Merge branch 'exif' into 'develop'

Strip GPS data without exiftool

See merge request pleroma/pleroma!4178

changelog.d/4178-strip-gps-without-exiftool.change

@@ -0,0 +1 @@
+Strip GPS data of JPGs and PNGs without exiftool.

lib/pleroma/upload/filter/exiftool/strip_location.ex

@@ -15,18 +15,109 @@ defmodule Pleroma.Upload.Filter.Exiftool.StripLocation do
   def filter(%Pleroma.Upload{content_type: "image/svg" <> _}), do: {:ok, :noop}
 
   def filter(%Pleroma.Upload{tempfile: file, content_type: "image" <> _}) do
-    try do
-      case System.cmd("exiftool", ["-overwrite_original", "-gps:all=", "-png:all=", file],
-             parallelism: true
-           ) do
-        {_response, 0} -> {:ok, :filtered}
-        {error, 1} -> {:error, error}
-      end
-    rescue
-      e in ErlangError ->
-        {:error, "#{__MODULE__}: #{inspect(e)}"}
+    case ExifGpsStripper.strip_gps_data(file, file) do
+      :ok -> {:ok, :filtered}
+      {:error, reason} -> {:error, reason}
     end
   end
 
   def filter(_), do: {:ok, :noop}
 end
+
+defmodule ExifGpsStripper do
+  @exif_header <<0xFF, 0xE1>>
+  @gps_ifd_tag 0x8825
+
+  def strip_gps_data(input_path, output_path) do
+    case File.read(input_path) do
+      {:ok, data} ->
+        case process_file(data) do
+          {:ok, stripped_data} -> File.write(output_path, stripped_data)
+          {:error, reason} -> {:error, reason}
+        end
+
+      {:error, reason} ->
+        {:error, "Failed to read file: #{reason}"}
+    end
+  end
+
+  defp process_file(<<0x89, "PNG", 0x0D, 0x0A, 0x1A, 0x0A, rest::binary>>) do
+    # PNG file
+    {:ok, <<0x89, "PNG", 0x0D, 0x0A, 0x1A, 0x0A>> <> strip_png_gps(rest)}
+  end
+
+  defp process_file(<<0xFF, 0xD8, rest::binary>>) do
+    # JPEG file
+    {:ok, <<0xFF, 0xD8>> <> strip_jpeg_gps(rest)}
+  end
+
+  defp process_file(_), do: {:error, "Unsupported file format"}
+
+  defp strip_png_gps(data) do
+    strip_png_chunks(data, [])
+  end
+
+  defp strip_png_chunks(<<>>, acc), do: IO.iodata_to_binary(Enum.reverse(acc))
+
+  defp strip_png_chunks(
+         <<chunk_size::32, chunk_type::binary-size(4), chunk_data::binary-size(chunk_size),
+           crc::32, rest::binary>>,
+         acc
+       ) do
+    case chunk_type do
+      "eXIf" ->
+        strip_png_chunks(rest, acc)
+
+      "tEXt" -> 
+        strip_png_chunks(rest, acc)
+
+      _ ->
+        chunk =
+          <<chunk_size::32, chunk_type::binary-size(4), chunk_data::binary-size(chunk_size),
+            crc::32>>
+
+        strip_png_chunks(rest, [chunk | acc])
+    end
+  end
+
+  defp strip_jpeg_gps(data) do
+    case :binary.match(data, @exif_header) do
+      :nomatch ->
+        data
+
+      {pos, _} ->
+        <<before::binary-size(pos), @exif_header, size::16, exif_data::binary-size(size - 2),
+          rest::binary>> = data
+
+        stripped_exif = strip_gps_from_exif(exif_data)
+        new_size = byte_size(stripped_exif) + 2
+        before <> @exif_header <> <<new_size::16>> <> stripped_exif <> rest
+    end
+  end
+
+  defp strip_gps_from_exif(<<"Exif", 0, 0, tiff_header::binary-size(8), ifd_data::binary>>) do
+    {stripped_ifd, _} = strip_gps_from_ifd(ifd_data)
+    <<"Exif", 0, 0, tiff_header::binary-size(8), stripped_ifd::binary>>
+  end
+
+  defp strip_gps_from_ifd(<<count::16-little, rest::binary>>) do
+    {entries, remaining} = strip_gps_from_entries(rest, count, [])
+    {<<count::16-little>> <> IO.iodata_to_binary(entries), remaining}
+  end
+
+  defp strip_gps_from_entries(data, 0, acc), do: {Enum.reverse(acc), data}
+
+  defp strip_gps_from_entries(
+         <<tag::16-little, type::16-little, count::32-little, value::32-little, rest::binary>>,
+         entries_left,
+         acc
+       ) do
+    entry = <<tag::16-little, type::16-little, count::32-little, value::32-little>>
+
+    if tag == @gps_ifd_tag do
+      strip_gps_from_entries(rest, entries_left - 1, acc)
+    else
+      strip_gps_from_entries(rest, entries_left - 1, [entry | acc])
+    end
+  end
+end