality is desired, it needs to be able to implemented by the
88 person that desires the new behaviour, and in a reasonably small amount
89 of additional code.
90 This module is also not intended to compensate for malicious behaviour
92 of any kind, it is quite possible that some malicious person might
93 proxy fake versions of sites that pass our content checks and then
94 proceed to show you other bad pages.
95 Test Mode
97 use LWP::Online ':skip_all';
98 As a convenience when writing tests scripts base on Test::More, the
100 special ':skip_all' param can be provided when loading LWP::Online.
101 This implements the functional equivalent of the following.
103 BEGIN {
105 require Test::More;
106 unless ( LWP::Online::online() ) {
107 Test::More->import(
108 skip_all => 'Test requires a working internet connection'
109 );
110 }
111 }
112 The :skip_all special import flag can be mixed with regular imports.
114
116 online
117 # Default check (uses http)
118 online() or die "No Internet";
119 # The above is equivalent to
121 online('http') or die "No Internet";
122 The importable online function is the main functionality provided by
124 LWP::Online. It takes a single optional transport name ('http' by
125 default) and checks that LWP connectivity is available for that
126 transport.
127 Because it is intended as a Do What You Mean function, it checks not
129 only that a network connection is available, and http requests return
130 content, but also that it returns the CORRECT content instead of
131 unexpected content supplied by a man in the middle.
132 For example, many wireless connections require login or payment, and
134 will return a service provider page for any URI that you attempt to
135 fetch.
136 The set of websites used for the testing is the Google, Amazon, Yahoo
138 and CNN websites. The check is for a copyright statement on their
139 homepage, and the function returns true as soon as two of the website
140 return correctly, making the method relatively redundant.
141 Returns true if the computer is "online" (has a working connection via
143 LWP) or false if not.
144 offline
146 The importable offline function is provided as a convenience.
147 It provides a simple pass-through (including any params) to the online
149 function, but with a negated result.
150
152 - Add more transport types that can be checked, somehow keeping the
153 code growth under control.
154
156 This module is stored in an Open Repository at the following address.
157 <http://svn.ali.as/cpan/trunk/LWP-Online>
159 Write access to the repository is made available automatically to any
161 published CPAN author, and to most other volunteers on request.
162 If you are able to submit your bug report in the form of new (failing)
164 unit tests (which for this module will be extremely difficult), or can
165 apply your fix directly instead of submitting a patch, you are strongly
166 encouraged to do so as the author currently maintains over 100 modules
167 and it can take some time to deal with non-Critical bug reports or
168 patches.
169 This will guarentee that your issue will be addressed in the next
171 release of the module.
172 If you cannot provide a direct test or fix, or don't have time to do
174 so, then regular bug reports are still accepted and appreciated via the
175 CPAN bug tracker.
176 <http://rt.cpan.org/NoAuth/ReportBug.html?Queue=LWP-Online>
178 For other issues, for commercial enhancement or support, or to have
180 your write access enabled for the repository, contact the author at the
181 email address above.
182
184 Adam Kennedy <adamk@cpan.org>
185
187 LWP::Simple
188
190 Copyright 2006 - 2011 Adam Kennedy.
191 This program is free software; you can redistribute it and/or modify it
193 under the same terms as Perl itself.
194 The full text of the license can be found in the LICENSE file included
196 with this module.
197perl v5.34.0 2021-07-22 LWP::Online(3)