community[patch]: BedrockChat -> Support Titan express as chat model (#15408)

Titan Express model was not supported as a chat model because LangChain
messages were not "translated" to a text prompt.

Co-authored-by: Guillem Orellana Trullols <guillem.orellana_trullols@siemens.com>

libs/community/langchain_community/chat_models/bedrock.py

@@ -32,6 +32,12 @@ class ChatPromptAdapter:
             prompt = convert_messages_to_prompt_anthropic(messages=messages)
         elif provider == "meta":
             prompt = convert_messages_to_prompt_llama(messages=messages)
+        elif provider == "amazon":
+            prompt = convert_messages_to_prompt_anthropic(
+                messages=messages,
+                human_prompt="\n\nUser:",
+                ai_prompt="\n\nBot:",
+            )
         else:
             raise NotImplementedError(
                 f"Provider {provider} model does not support chat."

libs/community/langchain_community/llms/bedrock.py

@@ -272,10 +272,12 @@ class BedrockBase(BaseModel, ABC):
 
         try:
             response = self.client.invoke_model(
-                body=body, modelId=self.model_id, accept=accept, contentType=contentType
+                body=body,
+                modelId=self.model_id,
+                accept=accept,
+                contentType=contentType,
             )
             text = LLMInputOutputAdapter.prepare_output(provider, response)
-
         except Exception as e:
             raise ValueError(f"Error raised by bedrock service: {e}").with_traceback(
                 e.__traceback__

libs/community/tests/unit_tests/chat_models/test_bedrock.py

@@ -37,17 +37,24 @@ def test_formatting(messages: List[BaseMessage], expected: str) -> None:
     assert result == expected
 
 
-def test_anthropic_bedrock() -> None:
+@pytest.mark.parametrize(
+    "model_id",
+    ["anthropic.claude-v2", "amazon.titan-text-express-v1"],
+)
+def test_different_models_bedrock(model_id: str) -> None:
+    provider = model_id.split(".")[0]
     client = MagicMock()
-    respbody = MagicMock(
-        read=MagicMock(
-            return_value=MagicMock(
-                decode=MagicMock(return_value=b'{"completion":"Hi back"}')
-            )
+    respbody = MagicMock()
+    if provider == "anthropic":
+        respbody.read.return_value = MagicMock(
+            decode=MagicMock(return_value=b'{"completion":"Hi back"}'),
         )
-    )
-    client.invoke_model.return_value = {"body": respbody}
-    model = BedrockChat(model_id="anthropic.claude-v2", client=client)
+        client.invoke_model.return_value = {"body": respbody}
+    elif provider == "amazon":
+        respbody.read.return_value = '{"results": [{"outputText": "Hi back"}]}'
+        client.invoke_model.return_value = {"body": respbody}
+
+    model = BedrockChat(model_id=model_id, client=client)
 
     # should not throw an error
     model.invoke("hello there")