ytdl_hook: whitelist protocols from urls retrieved from youtube-dl

Not very clean since there's a lot of potential unsafe urls that youtube-dl
can give us, depending on whether it's a single url, split tracks,
playlists, segmented dash, etc.

player/lua/ytdl_hook.lua

@@ -16,6 +16,18 @@ local ytdl = {
 
 local chapter_list = {}
 
+function Set (t)
+    local set = {}
+    for _, v in pairs(t) do set[v] = true end
+    return set
+end
+
+local safe_protos = Set {
+    "http", "https", "ftp", "ftps",
+    "rtmp", "rtmps", "rtmpe", "rtmpt", "rtmpts", "rtmpte",
+    "data"
+}
+
 local function exec(args)
     local ret = utils.subprocess({args = args})
     return ret.status, ret.stdout, ret
@@ -183,6 +195,9 @@ local function edl_track_joined(fragments, protocol, is_live, base)
 
     for i = offset, #fragments do
         local fragment = fragments[i]
+        if not url_is_safe(join_url(base, fragment)) then
+            return nil
+        end
         table.insert(parts, edl_escape(join_url(base, fragment)))
         if fragment.duration then
             parts[#parts] =
@@ -208,6 +223,15 @@ local function proto_is_dash(json)
            or json["protocol"] == "http_dash_segments"
 end
 
+local function url_is_safe(url)
+    local proto = type(url) == "string" and url:match("^(.+)://") or nil
+    local safe = proto and safe_protos[proto]
+    if not safe then
+        msg.error(("Ignoring potentially unsafe url: '%s'"):format(url))
+    end
+    return safe
+end
+
 local function add_single_video(json)
     local streamurl = ""
     local max_bitrate = 0
@@ -218,6 +242,8 @@ local function add_single_video(json)
         if not mpd_url then
             msg.error("No manifest URL found in JSON data.")
             return
+        elseif not url_is_safe(mpd_url) then
+            return
         end
 
         streamurl = mpd_url
@@ -238,14 +264,18 @@ local function add_single_video(json)
             edl_track = edl_track_joined(track.fragments,
                 track.protocol, json.is_live,
                 track.fragment_base_url)
+            local url = edl_track or track.url
+            if not url_is_safe(url) then
+                return
+            end
             if track.acodec and track.acodec ~= "none" then
                 -- audio track
                 mp.commandv("audio-add",
-                    edl_track or track.url, "auto",
+                    url, "auto",
                     track.format_note or "")
             elseif track.vcodec and track.vcodec ~= "none" then
                 -- video track
-                streamurl = edl_track or track.url
+                streamurl = url
             end
         end
 
@@ -264,7 +294,13 @@ local function add_single_video(json)
 
     msg.debug("streamurl: " .. streamurl)
 
-    mp.set_property("stream-open-filename", streamurl:gsub("^data:", "data://", 1))
+    streamurl = streamurl:gsub("^data:", "data://", 1)
+
+    if not url_is_safe(streamurl) then
+        return
+    end
+
+    mp.set_property("stream-open-filename", streamurl)
 
     mp.set_property("file-local-options/force-media-title", json.title)
 
@@ -526,14 +562,18 @@ mp.add_hook(o.try_ytdl_first and "on_load" or "on_load_fail", 10, function ()
                         site = entry["webpage_url"]
                     end
 
-                    if not (site:find("https?://") == 1) then
-                        site = "ytdl://" .. site
+                    -- links with only youtube id as returned by --flat-playlist
+                    if not site:find("://") then
+                        table.insert(playlist, "ytdl://" .. site)
+                    elseif url_is_safe(site) then
+                        table.insert(playlist, site)
                     end
-                    table.insert(playlist, site)
 
                 end
 
-                mp.set_property("stream-open-filename", "memory://" .. table.concat(playlist, "\n"))
+                if #playlist > 0 then
+                    mp.set_property("stream-open-filename", "memory://" .. table.concat(playlist, "\n"))
+                end
             end
 
         else -- probably a video