Fix case-insensitive request header merging

CHANGELOG.md

@@ -2,6 +2,11 @@
 
 All notable changes to `uipath_llm_client` (core package) will be documented in this file.
 
+## [1.16.3] - 2026-07-13
+
+### Fixed
+- Request headers that differ only by casing are now merged before authentication in the shared synchronous and asynchronous HTTPX clients. This prevents provider SDKs from emitting duplicate fields such as `User-Agent` and `user-agent`, while preserving intentionally repeated values that use the winning spelling.
+
 ## [1.16.2] - 2026-07-06
 
 ### Added

src/uipath/llm_client/__version__.py

@@ -1,3 +1,3 @@
 __title__ = "UiPath LLM Client"
 __description__ = "A Python client for interacting with UiPath's LLM services."
-__version__ = "1.16.2"
+__version__ = "1.16.3"

src/uipath/llm_client/httpx_client.py

@@ -55,6 +55,7 @@
     build_routing_headers,
     extract_matching_headers,
     get_dynamic_request_headers,
+    merge_request_headers_case_insensitively,
     set_captured_response_headers,
 )
 from uipath.llm_client.utils.logging import LoggingConfig
@@ -264,6 +265,7 @@ def send(self, request: Request, *, stream: bool = False, **kwargs: Any) -> Resp
         dynamic_headers = get_dynamic_request_headers()
         if dynamic_headers:
             request.headers.update(dynamic_headers)
+        merge_request_headers_case_insensitively(request)
         response = super().send(request, stream=stream, **kwargs)
         if self._captured_headers:
             captured = extract_matching_headers(response.headers, self._captured_headers)
@@ -425,6 +427,7 @@ async def send(self, request: Request, *, stream: bool = False, **kwargs: Any) -
         dynamic_headers = get_dynamic_request_headers()
         if dynamic_headers:
             request.headers.update(dynamic_headers)
+        merge_request_headers_case_insensitively(request)
         response = await super().send(request, stream=stream, **kwargs)
         if self._captured_headers:
             captured = extract_matching_headers(response.headers, self._captured_headers)

src/uipath/llm_client/utils/headers.py

@@ -1,7 +1,7 @@
 import contextvars
 from collections.abc import Mapping, Sequence
 
-from httpx import Headers
+from httpx import Headers, Request
 
 from uipath.llm_client.settings.base import UiPathAPIConfig
 from uipath.llm_client.settings.constants import ApiType, RoutingMode
@@ -20,6 +20,41 @@
 )
 
 
+def merge_headers_case_insensitively(headers: Headers) -> Headers:
+    """Collapse differently-cased copies of a header with later-value-wins semantics.
+
+    Header mappings are sometimes composed as plain dictionaries by provider SDKs.
+    Since dictionaries compare string keys case-sensitively, that can produce raw
+    duplicates such as ``User-Agent`` and ``user-agent`` even though HTTP field names
+    are case-insensitive. Preserve deliberately repeated fields that use the exact same
+    spelling, but merge casing variants as a dictionary merge should have done.
+    """
+    raw_headers = headers.raw
+    spellings: dict[bytes, set[bytes]] = {}
+    for name, _ in raw_headers:
+        spellings.setdefault(name.lower(), set()).add(name)
+
+    collisions = {name for name, variants in spellings.items() if len(variants) > 1}
+    if not collisions:
+        return headers
+
+    winning_spellings = {
+        name.lower(): name for name, _ in raw_headers if name.lower() in collisions
+    }
+    return Headers(
+        [
+            (name, value)
+            for name, value in raw_headers
+            if name.lower() not in collisions or winning_spellings[name.lower()] == name
+        ]
+    )
+
+
+def merge_request_headers_case_insensitively(request: Request) -> None:
+    """Merge differently-cased header copies on an HTTPX request in place."""
+    request.headers = merge_headers_case_insensitively(request.headers)
+
+
 def get_captured_response_headers() -> dict[str, str]:
     """Get response headers captured from the most recent request in this context.
 

tests/core/features/test_headers.py

@@ -6,6 +6,55 @@
 from uipath.llm_client.settings.constants import ApiType, RoutingMode
 
 
+def test_case_insensitive_header_merge_keeps_later_value():
+    from uipath.llm_client.utils.headers import merge_headers_case_insensitively
+
+    headers = Headers(
+        [
+            (b"User-Agent", b"provider-sdk"),
+            (b"user-agent", b"custom-httpx-client"),
+        ]
+    )
+
+    merged = merge_headers_case_insensitively(headers)
+
+    assert merged.raw == [(b"user-agent", b"custom-httpx-client")]
+
+
+def test_case_insensitive_header_merge_preserves_intentional_repeats():
+    from uipath.llm_client.utils.headers import merge_headers_case_insensitively
+
+    headers = Headers(
+        [
+            (b"x-test-value", b"first"),
+            (b"x-test-value", b"second"),
+        ]
+    )
+
+    merged = merge_headers_case_insensitively(headers)
+
+    assert merged.raw == headers.raw
+
+
+def test_case_insensitive_header_merge_preserves_repeated_winning_spelling():
+    from uipath.llm_client.utils.headers import merge_headers_case_insensitively
+
+    headers = Headers(
+        [
+            (b"X-Test-Value", b"losing-variant"),
+            (b"x-test-value", b"first"),
+            (b"x-test-value", b"second"),
+        ]
+    )
+
+    merged = merge_headers_case_insensitively(headers)
+
+    assert merged.raw == [
+        (b"x-test-value", b"first"),
+        (b"x-test-value", b"second"),
+    ]
+
+
 class TestHeaderUtilities:
     """Tests for extract_matching_headers and context var functions."""
 

tests/core/features/test_httpx_client.py

@@ -2,7 +2,8 @@
 
 from unittest.mock import MagicMock, patch
 
-from httpx import Client, Headers, Request, Response
+import pytest
+from httpx import Auth, Client, Headers, MockTransport, Request, Response
 
 from uipath.llm_client.settings import UiPathAPIConfig
 from uipath.llm_client.settings.constants import ApiType, RoutingMode
@@ -12,6 +13,16 @@
 )
 
 
+class RecordingHeaderAuth(Auth):
+    def __init__(self):
+        self.signed_user_agents = []
+
+    def auth_flow(self, request):
+        self.signed_user_agents = request.headers.get_list("user-agent")
+        request.headers["x-signed-user-agents"] = "|".join(self.signed_user_agents)
+        yield request
+
+
 class TestUiPathHttpxClient:
     """Tests for UiPathHttpxClient."""
 
@@ -239,6 +250,67 @@ def test_streaming_header_injected_true(self):
             assert sent_request.headers["X-UiPath-Streaming-Enabled"] == "true"
         client.close()
 
+    def test_case_variant_headers_are_merged_before_send(self):
+        from uipath.llm_client.httpx_client import UiPathHttpxClient
+
+        sent_requests = []
+
+        def handler(request: Request) -> Response:
+            sent_requests.append(request)
+            return Response(200, request=request)
+
+        client = UiPathHttpxClient(
+            base_url="https://example.com",
+            transport=MockTransport(handler),
+        )
+        request = Request(
+            "POST",
+            "https://example.com/test",
+            headers=Headers(
+                [
+                    (b"User-Agent", b"provider-sdk"),
+                    (b"user-agent", b"custom-httpx-client"),
+                ]
+            ),
+        )
+
+        client.send(request)
+
+        sent_request = sent_requests[0]
+        assert sent_request.headers.get_list("user-agent") == ["custom-httpx-client"]
+        client.close()
+
+    def test_case_variant_headers_are_merged_before_auth(self):
+        from uipath.llm_client.httpx_client import UiPathHttpxClient
+
+        auth = RecordingHeaderAuth()
+
+        def handler(request: Request) -> Response:
+            assert request.headers.get_list("user-agent") == auth.signed_user_agents
+            assert request.headers["x-signed-user-agents"] == "custom-httpx-client"
+            return Response(200, request=request)
+
+        client = UiPathHttpxClient(
+            auth=auth,
+            base_url="https://example.com",
+            transport=MockTransport(handler),
+        )
+        request = Request(
+            "POST",
+            "https://example.com/test",
+            headers=Headers(
+                [
+                    (b"User-Agent", b"provider-sdk"),
+                    (b"user-agent", b"custom-httpx-client"),
+                ]
+            ),
+        )
+
+        client.send(request)
+
+        assert auth.signed_user_agents == ["custom-httpx-client"]
+        client.close()
+
     def test_url_freezing_when_enabled(self):
         from uipath.llm_client.httpx_client import UiPathHttpxClient
 
@@ -314,3 +386,67 @@ def test_response_patched_with_raise_for_status(self):
             # raise_for_status should have been replaced by patch_raise_for_status
             assert result.raise_for_status is not original_raise
         client.close()
+
+
+class TestUiPathHttpxAsyncClientSend:
+    @pytest.mark.asyncio
+    async def test_case_variant_headers_are_merged_before_send(self):
+        from uipath.llm_client.httpx_client import UiPathHttpxAsyncClient
+
+        sent_requests = []
+
+        async def handler(request: Request) -> Response:
+            sent_requests.append(request)
+            return Response(200, request=request)
+
+        client = UiPathHttpxAsyncClient(
+            base_url="https://example.com",
+            transport=MockTransport(handler),
+        )
+        request = Request(
+            "POST",
+            "https://example.com/test",
+            headers=Headers(
+                [
+                    (b"User-Agent", b"provider-sdk"),
+                    (b"user-agent", b"custom-httpx-client"),
+                ]
+            ),
+        )
+        await client.send(request)
+
+        sent_request = sent_requests[0]
+        assert sent_request.headers.get_list("user-agent") == ["custom-httpx-client"]
+        await client.aclose()
+
+    @pytest.mark.asyncio
+    async def test_case_variant_headers_are_merged_before_auth(self):
+        from uipath.llm_client.httpx_client import UiPathHttpxAsyncClient
+
+        auth = RecordingHeaderAuth()
+
+        async def handler(request: Request) -> Response:
+            assert request.headers.get_list("user-agent") == auth.signed_user_agents
+            assert request.headers["x-signed-user-agents"] == "custom-httpx-client"
+            return Response(200, request=request)
+
+        client = UiPathHttpxAsyncClient(
+            auth=auth,
+            base_url="https://example.com",
+            transport=MockTransport(handler),
+        )
+        request = Request(
+            "POST",
+            "https://example.com/test",
+            headers=Headers(
+                [
+                    (b"User-Agent", b"provider-sdk"),
+                    (b"user-agent", b"custom-httpx-client"),
+                ]
+            ),
+        )
+
+        await client.send(request)
+
+        assert auth.signed_user_agents == ["custom-httpx-client"]
+        await client.aclose()