From 5ddc96e560c51e82178e44b0e093e4bd7dcfddb2 Mon Sep 17 00:00:00 2001
From: yassin <yassin@berri.ai>
Date: Thu, 17 Sep 2026 00:06:43 +0000
Subject: [PATCH] fix(vertex_ai): drop stale transfer headers when GCS serves
 an encoded file body

Co-Authored-By: Devin AI <158243242+devin-ai-integration[bot]@users.noreply.github.com>
---
 litellm/llms/custom_httpx/llm_http_handler.py | 21 ++++++++++++++++++-
 .../llms/vertex_ai/files/transformation.py    |  3 +--
 .../files/test_vertex_ai_files_streaming.py   | 19 +++++++++++++++++
 3 files changed, 40 insertions(+), 3 deletions(-)

diff --git a/litellm/llms/custom_httpx/llm_http_handler.py b/litellm/llms/custom_httpx/llm_http_handler.py
index 303368c064e..311aaddc8ee 100644
--- a/litellm/llms/custom_httpx/llm_http_handler.py
+++ b/litellm/llms/custom_httpx/llm_http_handler.py
@@ -317,6 +317,25 @@ async def _aiter_bytes_then_close(response: httpx.Response, *, chunk_size: int)
         await response.aclose()
 
 
+_DECODED_BODY_STALE_HEADERS: Final[frozenset[str]] = frozenset({"content-encoding", "content-length"})
+
+
+def _decoded_body_headers(response: httpx.Response) -> httpx.Headers:
+    """
+    `aiter_bytes` yields the decoded body, so the upstream transfer headers only
+    describe the bytes on the wire when no content-encoding was applied.
+    """
+    if response.headers.get("content-encoding", "identity").lower() == "identity":
+        return response.headers
+    return httpx.Headers(
+        [
+            (name, value)
+            for name, value in response.headers.multi_items()
+            if name.lower() not in _DECODED_BODY_STALE_HEADERS
+        ]
+    )
+
+
 def _collect_ws_project_quota_callbacks() -> tuple[ProjectQuotaCallback, ...]:
     """Duck-type discover proxy hooks exposing per-frame project ITPM/OTPM
     enforcement, so the Responses WebSocket loop can charge every
@@ -5312,7 +5331,7 @@ class BaseLLMHTTPHandler:
 
         return await provider_config.transform_file_content_stream(
             stream_iterator=_aiter_bytes_then_close(response, chunk_size=chunk_size),
-            headers=response.headers,
+            headers=_decoded_body_headers(response),
             request_url=str(response.request.url),
             logging_obj=logging_obj,
             litellm_params=litellm_params,
diff --git a/litellm/llms/vertex_ai/files/transformation.py b/litellm/llms/vertex_ai/files/transformation.py
index 12d4b67b791..40126b179a6 100644
--- a/litellm/llms/vertex_ai/files/transformation.py
+++ b/litellm/llms/vertex_ai/files/transformation.py
@@ -304,8 +304,7 @@ async def _peek_first_jsonl_line(
     buffered: bytes = b""  # rebind-ok: accumulates the prefix read while looking for the first newline
     async for chunk in chunks:
         buffered = buffered + chunk
-        *complete_lines, _partial = buffered.split(_JSONL_NEWLINE)
-        first_line = _first_non_empty_jsonl_line(complete_lines)
+        first_line = _first_non_empty_jsonl_line(buffered.split(_JSONL_NEWLINE)[:-1])
         if first_line is not None:
             return first_line, buffered
         if len(buffered) > peek_limit_bytes:
diff --git a/tests/test_litellm/llms/vertex_ai/files/test_vertex_ai_files_streaming.py b/tests/test_litellm/llms/vertex_ai/files/test_vertex_ai_files_streaming.py
index b176480c6a2..b94ea1ea269 100644
--- a/tests/test_litellm/llms/vertex_ai/files/test_vertex_ai_files_streaming.py
+++ b/tests/test_litellm/llms/vertex_ai/files/test_vertex_ai_files_streaming.py
@@ -23,6 +23,7 @@ replaced by a list-based pipeline:
 
 import asyncio
 import gc
+import gzip
 import io
 import json
 import tempfile
@@ -725,6 +726,24 @@ class TestFileContentStreaming:
         assert state["served"] < len(raw_chunks)
         assert state["closed"] is False
 
+    async def test_gzip_encoded_object_is_decoded_without_stale_transfer_headers(self):
+        raw = b'{"line": 1}\n{"line": 2}\n' * 200
+        encoded = gzip.compress(raw)
+        upstream = {
+            "content-type": "application/octet-stream",
+            "content-encoding": "gzip",
+            "content-length": str(len(encoded)),
+        }
+
+        result, state = await self._open([encoded[i : i + 64] for i in range(0, len(encoded), 64)], upstream)
+        streamed = b"".join([chunk async for chunk in result.stream_iterator])
+
+        assert streamed == raw
+        assert result.headers["content-type"] == "application/octet-stream"
+        assert "content-encoding" not in result.headers
+        assert "content-length" not in result.headers
+        assert state["closed"] is True
+
     async def test_vertex_batch_output_is_transformed_row_by_row(self):
         rows = [_vertex_batch_output_row(f"request-{i}", f"answer {i}") for i in range(30)]
         raw = b"\n".join(rows) + b"\n"