FIX: Handle unicode on tokenizer (#515)

* FIX: Handle unicode on tokenizer

Our fast track code broke when strings had characters who are longer in tokens than
in UTF-8.

Admins can set `DISCOURSE_AI_STRICT_TOKEN_COUNTING: true` in app.yml to ensure token counting is strict, even if slower.


Co-authored-by: wozulong <sidle.pax_0e@icloud.com>

config/settings.yml

@@ -177,6 +177,9 @@ discourse_ai:
     default: ""
     hidden: true
   ai_llava_api_key: ""
+  ai_strict_token_counting:
+    default: false
+    hidden: true
 
   composer_ai_helper_enabled:
     default: false

lib/tokenizer/basic_tokenizer.rb

@@ -17,14 +17,19 @@ module DiscourseAi
         end
 
         def truncate(text, max_length)
-          # Fast track the common case where the text is already short enough.
-          return text if text.size < max_length
+          # fast track common case, /2 to handle unicode chars
+          # than can take more than 1 token per char
+          return text if !SiteSetting.ai_strict_token_counting && text.size < max_length / 2
 
           tokenizer.decode(tokenizer.encode(text).ids.take(max_length))
         end
 
         def can_expand_tokens?(text, addition, max_length)
-          return true if text.size + addition.size < max_length
+          # fast track common case, /2 to handle unicode chars
+          # than can take more than 1 token per char
+          if !SiteSetting.ai_strict_token_counting && text.size + addition.size < max_length / 2
+            return true
+          end
 
           tokenizer.encode(text).ids.length + tokenizer.encode(addition).ids.length < max_length
         end

lib/tokenizer/open_ai_tokenizer.rb

@@ -13,8 +13,9 @@ module DiscourseAi
         end
 
         def truncate(text, max_length)
-          # Fast track the common case where the text is already short enough.
-          return text if text.size < max_length
+          # fast track common case, /2 to handle unicode chars
+          # than can take more than 1 token per char
+          return text if !SiteSetting.ai_strict_token_counting && text.size < max_length / 2
 
           tokenizer.decode(tokenize(text).take(max_length))
         rescue Tiktoken::UnicodeError
@@ -23,7 +24,11 @@ module DiscourseAi
         end
 
         def can_expand_tokens?(text, addition, max_length)
-          return true if text.size + addition.size < max_length
+          # fast track common case, /2 to handle unicode chars
+          # than can take more than 1 token per char
+          if !SiteSetting.ai_strict_token_counting && text.size + addition.size < max_length / 2
+            return true
+          end
 
           tokenizer.encode(text).length + tokenizer.encode(addition).length < max_length
         end

spec/shared/tokenizer_spec.rb

@@ -81,6 +81,31 @@ describe DiscourseAi::Tokenizer::OpenAiTokenizer do
       sentence = "foo bar 👨🏿‍👩🏿‍👧🏿‍👧🏿 baz qux quux corge grault garply waldo fred plugh xyzzy thud"
       expect(described_class.truncate(sentence, 7)).to eq("foo bar 👨🏿")
     end
+
+    it "truncates unicode characters properly when they use more than one token per char" do
+      sentence = "我喜欢吃比萨"
+      original_size = described_class.size(sentence)
+      expect(described_class.size(described_class.truncate(sentence, original_size - 1))).to be <
+        original_size
+    end
+  end
+
+  describe "#can_expand_tokens?" do
+    it "returns true when the tokens can be expanded" do
+      expect(described_class.can_expand_tokens?("foo bar", "baz qux", 6)).to eq(true)
+    end
+
+    it "returns false when the tokens cannot be expanded" do
+      expect(described_class.can_expand_tokens?("foo bar", "baz qux", 3)).to eq(false)
+    end
+
+    it "returns false when the tokens cannot be expanded due to multibyte unicode characters" do
+      expect(described_class.can_expand_tokens?("foo bar 👨🏿", "baz qux", 6)).to eq(false)
+    end
+
+    it "handles unicode characters properly when they use more than one token per char" do
+      expect(described_class.can_expand_tokens?("我喜欢吃比萨", "萨", 10)).to eq(false)
+    end
   end
 end