Working with Zip Files in Elixir

// under zip elixir erlang

Elixir File module does give an option to read compressed file, but I haven't really figured out how to use it. Erlang's standard libary does have zip module is much easier to use. Let's see how:

I have two files (posts.json and todos.json) in two_files.zip.

We can unzip the files with:

iex> :zip.unzip('two_files.zip')

{:ok, ['posts.json', 'todos.json']}

This command create the files posts.json and todos.json in the current working directory. If we only want to read the contents of the zipped file without actually create their unzipped versions in the file system we can use the :memory option,

iex> :zip.unzip(fpath, [:memory])

{:ok,
 [
   {'posts.json',
    "[\n  {\n   \"userId\": 2,\n    \"id\": 15,\n    \"title\": \"eveniet quod temporibus\",\n    \"body\": \"reprehenderit quos placeat\\nvelit minima officia dolores impedit repudiandae molestiae nam\\nvoluptas recusandae quis delectus\\nofficiis harum fugiat" <> ...},
   {'todos.json',
    "[\n  {\n    \"userId\": 2,\n    \"id\": 35,\n    \"title\": \"repellendus veritatis molestias dicta incidunt\",\n    \"completed\": true\n  },\n  {\n    \"userId\": 2,\n    \"id\": 36,\n " <> ...},
 ]}

NOTE : File path should be enclosed in single quote. Using double quotes will give an error.

iex> :zip.unzip("two_files.zip")

{:error,
 {:EXIT,
  {{:badmatch, "two_files.zip"},
   [
     ...
   ]}}}

The module provides many useful functions. For example:

We can list the contents of the zip file with list_dir.

iex> :zip.list_dir('two_files.zip')
{:ok,
[
{:zip_comment, []},
{:zip_file, 'posts.json',
    {:file_info, 27520, :regular, :read_write, {{2023, 3, 17}, {21, 56, 18}},
    {{2023, 3, 17}, {21, 56, 18}}, {{2023, 3, 17}, {21, 56, 18}}, 54, 1, 0, 0,
    0, 0, 0}, [], 0, 7048},
{:zip_file, 'todos.json',
    {:file_info, 24311, :regular, :read_write, {{2023, 3, 17}, {21, 56, 28}},
    {{2023, 3, 17}, {21, 56, 28}}, {{2023, 3, 17}, {21, 56, 28}}, 54, 1, 0, 0,
    0, 0, 0}, [], 7523, 3986}
]}

We can extract partially. In our example, if we want to only extract todo.json, we can do that by,

iex> :zip.unzip('two_files.zip', [:memory, file_list: ['todos.json']])

{:ok,
 [
   {'todos.json',
    "[\n  {\n    \"userId\": 2,\n    \"id\": 35,\n    \"title\": \"repellendus veritatis molestias dicta incidunt\",\n    \"completed\": true\n  },\n  {\n    \"userId\": 2,\n    \"id\": 36,\n " <> ...}
 ]}

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