[FIXED JENKINS-19947] Restore historical undocumented behavior of a top-level entry in a ZIP.

Noting that various DirScanner implementations handle this inconsistently.

changelog.html

@@ -58,6 +58,9 @@ Upcoming changes</a>
   <li class=bug>
     RuntimeException if you try to save a config with a choice parameter that has no choices.
     (<a href="https://issues.jenkins-ci.org/browse/JENKINS-18434">issue 18434</a>)
+  <li class=bug>
+    1.534 made ZIP downloads of artifacts work again, but missing a base directory inside the ZIP.
+    (<a href="https://issues.jenkins-ci.org/browse/JENKINS-19947">issue 19947</a>)
   <li class='major bug'>
     Upgrade Trilead SSH client library to version that does not cause connection loss when
     there is a lot of logging on the build slave and the performance improvements in

core/src/main/java/hudson/FilePath.java

@@ -392,7 +392,7 @@ public final class FilePath implements Serializable {
      *
      * @param glob
      *      Ant style glob, like "**/*.xml". If empty or null, this method
-     *      works like {@link #createZipArchive(OutputStream)}
+     *      works like {@link #createZipArchive(OutputStream)}, inserting a top-level directory into the ZIP.
      *
      * @since 1.315
      */

core/src/main/java/hudson/model/DirectoryBrowserSupport.java

@@ -341,7 +341,14 @@ public final class DirectoryBrowserSupport implements HttpResponse {
     private static void zip(OutputStream outputStream, VirtualFile dir, String glob) throws IOException {
         ZipOutputStream zos = new ZipOutputStream(outputStream);
         for (String n : dir.list(glob.length() == 0 ? "**" : glob)) {
-            ZipEntry e = new ZipEntry(n);
+            String relativePath;
+            if (glob.length() == 0) {
+                // JENKINS-19947: traditional behavior is to prepend the directory name
+                relativePath = dir.getName() + '/' + n;
+            } else {
+                relativePath = n;
+            }
+            ZipEntry e = new ZipEntry(relativePath);
             VirtualFile f = dir.child(n);
             e.setTime(f.lastModified());
             zos.putNextEntry(e);

core/src/main/java/hudson/util/DirScanner.java

@@ -51,6 +51,9 @@ public abstract class DirScanner implements Serializable {
 
     /**
      * Scans everything recursively.
+     * <p>Note that all file paths are prefixed by the name of the root directory.
+     * For example, when scanning a directory {@code /tmp/dir} containing a file {@code file},
+     * the {@code relativePath} sent to the {@link FileVisitor} will be {@code dir/file}.
      */
     public static class Full extends DirScanner {
         private void scan(File f, String path, FileVisitor visitor) throws IOException {
@@ -71,7 +74,8 @@ public abstract class DirScanner implements Serializable {
     }
 
     /**
-     * Scans by filtering things out from {@link FileFilter}
+     * Scans by filtering things out from {@link FileFilter}.
+     * <p>An initial basename is prepended as with {@link Full}.
      */
     public static class Filter extends Full {
         private final FileFilter filter;
@@ -90,6 +94,10 @@ public abstract class DirScanner implements Serializable {
 
     /**
      * Scans by using Ant GLOB syntax.
+     * <p>An initial basename is prepended as with {@link Full} <strong>if the includes and excludes are blank</strong>.
+     * Otherwise there is no prepended path. So for example when scanning a directory {@code /tmp/dir} containing a file {@code file},
+     * the {@code relativePath} sent to the {@link FileVisitor} will be {@code dir/file} if {@code includes} is blank
+     * but {@code file} if it is {@code **}. (This anomaly is historical.)
      */
     public static class Glob extends DirScanner {
         private final String includes, excludes;

test/src/test/java/hudson/model/DirectoryBrowserSupportTest.java

@@ -159,7 +159,7 @@ public class DirectoryBrowserSupportTest {
 
         ZipFile readzip = new ZipFile(zipfile);
 
-        InputStream is = readzip.getInputStream(readzip.getEntry("artifact.out"));
+        InputStream is = readzip.getInputStream(readzip.getEntry("archive/artifact.out"));
 
         // ZipException in case of JENKINS-19752
         assertFalse("Downloaded zip file must not be empty", is.read() == -1);