file-sniffer

elixir/file-sniffer/lib/file_sniffer.ex

@@ -0,0 +1,42 @@
+defmodule FileSniffer do
+  @signatures [
+    {<<0x7F, 0x45, 0x4C, 0x46>>, "application/octet-stream"},
+    {<<0x42, 0x4D>>, "image/bmp"},
+    {<<0x89, 0x50, 0x4E, 0x47, 0x0D, 0x0A, 0x1A, 0x0A>>, "image/png"},
+    {<<0xFF, 0xD8, 0xFF>>, "image/jpg"},
+    {<<0x47, 0x49, 0x46>>, "image/gif"}
+  ]
+
+  @file_types %{
+    "exe" => "application/octet-stream",
+    "bmp" => "image/bmp",
+    "png" => "image/png",
+    "jpg" => "image/jpg",
+    "gif" => "image/gif"
+  }
+
+  def type_from_extension(extension), do: @file_types[extension]
+
+  def type_from_binary(file_binary) do
+    Enum.find_value(@signatures, fn {signature, type} ->
+      with signature_size <- byte_size(signature),
+           <<file_signature::binary-size(signature_size), _rest::binary>> <- file_binary,
+           true <- file_signature == signature do
+        type
+      else
+        _ -> nil
+      end
+    end)
+  end
+
+  def verify(file_binary, extension) do
+    ext_type = type_from_extension(extension)
+    bin_type = type_from_binary(file_binary)
+    case ext_type == bin_type do
+      true when ext_type != nil and bin_type != nil ->
+        {:ok, ext_type}
+      _ ->
+        {:error, "Warning, file format and file extension do not match."}
+    end
+  end
+end