[Server] Publish the dev server's port through a file

The smoke test parsed the listening port out of the dev server's stdout,
but the server announces it from the main thread while the logger thread
writes to the same stream. A log line can land inside the announcement —
Arch CI caught it — leaving the digits on the next line, so the test read
nothing and failed.

Add --port-file, written through QSaveFile once the server listens, and
read the port from there instead of from the log. The file is either
absent or complete, so logging cannot corrupt the handshake.

servatrice/dev/main.cpp

@@ -15,12 +15,14 @@
 #include "smtpclient.h"
 #include "version_string.h"
 
+#include <QByteArray>
 #include <QCommandLineOption>
 #include <QCommandLineParser>
 #include <QCoreApplication>
 #include <QDir>
 #include <QFile>
 #include <QMetaObject>
+#include <QSaveFile>
 #include <QString>
 #include <QThread>
 #include <cstdlib>
@@ -88,6 +90,23 @@ void dumpState(Servatrice &server, const Servatrice_InMemoryDatabaseInterface &d
     std::cout << "servatrice-dev: log entries=" << database.getLogEntries().size() << std::endl;
 }
 
+/**
+ * @brief Publishes the bound port the way a script can read it.
+ *
+ * The stdout announcement is written from this thread while the logger thread writes to the same
+ * stream, so a reader can see a log line inside it. A file written through QSaveFile is either
+ * absent or complete, which makes the port deterministic to consume.
+ */
+bool writeListeningPort(const QString &path, int port)
+{
+    QSaveFile file(path);
+    if (!file.open(QIODevice::WriteOnly | QIODevice::Truncate)) {
+        return false;
+    }
+    file.write(QByteArray::number(port) + '\n');
+    return file.commit();
+}
+
 } // namespace
 
 int main(int argc, char *argv[])
@@ -103,9 +122,13 @@ int main(int argc, char *argv[])
     parser.addVersionOption();
 
     QCommandLineOption portOption({"p", "port"}, "TCP port to listen on; 0 picks an ephemeral port.", "port", "0");
+    QCommandLineOption portFileOption("port-file",
+                                      "Write the bound listening port to this file once the server listens.",
+                                      "path");
     QCommandLineOption seedOption("seed", "Seed for the game RNG; random when omitted.", "seed");
     QCommandLineOption dumpStateOption("dump-state", "Print the server state after startup and keep serving.");
     parser.addOption(portOption);
+    parser.addOption(portFileOption);
     parser.addOption(seedOption);
     parser.addOption(dumpStateOption);
     parser.process(app);
@@ -168,6 +191,12 @@ int main(int argc, char *argv[])
         if (listeningPort <= 0) {
             std::cerr << "servatrice-dev: the server is not listening" << std::endl;
             retval = EXIT_FAILURE;
+        } else {
+            const QString portFilePath = parser.value(portFileOption);
+            if (!portFilePath.isEmpty() && !writeListeningPort(portFilePath, listeningPort)) {
+                std::cerr << "servatrice-dev: cannot write the listening port to " << portFilePath.toStdString()
+                          << std::endl;
+                retval = EXIT_FAILURE;
             } else {
                 std::cout << "servatrice-dev: listening on port " << listeningPort << std::endl;
                 if (parser.isSet(dumpStateOption)) {
@@ -176,6 +205,7 @@ int main(int argc, char *argv[])
                 retval = QCoreApplication::exec();
             }
         }
+    }
 
     qInstallMessageHandler(nullptr);
 

tests/server_dev_smoke_test.cpp

@@ -17,6 +17,7 @@
 #include <QCoreApplication>
 #include <QElapsedTimer>
 #include <QEventLoop>
+#include <QFile>
 #include <QList>
 #include <QProcess>
 #include <QProcessEnvironment>
@@ -92,6 +93,7 @@ protected:
     void SetUp() override
     {
         ASSERT_TRUE(tempDir.isValid());
+        portFilePath = tempDir.filePath(QStringLiteral("listening-port"));
 
         // servatrice-dev writes its throwaway settings under QDir::tempPath(); pointing that at
         // a directory the test owns means a terminated server cannot leave an ini behind.
@@ -102,9 +104,10 @@ protected:
         process.setProcessEnvironment(environment);
         process.setProcessChannelMode(QProcess::SeparateChannels);
         process.start(QStringLiteral(SERVATRICE_DEV_BINARY),
-                      {QStringLiteral("--port"), QStringLiteral("0"), QStringLiteral("--seed"), QStringLiteral("42")});
+                      {QStringLiteral("--port"), QStringLiteral("0"), QStringLiteral("--seed"), QStringLiteral("42"),
+                       QStringLiteral("--port-file"), portFilePath});
         ASSERT_TRUE(process.waitForStarted(kStartupTimeoutMs)) << process.errorString().toStdString();
-        ASSERT_TRUE(readListeningPort()) << "servatrice-dev did not announce a listening port.\nstdout:\n"
+        ASSERT_TRUE(readListeningPort()) << "servatrice-dev did not publish its listening port.\nstdout:\n"
                                          << stdoutText.toStdString() << "\nstderr:\n"
                                          << stderrText.toStdString();
 
@@ -128,34 +131,32 @@ protected:
         }
     }
 
-    /// @brief Reads the child's output until it announces the ephemeral port it listens on.
+    /// @brief Waits for the child to publish the ephemeral port it listens on.
     bool readListeningPort()
     {
-        const QString prefix = QStringLiteral("servatrice-dev: listening on port ");
         QElapsedTimer elapsed;
         elapsed.start();
         while (elapsed.elapsed() < kStartupTimeoutMs) {
-            if (!process.waitForReadyRead(100)) {
+            // The child logs heavily during startup; keep its pipes drained so it cannot block.
+            drainProcessOutput();
+
+            QFile portFile(portFilePath);
+            if (portFile.open(QIODevice::ReadOnly)) {
+                bool ok = false;
+                const int port = QString::fromLatin1(portFile.readAll()).trimmed().toInt(&ok);
+                if (ok && port > 0) {
+                    listeningPort = port;
+                    return true;
+                }
+            }
+
             if (process.state() == QProcess::NotRunning) {
                 drainProcessOutput();
                 return false;
             }
-                continue;
+            QThread::msleep(20);
         }
         drainProcessOutput();
-
-            const int at = stdoutText.indexOf(prefix);
-            if (at < 0) {
-                continue;
-            }
-            const int end = stdoutText.indexOf(QLatin1Char('\n'), at);
-            if (end < 0) {
-                continue;
-            }
-            bool ok = false;
-            listeningPort = stdoutText.mid(at + prefix.size(), end - at - prefix.size()).trimmed().toInt(&ok);
-            return ok && listeningPort > 0;
-        }
         return false;
     }
 
@@ -228,6 +229,7 @@ protected:
 
     QProcess process;
     QTemporaryDir tempDir;
+    QString portFilePath;
     StubNetworkSettingsProvider provider;
     std::unique_ptr<RemoteClient> client;
     int listeningPort = 0;