Added File Mode to sockets and socket activation

1 files changed, 61 insertions, 0 deletions

diff --git a/http/systemd_linux.go b/http/systemd_linux.go
new file mode 100644
index 0000000..817b421
--- /dev/null
+++ b/http/systemd_linux.go
@@ -0,0 +1,61 @@
+//go:build linux
+
+package http
+
+import (
+	"fmt"
+
+	"net"
+	"os"
+	"strconv"
+)
+
+func getSystemdListeners() (Listeners, error) {
+	pidStr := os.Getenv("LISTEN_PID")
+	fdStr := os.Getenv("LISTEN_FDS")
+
+	if pidStr == "" || fdStr == "" {
+		return nil, nil // Not running under systemd
+	}
+
+	pid, err := strconv.Atoi(pidStr)
+	if err != nil {
+		// Not our activation — another process might have inherited the env.
+		return nil, nil
+	}
+	if pid != os.Getpid() {
+		return nil, fmt.Errorf("LISTEN_PID %d does not match current PID %d", pid, os.Getpid())
+	}
+
+	defer func() {
+		_ = os.Unsetenv("LISTEN_PID")
+		_ = os.Unsetenv("LISTEN_FDS")
+	}()
+
+	nfds, err := strconv.ParseUint(fdStr, 10, 64)
+	if err != nil {
+		return nil, fmt.Errorf("invalid LISTEN_FDS: %w", err)
+	}
+	if nfds == 0 {
+		return nil, nil // Nothing to do
+	}
+
+	lns := make(Listeners, 0, nfds)
+	for i := range nfds {
+		fd := i + 3
+		file := os.NewFile(uintptr(fd), fmt.Sprintf("fd_%d", fd))
+		if file == nil {
+			return nil, fmt.Errorf("fd %d was nil", fd)
+		}
+		ln, err := net.FileListener(file)
+		if err != nil {
+			file.Close()
+			return nil, fmt.Errorf("failed to create listener from fd %d: %w", fd, err)
+		}
+		lns = append(lns, ln)
+	}
+
+	return lns, nil
+}
+
+