model: Don't unconditionally add special tokens

We sometimes tokenize partial strings. For example, with
multimodal inputs, we split the input string around the images
and then tokenize each piece. In these cases, we should only add
the special tokens on the first piece.

llm/server.go

@@ -973,7 +973,7 @@ func (s *llmServer) Tokenize(ctx context.Context, content string) ([]int, error)
 		return s.llamaModel.Tokenize(content, false, true)
 	}
 	if s.textProcessor != nil {
-		tokens, err := s.textProcessor.Encode(content)
+		tokens, err := s.textProcessor.Encode(content, false)
 		if err != nil {
 			return nil, err
 		}

model/process_text.go

@@ -19,7 +19,7 @@ const (
 )
 
 type TextProcessor interface {
-	Encode(string) ([]int32, error)
+	Encode(s string, addSpecial bool) ([]int32, error)
 	Decode([]int32) (string, error)
 	Is(int32, Special) bool
 }
@@ -144,7 +144,7 @@ type merge struct {
 	runes []rune
 }
 
-func (bpe BytePairEncoding) Encode(s string) ([]int32, error) {
+func (bpe BytePairEncoding) Encode(s string, addSpecial bool) ([]int32, error) {
 	fragments := []fragment{{value: s}}
 	for _, special := range bpe.vocab.SpecialVocabulary() {
 		// TODO: process special tokens concurrently
@@ -282,7 +282,7 @@ func (bpe BytePairEncoding) Encode(s string) ([]int32, error) {
 		}
 	}
 
-	if len(ids) > 0 {
+	if addSpecial && len(ids) > 0 {
 		if bpe.vocab.AddBOS {
 			if ids[0] == bpe.vocab.BOS {
 				slog.Warn("adding bos token to prompt which already has it", "id", bpe.vocab.BOS)

model/process_text_test.go

@@ -74,7 +74,7 @@ func TestLlama(t *testing.T) {
 	t.Run("simple", func(t *testing.T) {
 		t.Parallel()
 
-		ids, err := tokenizer.Encode("hello world")
+		ids, err := tokenizer.Encode("hello world", true)
 		if err != nil {
 			t.Error(err)
 		}
@@ -92,7 +92,7 @@ func TestLlama(t *testing.T) {
 			t.Errorf("got %q, want hello world", s)
 		}
 
-		ids, err = tokenizer.Encode("hello <|end_of_text|>")
+		ids, err = tokenizer.Encode("hello <|end_of_text|>", true)
 		if err != nil {
 			t.Error(err)
 		}
@@ -126,7 +126,7 @@ func TestLlama(t *testing.T) {
 		}
 
 		for s, want := range cases {
-			ids, err := tokenizer.Encode(s)
+			ids, err := tokenizer.Encode(s, true)
 			if err != nil {
 				t.Error(err)
 			}
@@ -152,7 +152,7 @@ func TestLlama(t *testing.T) {
 		}
 
 		for _, want := range cases {
-			ids, err := tokenizer.Encode(want)
+			ids, err := tokenizer.Encode(want, true)
 			if err != nil {
 				t.Error(err)
 			}
@@ -176,7 +176,7 @@ func TestLlama(t *testing.T) {
 		}
 
 		for s, want := range cases {
-			ids, err := tokenizer.Encode(s)
+			ids, err := tokenizer.Encode(s, true)
 			if err != nil {
 				t.Fatal(err)
 			}
@@ -222,7 +222,7 @@ func BenchmarkBytePairEncoding(b *testing.B) {
 		b.Run("encode"+strconv.Itoa(n), func(b *testing.B) {
 			b.ResetTimer()
 			for range b.N {
-				_, err := tokenizer.Encode(string(bts))
+				_, err := tokenizer.Encode(string(bts), true)
 				if err != nil {
 					b.Fatal(err)
 				}
@@ -230,7 +230,7 @@ func BenchmarkBytePairEncoding(b *testing.B) {
 		})
 
 		b.Run("decode"+strconv.Itoa(n), func(b *testing.B) {
-			ids, err := tokenizer.Encode(string(bts))
+			ids, err := tokenizer.Encode(string(bts), true)
 			if err != nil {
 				b.Fatal(err)
 			}

runner/ollamarunner/runner.go

@@ -161,7 +161,7 @@ func (s *Server) inputs(prompt string, images []ImageData) ([]input, error) {
 
 	for i, part := range parts {
 		// text - tokenize
-		tokens, err := s.model.(model.TextProcessor).Encode(part)
+		tokens, err := s.model.(model.TextProcessor).Encode(part, i == 0)
 		if err != nil {
 			return nil, err
 		}