firmware.patch handles FAT resources

With the following patch fwup-home/fwup#202 ,
fwup is able to apply delta updates on FAT resources.

This patch update firmware.patch mix task to create firmware patches
including FAT resources delta updates.

lib/mix/tasks/firmware.patch.ex

@@ -5,7 +5,7 @@ defmodule Mix.Tasks.Firmware.Patch do
   Generate a firmware patch from a source and target firmware and output a new
   firmware file with the patch contents. The source firmware file
 
-  This requires fwup >= 1.6.0
+  This requires fwup >= 1.10.0
 
   ## Command line options
 
@@ -21,7 +21,7 @@ defmodule Mix.Tasks.Firmware.Patch do
   alias Mix.Nerves.Preflight
   alias Nerves.Utils.Shell
 
-  @fwup_semver "~> 1.6 or ~> 1.6.0-dev"
+  @fwup_semver ">= 1.10.0"
 
   @switches [source: :string, target: :string, output: :string]
 
@@ -56,27 +56,7 @@ defmodule Mix.Tasks.Firmware.Patch do
 
     target_stats = File.stat!(target)
 
-    source_work_dir = Path.join(work_dir, "source")
-    target_work_dir = Path.join(work_dir, "target")
-    output_work_dir = Path.join(work_dir, "output")
-
-    File.mkdir_p!(source_work_dir)
-    File.mkdir_p!(target_work_dir)
-    File.mkdir_p!(Path.join(output_work_dir, "data"))
-
-    {_, 0} = shell("unzip", ["-qq", source, "-d", source_work_dir])
-    {_, 0} = shell("unzip", ["-qq", target, "-d", target_work_dir])
-
-    source_rootfs = Path.join([source_work_dir, "data", "rootfs.img"])
-    target_rootfs = Path.join([target_work_dir, "data", "rootfs.img"])
-    out_rootfs = Path.join([output_work_dir, "data", "rootfs.img"])
-
-    {_, 0} = shell("xdelta3", ["-A", "-S", "-f", "-s", source_rootfs, target_rootfs, out_rootfs])
-
-    File.mkdir_p!(Path.dirname(output))
-    File.cp!(target, output)
-
-    {_, 0} = shell("zip", ["-qq", output, "data/rootfs.img"], cd: output_work_dir)
+    _ = create(source, target, output, work_dir)
 
     output_stats = File.stat!(output)
 
@@ -117,4 +97,50 @@ defmodule Mix.Tasks.Firmware.Patch do
     Mix.Tasks.Firmware.run(["--output", out_fw])
     out_fw
   end
+
+  defp create(source_path, target_path, output_path, work_dir) do
+    source_work_dir = Path.join(work_dir, "source")
+    target_work_dir = Path.join(work_dir, "target")
+    output_work_dir = Path.join(work_dir, "output")
+
+    _ = File.mkdir_p(source_work_dir)
+    _ = File.mkdir_p(target_work_dir)
+    _ = File.mkdir_p(output_work_dir)
+
+    {_, 0} = shell("unzip", ["-qq", source_path, "-d", source_work_dir])
+    {_, 0} = shell("unzip", ["-qq", target_path, "-d", target_work_dir])
+
+    for path <- Path.wildcard(target_work_dir <> "/**") do
+      path = Regex.replace(~r/^#{target_work_dir}\//, path, "")
+
+      unless File.dir?(Path.join(target_work_dir, path)) do
+        :ok = handle_content(path, source_work_dir, target_work_dir, output_work_dir)
+      end
+    end
+
+    {_, 0} = shell("zip", ["-r", "-qq", output_path, "."], cd: output_work_dir)
+    output_path
+  end
+
+  defp handle_content("meta." <> _ = path, _source_dir, target_dir, out_dir) do
+    do_copy(Path.join(target_dir, path), Path.join(out_dir, path))
+  end
+
+  defp handle_content(path, source_dir, target_dir, out_dir) do
+    do_delta(Path.join(source_dir, path), Path.join(target_dir, path), Path.join(out_dir, path))
+  end
+
+  defp do_copy(source, target) do
+    target |> Path.dirname() |> File.mkdir_p!()
+    File.cp(source, target)
+  end
+
+  defp do_delta(source, target, out) do
+    out |> Path.dirname() |> File.mkdir_p!()
+
+    case shell("xdelta3", ["-A", "-S", "-f", "-s", source, target, out]) do
+      {_, 0} -> :ok
+      {_, code} -> {:error, code}
+    end
+  end
 end