Display supported commands when subcommand is not provided

Signed-off-by: Shawn O. Pearce <sop@google.com>

src/main/java/com/google/gerrit/server/ssh/DispatchCommand.java

@@ -20,6 +20,7 @@ import com.google.inject.Provider;
 import org.apache.sshd.server.CommandFactory.Command;
 
 import java.io.IOException;
+import java.io.UnsupportedEncodingException;
 import java.util.Map;
 
 /**
@@ -37,8 +38,13 @@ public class DispatchCommand extends BaseCommand {
 
   @Override
   public void start() throws IOException {
-    int sp = commandLine.indexOf(' ');
+    if (commandLine.isEmpty()) {
+      usage();
+      return;
+    }
+
     final String name, args;
+    int sp = commandLine.indexOf(' ');
     if (0 < sp) {
       name = commandLine.substring(0, sp);
       while (Character.isWhitespace(commandLine.charAt(sp))) {
@@ -78,4 +84,20 @@ public class DispatchCommand extends BaseCommand {
       exit.onExit(127);
     }
   }
+
+  private void usage() throws IOException, UnsupportedEncodingException {
+    final StringBuilder usage = new StringBuilder();
+    usage.append("usage: " + prefix + " COMMAND [ARGS]\n");
+    usage.append("\n");
+    usage.append("Available commands of " + prefix + " are:\n");
+    for (Map.Entry<String, Provider<Command>> e : commands.entrySet()) {
+      usage.append("   ");
+      usage.append(e.getKey());
+      usage.append("\n");
+    }
+    usage.append("\n");
+    err.write(usage.toString().getBytes("UTF-8"));
+    err.flush();
+    exit.onExit(1);
+  }
 }

src/main/java/com/google/gerrit/server/ssh/DispatchCommandProvider.java

@@ -24,9 +24,10 @@ import org.apache.sshd.server.CommandFactory.Command;
 
 import java.lang.annotation.Annotation;
 import java.util.Collections;
-import java.util.HashMap;
+import java.util.LinkedHashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.TreeMap;
 
 /**
  * Creates DispatchCommand using commands registered by {@link CommandModule}.
@@ -76,7 +77,7 @@ public class DispatchCommandProvider implements Provider<DispatchCommand> {
   @SuppressWarnings("unchecked")
   private Map<String, Provider<Command>> createMap() {
     final Map<String, Provider<Command>> m =
-        new HashMap<String, Provider<Command>>();
+        new TreeMap<String, Provider<Command>>();
 
     for (final Binding<?> b : allCommands()) {
       final Annotation annotation = b.getKey().getAnnotation();
@@ -88,7 +89,7 @@ public class DispatchCommandProvider implements Provider<DispatchCommand> {
       }
     }
 
-    return Collections.unmodifiableMap(m);
+    return Collections.unmodifiableMap(new LinkedHashMap(m));
   }
 
   private static final TypeLiteral<Command> type =