Add Image.supported_save_suffixes/0

c_src/vips_foreign.c

@@ -134,3 +134,43 @@ ERL_NIF_TERM nif_foreign_find_save(ErlNifEnv *env, int argc,
   notify_consumed_timeslice(env, start, enif_monotonic_time(ERL_NIF_USEC));
   return ret;
 }
+
+ERL_NIF_TERM nif_foreign_get_suffixes(ErlNifEnv *env, int argc,
+                                      const ERL_NIF_TERM argv[]) {
+  ASSERT_ARGC(argc, 0);
+
+  ErlNifTime start;
+  ERL_NIF_TERM ret;
+  gchar **suffixes;
+  ERL_NIF_TERM list;
+  ERL_NIF_TERM bin;
+  ssize_t length;
+  unsigned char *temp;
+
+  start = enif_monotonic_time(ERL_NIF_USEC);
+
+  suffixes = vips_foreign_get_suffixes();
+
+  if (!suffixes) {
+    error("Failed to fetch suffixes. error: %s", vips_error_buffer());
+    vips_error_clear();
+    ret = make_error(env, "Failed to fetch suffixes");
+    goto exit;
+  }
+
+  list = enif_make_list(env, 0);
+  for (int i = 0; suffixes[i] != NULL; i++) {
+    length = strlen(suffixes[i]);
+    temp = enif_make_new_binary(env, length, &bin);
+    memcpy(temp, suffixes[i], length);
+
+    list = enif_make_list_cell(env, bin, list);
+  }
+  g_strfreev(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

@@ -15,4 +15,7 @@ ERL_NIF_TERM nif_foreign_find_load(ErlNifEnv *env, int argc,
 ERL_NIF_TERM nif_foreign_find_save(ErlNifEnv *env, int argc,
                                    const ERL_NIF_TERM argv[]);
 
+ERL_NIF_TERM nif_foreign_get_suffixes(ErlNifEnv *env, int argc,
+                                      const ERL_NIF_TERM argv[]);
+
 #endif

c_src/vix.c

@@ -138,6 +138,7 @@ static ErlNifFunc nif_funcs[] = {
     {"nif_foreign_find_save", 1, nif_foreign_find_save, 0},
     {"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},
 
     /* Syscalls */
     {"nif_pipe_open", 1, nif_pipe_open, 0},

lib/vix/nif.ex

@@ -174,6 +174,9 @@ defmodule Vix.Nif do
   def nif_foreign_find_save(_filename),
     do: :erlang.nif_error(:nif_library_not_loaded)
 
+  def nif_foreign_get_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

@@ -17,4 +17,8 @@ defmodule Vix.Vips.Foreign do
   def find_save(filename) do
     Nif.nif_foreign_find_save(filename)
   end
+
+  def get_suffixes do
+    Nif.nif_foreign_get_suffixes()
+  end
 end

lib/vix/vips/image.ex

@@ -610,6 +610,19 @@ defmodule Vix.Vips.Image do
     end
   end
 
+  @doc """
+  Returns list of supported extension for *saving* the image.
+
+  Supported suffix can be used to save image in a particular format.
+  See `write_to_file/2`.
+
+  Note that the image format supported for saving the image and the
+  format supported for loading image might be different. For example
+  SVG format can be loaded but can not be saved.
+  """
+  @spec supported_save_suffixes :: {:ok, [String.t()]} | {:error, term}
+  def supported_save_suffixes, do: Vix.Vips.Foreign.get_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
@@ -625,19 +638,20 @@ defmodule Vix.Vips.Image do
   @doc """
   Write `vips_image` to a file.
 
+  A saver is selected based on image extension in `path`. You can
+  get list of supported extensions by `supported_save_suffixes/0`.
+
   Save options may be encoded in the filename. For example:
 
   ```elixir
   Image.write_to_file(vips_image, "fred.jpg[Q=90]")
   ```
 
-  A saver is selected based on image extension in `path`. The full set
-  of save options depend on the selected saver. Try something like:
+  The full set of save options depend on the selected saver.
+  You can check the supported options for a saver by checking
+  docs for the particular format save function in `Operation` module.
+  For example, for you jpeg, `Vix.Vips.Operation.jpegsave/2`.
 
-  ```shell
-  $ vips jpegsave
-  ```
-  at the command-line to see all the available options for JPEG save.
 
   If you want more control over the saver, Use specific format saver
   from `Vix.Vips.Operation`. For example for jpeg use