Fix regression when extracting tar archive to a path containig a symlink

frontend-plugin-core/src/main/java/com/github/eirslett/maven/plugins/frontend/lib/ArchiveExtractor.java

@@ -104,15 +104,15 @@ public void extract(String archive, String destinationDirectory) throws ArchiveE
                     tarIn = new TarArchiveInputStream(new GzipCompressorInputStream(fis));
 
                     TarArchiveEntry tarEntry = tarIn.getNextTarEntry();
+                    String canonicalDestinationDirectory = new File(destinationDirectory).getCanonicalPath();
                     while (tarEntry != null) {
                         // Create a file for this tarEntry
                         final File destPath = new File(destinationDirectory + File.separator + tarEntry.getName());
                         prepDestination(destPath, tarEntry.isDirectory());
 
-
-                        if (!startsWithPath(destPath.getCanonicalPath(), destinationDirectory)) {
+                        if (!startsWithPath(destPath.getCanonicalPath(), canonicalDestinationDirectory)) {
                             throw new IOException(
-                                    "Expanding " + tarEntry.getName() + " would create file outside of " + destinationDirectory
+                                    "Expanding " + tarEntry.getName() + " would create file outside of " + canonicalDestinationDirectory
                             );
                         }
 

frontend-plugin-core/src/test/java/com/github/eirslett/maven/plugins/frontend/lib/DefaultArchiveExtractorTest.java

@@ -0,0 +1,68 @@
+package com.github.eirslett.maven.plugins.frontend.lib;
+
+import org.hamcrest.CoreMatchers;
+import org.junit.Assume;
+import org.junit.Before;
+import org.junit.Rule;
+import org.junit.Test;
+import org.junit.rules.TemporaryFolder;
+
+import java.io.File;
+import java.io.IOException;
+import java.nio.file.Files;
+import java.nio.file.Path;
+
+import static org.junit.Assert.assertThat;
+import static org.junit.Assert.fail;
+import static org.junit.Assume.assumeTrue;
+
+public class DefaultArchiveExtractorTest {
+
+    private final String BAD_TAR = "src/test/resources/bad.tgz";
+    private final String GOOD_TAR = "src/test/resources/good.tgz";
+
+    @Rule
+    public final TemporaryFolder temp = new TemporaryFolder();
+
+    private ArchiveExtractor extractor;
+
+    @Before
+    public void setup() {
+        extractor = new DefaultArchiveExtractor();
+    }
+
+    @Test
+    public void extractGoodTarFile() throws Exception {
+        File destination = temp.newFolder("destination");
+        extractor.extract(GOOD_TAR, destination.getPath());
+    }
+
+    @Test
+    public void extractGoodTarFileSymlink() throws Exception {
+        File destination = temp.newFolder("destination");
+        Path link = createSymlinkOrSkipTest(temp.getRoot().toPath().resolve("link"), destination.toPath());
+        extractor.extract(GOOD_TAR, link.toString());
+    }
+
+    @Test(expected = ArchiveExtractionException.class)
+    public void extractBadTarFile() throws Exception {
+        File destination = temp.newFolder("destination");
+        extractor.extract(BAD_TAR, destination.getPath());
+    }
+
+    @Test(expected = ArchiveExtractionException.class)
+    public void extractBadTarFileSymlink() throws Exception {
+        File destination = temp.newFolder("destination");
+        Path link = createSymlinkOrSkipTest(temp.getRoot().toPath().resolve("link"), destination.toPath());
+        extractor.extract(BAD_TAR, link.toString());
+    }
+
+    private Path createSymlinkOrSkipTest(Path link, Path target) {
+        try {
+            return Files.createSymbolicLink(link, target);
+        } catch (UnsupportedOperationException | IOException e) {
+            assumeTrue("symlinks not supported", false);
+            return null;
+        }
+    }
+}