The middleware specification

Middleware is an extension of basic Tesla functionality. It is a module that must export call/3 function.

Middleware options

Options can be passed to middleware in second param of Tesla.Builder.plug/2 macro:

plug Tesla.Middleware.BaseUrl, "https://example.com"

or inside tuple in case of dynamic middleware (Tesla.client/1)

Tesla.client([{Tesla.Middleware.BaseUrl, "https://example.com"}])

Writing custom middleware

Writing custom middleware is as simple as creating a module with call/3 function that:

• (optionally) read and/or writes request data
• calls Tesla.run/2
• (optionally) read and/or writes response data

call/3 params:

• env - Tesla.Env struct that stores request/response data
• stack - middlewares that should be called after current one
• options - middleware options provided by user

Example

defmodule MyProject.InspectHeadersMiddleware do
  @behaviour Tesla.Middleware

  @impl true
  def call(env, next, options) do
    env
    |> inspect_headers(options)
    |> Tesla.run(next)
    |> inspect_headers(options)
  end

  defp inspect_headers(env, options) do
    IO.inspect(env.headers, options)
  end
end