fix(companion): isolate caption cache keys

spec/invidious/subtitle_cache_spec.cr

@@ -81,6 +81,13 @@ Spectator.describe Invidious::SubtitleCache do
       expect(cache.get("video:123|label:Chinese|lang:zh|tlang:").try &.body).to eq(vtt_zh)
     end
 
+    it "builds cache keys that isolate delimiter-containing values" do
+      key_a = Invidious::SubtitleCache.caption_cache_key("video", "English|lang:x", "en", "")
+      key_b = Invidious::SubtitleCache.caption_cache_key("video", "English", "lang:x", "")
+
+      expect(key_a).not_to eq(key_b)
+    end
+
     it "returns miss on first fetch and hit on subsequent fetch" do
       cache = Invidious::SubtitleCache.new
       fetch_count = 0

src/invidious/helpers/subtitle_cache.cr

@@ -72,6 +72,10 @@ module Invidious
       header_end == trimmed.size || " \t\r\n".includes?(trimmed[header_end])
     end
 
+    def self.caption_cache_key(video_id : String, label : String, lang : String, tlang : String) : String
+      [video_id, label, lang, tlang].map { |value| Base64.urlsafe_encode(value) }.join('|')
+    end
+
     def self.read_limited_body(input : IO, limit : Int32 = MAX_ENTRY_BYTES) : LimitedBody
       output = IO::Memory.new
       buffer = Bytes.new(READ_CHUNK_BYTES)

src/invidious/routes/companion.cr

@@ -80,7 +80,7 @@ module Invidious::Routes::Companion
       return
     end
 
-    cache_key = "video:#{video_id}|label:#{label}|lang:#{lang}|tlang:#{tlang}"
+    cache_key = Invidious::SubtitleCache.caption_cache_key(video_id, label, lang, tlang)
 
     result = SUBTITLE_CACHE.get_or_fetch(cache_key) do
       fetch_from_companion(url, env.request.headers)