Index: /trunk/src/org/openstreetmap/josm/actions/ApiPreconditionChecker.java
===================================================================
--- /trunk/src/org/openstreetmap/josm/actions/ApiPreconditionChecker.java	(revision 1693)
+++ /trunk/src/org/openstreetmap/josm/actions/ApiPreconditionChecker.java	(revision 1693)
@@ -0,0 +1,128 @@
+// License: GPL. For details, see LICENSE file.
+package org.openstreetmap.josm.actions;
+
+import static org.openstreetmap.josm.tools.I18n.tr;
+
+import java.util.Collection;
+import java.util.LinkedList;
+import java.util.List;
+import java.util.Map.Entry;
+
+import javax.swing.JOptionPane;
+
+import org.openstreetmap.josm.Main;
+import org.openstreetmap.josm.actions.UploadAction.UploadHook;
+import org.openstreetmap.josm.data.osm.OsmPrimitive;
+import org.openstreetmap.josm.data.osm.Way;
+import org.openstreetmap.josm.io.OsmApi;
+import org.openstreetmap.josm.io.OsmApiInitializationException;
+
+public class ApiPreconditionChecker implements UploadHook {
+
+    public boolean checkUpload(Collection<OsmPrimitive> add, Collection<OsmPrimitive> update,
+            Collection<OsmPrimitive> delete) {
+        OsmApi api = OsmApi.getOsmApi();
+        try {
+            api.initialize();
+            long maxNodes = 0;
+            if (api.getCapabilities().isDefined("waynodes", "maximum")) {
+                maxNodes = api.getCapabilities().getLong("waynodes","maximum");
+            }
+            long maxElements = 0;
+            if (api.getCapabilities().isDefined("changesets", "maximum_elements")) {
+                maxElements = api.getCapabilities().getLong("changesets", "maximum_elements");
+            }
+
+            if (maxNodes > 0) {
+                if( !checkMaxNodes(add, maxNodes))
+                    return false;
+                if( !checkMaxNodes(update, maxNodes))
+                    return false;
+                if( !checkMaxNodes(delete, maxNodes))
+                    return false;
+            }
+
+            if (maxElements  > 0) {
+                int total = 0;
+                total = add.size() + update.size() + delete.size();
+                if(total > maxElements) {
+                    JOptionPane.showMessageDialog(
+                            Main.parent,
+                            tr("Current number of changes exceeds the max. number of changes, current is {0}, max is {1}",
+                                    total,
+                                    maxElements
+                            ),
+                            tr("API Capabilities Violation"),
+                            JOptionPane.ERROR_MESSAGE
+                    );
+                    return false;
+                }
+            }
+        } catch (OsmApiInitializationException e) {
+            e.printStackTrace();
+            JOptionPane.showMessageDialog(
+                    Main.parent,
+                    tr("Failed to initialize API. Please try again later."),
+                    tr("API initialization failed"),
+                    JOptionPane.ERROR_MESSAGE
+            );
+            return false;
+        }
+        return true;
+    }
+
+    private boolean checkMaxNodes(Collection<OsmPrimitive> add, long maxNodes) {
+        for (OsmPrimitive osmPrimitive : add) {
+            if (osmPrimitive.keys == null) {
+                continue;
+            }
+            for (Entry<String,String> e : osmPrimitive.keys.entrySet()) {
+                if(e.getValue().length() > 255) {
+                    if (osmPrimitive.deleted) {
+                        // if OsmPrimitive is going to be deleted we automatically shorten the
+                        // value
+                        System.out.println(
+                                tr("Warning: automatically truncating value of tag ''{0}'' on deleted primitive {1}",
+                                        e.getKey(),
+                                        Long.toString(osmPrimitive.id)
+                                )
+                        );
+                        osmPrimitive.put(e.getKey(), e.getValue().substring(0, 255));
+                        continue;
+                    }
+                    JOptionPane.showMessageDialog(Main.parent,
+                            tr("Length of value for tag ''{0}'' on primitive {1} exceeds the max. allowed length {2}. Values length is {3}.",
+                                    e.getKey(), Long.toString(osmPrimitive.id), 255, e.getValue().length()
+                            ),
+                            tr("Precondition Violation"),
+                            JOptionPane.ERROR_MESSAGE
+                    );
+                    List<OsmPrimitive> newNodes = new LinkedList<OsmPrimitive>();
+                    newNodes.add(osmPrimitive);
+                    Main.ds.setSelected(newNodes);
+                    return false;
+                }
+            }
+
+            if (osmPrimitive instanceof Way &&
+                    ((Way)osmPrimitive).nodes.size() > maxNodes) {
+                JOptionPane.showMessageDialog(
+                        Main.parent,
+                        tr("{0} nodes in way {1} exceed the max. allowed number of nodes {2}",
+                                ((Way)osmPrimitive).nodes.size(),
+                                Long.toString(osmPrimitive.id),
+                                maxNodes
+                        ),
+                        tr("API Capabilities Violation"),
+                        JOptionPane.ERROR_MESSAGE
+                );
+                List<OsmPrimitive> newNodes = new LinkedList<OsmPrimitive>();
+                newNodes.add(osmPrimitive);
+
+                Main.ds.setSelected(newNodes);
+                return false;
+            }
+        }
+        return true;
+    }
+}