generate checksum file for each target

lib/elixir_make/artefact.ex

@@ -23,13 +23,33 @@ defmodule ElixirMake.Artefact do
     cache_dir
   end
 
+  @doc """
+  Returns the checksum algorithm
+  """
+  def checksum_algo do
+    @checksum_algo
+  end
+
   @doc """
   Computes the checksum and artefact for the given contents.
   """
   def checksum(basename, contents) do
-    hash = :crypto.hash(@checksum_algo, contents)
+    hash = :crypto.hash(checksum_algo(), contents)
     checksum = Base.encode16(hash, case: :lower)
-    %Artefact{basename: basename, checksum: checksum, checksum_algo: @checksum_algo}
+    %Artefact{basename: basename, checksum: checksum, checksum_algo: checksum_algo()}
+  end
+
+  @doc """
+  Writes checksum for the target to disk.
+  """
+  def write_checksum_for_target!(%Artefact{
+        basename: basename,
+        checksum: checksum,
+        checksum_algo: checksum_algo
+      }) do
+    cache_dir = Artefact.cache_dir()
+    file = Path.join(cache_dir, "#{basename}.#{Atom.to_string(checksum_algo)}")
+    File.write!(file, [checksum, "  ", basename, "\n"])
   end
 
   @doc """

lib/mix/tasks/elixir_make.checksum.ex

@@ -103,38 +103,79 @@ defmodule Mix.Tasks.ElixirMake.Checksum do
     tasks =
       Task.async_stream(
         urls,
-        fn {{_target, _nif_version}, url} -> {url, Artefact.download(url)} end,
+        fn {{_target, _nif_version}, url} ->
+          checksum_algo = Artefact.checksum_algo()
+          checksum_file_url = "#{url}.#{Atom.to_string(checksum_algo)}"
+          artifact_checksum = Artefact.download(checksum_file_url)
+
+          from_checksum_file =
+            case artifact_checksum do
+              {:ok, body} ->
+                case String.split(body, " ", trim: true) do
+                  [checksum, basename] ->
+                    {:ok,
+                     {:checksum, url,
+                      %Artefact{
+                        basename: basename,
+                        checksum: checksum,
+                        checksum_algo: checksum_algo
+                      }}}
+
+                  _ ->
+                    :download_and_compute
+                end
+
+              _ ->
+                :download_and_compute
+            end
+
+          case from_checksum_file do
+            {:ok, packed} ->
+              packed
+
+            _ ->
+              {:download, url, Artefact.download(url)}
+          end
+        end,
         timeout: :infinity,
         ordered: false
       )
 
     cache_dir = Artefact.cache_dir()
 
-    Enum.flat_map(tasks, fn {:ok, {url, download}} ->
-      case download do
-        {:ok, body} ->
-          basename = basename_from_url(url)
-          path = Path.join(cache_dir, basename)
-          File.write!(path, body)
-          artefact = Artefact.checksum(basename, body)
-
-          Mix.shell().info(
-            "NIF cached at #{path} with checksum #{artefact.checksum} (#{artefact.checksum_algo})"
-          )
-
-          [artefact]
-
-        result ->
-          if ignore_unavailable? do
-            msg = "Skipped unavailable NIF artifact. Reason: #{inspect(result)}"
-            Mix.shell().info(msg)
-          else
-            msg = "Could not finish the download of NIF artifacts. Reason: #{inspect(result)}"
-            Mix.shell().error(msg)
-          end
+    Enum.flat_map(tasks, fn
+      {:ok, :checksum, url, artefact} ->
+        Mix.shell().info(
+          "NIF checksum file with checksum #{artefact.checksum} (#{artefact.checksum_algo})"
+        )
 
-          []
-      end
+        [artefact]
+
+      {:ok, {:download, url, download}} ->
+        case download do
+          {:ok, body} ->
+            basename = basename_from_url(url)
+            path = Path.join(cache_dir, basename)
+            File.write!(path, body)
+            artefact = Artefact.checksum(basename, body)
+
+            Mix.shell().info(
+              "NIF cached at #{path} with checksum #{artefact.checksum} (#{artefact.checksum_algo})"
+            )
+
+            [artefact]
+
+          result ->
+            if ignore_unavailable? do
+              msg = "Skipped unavailable NIF artifact. Reason: #{inspect(result)}"
+              Mix.shell().info(msg)
+            else
+              msg = "Could not finish the download of NIF artifacts. Reason: #{inspect(result)}"
+              Mix.shell().error(msg)
+            end
+
+            []
+        end
     end)
   end
 

lib/mix/tasks/elixir_make.precompile.ex

@@ -48,6 +48,8 @@ defmodule Mix.Tasks.ElixirMake.Precompile do
                 precompiler.post_precompile_target(target)
               end
 
+              Artefact.write_checksum_for_target!(precompiled_artefacts)
+
               precompiled_artefacts
 
             {:error, msg} ->