add license, update readme and start to work on encoding functions

LICENSE

@@ -0,0 +1,14 @@
+Copyright (c) 2021 Mathieu Kerjouan <contact [at] steepath [dot] eu>
+
+Permission to use, copy, modify, and distribute this software for any
+purpose with or without fee is hereby granted, provided that the above
+copyright notice and this permission notice appear in all copies.
+
+THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL
+WARRANTIES WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED
+WARRANTIES OF MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE
+AUTHOR BE LIABLE FOR ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL
+DAMAGES OR ANY DAMAGES WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR
+PROFITS, WHETHER IN AN ACTION OF CONTRACT, NEGLIGENCE OR OTHER
+TORTIOUS ACTION, ARISING OUT OF OR IN CONNECTION WITH THE USE OR
+PERFORMANCE OF THIS SOFTWARE.

README.md

@@ -1,5 +1,18 @@
 # Dotzip
 
+> ZIP is one of the most widely used compressed file formats. It is
+> universally used to aggregate, compress, and encrypt files into a
+> single interoperable container. No specific use or application need
+> is defined by this format and no specific implementation guidance is
+> provided. This document provides details on the storage format for
+> creating ZIP files.  Information is provided on the records and
+> fields that describe what a ZIP file is. -- from [official
+> specification
+> file](https://pkware.cachefly.net/webdocs/APPNOTE/APPNOTE-6.3.3.TXT)
+
+Note: This project is a work in progress. Please don't use it in
+production.
+
 ## Installation
 
 If [available in Hex](https://hex.pm/docs/publish), the package can be installed
@@ -36,6 +49,14 @@ Dotzip.decode(file)
  * https://pkware.cachefly.net/webdocs/APPNOTE/APPNOTE-6.3.3.TXT
  * https://en.wikipedia.org/wiki/ZIP_(file_format)
 
+## Trademarks
+
+> PKWARE, PKZIP, SecureZIP, and PKSFX are registered trademarks of
+> PKWARE, Inc. in the United States and elsewhere.  PKPatchMaker,
+> Deflate64, and ZIP64 are trademarks of PKWARE, Inc.  Other marks
+> referenced within this document appear for identification purposes
+> only and are the property of their respective owners.
+
 ## Notes
 
 Documentation can be generated with [ExDoc](https://github.com/elixir-lang/ex_doc)

lib/dotzip.ex

@@ -11,10 +11,19 @@ defmodule Dotzip do
     {local, central, e, rr}
   end
 
-  def read(file) do
+  def decode_file(file) do
     {:ok, data} = :file.read_file(file)
     decode(data)
   end
 
+
+  def encode(_data) do
+    {:error, :not_supported}
+  end
+
+  def encode_file(_file) do
+    {:error, :not_supported}
+  end
+  
 end
 

lib/dotzip/central_directory_header.ex

@@ -1,25 +1,49 @@
 defmodule Dotzip.CentralDirectoryHeader do
 
+  defp signature() do
+    << 0x50, 0x4b, 0x01, 0x02 >>
+  end
+  
   defp signature(<< 0x50, 0x4b, 0x01, 0x02, rest::bitstring >>) do
     {:ok, %{}, rest}
   end
 
+  defp encode_signature(data) when is_map(data) do
+    {:ok, data, signature()}
+  end
+
   defp version_made({:ok, data, << version::binary-size(2), rest::bitstring >>}) do
     {:ok, Map.put(data, :version_made, version), rest}
   end
 
+  defp encode_version_made({:ok, %{ :version_made => version_made } = data, buffer}) do
+    {:ok, data, << buffer::bitstring, version_made::binary-size(2) >>}
+  end
+  
   defp version_needed({:ok, data, << version::binary-size(2), rest::bitstring >>}) do
     {:ok, Map.put(data, :version_needed, version), rest}
   end
 
+  defp encode_version_needed({:ok, %{ :version_needed => version_needed } = data, buffer}) do
+    {:ok, data, << buffer::bitstring, version_needed::binary-size(2) >>}
+  end
+  
   defp purpose_flag({:ok, data, << purpose_flag::binary-size(2), rest::bitstring >>}) do
     {:ok, Map.put(data, :purpose_flag, purpose_flag), rest}
   end
 
+  defp encode_purpose_flag({:ok, %{ :purpose_flag => purpose_flag } = data, buffer}) do
+    {:ok, data, << buffer::bitstring, purpose_flag::binary-size(2) >>}
+  end
+
   defp compression_method({:ok, data, << compression_method::binary-size(2), rest::bitstring >>}) do
     {:ok, Map.put(data, :compression_method, compression_method), rest}
   end
 
+  defp encode_compression_method({:ok, %{ :compression_method => compression_method } = data, buffer}) do
+    {:ok, data, << buffer::bitstring, compression_method::binary-size(2) >>}
+  end
+  
   defp last_modification_time({:ok, data, << last_modification::little-size(16), rest::bitstring >>}) do
     {:ok, Map.put(data, :last_modification_time, last_modification), rest}
   end
@@ -86,8 +110,8 @@ defmodule Dotzip.CentralDirectoryHeader do
     {:ok, Map.put(data, :file_comment, file_comment), r}
   end
   
-  def decode(file) do
-    {:ok, central_directory_header, rest} = signature(file)
+  def decode(data) when is_bitstring(data) do
+    {:ok, central_directory_header, rest} = signature(data)
     |> version_made()
     |> version_needed()
     |> purpose_flag()
@@ -109,4 +133,12 @@ defmodule Dotzip.CentralDirectoryHeader do
     |> file_comment()
   end
 
+  def encode(data) when is_map(data) do
+    encode_signature(data)
+    |> encode_version_made()
+    |> encode_version_needed()
+    |> encode_purpose_flag()
+    |> encode_compression_method()
+  end
+  
 end