community: Ollama - Pass headers to post request (#15881)

## Feature
- Set additional headers in constructor
- Headers will be sent in post request

This feature is useful if deploying Ollama on a cloud service such as
hugging face, which requires authentication tokens to be passed in the
request header.

## Tests
- Test if header is passed
- Test if header is not passed

libs/community/langchain_community/llms/ollama.py

@@ -107,6 +107,12 @@ class _OllamaCommon(BaseLanguageModel):
     timeout: Optional[int] = None
     """Timeout for the request stream"""
 
+    headers: Optional[dict] = None
+    """Additional headers to pass to endpoint (e.g. Authorization, Referer).
+    This is useful when Ollama is hosted on cloud services that require
+    tokens for authentication.
+    """
+
     @property
     def _default_params(self) -> Dict[str, Any]:
         """Get the default parameters for calling Ollama."""
@@ -207,7 +213,10 @@ class _OllamaCommon(BaseLanguageModel):
 
         response = requests.post(
             url=api_url,
-            headers={"Content-Type": "application/json"},
+            headers={
+                "Content-Type": "application/json",
+                **(self.headers if isinstance(self.headers, dict) else {}),
+            },
             json=request_payload,
             stream=True,
             timeout=self.timeout,

libs/community/tests/unit_tests/llms/test_ollama.py

@@ -0,0 +1,68 @@
+import requests
+from pytest import MonkeyPatch
+
+from langchain_community.llms.ollama import Ollama
+
+
+def mock_response_stream():
+    mock_response = [b'{ "response": "Response chunk 1" }']
+
+    class MockRaw:
+        def read(self, chunk_size):
+            try:
+                return mock_response.pop()
+            except IndexError:
+                return None
+
+    response = requests.Response()
+    response.status_code = 200
+    response.raw = MockRaw()
+    return response
+
+
+def test_pass_headers_if_provided(monkeypatch: MonkeyPatch) -> None:
+    llm = Ollama(
+        base_url="https://ollama-hostname:8000",
+        model="foo",
+        headers={
+            "Authentication": "Bearer TEST-TOKEN-VALUE",
+            "Referer": "https://application-host",
+        },
+        timeout=300,
+    )
+
+    def mockPost(url, headers, json, stream, timeout):
+        assert url == "https://ollama-hostname:8000/api/generate/"
+        assert headers == {
+            "Content-Type": "application/json",
+            "Authentication": "Bearer TEST-TOKEN-VALUE",
+            "Referer": "https://application-host",
+        }
+        assert json is not None
+        assert stream is True
+        assert timeout == 300
+
+        return mock_response_stream()
+
+    monkeypatch.setattr(requests, "post", mockPost)
+
+    llm("Test prompt")
+
+
+def test_handle_if_headers_not_provided(monkeypatch: MonkeyPatch) -> None:
+    llm = Ollama(base_url="https://ollama-hostname:8000", model="foo", timeout=300)
+
+    def mockPost(url, headers, json, stream, timeout):
+        assert url == "https://ollama-hostname:8000/api/generate/"
+        assert headers == {
+            "Content-Type": "application/json",
+        }
+        assert json is not None
+        assert stream is True
+        assert timeout == 300
+
+        return mock_response_stream()
+
+    monkeypatch.setattr(requests, "post", mockPost)
+
+    llm("Test prompt")