Added pre download hook callback

CHANGELOG.md

@@ -11,6 +11,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 - Support for FreeBSD
 - `post_write_hook` callback that is invoked whenever a file is written
+- `pre_download_hook` callback that is invoked prior to starting a download
 
 ### Changed
 

lib/octo_fetch.ex

@@ -94,6 +94,11 @@ defmodule OctoFetch do
         :ok
       end
 
+      @impl true
+      def pre_download_hook(_, _) do
+        :cont
+      end
+
       @impl true
       def download(output_dir, opts \\ []) do
         opts = Keyword.merge(unquote(opts), opts)
@@ -148,6 +153,7 @@ defmodule OctoFetch do
          {:ok, artifact_name} <-
            generate_artifact_name(downloader_module, version, operating_system, architecture),
          full_download_url <- Path.join(github_base_url, artifact_name),
+         :cont <- downloader_module.pre_download_hook(artifact_name, output_dir),
          {:ok, artifact_contents} <- download_artifact(full_download_url, opts),
          :ok <- verify_artifact_checksum(artifact_contents, sha_checksum, full_download_url),
          {:ok, files_to_write} <-
@@ -173,6 +179,9 @@ defmodule OctoFetch do
       {:error, reason} ->
         Logger.warning("Failed to download release from GitHub. #{reason}")
         {:error, reason}
+
+      :skipped ->
+        :skipped
     end
   end
 

lib/octo_fetch/downloader.ex

@@ -9,7 +9,7 @@ defmodule OctoFetch.Downloader do
 
   @type os() :: :linux | :darwin | :freebsd | :windows
   @type arch() :: :arm64 | :amd64
-  @type download_result() :: {:ok, successful_files :: list(), failed_files :: list()} | {:error, String.t()}
+  @type download_result() :: {:ok, successful_files :: list(), failed_files :: list()} | {:error, String.t()} | :skipped
 
   @doc """
   This callback generates the base URL for the artifact based on the provided GitHub repo
@@ -51,6 +51,13 @@ defmodule OctoFetch.Downloader do
   """
   @callback post_write_hook(file :: String.t()) :: :ok
 
+  @doc """
+  This callback is invoked prior to a file being downloaded. This gives you
+  the opportunity to skip the download if you so chose by returning `:skip`. Otherwise,
+  return `:cont` to continue with the download.
+  """
+  @callback pre_download_hook(file :: String.t(), output_dir :: String.t()) :: :cont | :skip
+
   @doc """
   This callback acts as a pass through to the `OctoFetch` module for the
   downloader implementation. See `OctoFetch.download/3` for supported `opts`.