From d10fe1a3b71b23587fbe00fa0c51c46a2e22407a Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Eric=20Meadows-J=C3=B6nsson?=
 <eric.meadows.jonsson@gmail.com>
Date: Sat, 10 Dec 2016 00:27:48 +0100
Subject: [PATCH] Do not make conditional HTTP request if file is missing

Re: HashNuke/heroku-buildpack-elixir#93
---
 lib/hex/scm.ex | 6 +++---
 1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/lib/hex/scm.ex b/lib/hex/scm.ex
index 0d4a01a60..d6fbf6f95 100644
--- a/lib/hex/scm.ex
+++ b/lib/hex/scm.ex
@@ -193,10 +193,10 @@ defmodule Hex.SCM do
     fetch = fetch_from_lock(lock)
 
     Enum.each(fetch, fn {package, version} ->
-      etag = Hex.Registry.tarball_etag(package, version)
+      filename = "#{package}-#{version}.tar"
+      path = cache_path(filename)
+      etag = File.exists?(path) && Hex.Registry.tarball_etag(package, version)
       Hex.Parallel.run(:hex_fetcher, {:tarball, package, version}, fn ->
-        filename = "#{package}-#{version}.tar"
-        path = cache_path(filename)
         fetch(filename, path, etag)
       end)
     end)