Added Streaming Capability to SageMaker LLMs (#10535)

This PR adds the ability to declare a Streaming response in the
SageMaker LLM by leveraging the `invoke_endpoint_with_response_stream`
capability in `boto3`. It is heavily based on the AWS Blog Post
announcement linked
[here](https://aws.amazon.com/blogs/machine-learning/elevating-the-generative-ai-experience-introducing-streaming-support-in-amazon-sagemaker-hosting/).

It does not add any additional dependencies since it uses the existing
`boto3` version.

---------

Co-authored-by: Bagatur <baskaryan@gmail.com>

libs/langchain/langchain/llms/sagemaker_endpoint.py

@@ -1,6 +1,8 @@
 """Sagemaker InvokeEndpoint API."""
+import io
+import json
 from abc import abstractmethod
-from typing import Any, Dict, Generic, List, Mapping, Optional, TypeVar, Union
+from typing import Any, Dict, Generic, Iterator, List, Mapping, Optional, TypeVar, Union
 
 from langchain.callbacks.manager import CallbackManagerForLLMRun
 from langchain.llms.base import LLM
@@ -8,7 +10,66 @@ from langchain.llms.utils import enforce_stop_tokens
 from langchain.pydantic_v1 import Extra, root_validator
 
 INPUT_TYPE = TypeVar("INPUT_TYPE", bound=Union[str, List[str]])
-OUTPUT_TYPE = TypeVar("OUTPUT_TYPE", bound=Union[str, List[List[float]]])
+OUTPUT_TYPE = TypeVar("OUTPUT_TYPE", bound=Union[str, List[List[float]], Iterator])
+
+
+class LineIterator:
+    """
+    A helper class for parsing the byte stream input.
+
+    The output of the model will be in the following format:
+
+    b'{"outputs": [" a"]}\n'
+    b'{"outputs": [" challenging"]}\n'
+    b'{"outputs": [" problem"]}\n'
+    ...
+
+    While usually each PayloadPart event from the event stream will
+    contain a byte array with a full json, this is not guaranteed
+    and some of the json objects may be split acrossPayloadPart events.
+
+    For example:
+
+    {'PayloadPart': {'Bytes': b'{"outputs": '}}
+    {'PayloadPart': {'Bytes': b'[" problem"]}\n'}}
+
+
+    This class accounts for this by concatenating bytes written via the 'write' function
+    and then exposing a method which will return lines (ending with a '\n' character)
+    within the buffer via the 'scan_lines' function.
+    It maintains the position of the last read position to ensure
+    that previous bytes are not exposed again.
+
+    For more details see:
+    https://aws.amazon.com/blogs/machine-learning/elevating-the-generative-ai-experience-introducing-streaming-support-in-amazon-sagemaker-hosting/
+    """
+
+    def __init__(self, stream: Any) -> None:
+        self.byte_iterator = iter(stream)
+        self.buffer = io.BytesIO()
+        self.read_pos = 0
+
+    def __iter__(self) -> "LineIterator":
+        return self
+
+    def __next__(self) -> Any:
+        while True:
+            self.buffer.seek(self.read_pos)
+            line = self.buffer.readline()
+            if line and line[-1] == ord("\n"):
+                self.read_pos += len(line)
+                return line[:-1]
+            try:
+                chunk = next(self.byte_iterator)
+            except StopIteration:
+                if self.read_pos < self.buffer.getbuffer().nbytes:
+                    continue
+                raise
+            if "PayloadPart" not in chunk:
+                # Unknown Event Type
+                continue
+            self.buffer.seek(0, io.SEEK_END)
+            self.buffer.write(chunk["PayloadPart"]["Bytes"])
 
 
 class ContentHandlerBase(Generic[INPUT_TYPE, OUTPUT_TYPE]):
@@ -151,6 +212,9 @@ class SagemakerEndpoint(LLM):
     and the endpoint.
     """
 
+    streaming: bool = False
+    """Whether to stream the results."""
+
     """
      Example:
         .. code-block:: python
@@ -264,7 +328,28 @@ class SagemakerEndpoint(LLM):
         content_type = self.content_handler.content_type
         accepts = self.content_handler.accepts
 
-        # send request
+        if self.streaming and run_manager:
+            try:
+                resp = self.client.invoke_endpoint_with_response_stream(
+                    EndpointName=self.endpoint_name,
+                    Body=body,
+                    ContentType=self.content_handler.content_type,
+                    **_endpoint_kwargs,
+                )
+                iterator = LineIterator(resp["Body"])
+                current_completion: str = ""
+                for line in iterator:
+                    resp = json.loads(line)
+                    resp_output = resp.get("outputs")[0]
+                    if stop is not None:
+                        # Uses same approach as below
+                        resp_output = enforce_stop_tokens(resp_output, stop)
+                    current_completion += resp_output
+                    run_manager.on_llm_new_token(resp_output)
+                return current_completion
+            except Exception as e:
+                raise ValueError(f"Error raised by streaming inference endpoint: {e}")
+        else:
             try:
                 response = self.client.invoke_endpoint(
                     EndpointName=self.endpoint_name,