Add function to get list of supported loader suffixes

c_src/vips_foreign.c

@@ -174,3 +174,108 @@ ERL_NIF_TERM nif_foreign_get_suffixes(ErlNifEnv *env, int argc,
   notify_consumed_timeslice(env, start, enif_monotonic_time(ERL_NIF_USEC));
   return ret;
 }
+
+/**
+ *
+ * Based on https://github.com/libvips/libvips/blob/19eba89148695a2780f49b43bc70c426f21fdec1/libvips/foreign/foreign.c#L2056
+ *
+ */
+static void *vips_foreign_get_loader_suffixes_count_cb( VipsForeignLoadClass *load_class, void *a, void *b ) {
+  VipsForeignClass *foreign_class = VIPS_FOREIGN_CLASS( load_class );
+  int *n_fields = (int *) a;
+
+  int i;
+
+  if( foreign_class->suffs )
+    for( i = 0; foreign_class->suffs[i]; i++ )
+      *n_fields += 1;
+
+  return( NULL );
+}
+
+static void *vips_foreign_get_loader_suffixes_add_cb( VipsForeignLoadClass *load_class, void *a, void *b )
+{
+  VipsForeignClass *foreign_class = VIPS_FOREIGN_CLASS( load_class );
+  gchar ***p = (gchar ***) a;
+
+  int i;
+
+  if( foreign_class->suffs )
+    for( i = 0; foreign_class->suffs[i]; i++ ) {
+      **p = g_strdup( foreign_class->suffs[i] );
+      *p += 1;
+    }
+
+  return( NULL );
+}
+
+/**
+ * vips_foreign_get_loader_suffixes: (method)
+ *
+ * Get a %NULL-terminated array listing all the supported loader suffixes.
+ *
+ * Free the return result with g_strfreev().
+ *
+ * Returns: (transfer full): all supported file extensions, as a
+ * %NULL-terminated array.
+ */
+static gchar **vips_foreign_get_loader_suffixes( void ) {
+  int n_suffs;
+  gchar **suffs;
+  gchar **p;
+
+  n_suffs = 0;
+  (void) vips_foreign_map(
+    "VipsForeignLoad",
+    (VipsSListMap2Fn) vips_foreign_get_loader_suffixes_count_cb,
+    &n_suffs, NULL );
+
+  suffs = g_new0( gchar *, n_suffs + 1 );
+  p = suffs;
+  (void) vips_foreign_map(
+    "VipsForeignLoad",
+    (VipsSListMap2Fn) vips_foreign_get_loader_suffixes_add_cb,
+    &p, NULL );
+
+  return( suffs );
+}
+
+ERL_NIF_TERM nif_foreign_get_loader_suffixes(ErlNifEnv *env, int argc,
+                                     const ERL_NIF_TERM argv[]) {
+  ASSERT_ARGC(argc, 0);
+
+  ErlNifTime start;
+  ERL_NIF_TERM ret;
+  gchar **loader_suffixes;
+  ERL_NIF_TERM list;
+  ERL_NIF_TERM bin;
+  ssize_t length;
+  unsigned char *temp;
+
+  start = enif_monotonic_time(ERL_NIF_USEC);
+
+  loader_suffixes = vips_foreign_get_loader_suffixes();
+
+  if (!loader_suffixes) {
+    error("Failed to fetch loader suffixes. error: %s", vips_error_buffer());
+    vips_error_clear();
+    ret = make_error(env, "Failed to fetch loader_suffixes");
+    goto exit;
+  }
+
+  list = enif_make_list(env, 0);
+  for (int i = 0; loader_suffixes[i] != NULL; i++) {
+    length = strlen(loader_suffixes[i]);
+    temp = enif_make_new_binary(env, length, &bin);
+    memcpy(temp, loader_suffixes[i], length);
+
+    list = enif_make_list_cell(env, bin, list);
+  }
+  g_strfreev(loader_suffixes);
+
+  ret = make_ok(env, list);
+
+exit:
+  notify_consumed_timeslice(env, start, enif_monotonic_time(ERL_NIF_USEC));
+  return ret;
+}

c_src/vips_foreign.h

@@ -18,4 +18,7 @@ ERL_NIF_TERM nif_foreign_find_save(ErlNifEnv *env, int argc,
 ERL_NIF_TERM nif_foreign_get_suffixes(ErlNifEnv *env, int argc,
                                       const ERL_NIF_TERM argv[]);
 
+ERL_NIF_TERM nif_foreign_get_loader_suffixes(ErlNifEnv *env, int argc,
+                                             const ERL_NIF_TERM argv[]);
+
 #endif

c_src/vix.c

@@ -139,6 +139,7 @@ static ErlNifFunc nif_funcs[] = {
     {"nif_foreign_find_load_buffer", 1, nif_foreign_find_load_buffer, 0},
     {"nif_foreign_find_save_buffer", 1, nif_foreign_find_save_buffer, 0},
     {"nif_foreign_get_suffixes", 0, nif_foreign_get_suffixes, 0},
+    {"nif_foreign_get_loader_suffixes", 0, nif_foreign_get_loader_suffixes, 0},
 
     /* Syscalls */
     {"nif_pipe_open", 1, nif_pipe_open, 0},

lib/vix/nif.ex

@@ -177,6 +177,9 @@ defmodule Vix.Nif do
   def nif_foreign_get_suffixes,
     do: :erlang.nif_error(:nif_library_not_loaded)
 
+  def nif_foreign_get_loader_suffixes,
+    do: :erlang.nif_error(:nif_library_not_loaded)
+
   # OS Specific
   def nif_pipe_open(_mode),
     do: :erlang.nif_error(:nif_library_not_loaded)

lib/vix/vips/foreign.ex

@@ -23,4 +23,10 @@ defmodule Vix.Vips.Foreign do
       {:ok, Enum.uniq(suffixes)}
     end
   end
+
+  def get_loader_suffixes do
+    with {:ok, suffixes} <- Nif.nif_foreign_get_loader_suffixes() do
+      {:ok, Enum.uniq(suffixes)}
+    end
+  end
 end

lib/vix/vips/image.ex

@@ -626,6 +626,13 @@ defmodule Vix.Vips.Image do
   @spec supported_saver_suffixes :: {:ok, [String.t()]} | {:error, term}
   def supported_saver_suffixes, do: Vix.Vips.Foreign.get_suffixes()
 
+  # This function should *NOT* be used to get list of formats vix can load.
+  # libvips reads the file header to decide the loader to use.
+  # see: https://github.com/libvips/ruby-vips/issues/186#issuecomment-466763897
+  @doc false
+  @spec supported_loader_suffixes :: {:ok, [String.t()]} | {:error, term}
+  def supported_loader_suffixes, do: Vix.Vips.Foreign.get_loader_suffixes()
+
   # Copy an image to a memory area.
   # If image is already a memory buffer, just ref and return. If it's
   # a file on disc or a partial, allocate memory and copy the image to

test/vix/vips/image_test.exs

@@ -325,6 +325,14 @@ defmodule Vix.Vips.ImageTest do
     end
   end
 
+  test "supported_loader_suffixes" do
+    {:ok, list} = Image.supported_loader_suffixes()
+
+    for suffix <- ~w(.jpeg .png .gif .tiff .webp .heif .avif .svg) do
+      assert suffix in list
+    end
+  end
+
   test "new_from_binary and write_to_binary endianness handling", %{dir: dir} do
     {width, height} = {125, 125}