[FIXED JENKINS-19251] Use hashes rather than modification time to determine if...

[FIXED JENKINS-19251] Use hashes rather than modification time to determine if Maven agent JARs are up to date.

changelog.html

@@ -61,6 +61,9 @@ Upcoming changes</a>
   <li class='major bug'>
     As of 1.532 download of artifact ZIPs was broken.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-19752">issue 19752</a>)
+  <li class='major bug'>
+    Old copies of <code>maven3-agent.jar</code> on slaves were not being reliably updated, leading to errors.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-19251">issue 19251</a>)
   <li class='rfe'>
     Add option to disable "Remember me on this computer" checkbox in login screen.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-15757">issue 15757</a>)

maven-plugin/src/main/java/hudson/maven/AbstractMavenProcessFactory.java

@@ -8,6 +8,7 @@ import hudson.FilePath;
 import hudson.Launcher;
 import hudson.Platform;
 import hudson.Proc;
+import hudson.Util;
 import hudson.maven.ProcessCache.NewProcess;
 import hudson.model.BuildListener;
 import hudson.model.Computer;
@@ -534,7 +535,7 @@ public abstract class AbstractMavenProcessFactory
             zip.setProject(new Project());
             zip.execute();
             jar = t;
-        } else if (copiedJar.lastModified() > jar.lastModified()) {
+        } else if (copiedJar.exists() && copiedJar.digest().equals(Util.getDigestOf(jar))) {
             log.println(seedName + ".jar already up to date");
             return copiedJar;
         }

maven-plugin/src/main/java/hudson/maven/MavenProcessFactory.java

@@ -26,6 +26,7 @@ package hudson.maven;
 import hudson.FilePath;
 import hudson.Launcher;
 import hudson.EnvVars;
+import hudson.Util;
 import hudson.maven.agent.Main;
 import hudson.maven.agent.Maven21Interceptor;
 import hudson.model.BuildListener;
@@ -40,7 +41,6 @@ import java.io.FilenameFilter;
 import java.io.IOException;
 import java.io.InputStream;
 import java.net.URL;
-import java.net.URLConnection;
 
 
 /**
@@ -69,11 +69,10 @@ final class MavenProcessFactory extends AbstractMavenProcessFactory implements P
             // TODO why would we not pick it up using GetClassWorldsJar like we do for M2 on master or M3 anywhere?
             FilePath jar = slaveRoot.child("classworlds.jar");
             // copied to root of this JAR using dependency:generate-resources:
-            URLConnection conn = MavenProcessFactory.class.getClassLoader().getResource("classworlds.jar").openConnection();
-            if (jar.lastModified() > conn.getLastModified()) {
+            if (jar.exists() && jar.digest().equals(Util.getDigestOf(MavenProcessFactory.class.getClassLoader().getResourceAsStream("classworlds.jar")))) {
                 listener.getLogger().println("classworlds.jar already up to date");
             } else {
-                InputStream in = conn.getInputStream();
+                InputStream in = MavenProcessFactory.class.getClassLoader().getResourceAsStream("classworlds.jar");
                 try {
                     jar.copyFrom(in);
                 } finally {