Katütata!

lib/binary_kata.ex

@@ -4,17 +4,20 @@ 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(data) when is_binary(data), do: data
 
   @doc """
   Add a UTF8 BOM if not exists.
   """
-  def add_utf8_bom(_), do: raise "TODO: Implement me!"
+  def add_utf8_bom(<<0xef,0xbb,0xbf,rest :: binary>> = data), do: data
+  def add_utf8_bom(data), do: <<0xef,0xbb,0xbf,data :: binary>>
 
   @doc """
   Detecting types of images by their first bytes / magic numbers.
@@ -23,7 +26,12 @@ 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!(<<"GIF87a",_ :: binary>>), do: :gif
+  def image_type!(<<"GIF89a", _ :: binary>>), do: :gif
+  def image_type!(<<0x89,0x50,0x4e,0x47,0x0d,0x0a,0x1a,0x0a, _ :: binary>>), do: :png
+  def image_type!(<<0xff,0xd8, _ :: binary>>), do: :jfif
+  def image_type!(<<0xff,0xd9, _ :: binary>>), do: :jfif
+  def image_type!(_), do: :unknown
 
   @doc """
   Get the width and height from a GIF image.
@@ -32,15 +40,41 @@ 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!(<<header :: binary-size(6),_ :: binary>>) when header != <<"GIF87a">> and header != <<"GIF89a">>, do: :error
+  def gif_dimensions!(<<_ :: binary-size(6), width :: little-integer-size(16), height :: little-integer-size(16), _ :: binary>>), do: {width, height}
 
   @doc """
   Parsing Payload of a ARP packet. Padding will be omitted.
 
+  Internet Protocol (IPv4) over Ethernet ARP packet
+  octet offset 	0 	1
+  0 	Hardware type (HTYPE)
+  2 	Protocol type (PTYPE)
+  4 	Hardware address length (HLEN) | Protocol address length (PLEN)
+  6 	Operation (OPER)
+  8 	Sender hardware address (SHA) (first 2 bytes)
+  10 	(next 2 bytes)
+  12 	(last 2 bytes)
+  14 	Sender protocol address (SPA) (first 2 bytes)
+  16 	(last 2 bytes)
+  18 	Target hardware address (THA) (first 2 bytes)
+  20 	(next 2 bytes)
+  22 	(last 2 bytes)
+  24 	Target protocol address (TPA) (first 2 bytes)
+  26 	(last 2 bytes)
+
   @see https://en.wikipedia.org/wiki/Address_Resolution_Protocol
   """
-  def parse_arp_packet_ipv4!(_) do
-      raise "TODO: Implement me!"
+  def parse_arp_packet_ipv4!(<<_ :: binary-size(6), operation :: binary-size(2), sender_address :: integer-size(48), sender_ip :: binary-size(4), target_adress :: integer-size(48), target_ip :: binary-size(4), _ :: binary>>) do
+    operation = case operation do
+      <<0,1>> -> :request
+      <<0,2>> -> :response
+    end
+
+    <<a,b,c,d>> = sender_ip
+    <<e,f,g,h>> = target_ip
+
+    {operation, sender_address, {a,b,c,d}, target_adress, {e,f,g,h}}
   end
 
   # Helper for `parse_arp_packet_ipv4!`

test/binary_kata_test.exs

@@ -1,5 +1,5 @@
 defmodule BinaryKataTest do
-  use ExUnit.Case
+  use ExUnit.Case, async: false
   doctest BinaryKata
 
   test "has_utf8_bom?" do