(erlang#1743): store the etags in cache files

src/rebar_pkg_resource.erl

@@ -35,20 +35,22 @@ download(TmpDir, Pkg={pkg, Name, Vsn, _Hash}, State) ->
     CachePath = filename:join(PackageDir, Package),
     case rebar_utils:url_append_path(CDN, filename:join(?REMOTE_PACKAGE_DIR, Package)) of
         {ok, Url} ->
-            cached_download(TmpDir, CachePath, Pkg, Url, etag(CachePath), State);
+            cached_download(TmpDir, CachePath, Pkg, Url, etag(CachePath), State, CachePath);
         _ ->
             {fetch_fail, Name, Vsn}
     end.
 
-cached_download(TmpDir, CachePath, Pkg={pkg, Name, Vsn, _Hash}, Url, ETag, State) ->
+cached_download(TmpDir, CachePath, Pkg={pkg, Name, Vsn, _Hash}, Url, ETag, State, CachePath) ->
     case request(Url, ETag) of
         {ok, cached} ->
             ?INFO("Version cached at ~ts is up to date, reusing it", [CachePath]),
             serve_from_cache(TmpDir, CachePath, Pkg, State);
         {ok, Body, NewETag} ->
             ?INFO("Downloaded package, caching at ~ts", [CachePath]),
+            store_etag_in_cache(CachePath, NewETag),
             serve_from_download(TmpDir, CachePath, Pkg, NewETag, Body, State);
         error when ETag =/= false ->
+            store_etag_in_cache(CachePath, ETag),
             ?INFO("Download error, using cached file at ~ts", [CachePath]),
             serve_from_cache(TmpDir, CachePath, Pkg, State);
         error ->
@@ -130,10 +132,9 @@ request(Url, ETag) ->
     end.
 
 etag(Path) ->
-    case file:read_file(Path) of
-        {ok, Binary} ->
-            <<X:128/big-unsigned-integer>> = crypto:hash(md5, Binary),
-            rebar_string:lowercase(lists:flatten(io_lib:format("~32.16.0b", [X])));
+    case file:read_file(etag_path(Path)) of
+        {ok, Bin} ->
+            binary_to_list(Bin);
         {error, _} ->
             false
     end.
@@ -216,3 +217,9 @@ version_pad([Major, Minor, Patch]) ->
     {list_to_integer(Major), list_to_integer(Minor), list_to_integer(Patch)};
 version_pad([Major, Minor, Patch | _]) ->
     {list_to_integer(Major), list_to_integer(Minor), list_to_integer(Patch)}.
+
+store_etag_in_cache(Path, ETag) ->
+    ok = file:write_file(etag_path(Path), ETag).
+
+etag_path(Path) ->
+    string:join([Path, ".etag"], []).