Checking for internet connection.

Hi all.

I'w writing a PHP app that is designed to run over a LAN, so internet
connection for the server is not really essential. Some users may
deliberately not connect it to the internet as a security precaution.

But I'd like the app to make use of an internet connection if it exists to
check for an update, and notify the user.

Is there a simple way for a PHP script to check if it has an internet
connection?

I thought of this :

if(fsockopen("www.google.com", 80)){
// we are connected
}

Is this OK or is there something better for the purpose?



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Re: Checking for internet connection.

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On Sun, 2009-12-20 at 10:13 +1000, Angus Mann wrote:

> Hi all.
>
> I'w writing a PHP app that is designed to run over a LAN, so internet
> connection for the server is not really essential. Some users may
> deliberately not connect it to the internet as a security precaution.
>
> But I'd like the app to make use of an internet connection if it exists to
> check for an update, and notify the user.
>
> Is there a simple way for a PHP script to check if it has an internet
> connection?
>
> I thought of this :
>
> if(fsockopen("www.google.com", 80)){
> // we are connected
> }
>
> Is this OK or is there something better for the purpose?
>
>
>


Why can't you put the update on the same LAN server that the app
resides?

If that is not possible, what about using CURL, and update if it can
connect successfully, but don't if it cannot?

Thanks,
Ash
http://www.ashleysheridan.co.uk



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Re: Checking for internet connection.

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charset="utf-8"
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Why can't you put the update on the same LAN server that the app =
resides?

If that is not possible, what about using CURL, and update if it can =
connect successfully, but don't if it cannot?

Thanks,
Ash
http://www.ashleysheridan.co.uk

Since the LAN is remote (many hundreds of miles away) from the =
source of the update, the only practical way to deliver an update every =
month or week to multiple users is to make it available for download =
from a central "update server".

I'm just trying to maximize efficiency by checking if an internet =
connection exists, and abandoning further attempts to check for update =
availability if it does not.

The idea to use CURL seems valid, but it pre-supposes that I know =
the answer to my own question. To use your suggestion, I'd have to have =
some mechanism to detect if it "can connect successfully". I'm asking =
what that mechanism should be, and if the one I've suggested is good, or =
flawed in some way.=20



=20

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Re: Checking for internet connection.

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On Sun, 2009-12-20 at 10:36 +1000, Angus Mann wrote:

> Why can't you put the update on the same LAN server that the app resides?
>
> If that is not possible, what about using CURL, and update if it can connect successfully, but don't if it cannot?
>
> Thanks,
> Ash
> http://www.ashleysheridan.co.uk
>
> Since the LAN is remote (many hundreds of miles away) from the source of the update, the only practical way to deliver an update every month or week to multiple users is to make it available for download from a central "update server".
>
> I'm just trying to maximize efficiency by checking if an internet connection exists, and abandoning further attempts to check for update availability if it does not.
>
> The idea to use CURL seems valid, but it pre-supposes that I know the answer to my own question. To use your suggestion, I'd have to have some mechanism to detect if it "can connect successfully". I'm asking what that mechanism should be, and if the one I've suggested is good, or flawed in some way.
>
>
>
>


I think the only way to detect if it can connect to the Internet is to
see if you can grab a file from somewhere on the Internet. I'd hazard a
guess that when operating systems are able to tell you they can "connect
to the Internet" they are actually saying they can ping a predetermined
remote host. I think checking if PHP can grab a remote file with Curl
would be sufficient in this case.

Thanks,
Ash
http://www.ashleysheridan.co.uk



--=-m+Q0oNiHCvXZ/8uJAfKU--

Re: Checking for internet connection.

Curl_init() will return a resource or false if it fails, like it would
if no Internet connection were present.

J Corry
Sent from my iPhone

On Dec 19, 2009, at 5:36 PM, "Angus Mann" wrote:

>
> Why can't you put the update on the same LAN server that the app
> resides?
>
> If that is not possible, what about using CURL, and update if it can
> connect successfully, but don't if it cannot?
>
> Thanks,
> Ash
> http://www.ashleysheridan.co.uk
>
> Since the LAN is remote (many hundreds of miles away) from the
> source of the update, the only practical way to deliver an update
> every month or week to multiple users is to make it available for
> download from a central "update server".
>
> I'm just trying to maximize efficiency by checking if an
> internet connection exists, and abandoning further attempts to check
> for update availability if it does not.
>
> The idea to use CURL seems valid, but it pre-supposes that I
> know the answer to my own question. To use your suggestion, I'd have
> to have some mechanism to detect if it "can connect successfully".
> I'm asking what that mechanism should be, and if the one I've
> suggested is good, or flawed in some way.
>
>
>
>

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Re: Checking for internet connection.

The next way to handle this might be to code an AIR app. Then it's a
simple js trap to see if connectivity exists.

Bastien

Sent from my iPod

On Dec 19, 2009, at 7:13 PM, "Angus Mann" wrote:

> Hi all.
>
> I'w writing a PHP app that is designed to run over a LAN, so
> internet connection for the server is not really essential. Some
> users may deliberately not connect it to the internet as a security
> precaution.
>
> But I'd like the app to make use of an internet connection if it
> exists to check for an update, and notify the user.
>
> Is there a simple way for a PHP script to check if it has an
> internet connection?
>
> I thought of this :
>
> if(fsockopen("www.google.com", 80)){
> // we are connected
> }
>
> Is this OK or is there something better for the purpose?
>
>
>
> --
> PHP General Mailing List (http://www.php.net/)
> To unsubscribe, visit: http://www.php.net/unsub.php
>

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Re: Checking for internet connection.

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>=20
> I think the only way to detect if it can connect to the Internet is to
> see if you can grab a file from somewhere on the Internet. I'd hazard =
a
> guess that when operating systems are able to tell you they can =
"connect
> to the Internet" they are actually saying they can ping a =
predetermined
> remote host. I think checking if PHP can grab a remote file with Curl
> would be sufficient in this case.

Personally, I'd do a DNS lookup - even connecting to a server is a lot =
more overhead than a simple DNS request. You could force the DNS server =
to be one external to your network - e.g. dig @a.root-servers.net =
www.google.co.uk. If the dig command fails, you're not connected.

Or just try and get the update anyway - if the download fails, you're =
not connected (or there's something wrong with the update server.)=

--Apple-Mail-1--473503270--

Re: Checking for internet connection.

On Sun, Dec 20, 2009 at 2:32 AM, Andy Shellam w=
rote:
>>
>> I think the only way to detect if it can connect to the Internet is to
>> see if you can grab a file from somewhere on the Internet. I'd hazard a
>> guess that when operating systems are able to tell you they can "connect
>> to the Internet" they are actually saying they can ping a predetermined
>> remote host. I think checking if PHP can grab a remote file with Curl
>> would be sufficient in this case.
>
> Personally, I'd do a DNS lookup - even connecting to a server is a lot mo=
re overhead than a simple DNS request.  You could force the DNS server=
to be one external to your network - e.g. dig @a.root-servers.net www.goog=
le.co.uk.  If the dig command fails, you're not connected.
>
> Or just try and get the update anyway - if the download fails, you're not=
connected (or there's something wrong with the update server.)

By attempting to connect you will implicitly query DNS (which itself
is a connection to server). If you're not online you won't be able to
resolve the domain name. Hence no overhead of actually connecting,
because that won't even start to happen until the hostname is resolved
to an IP. If it happens to resolve from some cache, oh well. Not
like its that much overhead. You're nitpicking over the number of
packets it takes to SYN/ACK.

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Re: Checking for internet connection.

> By attempting to connect you will implicitly query DNS (which itself
> is a connection to server). =20

No it's not - it's putting out a packet targeted at an IP address and =
hoping a server will answer - hence why multi-cast works for DNS because =
you're not directly connecting to a specified server, like you do with =
TCP/IP. I believe it's similar for ping which is why it's used so =
commonly in monitoring applications.

> If you're not online you won't be able to
> resolve the domain name. =20

Exactly - so if all the OP wanted to check for was a working Internet =
connection, then DNS is a better way to go IMHO.

> Hence no overhead of actually connecting,
> because that won't even start to happen until the hostname is resolved
> to an IP. If it happens to resolve from some cache, oh well. Not
> like its that much overhead. You're nitpicking over the number of
> packets it takes to SYN/ACK.

Yep and if it's running inside a LAN with x number of computers all =
doing the same thing, that mounts up to a lot of unnecessary traffic - =
I've seen it.


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RE: Checking for internet connection.

From: Andy Shellam

>> By attempting to connect you will implicitly query DNS (which itself
>> is a connection to server). =20
>=20
> No it's not - it's putting out a packet targeted at an IP address
> and hoping a server will answer - hence why multi-cast works for
> DNS because you're not directly connecting to a specified server,
> like you do with TCP/IP. I believe it's similar for ping which is
> why it's used so commonly in monitoring applications.
>=20
> > If you're not online you won't be able to
>> resolve the domain name. =20
>=20
> Exactly - so if all the OP wanted to check for was a working
> Internet connection, then DNS is a better way to go IMHO.

Both at home and at work there are caching DNS on the LAN. So a DNS
request may come back with a valid IP address when the WAN connection is
down. I still won't be able to connect to the remote site.

Bob McConnell

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Re: Checking for internet connection.

On Sat, Dec 19, 2009 at 19:13, Angus Mann wrote:
> Hi all.
>
> I'w writing a PHP app that is designed to run over a LAN, so internet
> connection for the server is not really essential. Some users may
> deliberately not connect it to the internet as a security precaution.
>
> But I'd like the app to make use of an internet connection if it exists to
> check for an update, and notify the user.
>
> Is there a simple way for a PHP script to check if it has an internet
> connection?

If it's running on Linux, this will work. For other OS'es, you
may have to tweak it a bit.

$ip = '24.254.254.1'; // This is a bogus address. Replace it with yours.
exec('ping -c 1 -w 3 '.$ip,$ret,$err);
if($err) die('Internet connection unavailable.');
?>

This executes a system call to the PING utility, which then sends
a single packet with a deadline of 3 seconds to the address. If it
causes anything but a 0 return on STDERR, it dies with the message
"Internet connection unavailable."

Don't use name-based lookups unless you absolutely have to in this
case. There are more points of failure and bottlenecking, which can
make your code run really slow or fail completely.

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Re: Checking for internet connection.

Bob McConnell wrote on 21/12/2009 15:05:

> Both at home and at work there are caching DNS on the LAN. So a DNS
> request may come back with a valid IP address when the WAN connection is
> down. I still won't be able to connect to the remote site.

Then use fopen() to read a page you know exists?

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Re: Checking for internet connection.

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>=20
> Both at home and at work there are caching DNS on the LAN. So a DNS
> request may come back with a valid IP address when the WAN connection =
is
> down. I still won't be able to connect to the remote site.

Dig an external server - e.g. dig @a.root-servers.net google.co.uk

If your net is down the query will fail even if the reply is cached =
locally, because you're specifically requesting a response from =
a.root-servers.net.=

--Apple-Mail-9--350632636--

RE: Checking for internet connection.

From: Andy Shellam

>>=20
>> Both at home and at work there are caching DNS on the LAN. So a DNS
>> request may come back with a valid IP address when the WAN connection
is
>> down. I still won't be able to connect to the remote site.
>=20
> Dig an external server - e.g. dig @a.root-servers.net google.co.uk
>=20
> If your net is down the query will fail even if the reply is
> cached locally, because you're specifically requesting a response
> from a.root-servers.net.

What means dig? I can't find it in the function index of the online
manual.

Bob McConnell

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Re: Checking for internet connection.

On 21 Dec 2009, at 19:40, Andy Shellam wrote:

>>=20
>> Both at home and at work there are caching DNS on the LAN. So a DNS
>> request may come back with a valid IP address when the WAN connection =
is
>> down. I still won't be able to connect to the remote site.
>=20
> Dig an external server - e.g. dig @a.root-servers.net google.co.uk
>=20
> If your net is down the query will fail even if the reply is cached =
locally, because you're specifically requesting a response from =
a.root-servers.net.

I'm confused... what's the problem with just trying to hit the update =
server? If you can then you check for updates, if not then you, erm, =
don't. Simples, no?

-Stuart

--=20
http://stut.net/=

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RE: Checking for internet connection.

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On Tue, 2009-12-22 at 08:27 -0500, Bob McConnell wrote:

> From: Andy Shellam
>
> >>
> >> Both at home and at work there are caching DNS on the LAN. So a DNS
> >> request may come back with a valid IP address when the WAN connection
> is
> >> down. I still won't be able to connect to the remote site.
> >
> > Dig an external server - e.g. dig @a.root-servers.net google.co.uk
> >
> > If your net is down the query will fail even if the reply is
> > cached locally, because you're specifically requesting a response
> > from a.root-servers.net.
>
> What means dig? I can't find it in the function index of the online
> manual.
>
> Bob McConnell
>


It's not a PHP thing, it's a network thing (Domain Information Groper)

http://en.wikipedia.org/wiki/Domain_Information_Groper


Thanks,
Ash
http://www.ashleysheridan.co.uk



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Re: Checking for internet connection.

>=20
> I'm confused... what's the problem with just trying to hit the update =
server? If you can then you check for updates, if not then you, erm, =
don't. Simples, no?

True, I think I said this same thing in a previous post - I suggested =
the DNS option if all the OP wanted to do was check if an Internet =
connection was there.=

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RE: Checking for internet connection.

From: Andy Shellam

>>=20
>> I'm confused... what's the problem with just trying to hit
>> the update server? If you can then you check for updates, if
>> not then you, erm, don't. Simples, no?
>
> True, I think I said this same thing in a previous post - I
> suggested the DNS option if all the OP wanted to do was check
> if an Internet connection was there.

And I was pointing out that this would not be a valid test when there is
a caching DNS on the LAN.

Too much of the conversation and most of the attribution was stripped
too early for this to be coherent.

Bob McConnell

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Re: Checking for internet connection.

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>=20
> And I was pointing out that this would not be a valid test when there =
is
> a caching DNS on the LAN.

I also pointed out how to avoid caching issues - the comment was aimed =
at the author of the message before mine.

>=20
> Too much of the conversation and most of the attribution was stripped
> too early for this to be coherent.

Why the negativity? A question was asked and several possible solutions =
were provided based on that original question. All the "conversation" =
was relevant IMO.=

--Apple-Mail-1--255637207--

RE: Checking for internet connection.

From: Andy Shellam

>> And I was pointing out that this would not be a valid
>> test when there is a caching DNS on the LAN.

> I also pointed out how to avoid caching issues - the
> comment was aimed at the author of the message before mine.
>=20
>> Too much of the conversation and most of the attribution
>> was stripped too early for this to be coherent.
>=20
> Why the negativity? A question was asked and several
> possible solutions were provided based on that original
> question. All the "conversation" was relevant IMO.

But long before it was done it was impossible to tell who had asked
which questions, who had provided which answers and who had countered
those answers. In several instances, replies appeared to be directed to
the wrong individuals.

Some people here tend to go way too far when trimming context from
replies. Yes, I know it gets difficult to read when there are more than
ten or twelve levels of attribution, but stripping all but the last
layer is even worse. Removing the participants names from the top should
be a hanging offense. I don't keep copies of every message in any of the
dozens of mailing lists and news groups I follow, so there is no simple
way to go back through the conversation to figure out where it all came
from.

Bob McConnell

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Re: Checking for internet connection.

Hi Bob

Bob McConnell wrote on 23/12/2009 14:35:
> From: Andy Shellam
>
>>> And I was pointing out that this would not be a valid
>>> test when there is a caching DNS on the LAN.
>
>> I also pointed out how to avoid caching issues - the
>> comment was aimed at the author of the message before mine.
>>
>>> Too much of the conversation and most of the attribution
>>> was stripped too early for this to be coherent.
>> Why the negativity? A question was asked and several
>> possible solutions were provided based on that original
>> question. All the "conversation" was relevant IMO.
>
> But long before it was done it was impossible to tell who had asked
> which questions, who had provided which answers and who had countered
> those answers. In several instances, replies appeared to be directed to
> the wrong individuals.

Leaving the above for a reason. I find your answer to Andy rude and
offensive! Remind me not to try to help you next time.

> Some people here tend to go way too far when trimming context from
> replies. Yes, I know it gets difficult to read when there are more than
> ten or twelve levels of attribution, but stripping all but the last
> layer is even worse.

No, that's called netetiquette, have a look at:
http://www.the-eggman.com/writings/etiquitte_1.html

Quote: "When responding to E-Mail, don't quote the entire original
message in your reply. Only quote the relevant parts, and only to the
extent that they will help orient the recipient on your reply."

(and this mail is not to start a flame war)

> Removing the participants names from the top should
> be a hanging offense. I don't keep copies of every message in any of the
> dozens of mailing lists and news groups I follow, so there is no simple
> way to go back through the conversation to figure out where it all came
> from.

Well, because _you_ don't wanna follow proper netetiquette doesn't mean
everyone else should violate those rules, does it? :-)

And a merry christmas to you.

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RE: Checking for internet connection.

From: Kim Madsen

> Bob McConnell wrote on 23/12/2009 14:35:
>> From: Andy Shellam
>>=20
>>>> And I was pointing out that this would not be a valid
>>>> test when there is a caching DNS on the LAN.
>>=20
>>> I also pointed out how to avoid caching issues - the
>>> comment was aimed at the author of the message before mine.
>>>
>>>> Too much of the conversation and most of the attribution
>>>> was stripped too early for this to be coherent.
>>> Why the negativity? A question was asked and several
>>> possible solutions were provided based on that original
>>> question. All the "conversation" was relevant IMO.
>>=20
>> But long before it was done it was impossible to tell who had asked
>> which questions, who had provided which answers and who had countered
>> those answers. In several instances, replies appeared to be directed
to
>> the wrong individuals.
>=20
>> Some people here tend to go way too far when trimming context from
>> replies. Yes, I know it gets difficult to read when there are more
than
>> ten or twelve levels of attribution, but stripping all but the last
>> layer is even worse.
>=20
> No, that's called netetiquette, have a look at:=20
> http://www.the-eggman.com/writings/etiquitte_1.html
>=20
> Quote: "When responding to E-Mail, don't quote the entire original=20
> message in your reply. Only quote the relevant parts, and only to the=20
> extent that they will help orient the recipient on your reply."

The problem arises when too many of the relevant parts are also removed,
which happened far too often on this thread as well as others. When the
core context is not retained, the conversation drifts and quickly
becomes useless to either the early posters or later readers.

I did not mean to be rude, but to point out what I see as a serious
problem that has been growing on this list recently. On the other hand,
I have not had my cup of hot chocolate yet this morning, so am probably
not completely awake yet.

Bob McConnell

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Re: Checking for internet connection.

On Wed, Dec 23, 2009 at 14:35, Bob McConnell wrote:
> I don't keep copies of every message in any of the
> dozens of mailing lists and news groups I follow, so there is no simple
> way to go back through the conversation to figure out where it all came
> from.

Fortunately, other people keep complete archives for you:
http://news.php.net/php.general
http://marc.info/?l=php-general

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Re: Checking for internet connection.

Bob McConnell wrote on 23/12/2009 15:55:

> The problem arises when too many of the relevant parts are also removed,
> which happened far too often on this thread as well as others. When the
> core context is not retained, the conversation drifts and quickly
> becomes useless to either the early posters or later readers.

just don't delete mails that are recent, delete after 3 months for
instance? And if possible (I see some Exchange dirt in the mailheader
:-)) use a mailclient that supports thread, I use Thunderbird and when
subscribing to maillists this is really cool, I have a quick overview of
the mails on the subject.

> I did not mean to be rude, but to point out what I see as a serious
> problem that has been growing on this list recently. On the other hand,
> I have not had my cup of hot chocolate yet this morning, so am probably
> not completely awake yet.

Okay, explanation excepted, E-mails can easily be misunderstood :-) May
you have a merry Christmas (grab another cup of choco, just in case ;-))

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Re: Checking for internet connection.

Kim Madsen wrote on 23/12/2009 17:01:

> Okay, explanation excepted, E-mails can easily be misunderstood :-) May
> you have a merry Christmas (grab another cup of choco, just in case ;-))

correction: accepted

Now _I'M_ gonna get a cup of chocolate :-)

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