Finish

lib/binary_kata.ex

@@ -4,17 +4,19 @@ defmodule BinaryKata do
   Should return `true` when given parameter start with UTF8 Byte-Order-Mark, otherwise `false`.
   @see https://en.wikipedia.org/wiki/Byte_order_mark
   """
-  def has_utf8_bom?(_), do: raise "TODO: Implement me!"
+  def has_utf8_bom?(<<0xEF, 0xBB, 0xBF, _ :: binary>>), do: true
+  def has_utf8_bom?(_), do: false
 
   @doc """
   Remove a UTF8 BOM if exists.
   """
-  def remove_utf8_bom(_), do: raise "TODO: Implement me!"
+  def remove_utf8_bom(<<0xEF, 0xBB, 0xBF, rest :: binary>>), do: rest
+  def remove_utf8_bom(rest), do: rest
 
   @doc """
   Add a UTF8 BOM if not exists.
   """
-  def add_utf8_bom(_), do: raise "TODO: Implement me!"
+  def add_utf8_bom(rest), do: <<0xEF, 0xBB, 0xBF>> <> remove_utf8_bom(rest)
 
   @doc """
   Detecting types of images by their first bytes / magic numbers.
@@ -23,7 +25,10 @@ defmodule BinaryKata do
   @see https://en.wikipedia.org/wiki/Portable_Network_Graphics
   @see https://en.wikipedia.org/wiki/GIF
   """
-  def image_type!(_), do: raise "TODO: Implement me!"
+  def image_type!(<<0xFF, 0xD8, 0xFF, _ :: binary>>), do: :jfif
+  def image_type!(<<0x89, 0x50, 0x4e, 0x47, _ :: binary>>), do: :png
+  def image_type!(<<0x47, 0x49, 0x46, 0x38, 0x39, 0x61, _ :: binary>>), do: :gif
+  def image_type!(_), do: :unknown
 
   @doc """
   Get the width and height from a GIF image.
@@ -32,18 +37,35 @@ defmodule BinaryKata do
   `width` will be little-endian in byte 7 and 8.
   `height` will be little-endian in byte 9 and 10.
   """
-  def gif_dimensions!(_), do: raise "TODO: Implement me!"
+  def gif_dimensions!(<<0x47, 0x49, 0x46, 0x38, 0x39, 0x61, width :: little-size(16), height :: little-size(16), _ :: binary>>), do: {width, height}
+  def gif_dimensions!(_), do: :error
 
   @doc """
   Parsing Payload of a ARP packet. Padding will be omitted.
 
   @see https://en.wikipedia.org/wiki/Address_Resolution_Protocol
   """
-  def parse_arp_packet_ipv4!(_) do
-      raise "TODO: Implement me!"
+  def parse_arp_packet_ipv4!(<<
+    _ :: size(48),
+    operation :: size(16),
+    sender_address :: size(48),
+    sender_ip :: 4-binary,
+    target_address :: size(48),
+    target_ip :: 4-binary,
+    _ :: binary
+  >>) do
+    {
+      operation |> arp_operation_to_atom,
+      sender_address,
+      sender_ip |> ip_to_tuple,
+      target_address,
+      target_ip |> ip_to_tuple
+    }
   end
 
+
   # Helper for `parse_arp_packet_ipv4!`
+  defp ip_to_tuple(<< ip_1, ip_2, ip_3, ip_4 >>), do: {ip_1, ip_2, ip_3, ip_4}
   defp arp_operation_to_atom(1), do: :request
   defp arp_operation_to_atom(2), do: :response