diff --git a/src/stdplus/fd/intf.hpp b/src/stdplus/fd/intf.hpp
new file mode 100644
index 0000000..aac85a2
--- /dev/null
+++ b/src/stdplus/fd/intf.hpp
@@ -0,0 +1,108 @@
+#pragma once
+#include <cstddef>
+#include <fcntl.h>
+#include <stdplus/flags.hpp>
+#include <stdplus/types.hpp>
+#include <sys/socket.h>
+
+namespace stdplus
+{
+namespace fd
+{
+
+enum class RecvFlag : int
+{
+    DontWait = MSG_DONTWAIT,
+    ErrQueue = MSG_ERRQUEUE,
+    OutOfBounds = MSG_OOB,
+    Peek = MSG_PEEK,
+    Trunc = MSG_TRUNC,
+    WaitAll = MSG_WAITALL,
+};
+using RecvFlags = BitFlags<int, RecvFlag>;
+
+enum class SendFlag : int
+{
+    Confirm = MSG_CONFIRM,
+    DontRoute = MSG_DONTROUTE,
+    DontWait = MSG_DONTWAIT,
+    EndOfRecord = MSG_EOR,
+    More = MSG_MORE,
+    NoSignal = MSG_NOSIGNAL,
+    OutOfBounds = MSG_OOB,
+};
+using SendFlags = BitFlags<int, SendFlag>;
+
+enum class Whence : int
+{
+    Set = SEEK_SET,
+    Cur = SEEK_CUR,
+    End = SEEK_END,
+};
+
+enum class SockLevel : int
+{
+    Socket = SOL_SOCKET,
+};
+
+enum class SockOpt : int
+{
+    Debug = SO_DEBUG,
+    Broadcast = SO_BROADCAST,
+    ReuseAddr = SO_REUSEADDR,
+    KeepAlive = SO_KEEPALIVE,
+    Linger = SO_LINGER,
+    OOBInline = SO_OOBINLINE,
+    SendBuf = SO_SNDBUF,
+    RecvBuf = SO_RCVBUF,
+    DontRoute = SO_DONTROUTE,
+    RecvLowWait = SO_RCVLOWAT,
+    RecvTimeout = SO_RCVTIMEO,
+    SendLowWait = SO_SNDLOWAT,
+    SendTimeout = SO_SNDTIMEO,
+};
+
+enum class FdFlag : int
+{
+    CloseOnExec = FD_CLOEXEC,
+};
+using FdFlags = BitFlags<int, FdFlag>;
+
+enum class FileFlag : int
+{
+    Append = O_APPEND,
+    Async = O_ASYNC,
+    Direct = O_DIRECT,
+    NoAtime = O_NOATIME,
+    NonBlock = O_NONBLOCK,
+};
+using FileFlags = BitFlags<int, FileFlag>;
+
+class Fd
+{
+  public:
+    virtual ~Fd() = default;
+
+    virtual span<std::byte> read(span<std::byte> buf) = 0;
+    virtual span<std::byte> recv(span<std::byte> buf, RecvFlags flags) = 0;
+    virtual span<const std::byte> write(span<const std::byte> data) = 0;
+    virtual span<const std::byte> send(span<const std::byte> data,
+                                       SendFlags flags) = 0;
+    virtual size_t lseek(off_t offset, Whence whence) = 0;
+    virtual void truncate(off_t size) = 0;
+    virtual void bind(span<const std::byte> sockaddr) = 0;
+    virtual void setsockopt(SockLevel level, SockOpt optname,
+                            span<const std::byte> opt) = 0;
+    virtual int ioctl(unsigned long id, void* data) = 0;
+    virtual int constIoctl(unsigned long id, void* data) const = 0;
+    virtual void fcntlSetfd(FdFlags flags) = 0;
+    virtual FdFlags fcntlGetfd() const = 0;
+    virtual void fcntlSetfl(FileFlags flags) = 0;
+    virtual FileFlags fcntlGetfl() const = 0;
+};
+
+} // namespace fd
+
+using fd::Fd;
+
+} // namespace stdplus