From 60a7412c2fc35771a803039223c20560161d7687 Mon Sep 17 00:00:00 2001
From: Alva Swanson <alvasw@protonmail.com>
Date: Mon, 15 Apr 2024 17:55:30 +0200
Subject: [PATCH] Implement ControlPortFilePoller

---
 .../tor/process/ControlPortFilePoller.java    | 76 +++++++++++++++++++
 1 file changed, 76 insertions(+)
 create mode 100644 network/tor/tor/src/main/java/bisq/tor/process/ControlPortFilePoller.java

diff --git a/network/tor/tor/src/main/java/bisq/tor/process/ControlPortFilePoller.java b/network/tor/tor/src/main/java/bisq/tor/process/ControlPortFilePoller.java
new file mode 100644
index 0000000000..eb975897dc
--- /dev/null
+++ b/network/tor/tor/src/main/java/bisq/tor/process/ControlPortFilePoller.java
@@ -0,0 +1,76 @@
+/*
+ * This file is part of Bisq.
+ *
+ * Bisq is free software: you can redistribute it and/or modify it
+ * under the terms of the GNU Affero General Public License as published by
+ * the Free Software Foundation, either version 3 of the License, or (at
+ * your option) any later version.
+ *
+ * Bisq is distributed in the hope that it will be useful, but WITHOUT
+ * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
+ * FITNESS FOR A PARTICULAR PURPOSE. See the GNU Affero General Public
+ * License for more details.
+ *
+ * You should have received a copy of the GNU Affero General Public License
+ * along with Bisq. If not, see <http://www.gnu.org/licenses/>.
+ */
+
+package bisq.tor.process;
+
+import java.nio.file.Path;
+import java.util.Optional;
+import java.util.concurrent.CompletableFuture;
+import java.util.concurrent.atomic.AtomicBoolean;
+
+public class ControlPortFilePoller {
+    private final AtomicBoolean isRunning = new AtomicBoolean();
+    private final CompletableFuture<Integer> portCompletableFuture = new CompletableFuture<>();
+    private final Path controlPortFilePath;
+
+    public ControlPortFilePoller(Path controlPortFilePath) {
+        this.controlPortFilePath = controlPortFilePath;
+    }
+
+    public CompletableFuture<Integer> parsePort() {
+        boolean isSuccess = isRunning.compareAndSet(false, true);
+        if (isSuccess) {
+            startPoller();
+        }
+        return portCompletableFuture;
+    }
+
+    private void startPoller() {
+        Thread thread = new Thread(() -> {
+            try {
+                while (true) {
+                    Optional<Integer> optionalPort = parsePortFromFile();
+
+                    if (optionalPort.isPresent()) {
+                        portCompletableFuture.complete(optionalPort.get());
+                        break;
+                    } else {
+                        // We can't use Java's WatcherService because it misses events between event processing.
+                        // Tor writes the port to a swap file first, and renames it afterward.
+                        // The WatcherService can miss the second operation, causing a deadlock.
+                        //noinspection BusyWait
+                        Thread.sleep(100);
+                    }
+                }
+
+            } catch (ControlPortFileParseFailureException | InterruptedException e) {
+                portCompletableFuture.completeExceptionally(e);
+            }
+        });
+
+        thread.start();
+    }
+
+    private Optional<Integer> parsePortFromFile() {
+        if (!controlPortFilePath.toFile().exists()) {
+            return Optional.empty();
+        }
+
+        int controlPort = ControlPortFileParser.parse(controlPortFilePath);
+        return Optional.of(controlPort);
+    }
+}