fix(fetch-page): decode standard zlib-wrapped HTTP deflate (#711)

* fix(fetch-page): decode standard zlib-wrapped HTTP deflate

* docs(changelog): reference deflate fix PR 711

* chore: drop the CHANGELOG hunk, the file is frozen since #800

Release notes are generated from PR titles now.

Co-Authored-By: Claude Fable 5.1 <noreply@anthropic.com>

---------

Co-authored-by: Mads Lorentzen <madslorentzen17@gmail.com>
Co-authored-by: Claude Fable 5.1 <noreply@anthropic.com>

tests/test_fetch_deflate.py

@@ -0,0 +1,72 @@
+"""Actual HTTP responses through the CLI entry point and urllib backend."""
+import http.server
+import contextlib
+import io
+from pathlib import Path
+import sys
+from unittest.mock import patch
+from tempfile import TemporaryDirectory
+import threading
+import unittest
+import zlib
+
+sys.path.insert(0, str(Path(__file__).resolve().parent.parent / "tools"))
+import fetch_page  # noqa: E402
+PAGE = b"<html><body><h1>Software Engineer</h1><p>Posting details.</p></body></html>"
+
+
+class DeflateBackend(unittest.TestCase):
+    def test_standard_and_legacy_deflate_reach_saved_html_and_text(self):
+        requests = []
+
+        class Handler(http.server.BaseHTTPRequestHandler):
+            def do_GET(self):
+                if self.path == "/robots.txt":
+                    body = b"User-agent: *\nAllow: /\n"
+                    encoding = None
+                else:
+                    requests.append((self.path, self.headers.get("Accept-Encoding")))
+                    encoder = zlib.compressobj(wbits=-zlib.MAX_WBITS if self.path == "/raw" else zlib.MAX_WBITS)
+                    body = encoder.compress(PAGE) + encoder.flush()
+                    encoding = "deflate"
+                self.send_response(200)
+                if encoding:
+                    self.send_header("Content-Encoding", encoding)
+                self.send_header("Content-Length", str(len(body)))
+                self.end_headers()
+                self.wfile.write(body)
+
+            def log_message(self, *args):
+                pass
+
+        server = http.server.ThreadingHTTPServer(("127.0.0.1", 0), Handler)
+        thread = threading.Thread(target=server.serve_forever, daemon=True)
+        thread.start()
+        try:
+            with TemporaryDirectory() as directory:
+                root = Path(directory)
+                for path in ("/standard", "/raw"):
+                    with self.subTest(encoding=path):
+                        output = root / (path[1:] + ".html")
+                        stdout, stderr = io.StringIO(), io.StringIO()
+                        # Select the existing urllib backend; robots.txt still
+                        # goes through its real curl transport and parser.
+                        with patch.object(fetch_page.shutil, "which", return_value=None), \
+                             contextlib.redirect_stdout(stdout), contextlib.redirect_stderr(stderr):
+                            code = fetch_page.main([
+                                f"http://127.0.0.1:{server.server_port}{path}",
+                                "--out", str(output), "--text",
+                            ])
+                        self.assertEqual(code, 0, stdout.getvalue() + stderr.getvalue())
+                        self.assertEqual(output.read_bytes(), PAGE)
+                        self.assertIn("Software Engineer", stdout.getvalue())
+                        self.assertIn(f"HTTP 200 size={len(PAGE)}", stdout.getvalue())
+                self.assertEqual(requests, [("/standard", "gzip, deflate"), ("/raw", "gzip, deflate")])
+        finally:
+            server.shutdown()
+            server.server_close()
+            thread.join()
+
+
+if __name__ == "__main__":
+    unittest.main()

tools/fetch_page.py

@@ -168,7 +168,12 @@ def fetch_with_urllib(url: str, out: Path, timeout: float) -> tuple[int, str | N
     if encoding == "gzip":
         body = gzip.decompress(body)
     elif encoding == "deflate":
-        body = zlib.decompress(body, -zlib.MAX_WBITS)
+        try:
+            # HTTP deflate carries a zlib wrapper (RFC 9110 section 8.4.1.2).
+            body = zlib.decompress(body)
+        except zlib.error:
+            # Keep compatibility with servers that send legacy raw DEFLATE.
+            body = zlib.decompress(body, -zlib.MAX_WBITS)
     if len(body) > MAX_BYTES:
         raise RuntimeError(f"response exceeds {MAX_BYTES} bytes after decompression")
     out.write_bytes(body)