feat: support proxy for download fetch

lib/steps/fetch/fetch_musl.ex

@@ -53,7 +53,17 @@ defmodule Burrito.Steps.Fetch.FetchMusl do
   defp do_download(url, cache_key) do
     {:ok, _} = Application.ensure_all_started(:req)
     Log.info(:step, "Downloading file: #{url}")
-    resp = Req.get!(url, raw: true)
+
+    resp =
+      case Burrito.Util.get_proxy() do
+        proxy = %{scheme: scheme, host: host, port: port} when scheme in ["http", "https"] ->
+          Log.info(:step, "Using PROXY: #{proxy}")
+          proxy = {String.to_atom(scheme), host, port, []}
+          Req.get!(url, raw: true, connect_options: [proxy: proxy])
+
+        _ ->
+          Req.get!(url, raw: true)
+      end
 
     if resp.status != 200 do
       raise "Failed to fetch musl runtime: #{url}! (Got #{resp.status}) -- please file an issue! Thanks!"

lib/util/default_erts_resolver.ex

@@ -98,7 +98,17 @@ defmodule Burrito.Util.DefaultERTSResolver do
   defp do_download(url, cache_key) do
     {:ok, _} = Application.ensure_all_started(:req)
     Log.info(:step, "Downloading file: #{url}")
-    resp = Req.get!(url, raw: true)
+
+    resp =
+      case Burrito.Util.get_proxy() do
+        proxy = %{scheme: scheme, host: host, port: port} when scheme in ["http", "https"] ->
+          Log.info(:step, "Using PROXY: #{proxy}")
+          proxy = {String.to_atom(scheme), host, port, []}
+          Req.get!(url, raw: true, connect_options: [proxy: proxy])
+
+        _ ->
+          Req.get!(url, raw: true)
+      end
 
     if resp.status != 200 do
       raise "Failed to fetch #{url}! (Got #{resp.status}) Perhaps we haven't built a pre-compiled Erlang for this release yet? If this was a 404, please file an issue! Thanks!"

lib/util/util.ex

@@ -47,4 +47,24 @@ defmodule Burrito.Util do
   def running_standalone?() do
     System.get_env("__BURRITO") != nil
   end
+
+  @doc """
+  Gets the HTTP or HTTPS proxy from environment variables, if set.
+  1. Checks `HTTP_PROXY` and `http_proxy`
+  2. Checks `HTTPS_PROXY` and `https_proxy`
+  3. Returns `nil` if no proxy is set
+  """
+  @spec get_proxy :: URI.t() | nil
+  def get_proxy do
+    cond do
+      proxy = System.get_env("HTTP_PROXY") || System.get_env("http_proxy") ->
+        URI.parse(proxy)
+
+      proxy = System.get_env("HTTPS_PROXY") || System.get_env("https_proxy") ->
+        URI.parse(proxy)
+
+      true ->
+        nil
+    end
+  end
 end