[NaCl SDK] nacl_io: Add initial support for getsockopt

native_client_sdk/src/libraries/nacl_io/mount_node_socket.cc

Index: native_client_sdk/src/libraries/nacl_io/mount_node_socket.cc
diff --git a/native_client_sdk/src/libraries/nacl_io/mount_node_socket.cc b/native_client_sdk/src/libraries/nacl_io/mount_node_socket.cc
index abaf55ba1e9e48ae0a89fa16d08b65d87ce62962..87d6f484d3a33b5852fff6bfd09cbea7e1176386 100644
--- a/native_client_sdk/src/libraries/nacl_io/mount_node_socket.cc
+++ b/native_client_sdk/src/libraries/nacl_io/mount_node_socket.cc
@@ -204,14 +204,27 @@ Error MountNodeSocket::GetSockOpt(int lvl,
                                   int optname,
                                   void* optval,
                                   socklen_t* len) {
-  return EINVAL;
+  if (lvl != SOL_SOCKET)
+    return ENOPROTOOPT;
+
+  switch (optname) {
+    case SO_ERROR: {
+      int copy_bytes = std::min(sizeof(int), *len);
+      memcpy(optval, &last_errno_, copy_bytes);
+      *len = sizeof(int);
+      last_errno_ = 0;
+      return 0;
+    }
+  }
+
+  return ENOPROTOOPT;
 }
 
 Error MountNodeSocket::SetSockOpt(int lvl,
                                   int optname,
                                   const void* optval,
                                   socklen_t len) {
-  return EINVAL;
+  return ENOPROTOOPT;
 }
 
 Error MountNodeSocket::Bind(const struct sockaddr* addr, socklen_t len) {
@@ -372,4 +385,4 @@ Error MountNodeSocket::GetSockName(struct sockaddr* addr, socklen_t* len) {
 
 }  // namespace nacl_io
 
-#endif  // PROVIDES_SOCKET_API
+#endif  // PROVIDES_SOCKET_API