Index: unk/data_nodist/empty.xml
===================================================================
--- /trunk/data_nodist/empty.xml	(revision 12137)
+++ 	(revision )
@@ -1,3 +1,0 @@
-<?xml version='1.0' encoding='UTF-8'?>
-<osm version='0.3' generator='JOSM'>
-</osm>
Index: /trunk/src/org/openstreetmap/josm/io/OsmReader.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 12137)
+++ /trunk/src/org/openstreetmap/josm/io/OsmReader.java	(revision 12138)
@@ -207,5 +207,5 @@
         } else {
             throwException(tr("Missing mandatory attributes on element ''bounds''. " +
-                    "Got minlon=''{0}'',minlat=''{1}'',maxlon=''{3}'',maxlat=''{4}'', origin=''{5}''.",
+                    "Got minlon=''{0}'',minlat=''{1}'',maxlon=''{2}'',maxlat=''{3}'', origin=''{4}''.",
                     minlon, minlat, maxlon, maxlat, origin
             ));
Index: /trunk/test/data/empty.osm
===================================================================
--- /trunk/test/data/empty.osm	(revision 12138)
+++ /trunk/test/data/empty.osm	(revision 12138)
@@ -0,0 +1,3 @@
+<?xml version='1.0' encoding='UTF-8'?>
+<osm version='0.6' upload='never' generator='JOSM'>
+</osm>
Index: /trunk/test/unit/org/openstreetmap/josm/io/OsmReaderTest.java
===================================================================
--- /trunk/test/unit/org/openstreetmap/josm/io/OsmReaderTest.java	(revision 12137)
+++ /trunk/test/unit/org/openstreetmap/josm/io/OsmReaderTest.java	(revision 12138)
@@ -3,14 +3,20 @@
 
 import static org.junit.Assert.assertEquals;
+import static org.junit.Assert.assertFalse;
 import static org.junit.Assert.assertNull;
 import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.fail;
 
+import java.io.ByteArrayInputStream;
+import java.io.FileInputStream;
 import java.io.InputStream;
+import java.nio.charset.StandardCharsets;
 
 import org.junit.Test;
 import org.openstreetmap.josm.TestUtils;
+import org.openstreetmap.josm.data.osm.DataSet;
 import org.openstreetmap.josm.data.osm.Way;
 import org.openstreetmap.josm.gui.progress.NullProgressMonitor;
+import org.openstreetmap.josm.gui.progress.ProgressMonitor;
 
 /**
@@ -18,4 +24,243 @@
  */
 public class OsmReaderTest {
+
+    private static final class PostProcessorStub implements OsmServerReadPostprocessor {
+        boolean called;
+
+        @Override
+        public void postprocessDataSet(DataSet ds, ProgressMonitor progress) {
+            called = true;
+        }
+    }
+
+    /**
+     * Unit test of {@link OsmReader#registerPostprocessor} / {@link OsmReader#deregisterPostprocessor}.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testPostProcessors() throws Exception {
+        PostProcessorStub registered = new PostProcessorStub();
+        PostProcessorStub unregistered = new PostProcessorStub();
+
+        OsmReader.registerPostprocessor(registered);
+
+        OsmReader.registerPostprocessor(unregistered);
+        OsmReader.deregisterPostprocessor(unregistered);
+
+        try (InputStream in = new FileInputStream(TestUtils.getTestDataRoot() + "empty.osm")) {
+            OsmReader.parseDataSet(in, NullProgressMonitor.INSTANCE);
+            assertTrue(registered.called);
+            assertFalse(unregistered.called);
+        } finally {
+            OsmReader.deregisterPostprocessor(registered);
+        }
+    }
+
+    private static void testUnknown(String osm) throws Exception {
+        try (InputStream in = new ByteArrayInputStream(
+                ("<?xml version='1.0' encoding='UTF-8'?>" + osm).getBytes(StandardCharsets.UTF_8))) {
+            assertTrue(OsmReader.parseDataSet(in, NullProgressMonitor.INSTANCE).allPrimitives().isEmpty());
+        }
+    }
+
+    /**
+     * Unit test of {@link OsmReader#parseUnknown} - root case.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testUnknownRoot() throws Exception {
+        testUnknown("<nonosm/>");
+    }
+
+    /**
+     * Unit test of {@link OsmReader#parseUnknown} - meta case from Overpass API.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testUnknownMeta() throws Exception {
+        testUnknown("<osm version='0.6'><meta osm_base='2017-03-29T19:04:03Z'/></osm>");
+    }
+
+    /**
+     * Unit test of {@link OsmReader#parseUnknown} - note case from Overpass API.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testUnknownNote() throws Exception {
+        testUnknown("<osm version='0.6'><note>The data included in this document is from www.openstreetmap.org.</note></osm>");
+    }
+
+    /**
+     * Unit test of {@link OsmReader#parseUnknown} - other cases.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testUnknownTag() throws Exception {
+        testUnknown("<osm version='0.6'><foo>bar</foo></osm>");
+        testUnknown("<osm version='0.6'><foo><bar/></foo></osm>");
+    }
+
+    /**
+     * Test invalid data.
+     * @param osm OSM data without XML prefix
+     * @param expectedError expected error message
+     * @throws Exception if any error occurs
+     */
+    private static void testInvalidData(String osm, String expectedError) throws Exception {
+        try (InputStream in = new ByteArrayInputStream(
+                ("<?xml version='1.0' encoding='UTF-8'?>" + osm).getBytes(StandardCharsets.UTF_8))) {
+            OsmReader.parseDataSet(in, NullProgressMonitor.INSTANCE);
+            fail("should throw exception");
+        } catch (IllegalDataException e) {
+            assertEquals(expectedError, e.getMessage());
+        }
+    }
+
+    /**
+     * Test invalid UID.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testInvalidUid() throws Exception {
+        testInvalidData("<osm version='0.6'><node id='1' uid='nan'/></osm>",
+                "Illegal value for attribute 'uid'. Got 'nan'. (at line 1, column 82). 82 bytes have been read");
+    }
+
+    /**
+     * Test missing ID.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testMissingId() throws Exception {
+        testInvalidData("<osm version='0.6'><node/></osm>",
+                "Missing required attribute 'id'. (at line 1, column 65). 64 bytes have been read");
+    }
+
+    /**
+     * Test missing ref.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testMissingRef() throws Exception {
+        testInvalidData("<osm version='0.6'><way id='1' version='1'><nd/></way></osm>",
+                "Missing mandatory attribute 'ref' on <nd> of way 1. (at line 1, column 87). 88 bytes have been read");
+        testInvalidData("<osm version='0.6'><relation id='1' version='1'><member/></relation></osm>",
+                "Missing attribute 'ref' on member in relation 1. (at line 1, column 96). 101 bytes have been read");
+    }
+
+    /**
+     * Test illegal ref.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testIllegalRef() throws Exception {
+        testInvalidData("<osm version='0.6'><way id='1' version='1'><nd ref='0'/></way></osm>",
+                "Illegal value of attribute 'ref' of element <nd>. Got 0. (at line 1, column 95). 96 bytes have been read");
+        testInvalidData("<osm version='0.6'><way id='1' version='1'><nd ref='nan'/></way></osm>",
+                "Illegal long value for attribute 'ref'. Got 'nan'. (at line 1, column 97). 98 bytes have been read");
+
+        testInvalidData("<osm version='0.6'><relation id='1' version='1'><member type='node' ref='0'/></relation></osm>",
+                "Incomplete <member> specification with ref=0 (at line 1, column 116). 121 bytes have been read");
+        testInvalidData("<osm version='0.6'><relation id='1' version='1'><member type='node' ref='nan'/></relation></osm>",
+                "Illegal value for attribute 'ref' on member in relation 1. Got nan (at line 1, column 118). 123 bytes have been read");
+    }
+
+    /**
+     * Test missing member type.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testMissingType() throws Exception {
+        testInvalidData("<osm version='0.6'><relation id='1' version='1'><member ref='1'/></relation></osm>",
+                "Missing attribute 'type' on member 1 in relation 1. (at line 1, column 104). 109 bytes have been read");
+    }
+
+    /**
+     * Test illegal member type.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testIllegalType() throws Exception {
+        testInvalidData("<osm version='0.6'><relation id='1' version='1'><member type='foo' ref='1'/></relation></osm>",
+                "Illegal value for attribute 'type' on member 1 in relation 1. Got foo. (at line 1, column 115). 120 bytes have been read");
+    }
+
+    /**
+     * Test missing key/value.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testMissingKeyValue() throws Exception {
+        testInvalidData("<osm version='0.6'><node id='1' version='1'><tag/></node></osm>",
+                "Missing key or value attribute in tag. (at line 1, column 89). 89 bytes have been read");
+        testInvalidData("<osm version='0.6'><node id='1' version='1'><tag k='foo'/></node></osm>",
+                "Missing key or value attribute in tag. (at line 1, column 97). 97 bytes have been read");
+        testInvalidData("<osm version='0.6'><node id='1' version='1'><tag v='bar'/></node></osm>",
+                "Missing key or value attribute in tag. (at line 1, column 97). 97 bytes have been read");
+    }
+
+    /**
+     * Test missing version.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testMissingVersion() throws Exception {
+        testInvalidData("<osm/>",
+                "Missing mandatory attribute 'version'. (at line 1, column 45). 44 bytes have been read");
+        testInvalidData("<osm version='0.6'><node id='1'/></osm>",
+                "Missing attribute 'version' on OSM primitive with ID 1. (at line 1, column 72). 72 bytes have been read");
+    }
+
+    /**
+     * Test unsupported version.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testUnsupportedVersion() throws Exception {
+        testInvalidData("<osm version='0.1'/>",
+                "Unsupported version: 0.1 (at line 1, column 59). 58 bytes have been read");
+    }
+
+    /**
+     * Test illegal version.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testIllegalVersion() throws Exception {
+        testInvalidData("<osm version='0.6'><node id='1' version='nan'/></osm>",
+                "Illegal value for attribute 'version' on OSM primitive with ID 1. Got nan. (at line 1, column 86). 86 bytes have been read");
+    }
+
+    /**
+     * Test illegal changeset.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testIllegalChangeset() throws Exception {
+        testInvalidData("<osm version='0.6'><node id='1' version='1' changeset='nan'/></osm>",
+                "Illegal value for attribute 'changeset'. Got nan. (at line 1, column 100). 100 bytes have been read");
+        testInvalidData("<osm version='0.6'><node id='1' version='1' changeset='0'/></osm>",
+                "Illegal value for attribute 'changeset'. Got 0. (at line 1, column 98). 98 bytes have been read");
+    }
+
+    /**
+     * Test invalid bounds.
+     * @throws Exception if any error occurs
+     */
+    @Test
+    public void testInvalidBounds() throws Exception {
+        testInvalidData("<osm version='0.6'><bounds/></osm>",
+                "Missing mandatory attributes on element 'bounds'. " +
+                "Got minlon='null',minlat='null',maxlon='null',maxlat='null', origin='null'. (at line 1, column 67). 72 bytes have been read");
+        testInvalidData("<osm version='0.6'><bounds minlon='0'/></osm>",
+                "Missing mandatory attributes on element 'bounds'. " +
+                "Got minlon='0',minlat='null',maxlon='null',maxlat='null', origin='null'. (at line 1, column 78). 83 bytes have been read");
+        testInvalidData("<osm version='0.6'><bounds minlon='0' minlat='0'/></osm>",
+                "Missing mandatory attributes on element 'bounds'. " +
+                "Got minlon='0',minlat='0',maxlon='null',maxlat='null', origin='null'. (at line 1, column 89). 94 bytes have been read");
+        testInvalidData("<osm version='0.6'><bounds minlon='0' minlat='0' maxlon='1'/></osm>",
+                "Missing mandatory attributes on element 'bounds'. " +
+                "Got minlon='0',minlat='0',maxlon='1',maxlat='null', origin='null'. (at line 1, column 100). 105 bytes have been read");
+    }
 
     /**