[FIXED JENKINS-17681] Do not try to call resolveSymlink on a nonexistent link...

[FIXED JENKINS-17681] Do not try to call resolveSymlink on a nonexistent link as you will just get an IOException, breaking peephole permalinks in some Windows environments.

changelog.html

@@ -58,6 +58,9 @@ Upcoming changes</a>
   <li class=bug>
     Display Name is not shown.
      (<a href="https://issues.jenkins-ci.org/browse/JENKINS-17715">issue 17715</a>)
+  <li class='major bug'>
+    Symlink handling problem with build permalinks on Windows.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-17681">issue 17681</a>)
   <li class=bug>
     List views missing a required field were unloadable.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-15309">issue 15309</a>)

core/src/main/java/hudson/Util.java

@@ -1200,6 +1200,10 @@ public class Util {
             } catch (ClassNotFoundException x3) {
                 assert false : x3; // should be Java 7+ here
             }
+            if (x2.getClass().getName().equals("java.nio.file.FileSystemException")) {
+                // Thrown ("Incorrect function.") on JDK 7u21 in Windows 2012 when called on a non-symlink, rather than NotLinkException, contrary to documentation. Maybe only when not on NTFS?
+                return null;
+            }
             if (x2 instanceof IOException) {
                 throw (IOException) x2;
             }

core/src/main/java/jenkins/model/PeepholePermalink.java

@@ -17,6 +17,7 @@ import javax.annotation.Nullable;
 import java.io.File;
 import java.io.IOException;
 import java.io.StringWriter;
+import java.util.Arrays;
 import java.util.logging.Level;
 import java.util.logging.Logger;
 
@@ -143,6 +144,12 @@ public abstract class PeepholePermalink extends Permalink implements Predicate<R
         }
     }
 
+    // File.exists returns false for a link with a missing target, so for Java 6 compatibility we have to use this circuitous method to see if it was created.
+    private static boolean exists(File link) {
+        File[] kids = link.getParentFile().listFiles();
+        return kids != null && Arrays.asList(kids).contains(link);
+    }
+
     static String readSymlink(File cache) throws IOException, InterruptedException {
         String target = Util.resolveSymlink(cache);
         if (target==null && cache.exists()) {
@@ -158,7 +165,8 @@ public abstract class PeepholePermalink extends Permalink implements Predicate<R
         File tmp = new File(cache.getPath()+".tmp");
         try {
             Util.createSymlink(tmp.getParentFile(),target,tmp.getName(),listener);
-            if (Util.resolveSymlink(tmp)==null) {
+            // Avoid calling resolveSymlink on a nonexistent file as it will probably throw an IOException:
+            if (!exists(tmp) || Util.resolveSymlink(tmp)==null) {
                 // symlink not supported. use a regular file
                 AtomicFileWriter cw = new AtomicFileWriter(cache);
                 try {