decoding.frequency.zip.example.md

Reading the contents of a zip archive file in Elixir

We want to read (and extract all data from) the zip archive file frequency.zip.

Erlang has built in support for reading zip archives.

The documentation is here:

We'll be using :zip.foldl/3 to itterate the file contents.

Here's it's spec:

h :zip.foldl/3

@spec foldl(fun, acc0, archive) :: {:ok, acc1} | {:error, reason}
        when fun: (fileInArchive, getInfo, getBin, accIn -> accOut),
             fileInArchive: :file.name(),
             getInfo: (() -> :file.file_info()),
             getBin: (() -> binary()),
             acc0: term(),
             acc1: term(),
             accIn: term(),
             accOut: term(),
             archive: :file.name() | {:file.name(), binary()},
             reason: term()

The contents of the file

example1/config/config.exs
example1/lib/frequency.ex
example1/mix.exs
example1/mix.lock
example1/README.md
example1/test/frequency_test.exs
example1/test/test_helper.exs

Here's how we do it

1. Read the file as a binary blob into the varible 'data'.

iex(33)> data = File.read!("/Users/b/Downloads/frequency.zip")
<<80, 75, 3, 4, 10, 0, 0, 8, 8, 0, 140, 89, 175, 80, 0, 0, 0, 0, 2, 0, 0, 0, 0,
  0, 0, 0, 10, 0, 0, 0, 102, 114, 101, 113, 117, 101, 110, 99, 121, 47, 3, 0,
  80, 75, 3, 4, 10, 0, 0, 8, ...>>

2. Use :zip.fold1 to itterate over the file contents:

iex(36)> {:ok, file_spec} = :zip.foldl(fn(n, i, b, acc) -> [{n, b.(), i.()} | acc] end, [], {'dummy.zip', data})
{:ok,
 [
   {'frequency/.formatter.exs',
    "# Used by \"mix format\"\n[\n  inputs: [\"{mix,.formatter}.exs\", \"{config,lib,test}/**/*.{ex,exs}\"]\n]\n",
    {:file_info, 97, :regular, :read_write, {{2020, 5, 14}, {15, 3, 11}},
     {{2020, 5, 14}, {15, 3, 11}}, {{2020, 5, 14}, {15, 3, 11}}, 54, 1, 0, 0, 0,
     0, 0}},
   {'frequency/lib/', "",
    {:file_info, 0, :directory, :read_write, {{2020, 5, 15}, {11, 12, 10}},
     {{2020, 5, 15}, {11, 12, 10}}, {{2020, 5, 15}, {11, 12, 10}}, 54, 1, 0, 0,
     0, 0, 0}},
..... ...  
  {'frequency/test/test_helper.exs', "ExUnit.start()\n",
    {:file_info, 15, :regular, :read_write, {{2020, 5, 14}, {15, 3, 11}},
     {{2020, 5, 14}, {15, 3, 11}}, {{2020, 5, 14}, {15, 3, 11}}, 54, 1, 0, 0, 0,
     0, 0}},
....