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<title>Proxy Configuration</title>
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<body>
<h2>Proxy Configuration</h2>
<p>
This page discussing proxy issues on command-line Apache Ant.
Consult your IDE documentation for IDE-specific information upon
proxy setup.
</p>
<p>
All tasks and threads running in Ant's JVM share the same
HTTP/FTP/Socks proxy configuration.
</p>
<p>
When any task tries to retrieve content from an HTTP page, including
the <code><get></code> task, any automated URL retrieval in an
XML/XSL task, or any third-party task that uses
the <code>java.net.URL</code> classes, the proxy settings may make
the difference between success and failure.
</p>
<p>
Anyone authoring a build file behind a blocking firewall will
immediately appreciate the problems and may want to write a build
file to deal with the problem, but users of third party build build
files may find that the build file itself does not work behind the
firewall.
</p>
<p>
This is a long standing problem with Java and Ant. The only way to
fix it is to explicitly configure Ant with the proxy settings,
either by passing down the proxy details as JVM properties, or to
tell Ant on a Java 5+ system to have the JVM work it out for itself.
</p>
<h3>Java 5+ proxy support</h3>
<p><em>Since Ant 1.7</em></p>
<p>
When Ant starts up, if the <kbd>-autoproxy</kbd> command is
supplied, Ant sets the <code>java.net.useSystemProxies</code> system
property. This tells a Java 5+ runtime to use the current set of
property settings of the host environment. Other JVMs, such as
Kaffe and Apache Harmony, may also use this property in
future. It is ignored on the Java 1.4 and earlier runtimes.
</p>
<p>
This property maybe enough to give command-line Ant builds network
access, although in practise the results are inconsistent.
</p>
<p>
It is has also been reported a breaking the IBM Java 5 runtime on AIX,
and does not always work on Linux (presumably due to
missing <code>gconf</code> settings) Other odd things can go wrong,
like Oracle JDBC drivers or pure Java SVN clients.
</p>
<p>
To make the <kbd>-autoproxy</kbd> option the default, add it to
the environment variable <code>ANT_ARGS</code>, which contains a
list of arguments to pass to Ant on every command line run.
</p>
<h4>How Autoproxy works</h4>
<p>
The <code>java.net.useSystemProxies</code> is checked only once, at
startup time, the other checks (registry, <code>gconf</code>, system
properties) are done dynamically whenever needed (socket connection,
URL connection etc..).
</p>
<h5>Windows</h5>
<p>
The JVM goes straight to the registry, bypassing WinInet, as it is
not present/consistent on all supported Windows platforms (it is
part of IE, really). Java 7 may use the Windows APIs on the
platforms when it is present.
</p>
<h5>Linux</h5>
<p>
The JVM uses the <code>gconf</code> library to look at specific
entries. The <code>GConf-2</code> settings used are:
</p>
<pre>
- /system/http_proxy/use_http_proxy boolean
- /system/http_proxy/use_authentication boolean
- /system/http_proxy/host string
- /system/http_proxy/authentication_user string
- /system/http_proxy/authentication_password string
- /system/http_proxy/port int
- /system/proxy/socks_host string
- /system/proxy/mode string
- /system/proxy/ftp_host string
- /system/proxy/secure_host string
- /system/proxy/socks_port int
- /system/proxy/ftp_port int
- /system/proxy/secure_port int
- /system/proxy/no_proxy_for list
- /system/proxy/gopher_host string
- /system/proxy/gopher_port int
</pre>
<p>
If you are using KDE or another GUI than Gnome, you can still use
the <code>gconf-editor</code> tool to add these entries.
</p>
<h3>Manual JVM options</h3>
<p>
Any JVM can have its proxy options explicitly configured by passing
the appropriate <kbd>-D</kbd> system property options to the
runtime. Ant can be configured through all its shell scripts via
the <code>ANT_OPTS</code> environment variable, which is a list of
options to supply to Ant's JVM:
</p>
<p>
For bash:
</p>
<pre>export ANT_OPTS="-Dhttp.proxyHost=proxy -Dhttp.proxyPort=8080"</pre>
<p>
For csh/tcsh:
</p>
<pre>setenv ANT_OPTS "-Dhttp.proxyHost=proxy -Dhttp.proxyPort=8080"</pre>
<p>
If you insert this line into the Ant shell script itself, it gets
picked up by all continuous integration tools running on the system
that call Ant via the command line.
</p>
<p>
For Windows, set the <code>ANT_OPTS</code> environment variable in
the appropriate "My Computer" properties dialog box (XP), "Computer"
properties (Vista)
</p>
<p>
This mechanism works across Java versions, is cross-platform and
reliable. Once set, all build files run via the command line will
automatically have their proxy setup correctly, without needing any
build file changes. It also apparently overrides Ant's automatic
proxy settings options.
</p>
<p>
It is limited in the following ways:
</p>
<ol>
<li>Does not work under IDEs. These need their own proxy settings changed</li>
<li>Not dynamic enough to deal with laptop configuration changes.</li>
</ol>
<h3>SetProxy Task</h3>
<p>
The <a href="Tasks/setproxy.html">setproxy task</a> can be used to
explicitly set a proxy in a build file. This manipulates the many
proxy configuration properties of a JVM, and controls the proxy
settings for all network operations in the same JVM from that
moment.
</p>
<p>
If you have a build file that is only to be used in-house, behind a
firewall, on an older JVM, <em>and you cannot change Ant's JVM proxy
settings</em>, then this is your best option. It is ugly and
brittle, because the build file now contains system configuration
information. It is also hard to get this right across the many
possible proxy options of different users (none, HTTP, SOCKS).
</p>
<p>
Note that proxy configurations set with this task will probably
override any set by other mechanisms. It can also be used with fancy
tricks to only set a proxy if the proxy is considered reachable:
</p>
<pre>
<target name="probe-proxy" depends="init">
<condition property="proxy.enabled">
<and>
<isset property="proxy.host"/>
<isreachable host="${proxy.host}"/>
</and>
</condition>
</target>
<target name="proxy" depends="probe-proxy" if="proxy.enabled">
<property name="proxy.port" value="80"/>
<property name="proxy.user" value=""/>
<property name="proxy.pass" value=""/>
<setproxy proxyhost="${proxy.host}" proxyport="${proxy.port}"
proxyuser="${proxy.user}" proxypassword="${proxy.pass}"/>
</target></pre>
<h3>Custom ProxySelector implementations</h3>
<p>
As Java lets developers write their own ProxySelector
implementations, it is theoretically possible for someone to write
their own proxy selector class that uses different policies to
determine proxy settings. There is no explicit support for this in
Ant, and it has not, to the team's knowledge, been attempted.
</p>
<p>
This could be the most flexible of solutions, as one could easily
imagine an Ant-specific proxy selector that was driven off ant
properties, rather than system properties. Developers could set
proxy options in their custom build.properties files, and have this
propagate.
</p>
<p>
One issue here is with concurrency: the default proxy selector is
per-JVM, not per-thread, and so the proxy settings will apply to all
sockets opened on all threads; we also have the problem of how to
propagate options from one build to the JVM-wide selector.
</p>
<h3>Configuring the Proxy settings of Java programs under Ant</h3>
<p>
Any program that is executed with <code><java></code> without
setting <var>fork</var>=<q>true</q> will pick up the Ant's
settings. If you need different values,
set <var>fork</var>=<q>false</q> and provide the values
in <code><sysproperty></code> elements.
</p>
<p>
If you wish to have a forked process pick up the Ant's settings, use
the <a href="Types/propertyset.html"><code><syspropertyset></code></a>
element to propagate the normal proxy settings. The following
propertyset is a datatype which can be referenced in
a <code><java></code> task to pass down the current values.
</p>
<pre>
<propertyset id="proxy.properties">
<propertyref prefix="java.net.useSystemProxies"/>
<propertyref prefix="http."/>
<propertyref prefix="https."/>
<propertyref prefix="ftp."/>
<propertyref prefix="socksProxy"/>
</propertyset></pre>
<h3>Summary and conclusions</h3>
<p>
There are four ways to set up proxies in Ant.
</p>
<ol>
<li>With Ant 1.7 and Java 5+ using the <kbd>-autoproxy</kbd> parameter.</li>
<li>Via JVM system properties—set these in the <code>ANT_ARGS</code> environment variable.</li>
<li>Via the <code><setproxy></code> task.</li>
<li>Custom ProxySelector implementations</li>
</ol>
<p>
Proxy settings are automatically shared with Java programs started
under Ant <em>that are not forked</em>; to pass proxy settings down
to subsidiary programs, use a propertyset.
</p>
<p>
Over time, we expect the Java 5+ proxy features to stabilize, and
for Java code to adapt to them. However, given the fact that it
currently does break some builds, it will be some time before Ant
enables the automatic proxy feature by default. Until then, you have
to enable the <kbd>-autoproxy</kbd> option or use one of the
alternate mechanisms to configure the JVM.
</p>
<h4>Further reading</h4>
<ul>
<li><a href="https://docs.oracle.com/javase/8/docs/technotes/guides/net/properties.html"
target="_top">Java Networking Properties</a>.</li>
</ul>
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