feat: support rss datasource (#13721)

### What problem does this PR solve?

Supporting public RSS/Atom feed URLs as data sources for RagFlow.

link https://github.com/infiniflow/ragflow/issues/12313

### Type of change

- [x] New Feature (non-breaking change which adds functionality)

test/testcases/test_common_data_source/test_rss_connector_unit.py

@@ -0,0 +1,120 @@
+from datetime import datetime, timezone
+import importlib
+import sys
+from pathlib import Path
+from types import SimpleNamespace
+from types import ModuleType
+
+import pytest
+
+import common
+
+repo_root = Path(__file__).resolve().parents[3]
+data_source_pkg = ModuleType("common.data_source")
+data_source_pkg.__path__ = [str(repo_root / "common" / "data_source")]
+sys.modules["common.data_source"] = data_source_pkg
+setattr(common, "data_source", data_source_pkg)
+
+DocumentSource = importlib.import_module("common.data_source.config").DocumentSource
+RSSConnector = importlib.import_module("common.data_source.rss_connector").RSSConnector
+
+
+class _FakeResponse:
+    def __init__(self, content: bytes = b"feed") -> None:
+        self.content = content
+
+    def raise_for_status(self) -> None:
+        return None
+
+
+def _mock_feed(*entries, bozo=False, bozo_exception=None):
+    return SimpleNamespace(
+        entries=list(entries),
+        bozo=bozo,
+        bozo_exception=bozo_exception,
+    )
+
+
+def test_validate_connector_settings_rejects_invalid_feed_url():
+    connector = RSSConnector(feed_url="ftp://example.com/feed.xml")
+
+    with pytest.raises(ValueError, match="valid http or https URL"):
+        connector.validate_connector_settings()
+
+
+def test_validate_connector_settings_rejects_empty_feed(monkeypatch):
+    monkeypatch.setattr("common.data_source.rss_connector.requests.get", lambda *_args, **_kwargs: _FakeResponse())
+    monkeypatch.setattr(
+        "common.data_source.rss_connector.feedparser.parse",
+        lambda _content: _mock_feed(),
+    )
+
+    connector = RSSConnector(feed_url="https://example.com/feed.xml")
+
+    with pytest.raises(ValueError, match="contains no entries"):
+        connector.validate_connector_settings()
+
+
+def test_load_from_state_builds_documents(monkeypatch):
+    monkeypatch.setattr("common.data_source.rss_connector.requests.get", lambda *_args, **_kwargs: _FakeResponse())
+    monkeypatch.setattr(
+        "common.data_source.rss_connector.feedparser.parse",
+        lambda _content: _mock_feed(
+            {
+                "id": "entry-1",
+                "link": "https://example.com/posts/1",
+                "title": "Post One",
+                "content": [{"value": "<p>Hello <b>world</b></p>"}],
+                "author": "Alice",
+                "tags": [{"term": "news"}, {"term": "product"}],
+                "updated": "Tue, 02 Jan 2024 15:04:05 GMT",
+            }
+        ),
+    )
+
+    connector = RSSConnector(feed_url="https://example.com/feed.xml")
+    batch = next(connector.load_from_state())
+
+    assert len(batch) == 1
+    doc = batch[0]
+    assert doc.source == DocumentSource.RSS
+    assert doc.semantic_identifier == "Post One"
+    assert doc.extension == ".txt"
+    assert doc.metadata == {
+        "feed_url": "https://example.com/feed.xml",
+        "link": "https://example.com/posts/1",
+        "author": "Alice",
+        "categories": ["news", "product"],
+    }
+    assert "Hello" in doc.blob.decode("utf-8")
+    assert "world" in doc.blob.decode("utf-8")
+
+
+def test_poll_source_filters_entries_by_timestamp(monkeypatch):
+    monkeypatch.setattr("common.data_source.rss_connector.requests.get", lambda *_args, **_kwargs: _FakeResponse())
+    monkeypatch.setattr(
+        "common.data_source.rss_connector.feedparser.parse",
+        lambda _content: _mock_feed(
+            {
+                "id": "entry-1",
+                "title": "Older",
+                "summary": "older summary",
+                "updated": "Mon, 01 Jan 2024 00:00:00 GMT",
+            },
+            {
+                "id": "entry-2",
+                "title": "Newer",
+                "summary": "new summary",
+                "updated": "Tue, 02 Jan 2024 00:00:00 GMT",
+            },
+        ),
+    )
+
+    connector = RSSConnector(feed_url="https://example.com/feed.xml")
+    start = datetime(2024, 1, 1, tzinfo=timezone.utc).timestamp()
+    end = datetime(2024, 1, 2, tzinfo=timezone.utc).timestamp()
+
+    batches = list(connector.poll_source(start, end))
+
+    assert len(batches) == 1
+    assert [doc.semantic_identifier for doc in batches[0]] == ["Newer"]