llmodel: change tokenToString to not use string_view (#968)

fixes a definite use-after-free and likely avoids some other
potential ones - std::string will convert to a std::string_view
automatically but as soon as the std::string in question goes out of
scope it is already freed and the string_view is pointing at freed
memory - this is *mostly* fine if its returning a reference to the
tokenizer's internal vocab table but it's, imo, too easy to return a
reference to a dynamically constructed string with this as replit is
doing (and unfortunately needs to do to convert the internal whitespace
replacement symbol back to a space)

gpt4all-backend/gptj.cpp

@@ -907,7 +907,7 @@ LLModel::Token GPTJ::sampleToken(PromptContext &promptCtx) const
         d_ptr->rng);
 }
 
-std::string_view GPTJ::tokenToString(Token id) const
+std::string GPTJ::tokenToString(Token id) const
 {
     return d_ptr->vocab.id_to_token[id];
 }

gpt4all-backend/gptj_impl.h

@@ -29,7 +29,7 @@ private:
 protected:
     std::vector<Token> tokenize(PromptContext &, const std::string&) const override;
     Token sampleToken(PromptContext &ctx) const override;
-    std::string_view tokenToString(Token) const override;
+    std::string tokenToString(Token) const override;
     bool evalTokens(PromptContext &ctx, const std::vector<int32_t> &tokens) const override;
     int32_t contextLength() const override;
     const std::vector<Token>& endTokens() const override;

gpt4all-backend/llamamodel.cpp

@@ -177,7 +177,7 @@ std::vector<LLModel::Token> LLamaModel::tokenize(PromptContext &ctx, const std::
     return fres;
 }
 
-std::string_view LLamaModel::tokenToString(Token id) const
+std::string LLamaModel::tokenToString(Token id) const
 {
     return llama_token_to_str(d_ptr->ctx, id);
 }

gpt4all-backend/llamamodel_impl.h

@@ -28,7 +28,7 @@ private:
 
 protected:
     std::vector<Token> tokenize(PromptContext &, const std::string&) const override;
-    std::string_view tokenToString(Token) const override;
+    std::string tokenToString(Token) const override;
     Token sampleToken(PromptContext& ctx) const override;
     bool evalTokens(PromptContext& ctx, const std::vector<int32_t> &tokens) const override;
     int32_t contextLength() const override;

gpt4all-backend/llmodel.h

@@ -86,7 +86,7 @@ protected:
     // These are pure virtual because subclasses need to implement as the default implementation of
     // 'prompt' above calls these functions
     virtual std::vector<Token> tokenize(PromptContext &, const std::string&) const = 0;
-    virtual std::string_view tokenToString(Token) const = 0;
+    virtual std::string tokenToString(Token) const = 0;
     virtual Token sampleToken(PromptContext &ctx) const = 0;
     virtual bool evalTokens(PromptContext &/*ctx*/, const std::vector<int32_t>& /*tokens*/) const = 0;
     virtual int32_t contextLength() const = 0;

gpt4all-backend/llmodel_shared.cpp

@@ -121,7 +121,7 @@ void LLModel::prompt(const std::string &prompt,
             if (id == token) return;
         }
 
-        const std::string_view str = tokenToString(id);
+        const std::string str = tokenToString(id);
 
         // Check if the provided str is part of our reverse prompts
         bool foundPartialReversePrompt = false;

gpt4all-backend/mpt.cpp

@@ -820,7 +820,7 @@ std::vector<LLModel::Token> MPT::tokenize(PromptContext &, const std::string &st
     return ::gpt_tokenize(d_ptr->vocab, str);
 }
 
-std::string_view MPT::tokenToString(Token id) const
+std::string MPT::tokenToString(Token id) const
 {
     return d_ptr->vocab.id_to_token[id];
 }

gpt4all-backend/mpt_impl.h

@@ -28,7 +28,7 @@ private:
 
 protected:
     std::vector<Token> tokenize(PromptContext &, const std::string&) const override;
-    std::string_view tokenToString(Token) const override;
+    std::string tokenToString(Token) const override;
     Token sampleToken(PromptContext &ctx) const override;
     bool evalTokens(PromptContext &ctx, const std::vector<int32_t> &tokens) const override;
     int32_t contextLength() const override;

gpt4all-backend/replit.cpp

@@ -910,7 +910,7 @@ std::vector<LLModel::Token> Replit::tokenize(PromptContext &, const std::string
     return replit_tokenizer_tokenize(d_ptr->vocab, str);
 }
 
-std::string_view Replit::tokenToString(LLModel::Token id) const
+std::string Replit::tokenToString(LLModel::Token id) const
 {
     return replit_tokenizer_detokenize(d_ptr->vocab, {id});
 }

gpt4all-backend/replit_impl.h

@@ -30,7 +30,7 @@ private:
 
 protected:
     std::vector<Token> tokenize(PromptContext &, const std::string&) const override;
-    std::string_view tokenToString(Token) const override;
+    std::string tokenToString(Token) const override;
     Token sampleToken(PromptContext &ctx) const override;
     bool evalTokens(PromptContext &ctx, const std::vector<int32_t> &tokens) const override;
     int32_t contextLength() const override;

gpt4all-chat/chatgpt.h

@@ -39,7 +39,7 @@ protected:
     // them as they are only called from the default implementation of 'prompt' which we override and
     // completely replace
     std::vector<Token> tokenize(PromptContext &, const std::string&) const override { return std::vector<Token>(); }
-    std::string_view tokenToString(Token) const override { return std::string_view(); }
+    std::string tokenToString(Token) const override { return std::string(); }
     Token sampleToken(PromptContext &ctx) const override { return -1; }
     bool evalTokens(PromptContext &/*ctx*/, const std::vector<int32_t>& /*tokens*/) const override { return false; }
     int32_t contextLength() const override { return -1; }