[ADD] XQuery: session:client-id. Closes BaseXdb#2132

Author: ChristianGruen

basex-api/src/main/java/org/basex/query/func/ApiFunction.java

@@ -112,6 +112,9 @@ public enum ApiFunction implements AFunction {
   _SESSION_ACCESSED(SessionAccessed::new, "accessed()",
       params(), DATE_TIME_O, SESSION_URI),
   /** XQuery function. */
+  _SESSION_CLIENT_ID(SessionClientId::new, "client-id()",
+      params(), STRING_ZO, SESSION_URI),
+  /** XQuery function. */
   _SESSION_CLOSE(SessionClose::new, "close()",
       params(), EMPTY_SEQUENCE_Z, SESSION_URI),
   /** XQuery function. */

basex-api/src/main/java/org/basex/query/func/session/SessionClientId.java

@@ -0,0 +1,20 @@
+package org.basex.query.func.session;
+
+import org.basex.query.*;
+import org.basex.query.value.item.*;
+import org.basex.query.value.seq.*;
+import org.basex.util.*;
+
+/**
+ * Function implementation.
+ *
+ * @author BaseX Team 2005-22, BSD License
+ * @author Christian Gruen
+ */
+public final class SessionClientId extends SessionFn {
+  @Override
+  public Item item(final QueryContext qc, final InputInfo ii) throws QueryException {
+    final String id = request(qc).getRequestedSessionId();
+    return id != null ? Str.get(id) : Empty.VALUE;
+  }
+}