utils/filedescriptor: add helper to query if the fd is readable

src/utils/filedescriptor.cpp

@@ -9,6 +9,7 @@
 #include "filedescriptor.h"
 
 #include <fcntl.h>
+#include <sys/poll.h>
 #include <unistd.h>
 #include <utility>
 
@@ -72,4 +73,14 @@ FileDescriptor FileDescriptor::duplicate() const
         return {};
     }
 }
+
+bool FileDescriptor::isReadable() const
+{
+    pollfd fd = {
+        .fd = m_fd,
+        .events = POLLIN,
+        .revents = 0,
+    };
+    return poll(&fd, 1, 0) && (fd.revents & (POLLIN | POLLNVAL)) != 0;
+}
 }

src/utils/filedescriptor.h

@@ -28,6 +28,8 @@ public:
     void reset();
     FileDescriptor duplicate() const;
 
+    bool isReadable() const;
+
 private:
     int m_fd = -1;
 };