Studio: reject binary web_search fetches instead of decoding them into replacement chars

studio/backend/core/inference/tools.py

@@ -1381,6 +1381,12 @@ def build_rag_autoinject(conversation: list[dict], rag_scope: dict | None) -> di
 # sections stripped during conversion; 512 KB reaches article content even
 # where <head> alone is ~200 KB.
 _MAX_FETCH_BYTES = 512 * 1024
+# A decoded page is treated as binary when more than 1/_BINARY_REPLACEMENT_DIVISOR
+# (12.5%) of its chars are U+FFFD, but always tolerating up to
+# _MIN_REPLACEMENT_CHARS stray bad bytes so minor encoding glitches don't drop a
+# real page.
+_MIN_REPLACEMENT_CHARS = 16
+_BINARY_REPLACEMENT_DIVISOR = 8
 
 _USER_AGENTS = (
     "Mozilla/5.0 (Windows NT 10.0; Win64; x64) AppleWebKit/537.36 (KHTML, like Gecko) Chrome/131.0.0.0 Safari/537.36",
@@ -1482,6 +1488,26 @@ def _validate_and_resolve_host(hostname: str, port: int) -> tuple[bool, str, str
     return True, "", first_ip
 
 
+def _is_texty_content_type(content_type: str) -> bool:
+    """True for MIME types safe to decode as text (HTML pages, plain text,
+    JSON/XML feeds). Binary types (PDF, images, archives, octet-stream) return
+    False so the fetcher never decodes them into a flood of U+FFFD replacement
+    chars that poison the model context (unslothai/unsloth#7084).
+
+    A missing Content-Type coerces to ``text/plain`` upstream, so unlabeled
+    bodies pass here and are caught instead by the replacement-char fallback.
+    """
+    ct = (content_type or "").lower()
+    if not ct:
+        return True  # unlabeled: let the replacement-char fallback decide
+    if ct.startswith("text/"):
+        return True
+    if ct.startswith("application/"):
+        # "xml" also covers xhtml+xml / *+xml; "json" covers *+json.
+        return any(marker in ct for marker in ("json", "xml", "javascript", "csv"))
+    return False
+
+
 def _fetch_page_text(
     url: str,
     max_chars: int = _MAX_PAGE_CHARS,
@@ -1562,8 +1588,29 @@ def _fetch_page_text(
         else:
             return "Failed to fetch URL: too many redirects."
 
+        # Reject binary bodies (PDF, image, archive): decoding them as text
+        # floods the model context with U+FFFD replacement chars (#7084).
+        content_type = resp.headers.get_content_type()
+        if not _is_texty_content_type(content_type):
+            # Trim to a clean MIME token: get_content_type() can echo control
+            # chars from an obs-folded header, and this string is returned to
+            # the model.
+            m = re.match(r"[\w.+-]+/[\w.+-]+", content_type or "")
+            safe_type = m.group(0) if m else "unknown type"
+            return (
+                f"(non-text content: {safe_type}, {len(raw_bytes)} bytes; "
+                "not readable as text)"
+            )
+
         charset = resp.headers.get_content_charset() or "utf-8"
         raw_html = raw_bytes.decode(charset, errors = "replace")
+
+        # Fallback for binary mislabeled as text/* or sent with no Content-Type:
+        # a real text page has only a few replacement chars, if any.
+        if raw_html.count("\ufffd") > max(
+            _MIN_REPLACEMENT_CHARS, len(raw_html) // _BINARY_REPLACEMENT_DIVISOR
+        ):
+            return f"(binary content, {len(raw_bytes)} bytes; not readable as text)"
     except _HTTPError as e:
         return f"Failed to fetch URL: HTTP {e.code} {getattr(e, 'reason', '')}"
     except Exception as e:

studio/backend/tests/test_web_fetch_binary_guard.py

@@ -0,0 +1,150 @@
+# SPDX-License-Identifier: AGPL-3.0-only
+# Copyright 2026-present the Unsloth AI Inc. team. All rights reserved. See /studio/LICENSE.AGPL-3.0
+
+"""Regression for unslothai/unsloth#7084: the web_search fetcher must not decode
+a binary body (PDF, image, octet-stream) into a flood of U+FFFD replacement
+chars that poison the model context. It rejects non-text Content-Types up front
+and, for binary mislabeled as text/* or sent unlabeled, falls back to a
+replacement-char ratio check. Real HTML pages are unaffected.
+"""
+
+from __future__ import annotations
+
+import sys
+from email.message import Message
+from pathlib import Path
+
+import pytest
+
+_BACKEND_DIR = str(Path(__file__).resolve().parent.parent)
+if _BACKEND_DIR not in sys.path:
+    sys.path.insert(0, _BACKEND_DIR)
+
+from core.inference import tools
+
+
+class _FakeResp:
+    def __init__(self, body: bytes, content_type: str | None):
+        self._body = body
+        self.headers = Message()
+        if content_type is not None:
+            self.headers["Content-Type"] = content_type
+
+    def read(self, n: int | None = None) -> bytes:
+        return self._body if n is None else self._body[:n]
+
+
+class _FakeOpener:
+    def __init__(self, resp):
+        self._resp = resp
+
+    def open(self, req, timeout=None):
+        return self._resp
+
+
+def _fetch_with(monkeypatch, body: bytes, content_type: str | None) -> str:
+    # Pass SSRF validation and skip real DNS/network.
+    monkeypatch.setattr(
+        tools, "_validate_and_resolve_host", lambda host, port: (True, "", "93.184.216.34")
+    )
+    monkeypatch.setattr(
+        tools.urllib.request, "build_opener", lambda *a, **k: _FakeOpener(_FakeResp(body, content_type))
+    )
+    return tools._fetch_page_text("https://example.com/thing", timeout=5)
+
+
+# ── content-type classifier ──
+
+
+@pytest.mark.parametrize(
+    "content_type,expected",
+    [
+        ("text/html", True),
+        ("text/plain; charset=utf-8", True),
+        ("application/json", True),
+        ("application/xml", True),
+        ("application/xhtml+xml", True),
+        ("application/ld+json", True),
+        ("application/pdf", False),
+        ("image/png", False),
+        ("image/svg+xml", False),  # SVG source isn't extracted downstream; reject
+        ("application/octet-stream", False),
+        ("application/zip", False),
+        ("", True),  # unlabeled: defer to the replacement-char fallback
+        (None, True),
+    ],
+)
+def test_is_texty_content_type(content_type, expected):
+    assert tools._is_texty_content_type(content_type) is expected
+
+
+# ── fetcher end-to-end (mocked network) ──
+
+
+def test_pdf_rejected_by_content_type(monkeypatch):
+    out = _fetch_with(monkeypatch, b"%PDF-1.7\n\xff\xd8\xff\x00\x89PNG" * 200, "application/pdf")
+    assert "�" not in out
+    assert "non-text content" in out and "application/pdf" in out
+
+
+def test_image_rejected_by_content_type(monkeypatch):
+    out = _fetch_with(monkeypatch, b"\x89PNG\r\n\x1a\n" + bytes(range(256)) * 4, "image/png")
+    assert "�" not in out
+    assert "non-text content" in out and "image/png" in out
+
+
+def test_binary_mislabeled_as_text_caught_by_fallback(monkeypatch):
+    # A server sends binary but labels it text/plain -> the type check passes,
+    # so the replacement-char fallback must catch it.
+    out = _fetch_with(monkeypatch, bytes(range(256)) * 20, "text/plain")
+    assert "�" not in out
+    assert "binary content" in out
+
+
+def test_binary_unlabeled_caught_by_fallback(monkeypatch):
+    # No Content-Type coerces to text/plain upstream; the fallback still catches it.
+    out = _fetch_with(monkeypatch, bytes(range(256)) * 20, None)
+    assert "�" not in out
+    assert "binary content" in out
+
+
+def test_html_page_unaffected(monkeypatch):
+    html = b"<html><body><h1>Hello</h1><p>Real text content here.</p></body></html>"
+    out = _fetch_with(monkeypatch, html, "text/html; charset=utf-8")
+    assert "Hello" in out
+    assert "non-text content" not in out and "binary content" not in out
+
+
+def test_content_type_sanitized_in_message(monkeypatch):
+    # An obs-folded Content-Type can smuggle control chars into get_content_type();
+    # the returned message must be trimmed to a clean MIME token.
+    out = _fetch_with(monkeypatch, b"\x00\x01\x02" * 500, "application/octet-stream\r\n data: injected")
+    assert "\n" not in out and "\r" not in out
+    assert "injected" not in out
+    assert "application/octet-stream" in out
+
+
+@pytest.mark.parametrize(
+    "n_bad,n_total,expect_binary",
+    [
+        # Straddle the 12.5% ratio (well above the 16-char floor): just under vs
+        # just over len//8. Locks the divisor so it can't silently drift.
+        (120, 1000, False),  # 120 <= 1000//8 (125) -> kept
+        (130, 1000, True),   # 130 >  1000//8 (125) -> binary
+    ],
+)
+def test_replacement_ratio_boundary(monkeypatch, n_bad, n_total, expect_binary):
+    # Body of n_total chars: n_bad undecodable bytes + ASCII filler. Labeled
+    # text/plain so only the ratio fallback (not the type check) can fire.
+    body = b"\xff" * n_bad + b"a" * (n_total - n_bad)
+    out = _fetch_with(monkeypatch, body, "text/plain")
+    assert ("binary content" in out) is expect_binary
+
+
+def test_text_with_a_few_stray_replacement_chars_kept(monkeypatch):
+    # A mostly-clean page with a handful of bad bytes stays (below the floor),
+    # so we don't drop legitimate pages over minor encoding glitches.
+    body = ("Real article text. " * 200).encode() + b"\xff\xfe\xff"
+    out = _fetch_with(monkeypatch, body, "text/html")
+    assert "Real article text." in out
+    assert "binary content" not in out