fail proxy pac on windows if no URL

[ebarboni]

This is a "fix" to get rid of an annoying exception thrown on every launchd as info during windows autoproxy.
I'm not sure this is right approach but "to me" as no URL are set I don't get why it should use http://wdap/wdap.dat.
So exiting early.

That the exception scaring user :p :
INFO [org.netbeans.core.network.proxy.ProxyAutoConfig]: InputStream for http://wpad/wpad.dat throws
java.net.UnknownHostException: wpad
at java.base/sun.nio.ch.NioSocketImpl.connect(NioSocketImpl.java:567)
at java.base/java.net.Socket.connect(Socket.java:633)
at java.base/java.net.Socket.connect(Socket.java:583)
at java.base/sun.net.NetworkClient.doConnect(NetworkClient.java:183)
at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:531)
at java.base/sun.net.www.http.HttpClient.openServer(HttpClient.java:636)
at java.base/sun.net.www.http.HttpClient.(HttpClient.java:279)
at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:384)
at java.base/sun.net.www.http.HttpClient.New(HttpClient.java:406)
at java.base/sun.net.www.protocol.http.HttpURLConnection.getNewHttpClient(HttpURLConnection.java:1309)
at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect0(HttpURLConnection.java:1287)
at java.base/sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1118)
at java.base/sun.net.www.protocol.http.HttpURLConnection$6.run(HttpURLConnection.java:1116)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
at java.base/java.security.AccessController.doPrivilegedWithCombiner(AccessController.java:962)
at java.base/sun.net.www.protocol.http.HttpURLConnection.plainConnect(HttpURLConnection.java:1115)
at java.base/sun.net.www.protocol.http.HttpURLConnection.connect(HttpURLConnection.java:1057)
at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream0(HttpURLConnection.java:1665)
at java.base/sun.net.www.protocol.http.HttpURLConnection$9.run(HttpURLConnection.java:1581)
at java.base/sun.net.www.protocol.http.HttpURLConnection$9.run(HttpURLConnection.java:1579)
at java.base/java.security.AccessController.doPrivileged(AccessController.java:712)
at java.base/java.security.AccessController.doPrivilegedWithCombiner(AccessController.java:962)
at java.base/sun.net.www.protocol.http.HttpURLConnection.getInputStream(HttpURLConnection.java:1578)
at org.netbeans.core.network.proxy.ProxyAutoConfig.downloadPAC(ProxyAutoConfig.java:155)
[catch] at org.netbeans.core.network.proxy.ProxyAutoConfig.initEngine(ProxyAutoConfig.java:94)
at org.netbeans.core.network.proxy.ProxyAutoConfig$1.run(ProxyAutoConfig.java:82)
at org.openide.util.RequestProcessor$Task.run(RequestProcessor.java:1418)
at org.netbeans.modules.openide.util.GlobalLookup.execute(GlobalLookup.java:45)
at org.openide.util.lookup.Lookups.executeWith(Lookups.java:287)
at org.openide.util.RequestProcessor$Processor.run(RequestProcessor.java:2033)

[matthiasblaesing]

To my understanding the download URL http://wpad/wpad.dat is correct. The system will resolve the host wpad in the local DNS prefix. And try to download the wpad file from there. This can be read into

https://datatracker.ietf.org/doc/html/draft-ietf-wrec-wpad-01#section-4.4.3

To get that URL on Windows, the following sequence has to run:

The system is queried for proxy configuration:

netbeans/platform/core.network/src/org/netbeans/core/network/proxy/windows/WindowsNetworkProxy.java

Lines 47 to 49 in 75bb740

	WindowsNetworkProxyLibrary.ProxyConfig.ByReference prxCnf = new WindowsNetworkProxyLibrary.ProxyConfig.ByReference();
	boolean result = WindowsNetworkProxyLibrary.LIBRARY.WinHttpGetIEProxyConfigForCurrentUser(prxCnf);

Only if that is present:

https://learn.microsoft.com/en-us/windows/win32/api/winhttp/nf-winhttp-winhttpgetieproxyconfigforcurrentuser

netbeans/platform/core.network/src/org/netbeans/core/network/proxy/windows/WindowsNetworkProxy.java

Line 51 in 75bb740

if (result) {

And only if there is no PAC url configured, but autodetection is enabled:

https://learn.microsoft.com/en-us/windows/win32/api/winhttp/ns-winhttp-winhttp_current_user_ie_proxy_config

netbeans/platform/core.network/src/org/netbeans/core/network/proxy/windows/WindowsNetworkProxy.java

Lines 59 to 60 in 75bb740

	if (pacFilePointer != null || prxCnf.autoDetect) {
	String pacFileUrl = pacFilePointer != null ? pacFilePointer.getWideString(0) : "http://wpad/wpad.dat"; // NOI18N

that URL is returned.

Sounds reasonable to me.

It was added recently: #5210 and maybe the java.net.UnknownHostException should be caught and a sensible message issued. This PR would just reintroduce the issue, that was fixed by #5210.

@sdedic could you have a look at this?

[ebarboni]

@matthiasblaesing thanks for precision. I have no idea why wpad not working on my computer and others. By the way more simple PR with only a triage of exception
(we have domain controled computer and it fail)

[sdedic]

@ebarboni thanks for the update. The UnknownHostException catch handler is indeed missing - but I'd say it should not log at all, or just note something like PAC script {0} unavailable, proxy disabled. It usually happens on systems with autoproxy enabled or even the URL configured that are outside of the proxied network. Then the DNS resolver does not know the hostname wpad and the automatic proxy configuration ends.

http://wpad/wpad.dat (hostname w/o the domain suffix) is used as a default in a hope that the OS resolver will add the domain name(s) from the domain search list and find a suitable one.

[ebarboni]

@sdedic I do the proposed Info log message