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<title>Proxy Configuration</title>
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<body>
<h2>Proxy Configuration</h2>

<p>

All tasks 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>&lt;get&gt;</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 longstanding problem with Java and Ant, which Java1.5 finally 
    addresses. When Ant is run under Java1.5, it automatically sets the 
    <code>java.net.useSystemProxies</code> system property, telling the JVM to 
    switch to the OS-configured proxy settings.This is automatic, but it can be disabled.
</p>
<p>
    When running Ant on older JVMs, this property is ignored. There are two other
    ways to configure Ant's proxy settings in these cases.
</p>


<h3>Java1.5 automatic proxy support (new for Ant1.7)</h3>
<p>
    When Ant starts up, it automatically sets the 
    <code>java.net.useSystemProxies</code> system property. This tells 
    a Java1.5+ JVM to use the current set of property settings of the host
    environment. Other JVMs, such as the Kaffe and Apache Harmony runtimes,
    may also use this property in future, which is why Ant always sets the
    property -it is ignored on the Java1.4 and earlier runtimes.
</p>
<p>
    This property should be enough to automatically give Ant hosted
    builds network access. It may also work under an IDE, though that depends
    upon the IDE and how it starts ant. If it bypasses Ant's Main entry point,
    the proxy setup may be skipped, and if networking has already started up
    by the time ant is run, the option may be ignored. Consult your IDE 
    documentation for IDE-specific information upon proxy setup.
</p>
<p>
    To disable this automatic feature, set the command line option
    <tt>-noproxy</tt>, or set a JVM or Ant property 
    <code>java.net.useSystemProxies</code> to a value other than
    <code>true</code> or <code>on</code>. If the JVM option is already set, 
    Ant will not touch it; if an Ant property of that name is set, Ant will
    pass the value of that property down to the JVM.
</p>
<p>
    We are not entirely sure where it reads the property settings from. 
    For windows, it probably reads the appropriate bits of the registry. For
    Unix/Linux it may use the current Gnome2 settings. 
    
<p>
    The biggest limitation of this feature, other than requiring a 1.5+ JVM,
    is that it is not dynamic. A long-lasting build hosted on a laptop will
    not adapt to changes in proxy settings. Furthermore, unless the user
    is running <a
    href="http://www.hpl.hp.com/techreports/2001/HPL-2001-158.html">an adaptive
    laptop</a>, the host's proxy settings will not-automatically adapt to
    changes in network context. The <code>-noproxy</code> option may be a useful
    one to use when roaming.
</p>

<h3>JVM options</h3>
<p>
    Any JVM can have its proxy options explicitly configured by passing
    the appropriate <code>-D</code> 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>
  For csh/tcsh:
<pre>
    setenv ANT_OPTS "-Dhttp.proxyHost=proxy -Dhttp.proxyPort=8080"
</pre>
<p>
  For Windows, set the ANT_OPTS environment variable in the appropriate "MyComputer" 
  properties dialog box.
</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>
<p>  
    If you are using Ant on a pre-Java1.5 machine behind a firewall, this is
    the simplest and best way to configure your runtime to work with build files
    that go beyond the firewall.
</p>

<h3>SetProxy Task</h3>
<p>
    The <a href="OptionalTasks/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, <i>and you cannot change Ant's JVM proxy settings</i>, 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>
  &lt;target name="probe-proxy" depends="init"&gt;
    &lt;condition property="proxy.enabled"&gt;
      &lt;and&gt;
        &lt;isset property="proxy.host"/&gt;
        &lt;isreachable host="${proxy.host}"/&gt;
      &lt;/and&gt;
    &lt;/condition&gt;
  &lt;/target&gt;

  &lt;target name="proxy" depends="probe-proxy" if="proxy.enabled"&gt;
    &lt;property name="proxy.port" value="80"/&gt;
    &lt;property name="proxy.user" value=""/&gt;
    &lt;property name="proxy.pass" value=""/&gt;
    &lt;setproxy proxyhost="${proxy.host}" proxyport="${proxy.port}"
      proxyuser="${proxy.user}" proxypassword="${proxy.pass}"/&gt;
  &lt;/target&gt;
</pre>

<h3>Summary and conclusions</h3>
<p>
There are three ways to set up proxies in Ant.
</p>
<ol>
<li>Automatically, with Ant1.7 -use <code>-noproxy</code> to disable this.</li>
<li>Via JVM system properties -set these in the ANT_ARGS environment variable.</li>
<li>Via the &lt;setproxy&gt; task.</li>
</ol>

<p>
As Java1.5 adoption increases, automatic proxy support should become more
widespread. For this reason, we would encourage users not to try and
second-guess network configurations with setproxy, and instead to encourage
users to move up to Ant1.7/Java1.5, and if they cannot, to set proxy options
in the ANT_ARGS environment variable.
</p>

<h4>Further reading</h4>

<ul>
<li><a href="http://java.sun.com/j2se/1.5.0/docs/guide/net/properties.html">
Java Networking Properties</a>. Notice how not all proxy settings are documented
there.
<li><a href="http://blogs.sun.com/roller/resources/jcc/Proxies.pdf">Proxies</a>
</li>
</ul>

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