Allow to listen for script output

Add a listener for script output, which provides the script and the
output being written.

Part of zaproxy#5113 - Allow to differentiate scripts' output

src/org/zaproxy/zap/extension/script/ExtensionScript.java

@@ -40,6 +40,8 @@
 import java.util.HashMap;
 import java.util.List;
 import java.util.Map;
+import java.util.Objects;
+import java.util.concurrent.CopyOnWriteArrayList;
 
 import javax.script.Invocable;
 import javax.script.ScriptContext;
@@ -152,6 +154,15 @@ public class ExtensionScript extends ExtensionAdaptor implements CommandLineList
 	 */
 	private List<File> trackedDirs = Collections.synchronizedList(new ArrayList<>());
 
+    /**
+     * The script output listeners added to the extension.
+     * 
+     * @see #addScriptOutputListener(ScriptOutputListener)
+     * @see #invokeScriptImpl(ScriptWrapper)
+     * @see #removeScriptOutputListener(ScriptOutputListener)
+     */
+    private List<ScriptOutputListener> outputListeners = new CopyOnWriteArrayList<>();
+
     public ExtensionScript() {
         super(NAME);
         this.setOrder(EXTENSION_ORDER);
@@ -1191,17 +1202,16 @@ public List<ScriptWrapper> getTemplates(ScriptType type) {
 	 * ever script. It also supports script specific writers.
 	 */
 	private Writer getWriters(ScriptWrapper script) {
+		Writer delegatee = this.writers;
 		Writer writer = script.getWriter();
-		if (writer == null) {
-			// No script specific writer, just return the std one
-			return this.writers;
-		} else {
-			// Return the script specific writer in addition to the std one
+		if (writer != null) {
+			// Use the script specific writer in addition to the std one
 			MultipleWriters scriptWriters = new MultipleWriters();
 			scriptWriters.addWriter(writer);
 			scriptWriters.addWriter(writers);
-			return scriptWriters;
+			delegatee = scriptWriters;
 		}
+		return new ScriptWriter(script, delegatee, outputListeners);
 	}
 
 	/**
@@ -1609,14 +1619,53 @@ public void removeListener(ScriptEventListener listener) {
 		this.listeners.remove(listener);
 	}
 
+	/**
+	 * Adds the given writer.
+	 * <p>
+	 * It will be written to each time a script writes some output.
+	 *
+	 * @param writer the writer to add.
+	 * @see #removeWriter(Writer)
+	 * @see #addScriptOutputListener(ScriptOutputListener)
+	 */
 	public void addWriter(Writer writer) {
 		this.writers.addWriter(writer);
 	}
 
+	/**
+	 * Removes the given writer.
+	 *
+	 * @param writer the writer to remove.
+	 * @see #addWriter(Writer)
+	 */
 	public void removeWriter(Writer writer) {
 		this.writers.removeWriter(writer);
 	}
 
+	/**
+	 * Adds the given script output listener.
+	 *
+	 * @param listener the listener to add.
+	 * @since TODO add version
+	 * @throws NullPointerException if the given listener is {@code null}.
+	 * @see #removeScriptOutputListener(ScriptOutputListener)
+	 */
+	public void addScriptOutputListener(ScriptOutputListener listener) {
+		outputListeners.add(Objects.requireNonNull(listener, "The parameter listener must not be null."));
+	}
+
+	/**
+	 * Removes the given script output listener.
+	 *
+	 * @param listener the listener to remove.
+	 * @since TODO add version
+	 * @throws NullPointerException if the given listener is {@code null}.
+	 * @see #addScriptOutputListener(ScriptOutputListener)
+	 */
+	public void removeScriptOutputListener(ScriptOutputListener listener) {
+		outputListeners.remove(Objects.requireNonNull(listener, "The parameter listener must not be null."));
+	}
+
 	public ScriptUI getScriptUI() {
 		return scriptUI;
 	}
@@ -1852,4 +1901,39 @@ public void sessionModeChanged(Mode mode) {
 		}
 
 	}
+
+    /**
+     * A {@code Writer} that notifies {@link ScriptOutputListener}s when writing.
+     */
+    private static class ScriptWriter extends Writer {
+
+        private final ScriptWrapper script;
+        private final Writer delegatee;
+        private final List<ScriptOutputListener> outputListeners;
+
+        public ScriptWriter(ScriptWrapper script, Writer delegatee, List<ScriptOutputListener> outputListeners) {
+            this.script = Objects.requireNonNull(script);
+            this.delegatee = Objects.requireNonNull(delegatee);
+            this.outputListeners = Objects.requireNonNull(outputListeners);
+        }
+
+        @Override
+        public void write(char[] cbuf, int off, int len) throws IOException {
+            delegatee.write(cbuf, off, len);
+            if (!outputListeners.isEmpty()) {
+                String output = new String(cbuf, off, len);
+                outputListeners.forEach(e -> e.output(script, output));
+            }
+        }
+
+        @Override
+        public void flush() throws IOException {
+            delegatee.flush();
+        }
+
+        @Override
+        public void close() throws IOException {
+            delegatee.close();
+        }
+    }
 }

src/org/zaproxy/zap/extension/script/ScriptOutputListener.java

@@ -0,0 +1,40 @@
+/*
+ * Zed Attack Proxy (ZAP) and its related class files.
+ *
+ * ZAP is an HTTP/HTTPS proxy for assessing web application security.
+ *
+ * Copyright 2018 The ZAP Development Team
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+package org.zaproxy.zap.extension.script;
+
+/**
+ * A listener for scripts' output.
+ *
+ * @since TODO add version
+ * @see ExtensionScript#addScriptOutputListener(ScriptOutputListener)
+ */
+@FunctionalInterface
+public interface ScriptOutputListener {
+
+    /**
+     * Called each time a script writes some output.
+     * <p>
+     * Can be called concurrently.
+     *
+     * @param script the source of the output.
+     * @param output the new output.
+     */
+    void output(ScriptWrapper script, String output);
+}