core: allow signaling a parent that the screen was locked

src/core/hyprlock.cpp

@@ -23,7 +23,9 @@
 
 using namespace Hyprutils::OS;
 
-CHyprlock::CHyprlock(const std::string& wlDisplay, const bool immediate, const bool immediateRender, const bool noFadeIn) {
+CHyprlock::CHyprlock(const std::string& wlDisplay, const bool immediate, const bool immediateRender, const bool noFadeIn, const int notifyFd) {
+    m_iNotifyFd = notifyFd;
+
     m_sWaylandState.display = wl_display_connect(wlDisplay.empty() ? nullptr : wlDisplay.c_str());
     if (!m_sWaylandState.display) {
         Debug::log(CRIT, "Couldn't connect to a wayland compositor");
@@ -1013,6 +1015,16 @@ void CHyprlock::onLockLocked() {
     Debug::log(LOG, "onLockLocked called");
 
     m_bLocked = true;
+
+    if (m_iNotifyFd >= 0) {
+        const char ready = '\n';
+        while (true) {
+            if (write(m_iNotifyFd, &ready, 1) == 1 || errno != EINTR)
+                break;
+        }
+        close(m_iNotifyFd);
+        m_iNotifyFd = -1;
+    }
 }
 
 void CHyprlock::onLockFinished() {

src/core/hyprlock.hpp

@@ -26,7 +26,7 @@ struct SDMABUFModifier {
 
 class CHyprlock {
   public:
-    CHyprlock(const std::string& wlDisplay, const bool immediate, const bool immediateRender, const bool noFadeIn);
+    CHyprlock(const std::string& wlDisplay, const bool immediate, const bool immediateRender, const bool noFadeIn, const int notifyFd);
     ~CHyprlock();
 
     void                            run();
@@ -168,6 +168,8 @@ class CHyprlock {
     std::vector<std::shared_ptr<CTimer>> m_vTimers;
 
     std::vector<uint32_t>                m_vPressedKeys;
+
+    int                                  m_iNotifyFd;
 };
 
 inline std::unique_ptr<CHyprlock> g_pHyprlock;

src/main.cpp

@@ -5,6 +5,10 @@
 #include <cstddef>
 #include <iostream>
 #include <string_view>
+#include <charconv>
+#include <unistd.h>
+#include <fcntl.h>
+#include <errno.h>
 
 void help() {
     std::cout << "Usage: hyprlock [options]\n\n"
@@ -16,6 +20,8 @@ void help() {
                  "  --immediate              - Lock immediately, ignoring any configured grace period\n"
                  "  --immediate-render       - Do not wait for resources before drawing the background\n"
                  "  --no-fade-in             - Disable the fade-in animation when the lock screen appears\n"
+                 "  -R, --ready-fd FD        - Write a single newline character to this file descriptor after locking the screen\n"
+                 "  -D, --daemonize          - Run hyprlock in the background. This command will return after the screen has been locked\n"
                  "  -V, --version            - Show version information\n"
                  "  -h, --help               - Show this help message\n";
 }
@@ -35,6 +41,8 @@ int main(int argc, char** argv, char** envp) {
     bool                     immediate       = false;
     bool                     immediateRender = false;
     bool                     noFadeIn        = false;
+    bool                     daemonize       = false;
+    int                      notifyFd        = -1;
 
     std::vector<std::string> args(argv, argv + argc);
 
@@ -83,13 +91,58 @@ int main(int argc, char** argv, char** envp) {
         else if (arg == "--no-fade-in")
             noFadeIn = true;
 
+        else if (arg == "--ready-fd" || arg == "-R") {
+            if (auto value = parseArg(args, arg, i); value) {
+                auto [ptr, ec] = std::from_chars(value->data(), value->data() + value->size(), notifyFd);
+                if (ptr != value->data() + value->size() || notifyFd < 0)
+                    return 1;
+            } else
+                return 1;
+        }
+
+        else if (arg == "--daemonize" || arg == "-D")
+            daemonize = true;
+
         else {
             std::cerr << "Unknown option: " << arg << "\n";
             help();
             return 1;
         }
     }
 
+    if (daemonize) {
+        int pipe_fds[2];
+        if (pipe(pipe_fds) != 0) {
+            Debug::log(CRIT, "Cannot open pipe to child process\n");
+            return 1;
+        }
+
+        pid_t pid = fork();
+        if (pid < 0) {
+            Debug::log(CRIT, "Cannot create child process\n");
+            return 1;
+        }
+
+        if (pid > 0) {
+            close(pipe_fds[1]);
+
+            char tmp;
+            ssize_t n_read;
+            do {
+                // if the child exits without writing, read() will return zero
+                n_read = read(pipe_fds[0], &tmp, 1);
+            } while (n_read == -1 && errno == EINTR);
+
+            if (n_read == 1) return 0; // screen is now locked
+            return 1; // child failed to lock the screen
+        }
+
+        int flags = fcntl(pipe_fds[1], F_GETFD);
+        fcntl(pipe_fds[1], F_SETFD, flags | FD_CLOEXEC);
+        close(pipe_fds[0]);
+        notifyFd = pipe_fds[1];
+    }
+
     try {
         g_pConfigManager = std::make_unique<CConfigManager>(configPath);
         g_pConfigManager->init();
@@ -102,7 +155,7 @@ int main(int argc, char** argv, char** envp) {
     }
 
     try {
-        g_pHyprlock = std::make_unique<CHyprlock>(wlDisplay, immediate, immediateRender, noFadeIn);
+        g_pHyprlock = std::make_unique<CHyprlock>(wlDisplay, immediate, immediateRender, noFadeIn, notifyFd);
         g_pHyprlock->run();
     } catch (const std::exception& ex) {
         Debug::log(CRIT, "Hyprlock threw: {}", ex.what());