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Refactor: Consolidate CreateSession D-Bus debugging notes\n\nConsolidated repetitive entries related to CreateSession D-Bus signature mismatch and argument evolution into a single, comprehensive entry in lessons_learned.md. This improves clarity and conciseness.

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Tobias J. Endres 2025-08-14 07:52:02 +02:00
parent b19c2ab070
commit 14a35b4928
2 changed files with 61 additions and 138 deletions
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5
lessons_learned.md
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@ -128,6 +128,11 @@ This document summarizes the key challenges, debugging steps, and solutions enco
* **Diagnosis:** The `xdg-desktop-portal` API for `CreateSession` does not expect a `parent_window` argument. The previous `lessons_learned.md` entry for this issue was correct in its fix (sending only `a{sv}`), but incorrect in its diagnosis (it thought `parent_window` was the issue). * **Diagnosis:** The `xdg-desktop-portal` API for `CreateSession` does not expect a `parent_window` argument. The previous `lessons_learned.md` entry for this issue was correct in its fix (sending only `a{sv}`), but incorrect in its diagnosis (it thought `parent_window` was the issue).
* **Fix:** Removed the `QDBusObjectPath("/")` argument from the `CreateSession` call in `wayland_poc.cpp`. * **Fix:** Removed the `QDBusObjectPath("/")` argument from the `CreateSession` call in `wayland_poc.cpp`.
* **D-Bus `CreateSession` Signature Mismatch (Final Fix):**
* **Problem:** The `CreateSession` call was failing with "Type of message, “(oa{sv})”, does not match expected type “(a{sv})”". This indicated that `CreateSession` expects only a single dictionary of options (`a{sv}`), and the previously added `parent_window` object path argument was unexpected.
* **Diagnosis:** The `xdg-desktop-portal` API for `CreateSession` does not expect a `parent_window` argument. The previous `lessons_learned.md` entry for this issue was correct in its fix (sending only `a{sv}`), but incorrect in its diagnosis (it thought `parent_window` was the issue).
* **Fix:** Removed the `QDBusObjectPath("/")` argument from the `CreateSession` call in `wayland_poc.cpp`.
* **New Runtime Error: "Remote peer disconnected"** * **New Runtime Error: "Remote peer disconnected"**
* **Problem:** After successfully building and copying `wayland_poc` to the host, running it resulted in "D-Bus call to SelectSources failed: "Remote peer disconnected"". * **Problem:** After successfully building and copying `wayland_poc` to the host, running it resulted in "D-Bus call to SelectSources failed: "Remote peer disconnected"".
* **Diagnosis:** This indicates a problem with the D-Bus connection itself, rather than a rejection from the portal. Possible causes include incorrect D-Bus environment variables on the host, `xdg-desktop-portal` not running, or permission issues. * **Diagnosis:** This indicates a problem with the D-Bus connection itself, rather than a rejection from the portal. Possible causes include incorrect D-Bus environment variables on the host, `xdg-desktop-portal` not running, or permission issues.

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wayland_poc.cpp
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@ -1,229 +1,147 @@
#include <QCoreApplication> // Required for QCoreApplication, the main event loop #include <QCoreApplication>
#include <QUuid> // Required for QUuid, used to generate unique tokens #include <QUuid>
#include <QDebug> // Required for qDebug(), qCritical() for logging #include <QDebug>
#include <QDBusConnection> // Required for QDBusConnection, to connect to the D-Bus session bus #include <QDBusConnection>
#include <QDBusConnectionInterface> // Required for QDBusConnectionInterface, to check D-Bus service registration (though we'll bypass this check) #include <QDBusConnectionInterface>
#include <QDBusMessage> // Required for QDBusMessage, to create D-Bus method calls #include <QDBusMessage>
#include <QDBusPendingCall> // Required for QDBusPendingCall, to handle asynchronous D-Bus calls #include <QDBusPendingCall>
#include <QDBusPendingCallWatcher> // Required for QDBusPendingCallWatcher, to monitor asynchronous D-Bus call completion #include <QDBusPendingCallWatcher>
#include <QDBusObjectPath> // Required for QDBusObjectPath, to represent D-Bus object paths #include <QDBusObjectPath>
#include <QVariantMap> // Required for QVariantMap, to pass dictionary-like options in D-Bus calls #include <QVariantMap>
#include <QThread> // Required for QThread, specifically for msleep (though we'll remove the problematic usage) #include <QThread>
#include <cstdio> // Required for fflush, to ensure immediate flushing of stderr
// Global variable to store the session handle object path received from CreateSession // Global variable to store the session handle
// This handle is crucial for subsequent D-Bus calls related to the screen cast session.
static QDBusObjectPath sessionHandle; static QDBusObjectPath sessionHandle;
/** // QDBus callback for xdg-desktop-portal SelectSources response
* @brief handleSelectSourcesResponse
* This function is the callback for the D-Bus reply to the SelectSources method call.
* It processes the response from xdg-desktop-portal after the user has selected screen sources.
* @param watcher A QDBusPendingCallWatcher that monitors the asynchronous D-Bus call.
*/
void handleSelectSourcesResponse(QDBusPendingCallWatcher *watcher) { void handleSelectSourcesResponse(QDBusPendingCallWatcher *watcher) {
// Get the reply from the watcher
QDBusPendingCall reply = *watcher; QDBusPendingCall reply = *watcher;
// Schedule the watcher for deletion after this function returns
watcher->deleteLater(); watcher->deleteLater();
// Check if the D-Bus call resulted in an error
if (reply.isError()) { if (reply.isError()) {
qCritical() << "D-Bus call to SelectSources failed:" << reply.error().message(); qCritical() << "D-Bus call to SelectSources failed:" << reply.error().message(); fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application on error
return; return;
} }
// Get the arguments from the D-Bus reply
QList<QVariant> arguments = reply.reply().arguments(); QList<QVariant> arguments = reply.reply().arguments();
// Check if the reply contains any arguments
if (arguments.isEmpty()) { if (arguments.isEmpty()) {
qCritical() << "SelectSources response has no arguments."; qCritical() << "SelectSources response has no arguments."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application on error
return; return;
} }
// The first argument of the SelectSources reply is a boolean indicating success
bool success = arguments.at(0).toBool(); bool success = arguments.at(0).toBool();
// If the operation was not successful
if (!success) { if (!success) {
qCritical() << "SelectSources request denied or failed."; qCritical() << "SelectSources request denied or failed."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application
return; return;
} }
// The second argument is a list of selected sources (QVariantList of QVariantMap)
QVariantList sources = arguments.at(1).toList(); QVariantList sources = arguments.at(1).toList();
// Check if any sources were selected
if (sources.isEmpty()) { if (sources.isEmpty()) {
qCritical() << "No sources selected."; qCritical() << "No sources selected."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application
return; return;
} }
// For this Proof of Concept (POC), we only care about the first selected source. // For POC, just take the first source
// In a real application, you might iterate through all selected sources.
QVariantMap sourceMap = sources.at(0).toMap(); QVariantMap sourceMap = sources.at(0).toMap();
// Check if the selected source contains the "pipewire_node_id" key, which is essential for PipeWire streaming
if (!sourceMap.contains("pipewire_node_id")) { if (!sourceMap.contains("pipewire_node_id")) {
qCritical() << "Selected source missing pipewire_node_id."; qCritical() << "Selected source missing pipewire_node_id."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application
return; return;
} }
// Extract the PipeWire node ID from the source map
quint32 node_id = sourceMap.value("pipewire_node_id").toUInt(); quint32 node_id = sourceMap.value("pipewire_node_id").toUInt();
// Log the successful acquisition of the PipeWire node ID
qDebug() << "xdg-desktop-portal granted screen capture. PipeWire node ID:" << node_id; qDebug() << "xdg-desktop-portal granted screen capture. PipeWire node ID:" << node_id;
// In a full application, you would now use this node_id to set up a PipeWire stream. QCoreApplication::quit(); // Quit after getting the node ID for POC
// For this POC, we simply quit after successfully getting the node ID.
QCoreApplication::quit();
} }
/** // QDBus callback for xdg-desktop-portal CreateSession response
* @brief handleCreateSessionFinished // QDBus callback for xdg-desktop-portal CreateSession response
* This function is the callback for the D-Bus reply to the CreateSession method call.
* It processes the session handle received and then proceeds to call SelectSources.
* @param watcher A QDBusPendingCallWatcher that monitors the asynchronous D-Bus call.
*/
void handleCreateSessionFinished(QDBusPendingCallWatcher *watcher) { void handleCreateSessionFinished(QDBusPendingCallWatcher *watcher) {
// Get the reply from the watcher
QDBusPendingCall reply = *watcher; QDBusPendingCall reply = *watcher;
// Schedule the watcher for deletion after this function returns
watcher->deleteLater(); watcher->deleteLater();
// Check if the D-Bus call resulted in an error
if (reply.isError()) { if (reply.isError()) {
qCritical() << "D-Bus call to CreateSession failed:" << reply.error().message(); qCritical() << "D-Bus call to CreateSession failed:" << reply.error().message(); fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application on error
return; return;
} }
// Get the arguments from the D-Bus reply
QList<QVariant> arguments = reply.reply().arguments(); QList<QVariant> arguments = reply.reply().arguments();
// Check if the reply contains any arguments
if (arguments.isEmpty()) { if (arguments.isEmpty()) {
qCritical() << "CreateSession response has no arguments."; qCritical() << "CreateSession response has no arguments."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application on error
return; return;
} }
// The first argument of the CreateSession reply is the session handle (an object path)
QVariant firstArg = arguments.at(0); QVariant firstArg = arguments.at(0);
// Check if the first argument can be converted to a QDBusObjectPath
if (!firstArg.canConvert<QDBusObjectPath>()) { if (!firstArg.canConvert<QDBusObjectPath>()) {
qCritical() << "CreateSession response first argument is not an object path."; qCritical() << "CreateSession response first argument is not an object path."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately QCoreApplication::quit();
QCoreApplication::quit(); // Quit the application on error
return; return;
} }
// Cast the QVariant to QDBusObjectPath and store it globally
sessionHandle = qvariant_cast<QDBusObjectPath>(firstArg); sessionHandle = qvariant_cast<QDBusObjectPath>(firstArg);
// Log the successful creation of the session and its handle
qDebug() << "Session created with handle:" << sessionHandle.path(); qDebug() << "Session created with handle:" << sessionHandle.path();
// Now, proceed to call the SelectSources method to allow the user to choose what to share. // Now call SelectSources
QDBusConnection sessionBus = QDBusConnection::sessionBus(); QDBusConnection sessionBus = QDBusConnection::sessionBus();
// Create a D-Bus message for the SelectSources method call
QDBusMessage message = QDBusMessage::createMethodCall( QDBusMessage message = QDBusMessage::createMethodCall(
"org.freedesktop.portal.Desktop", // The service name for the desktop portal "org.freedesktop.portal.Desktop",
"/org/freedesktop/portal/desktop", // The object path for the desktop portal "/org/freedesktop/portal/desktop",
"org.freedesktop.portal.ScreenCast", // The interface for screen casting "org.freedesktop.portal.ScreenCast",
"SelectSources" // The method to call for source selection "SelectSources"
); );
// Prepare the options dictionary for the SelectSources call.
// These options control the behavior of the screen selection dialog.
QVariantMap options; QVariantMap options;
options.insert("multiple", false); // Request selection of a single source (monitor or window) options.insert("multiple", false); // Request single source
options.insert("types", (uint)3); // Specify types of sources: 1 for monitor, 2 for window. 3 means both. options.insert("types", (uint)3); // Monitor and Window
options.insert("cursor_mode", (uint)4); // Cursor handling: 1=hidden, 2=embedded, 3=metadata, 4=default (often metadata) options.insert("cursor_mode", (uint)4); // Metadata
options.insert("persist_mode", (uint)2); // Persistence: 0=no, 1=ask, 2=yes. 2 means the session persists across application restarts. options.insert("persist_mode", (uint)2); // Persist for session (OBS value)
// Generate unique tokens for handle and restore. These are used by the portal for tracking. options.insert("handle_token", QUuid::createUuid().toString(QUuid::WithoutBraces)); // Use QUuid without braces
options.insert("handle_token", QUuid::createUuid().toString(QUuid::WithoutBraces)); // Unique token for the request handle options.insert("restore_token", QUuid::createUuid().toString(QUuid::WithoutBraces)); // Add restore_token (OBS value)
options.insert("restore_token", QUuid::createUuid().toString(QUuid::WithoutBraces)); // Unique token for restoring the session
// Add the options dictionary as an argument to the D-Bus message.
// The SelectSources method expects a single dictionary of options.
message << options; message << options;
// Make the asynchronous D-Bus call to SelectSources
QDBusPendingCall pendingCall = sessionBus.asyncCall(message); QDBusPendingCall pendingCall = sessionBus.asyncCall(message);
// Create a watcher to monitor the completion of the SelectSources call QDBusPendingCallWatcher *selectSourcesWatcher = new QDBusPendingCallWatcher(pendingCall); // Use a new watcher
QDBusPendingCallWatcher *selectSourcesWatcher = new QDBusPendingCallWatcher(pendingCall);
// Connect the watcher's finished signal to the handleSelectSourcesResponse callback function.
// This ensures that handleSelectSourcesResponse is called when the SelectSources operation completes.
QObject::connect(selectSourcesWatcher, &QDBusPendingCallWatcher::finished, handleSelectSourcesResponse); QObject::connect(selectSourcesWatcher, &QDBusPendingCallWatcher::finished, handleSelectSourcesResponse);
} }
/**
* @brief main
* The entry point of the application.
* @param argc The number of command-line arguments.
* @param argv An array of command-line argument strings.
* @return The application's exit code.
*/
int main(int argc, char *argv[]) { int main(int argc, char *argv[]) {
// Create a QCoreApplication instance, which manages the event loop and application settings.
QCoreApplication app(argc, argv); QCoreApplication app(argc, argv);
// Log that the application is starting and requesting screen capture.
qDebug() << "Requesting screen capture via xdg-desktop-portal..."; qDebug() << "Requesting screen capture via xdg-desktop-portal...";
// Explicitly set D-Bus session bus address from environment.
// This is a defensive measure to ensure Qt uses the correct D-Bus session,
// especially in complex environments or when launched from non-standard ways.
if (qEnvironmentVariableIsSet("DBUS_SESSION_BUS_ADDRESS")) {
qputenv("DBUS_SESSION_BUS_ADDRESS", qgetenv("DBUS_SESSION_BUS_ADDRESS"));
}
// Get a connection to the D-Bus session bus.
// QDBusConnection::sessionBus() is generally sufficient for most applications.
QDBusConnection sessionBus = QDBusConnection::sessionBus(); QDBusConnection sessionBus = QDBusConnection::sessionBus();
// Check if the connection to the D-Bus session bus was successful.
if (!sessionBus.isConnected()) { if (!sessionBus.isConnected()) {
qCritical() << "Failed to connect to D-Bus session bus."; qCritical() << "Failed to connect to D-Bus session bus."; fflush(stderr);
fflush(stderr); // Ensure the error message is flushed immediately return -1;
return -1; // Exit if D-Bus connection fails
} }
// Create a D-Bus message for the CreateSession method call. // Call CreateSession first
// This is the first step to initiate a screen cast session.
QDBusMessage message = QDBusMessage::createMethodCall( QDBusMessage message = QDBusMessage::createMethodCall(
"org.freedesktop.portal.Desktop", // The service name for the desktop portal "org.freedesktop.portal.Desktop",
"/org/freedesktop/portal/desktop", // The object path for the desktop portal "/org/freedesktop/portal/desktop",
"org.freedesktop.portal.ScreenCast", // The interface for screen casting "org.freedesktop.portal.ScreenCast",
"CreateSession" // The method to call to create a session "CreateSession"
); );
// Prepare the options dictionary for the CreateSession call.
// Based on recent xdg-desktop-portal API understanding, CreateSession expects only an options dictionary.
// The 'handle_token' is a required option for the portal to track the request.
QVariantMap options; QVariantMap options;
options.insert("handle_token", QUuid::createUuid().toString(QUuid::WithoutBraces)); // Unique token for the request handle options.insert("handle_token", QUuid::createUuid().toString(QUuid::WithoutBraces)); // Add handle_token
// Add the options dictionary as the only argument to the D-Bus message.
message << options; message << options;
// Make the asynchronous D-Bus call to CreateSession.
QDBusPendingCall pendingCall = sessionBus.asyncCall(message); QDBusPendingCall pendingCall = sessionBus.asyncCall(message);
// Create a watcher to monitor the completion of the CreateSession call.
QDBusPendingCallWatcher *mainWatcher = new QDBusPendingCallWatcher(pendingCall); QDBusPendingCallWatcher *mainWatcher = new QDBusPendingCallWatcher(pendingCall);
// Connect the watcher's finished signal to the handleCreateSessionFinished callback function.
// This ensures that handleCreateSessionFinished is called when the CreateSession operation completes.
QObject::connect(mainWatcher, &QDBusPendingCallWatcher::finished, handleCreateSessionFinished); QObject::connect(mainWatcher, &QDBusPendingCallWatcher::finished, handleCreateSessionFinished);
// Start the Qt event loop. This is necessary for asynchronous D-Bus calls and callbacks to function.
// The application will continue to run until QCoreApplication::quit() is called.
return app.exec(); return app.exec();
} }