feat: Use non-gated tokenizer as fallback for mistral in AmazonBedroc…

…kChatGenerator (#843)

* feat: Use non-gated tokenizer as fallback for mistral

* formatting

* fix linter issues

integrations/amazon_bedrock/src/haystack_integrations/components/generators/amazon_bedrock/chat/adapters.py

@@ -1,5 +1,6 @@
 import json
 import logging
+import os
 from abc import ABC, abstractmethod
 from typing import Any, Callable, ClassVar, Dict, List
 
@@ -332,7 +333,19 @@ def __init__(self, generation_kwargs: Dict[str, Any]):
         # Use `mistralai/Mistral-7B-v0.1` as tokenizer, all mistral models likely use the same tokenizer
         # a) we should get good estimates for the prompt length
         # b) we can use apply_chat_template with the template above to delineate ChatMessages
-        tokenizer: PreTrainedTokenizer = AutoTokenizer.from_pretrained("mistralai/Mistral-7B-Instruct-v0.1")
+        # Mistral models are gated on HF Hub. If no HF_TOKEN is found we use a non-gated alternative tokenizer model.
+        tokenizer: PreTrainedTokenizer
+        if os.environ.get("HF_TOKEN"):
+            tokenizer = AutoTokenizer.from_pretrained("mistralai/Mistral-7B-Instruct-v0.1")
+        else:
+            tokenizer = AutoTokenizer.from_pretrained("NousResearch/Llama-2-7b-chat-hf")
+            logger.warning(
+                "Gated mistralai/Mistral-7B-Instruct-v0.1 model cannot be used as a tokenizer for "
+                "estimating the prompt length because no HF_TOKEN was found. Using "
+                "NousResearch/Llama-2-7b-chat-hf instead. To use a mistral tokenizer export an env var "
+                "HF_TOKEN containing a Hugging Face token and make sure you have access to the model."
+            )
+
         self.prompt_handler = DefaultPromptHandler(
             tokenizer=tokenizer,
             model_max_length=model_max_length,

integrations/amazon_bedrock/tests/test_chat_generator.py

@@ -1,5 +1,7 @@
+import logging
 import os
 from typing import Optional, Type
+from unittest.mock import patch
 
 import pytest
 from haystack.components.generators.utils import print_streaming_chunk
@@ -183,13 +185,6 @@ def test_prepare_body_with_custom_inference_params(self) -> None:
         assert body == expected_body
 
 
-@pytest.mark.skipif(
-    not os.environ.get("HF_API_TOKEN", None),
-    reason=(
-        "To run this test, you need to set the HF_API_TOKEN environment variable. The associated account must also "
-        "have requested access to the gated model `mistralai/Mistral-7B-Instruct-v0.1`"
-    ),
-)
 class TestMistralAdapter:
     def test_prepare_body_with_default_params(self) -> None:
         layer = MistralChatAdapter(generation_kwargs={})
@@ -245,6 +240,33 @@ def test_mistral_chat_template_incorrect_order(self):
         except Exception as e:
             assert "Conversation roles must alternate user/assistant/" in str(e)
 
+    def test_use_mistral_adapter_without_hf_token(self, monkeypatch, caplog) -> None:
+        monkeypatch.delenv("HF_TOKEN", raising=False)
+        with (
+            patch("transformers.AutoTokenizer.from_pretrained") as mock_pretrained,
+            patch("haystack_integrations.components.generators.amazon_bedrock.chat.adapters.DefaultPromptHandler"),
+            caplog.at_level(logging.WARNING),
+        ):
+            MistralChatAdapter(generation_kwargs={})
+            mock_pretrained.assert_called_with("NousResearch/Llama-2-7b-chat-hf")
+            assert "no HF_TOKEN was found" in caplog.text
+
+    def test_use_mistral_adapter_with_hf_token(self, monkeypatch) -> None:
+        monkeypatch.setenv("HF_TOKEN", "test")
+        with (
+            patch("transformers.AutoTokenizer.from_pretrained") as mock_pretrained,
+            patch("haystack_integrations.components.generators.amazon_bedrock.chat.adapters.DefaultPromptHandler"),
+        ):
+            MistralChatAdapter(generation_kwargs={})
+            mock_pretrained.assert_called_with("mistralai/Mistral-7B-Instruct-v0.1")
+
+    @pytest.mark.skipif(
+        not os.environ.get("HF_API_TOKEN", None),
+        reason=(
+            "To run this test, you need to set the HF_API_TOKEN environment variable. The associated account must also "
+            "have requested access to the gated model `mistralai/Mistral-7B-Instruct-v0.1`"
+        ),
+    )
     @pytest.mark.parametrize("model_name", MISTRAL_MODELS)
     @pytest.mark.integration
     def test_default_inference_params(self, model_name, chat_messages):