wangwei
/
antliscence
forked from youys/ant

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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>&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 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 (<em>since Ant 1.7</em>)</h3>
<p>
  When Ant starts up, if the <code>-autoproxy</code> command is
  supplied, Ant sets the <code>java.net.useSystemProxies</code> system
  property. This tells a Java 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.  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 JRE 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 <code>-autoproxy</code> 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 <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>
<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>
&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>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>&lt;java&gt;</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>&lt;sysproperty&gt;</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>&lt;syspropertyset&gt;</code></a>
  element to propagate the normal proxy settings. The following
  propertyset is a datatype which can be referenced in
  a <code>&lt;java&gt;</code> task to pass down the current values.
</p>
<pre>
&lt;propertyset id="proxy.properties"&gt;
  &lt;propertyref prefix="java.net.useSystemProxies"/&gt;
  &lt;propertyref prefix="http."/&gt;
  &lt;propertyref prefix="https."/&gt;
  &lt;propertyref prefix="ftp."/&gt;
  &lt;propertyref prefix="socksProxy"/&gt;
&lt;/propertyset&gt;</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 <code>-autoproxy</code> parameter.</li>
  <li>Via JVM system properties&mdash;set these in the <code>ANT_ARGS</code> environment variable.</li>
  <li>Via the <code>&lt;setproxy&gt;</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 <code>-autoproxy</code> 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">Java Networking Properties</a>.</li>
</ul>

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