fix: filter empty SSE lines in BaseModelResponseIterator to prevent extra empty chunks

When streaming with stream_options={"include_usage": True}, xAI and other
providers using BaseLLMHTTPHandler were returning an extra empty chunk after
the usage chunk. This was caused by empty SSE lines (separators between events)
being processed as empty GenericStreamingChunks.

The fix adds a loop in __next__ and __anext__ to skip empty lines before
processing, ensuring only meaningful SSE data events are converted to chunks.

Fixes #17136

litellm/llms/base_llm/base_model_iterator.py

@@ -125,26 +125,32 @@ class BaseModelResponseIterator:
             )
 
     def __next__(self):
-        try:
-            chunk = self.response_iterator.__next__()
-        except StopIteration:
-            raise StopIteration
-        except ValueError as e:
-            raise RuntimeError(f"Error receiving chunk from stream: {e}")
+        while True:
+            try:
+                chunk = self.response_iterator.__next__()
+            except StopIteration:
+                raise StopIteration
+            except ValueError as e:
+                raise RuntimeError(f"Error receiving chunk from stream: {e}")
 
-        try:
-            str_line = chunk
-            if isinstance(chunk, bytes):  # Handle binary data
-                str_line = chunk.decode("utf-8")  # Convert bytes to string
-                index = str_line.find("data:")
-                if index != -1:
-                    str_line = str_line[index:]
-            # chunk is a str at this point
-            return self._handle_string_chunk(str_line=str_line)
-        except StopIteration:
-            raise StopIteration
-        except ValueError as e:
-            raise RuntimeError(f"Error parsing chunk: {e},\nReceived chunk: {chunk}")
+            try:
+                str_line = chunk
+                if isinstance(chunk, bytes):  # Handle binary data
+                    str_line = chunk.decode("utf-8")  # Convert bytes to string
+                    index = str_line.find("data:")
+                    if index != -1:
+                        str_line = str_line[index:]
+
+                # Skip empty lines (common in SSE streams between events)
+                if not str_line or not str_line.strip():
+                    continue
+
+                # chunk is a str at this point
+                return self._handle_string_chunk(str_line=str_line)
+            except StopIteration:
+                raise StopIteration
+            except ValueError as e:
+                raise RuntimeError(f"Error parsing chunk: {e},\nReceived chunk: {chunk}")
 
     # Async iterator
     def __aiter__(self):
@@ -152,30 +158,35 @@ class BaseModelResponseIterator:
         return self
 
     async def __anext__(self):
-        try:
-            chunk = await self.async_response_iterator.__anext__()
+        while True:
+            try:
+                chunk = await self.async_response_iterator.__anext__()
 
-        except StopAsyncIteration:
-            raise StopAsyncIteration
-        except ValueError as e:
-            raise RuntimeError(f"Error receiving chunk from stream: {e}")
+            except StopAsyncIteration:
+                raise StopAsyncIteration
+            except ValueError as e:
+                raise RuntimeError(f"Error receiving chunk from stream: {e}")
 
-        try:
-            str_line = chunk
-            if isinstance(chunk, bytes):  # Handle binary data
-                str_line = chunk.decode("utf-8")  # Convert bytes to string
-                index = str_line.find("data:")
-                if index != -1:
-                    str_line = str_line[index:]
+            try:
+                str_line = chunk
+                if isinstance(chunk, bytes):  # Handle binary data
+                    str_line = chunk.decode("utf-8")  # Convert bytes to string
+                    index = str_line.find("data:")
+                    if index != -1:
+                        str_line = str_line[index:]
 
-            # chunk is a str at this point
-            chunk = self._handle_string_chunk(str_line=str_line)
+                # Skip empty lines (common in SSE streams between events)
+                if not str_line or not str_line.strip():
+                    continue
 
-            return chunk
-        except StopAsyncIteration:
-            raise StopAsyncIteration
-        except ValueError as e:
-            raise RuntimeError(f"Error parsing chunk: {e},\nReceived chunk: {chunk}")
+                # chunk is a str at this point
+                chunk = self._handle_string_chunk(str_line=str_line)
+
+                return chunk
+            except StopAsyncIteration:
+                raise StopAsyncIteration
+            except ValueError as e:
+                raise RuntimeError(f"Error parsing chunk: {e},\nReceived chunk: {chunk}")
 
 
 class MockResponseIterator:  # for returning ai21 streaming responses