Support OTP<21.3

Makefile

@@ -1,15 +1,20 @@
 CFLAGS = -std=c99 -g -Wall -Werror
-CPPFLAGS = -I$(ERL_EI_INCLUDE_DIR)
-LDFLAGS = -L$(ERL_EI_LIBDIR)
+CPPFLAGS = -I$(ERL_EI_INCLUDE_DIR) -I/usr/local/include
+LDFLAGS = -L$(ERL_EI_LIBDIR) -L/usr/local/lib
 LDLIBS = -lpthread -lei -lm -lmagic
 PRIV = priv/
 RM = rm -Rf
 
+ifeq ($(EI_INCOMPLETE),YES)
+  LDLIBS += -lerl_interface
+  CFLAGS += -DEI_INCOMPLETE
+endif
+
 all: priv/libmagic_port
 
 priv/libmagic_port: src/libmagic_port.c
 	mkdir -p priv
-	$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $^ $(LDLIBS) -o $@
+	$(CC) $(CPPFLAGS) $(CFLAGS) $(LDFLAGS) $< $(LDLIBS) -o $@
 
 clean:
 	$(RM) $(PRIV)

mix.exs

@@ -14,6 +14,7 @@ defmodule Majic.MixProject do
       elixirc_options: [warnings_as_errors: warnings_as_errors(Mix.env())],
       start_permanent: Mix.env() == :prod,
       compilers: [:elixir_make] ++ Mix.compilers(),
+      make_env: make_env(),
       package: package(),
       deps: deps(),
       dialyzer: dialyzer(),
@@ -70,4 +71,14 @@ defmodule Majic.MixProject do
 
   defp warnings_as_errors(:dev), do: false
   defp warnings_as_errors(_), do: true
+
+  defp make_env() do
+    otp = :erlang.system_info(:otp_release)
+          |> to_string()
+          |> String.to_integer()
+
+    ei_incomplete = if(otp < 21.3, do: "YES", else: "NO")
+    %{"EI_INCOMPLETE" => ei_incomplete}
+  end
+
 end

src/libmagic_port.c

@@ -43,6 +43,9 @@
 
 #include <arpa/inet.h>
 #include <ei.h>
+#ifdef EI_INCOMPLETE
+#include <erl_interface.h>
+#endif
 #include <errno.h>
 #include <getopt.h>
 #include <libgen.h>
@@ -104,7 +107,11 @@ static magic_t magic_type_name;     // MAGIC_NONE
 bool magic_loaded = false;
 
 int main(int argc, char **argv) {
+#ifdef EI_INCOMPLETE
+  erl_init(NULL, -1);
+#else
   EI_ENSURE(ei_init());
+#endif
   setup_environment();
   magic_open_all();