Avoid exception when getting zero-length xattrs

Closes: #1041

Author: matthiasblaesing

CHANGES.md

@@ -14,6 +14,7 @@ Bug Fixes
 ---------
 * [#1036](https://github.com/java-native-access/jna/issues/1036): `Advapi32Util.registryValueExists` called on non existing key raises exception instead of returning `false` - [@matthiasblaesing](https://github.com/matthiasblaesing).
 * [#384](https://github.com/java-native-access/jna/issues/384): Android only supports loading libraries through the JVM `System#loadLibrary` mechanism, defaulting `jna.nosys` to `true` disabled that code path - [@matthiasblaesing](https://github.com/matthiasblaesing).
+* [#1041](https://github.com/java-native-access/jna/pull/1041): Avoid IllegalArgumentException when reading xattrs with zero length - [@jrobhoward](https://github.com/jrobhoward).
 
 Release 5.1.0
 =============

contrib/platform/src/com/sun/jna/platform/linux/XAttrUtil.java

@@ -255,6 +255,10 @@ public static Memory getXAttrAsMemory(String path, String name) throws IOExcepti
                 throw new IOException("errno: " + eno);
             }
 
+            if (retval.longValue() == 0) {
+                return null;
+            }
+
             valueMem = new Memory(retval.longValue());
             retval = XAttr.INSTANCE.getxattr(path, name, valueMem, new size_t(valueMem.size()));
             if (retval.longValue() < 0) {
@@ -352,6 +356,10 @@ public static Memory lGetXAttrAsMemory(String path, String name) throws IOExcept
                 throw new IOException("errno: " + eno);
             }
 
+            if (retval.longValue() == 0) {
+                return null;
+            }
+
             valueMem = new Memory(retval.longValue());
             retval = XAttr.INSTANCE.lgetxattr(path, name, valueMem, new size_t(valueMem.size()));
             if (retval.longValue() < 0) {
@@ -445,6 +453,10 @@ public static Memory fGetXAttrAsMemory(int fd, String name) throws IOException {
                 throw new IOException("errno: " + eno);
             }
 
+            if (retval.longValue() == 0) {
+                return null;
+            }
+
             valueMem = new Memory(retval.longValue());
             retval = XAttr.INSTANCE.fgetxattr(fd, name, valueMem, new size_t(valueMem.size()));
             if (retval.longValue() < 0) {

contrib/platform/src/com/sun/jna/platform/mac/XAttrUtil.java

@@ -58,6 +58,9 @@ public static String getXAttr(String path, String name) {
 		if (bufferLength < 0)
 			return null;
 
+		if (bufferLength == 0)
+			return "";
+
 		Memory valueBuffer = new Memory(bufferLength);
 		long valueLength = XAttr.INSTANCE.getxattr(path, name, valueBuffer, bufferLength, 0, 0);
 

contrib/platform/test/com/sun/jna/platform/linux/XAttrUtilTest.java

@@ -24,6 +24,7 @@
  */
 package com.sun.jna.platform.linux;
 
+import com.sun.jna.Memory;
 import java.io.File;
 import java.io.IOException;
 import java.util.Collection;
@@ -33,12 +34,16 @@
 import static org.junit.Assert.assertEquals;
 import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertTrue;
+import static org.junit.Assert.assertNull;
+import static org.junit.Assert.assertNotNull;
 
 public class XAttrUtilTest {
     private static final String TEST_STRING = "Žluťoučký kůň úpěl nebo tak něco.";
     private static final String TEST_STRING_2 = "Příliš žluťoučký kůň úpěl ďábelské ódy.";
+    private static final String TEST_EMPTY_STRING = "";
     private static final String TEST_ATTRIBUTE = "user.test";
     private static final String TEST_ATTRIBUTE_FOO = TEST_ATTRIBUTE + ".foo";
+    private static final String TEST_ATTRIBUTE_EMPTY = TEST_ATTRIBUTE + ".empty";
 
     @Test
     public void setXAttr() throws IOException {
@@ -66,5 +71,26 @@ public void setXAttr() throws IOException {
         xattrs = XAttrUtil.lListXAttr(file.getAbsolutePath());
         assertFalse(xattrs.contains(TEST_ATTRIBUTE));
         assertTrue(xattrs.contains(TEST_ATTRIBUTE_FOO));
+
+        file.delete();
+    }
+
+    @Test
+    public void testGetXAttr() throws IOException {
+        File file = File.createTempFile("xattr", "test");
+        file.deleteOnExit();
+
+        XAttrUtil.setXAttr(file.getAbsolutePath(), TEST_ATTRIBUTE_EMPTY, TEST_EMPTY_STRING);
+
+        Memory memoryReadMissing = XAttrUtil.getXAttrAsMemory(file.getAbsolutePath(), TEST_ATTRIBUTE_EMPTY);
+        byte[] byteReadMissing = XAttrUtil.getXAttrBytes(file.getAbsolutePath(), TEST_ATTRIBUTE_EMPTY);
+        String stringReadMissing = XAttrUtil.getXAttr(file.getAbsolutePath(), TEST_ATTRIBUTE_EMPTY);
+        assertNull(memoryReadMissing);
+        assertNotNull(byteReadMissing);
+        assertEquals(0, byteReadMissing.length);
+        assertNotNull(stringReadMissing);
+        assertTrue(stringReadMissing.isEmpty());
+
+        file.delete();
     }
 }

contrib/platform/test/com/sun/jna/platform/mac/XAttrUtilTest.java

@@ -12,6 +12,8 @@
  */
 package com.sun.jna.platform.mac;
 
+import com.sun.jna.Memory;
+import com.sun.jna.Pointer;
 import java.io.File;
 import java.util.Arrays;
 import java.util.List;
@@ -58,6 +60,10 @@ public void testGetXAttr() {
 		value = XAttrUtil.getXAttr(testPath, "JNA");
 
 		assertEquals(Arrays.toString("Java Native Access".getBytes()), Arrays.toString(value.getBytes()));
+
+                XAttr.INSTANCE.setxattr(testPath, "JNA.empty", Pointer.NULL, 0, 0, 0);
+                value = XAttrUtil.getXAttr(testPath, "JNA.empty");
+                assertEquals("", value);
 	}
 
 	public void testSetXAttr() {