diff --git a/lib/gen_magic/helpers.ex b/lib/gen_magic/helpers.ex
index 183fe31..13ab3de 100644
--- a/lib/gen_magic/helpers.ex
+++ b/lib/gen_magic/helpers.ex
@@ -5,7 +5,9 @@ defmodule GenMagic.Helpers do
 
   alias GenMagic.Result
   alias GenMagic.Server
-  @spec perform_once(Path.t(), [Server.option()]) :: {:ok, Result.t()} | {:error, term()}
+
+  @spec perform_once(Path.t() | {:bytes, binary}, [Server.option()]) ::
+          {:ok, Result.t()} | {:error, term()}
 
   @doc """
   Runs a one-shot process without supervision.
diff --git a/lib/gen_magic/server.ex b/lib/gen_magic/server.ex
index c0f07d7..f057dda 100644
--- a/lib/gen_magic/server.ex
+++ b/lib/gen_magic/server.ex
@@ -81,7 +81,8 @@ defmodule GenMagic.Server do
 
   @spec child_spec([option()]) :: Supervisor.child_spec()
   @spec start_link([option()]) :: :gen_statem.start_ret()
-  @spec perform(t(), Path.t(), timeout()) :: {:ok, Result.t()} | {:error, term() | String.t()}
+  @spec perform(t(), Path.t() | {:bytes, binary()}, timeout()) ::
+          {:ok, Result.t()} | {:error, term() | String.t()}
   @spec status(t(), timeout()) :: {:ok, Status.t()} | {:error, term()}
   @spec stop(t(), term(), timeout()) :: :ok
 
@@ -185,10 +186,9 @@ defmodule GenMagic.Server do
   end
 
   @doc false
-  def starting(:info, {port, {:data, binary}}, %{port: port} = data) do
-    case :erlang.binary_to_term(binary) do
-      :ready ->
-        {:next_state, :available, data}
+  def starting(:info, {port, {:data, ready}}, %{port: port} = data) do
+    case :erlang.binary_to_term(ready) do
+      :ready -> {:next_state, :available, data}
     end
   end
 
@@ -198,6 +198,7 @@ defmodule GenMagic.Server do
         1 -> :no_database
         2 -> :no_argument
         3 -> :missing_database
+        code -> {:unexpected_error, code}
       end
 
     {:stop, {:error, error}, data}
@@ -243,12 +244,10 @@ defmodule GenMagic.Server do
   end
 
   @doc false
-  def processing(:info, {port, {:data, response}}, %{port: port} = data) do
-    {_, from, _} = data.request
-    data = %{data | request: nil}
+  def processing(:info, {port, {:data, response}}, %{port: port, request: {_, from, _}} = data) do
     response = {:reply, from, handle_response(response)}
     next_state = (data.cycles >= data.recycle_threshold && :recycling) || :available
-    {:next_state, next_state, data, [response, :hibernate]}
+    {:next_state, next_state, %{data | request: nil}, [response, :hibernate]}
   end
 
   @doc false
@@ -279,7 +278,6 @@ defmodule GenMagic.Server do
   @errnos %{
     2 => :enoent,
     13 => :eaccess,
-    21 => :eisdir,
     20 => :enotdir,
     12 => :enomem,
     24 => :emfile,
diff --git a/src/apprentice.c b/src/apprentice.c
index 1afd53c..10c09b9 100644
--- a/src/apprentice.c
+++ b/src/apprentice.c
@@ -192,7 +192,6 @@ int process_command(uint16_t len, byte *buf) {
     return 1;
   }
 
-  // Empty the buffer.
   write_cmd(result.buff, result.index);
 
   if (ei_x_free(&result) != 0) {
@@ -406,7 +405,7 @@ size_t read_cmd(byte *buf) {
 
   // Buffer isn't large enough: just return possible len, without reading.
   // Up to the caller of verifying the size again and return an error.
-  // buf left unchanged.
+  // buf left unchanged, stdin emptied of X bytes.
   if (len16 > COMMAND_LEN) {
     fdseek(len16);
     return len16;