Only proxy HTTP and HTTP urls via Media Proxy

We make an assumption that we are only proxying HTTP/HTTPS hosted
media through the media proxy endpoint.

Fixes: #859

lib/pleroma/web/media_proxy.ex

@@ -52,11 +52,11 @@ def url(url) do
 
   @spec url_proxiable?(String.t()) :: boolean()
   def url_proxiable?(url) do
-    not local?(url) and not whitelisted?(url) and not blocked?(url)
+    not local?(url) and not whitelisted?(url) and not blocked?(url) and http_scheme?(url)
   end
 
   def preview_url(url, preview_params \\ []) do
-    if preview_enabled?() do
+    if preview_enabled?() and url_proxiable?(url) do
       encode_preview_url(url, preview_params)
     else
       url(url)
@@ -71,6 +71,8 @@ def preview_enabled?, do: enabled?() and !!Config.get([:media_preview_proxy, :en
 
   def local?(url), do: String.starts_with?(url, Endpoint.url())
 
+  def http_scheme?(url), do: String.starts_with?(url, ["http:", "https:"])
+
   def whitelisted?(url) do
     %{host: domain} = URI.parse(url)
 

test/pleroma/web/media_proxy_test.exs

@@ -37,6 +37,10 @@ test "ignores local url" do
       assert MediaProxy.url(local_root) == local_root
     end
 
+    test "ignores data url" do
+      assert MediaProxy.url("data:image/png;base64,") == "data:image/png;base64,"
+    end
+
     test "encodes and decodes URL" do
       url = "https://pleroma.soykaf.com/static/logo.png"
       encoded = MediaProxy.url(url)