Handwrite - Unofficial API wrapper for Handwrite.io

I started using the Handwrite REST API for a side project and since they don’t have an API library for Elixir I decided to make an unofficial one for them: https://hex.pm/packages/handwrite.

This is my first published Hex package and I have only used Elixir for side projects, so I’d love to make this library more stable and usable. I’m sure there is a lot of improve on, so any feedback or code reviews would be greatly appreciated!

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I checked out handwrite.io because of your library, but I see their pricing policy is “inquire within”. I’m guessing they’ve got reasonable pricing if you’re using it on side projects?

I’m still only using it in a sandbox environment, but as far as I can tell the pricing is comparable to other card printing services. They are very responsive, if you reach out to them I’m sure they can give you a better answer.

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Welcome! My first hex package was also a rest api wrapper (ex_force) :slight_smile:

Here are some feedback/thoughts:


  • Although they are mostly swappable, recent packages chose jason instead of poison for json
  • http client - I’m using tesla whenever possible since users can swap the http library easily.


  • Instead of "#{secret_key()}", you can make sure secret_key returns string value… which leads to the next point
  • secret_key/0 calls System.get_env/1 on runtime - it may be okay for application (although not recommended), but for library, you should use application configuration (e.g. Application.get_env/3) (for global config) or pass that value down to the function.

Code organization

  • I found you made a module for each resource - such as Handwrite.Endpoint.Handwriting. There is no right answer, but I found it’s actually easier to read, use, and maintain the code I put the all things under one module if they’re at the similar level resources. See ExForce module source.
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Thanks for the great suggestions!

These are all super helpful and I appreciate the links to examples as well. I’ll have to spend some time digging through it all and prioritizing my todo list.

I’ll definitely at least move the secrets to the application config. That seems like a quick win and an important change.

I disagree. Strongly. If an application were to have two dependencies using this library, then the configuration must be global. That’s a bad thing. The library should accept configuration given to it. A default in application config is acceptable, but I still don’t love it.

Terminology is confusing here. Mix config has initial keys in the namespace that correspond to OTP apps, however, in an umbrella project, multiple OTP apps must be considered. In addition, umbrella projects can support multiple releases, each of which should be able to have their own configuration. What we commonly refer to as application config should probably be better thought of as release config.

Oh, I agree with you in that global config for a library must be avoided.

I should have been more clear on this part :man_facepalming: I wanted to give hints to move away from using System.get_env/1 first…

For starter - and this kind of library, this is very likely to have one instance - which is “acceptable” (although I don’t prefer) to have (global) application config. That’s why I refer to the library guides lines, which has a section for Avoid application configuration :slight_smile:

@timpile for the configuration - it’s better to have a library to provide building blocks and let library users load config as needed.

For example:

# in config
config :my_app, :handwrite, url: "https://example.com", api_key: "..."

# in your helper module

defmodule MyApp.Handwrite do
  def client do
    opts = Application.get_env(:my_app, :handwrite)
   Handwrite.client(Keyword.fetch!(opts, :url), Keyword.fetch!(opts, :api_key)

# then you use it like this

|> Handwrite.create_whatever(my_opts)

By doing this, your library does not care how to store and retrieve the configuration at all - and that is in the library user code.

I did make a mistake when I wrote the first library - I had default config value and make authentication happens when not passed to make it easy to use… but I found it’s not good. See my commit to change from httpoison to tesla with 1) dropping default config and 2) making all functions to take a tesla struct, which holds the all information such as url and auth token - see https://github.com/chulkilee/ex_force/commit/8d32d9a3556761305ca772b7e192b19a6fa12d7f#diff-5b23f360e1b1c574d1241617a5235628