feat(knowledge): 知识源维护与 TXT/Markdown/PDF 导入

支持文本、Markdown 与非扫描 PDF 上传解析，展示提取文本与切块结果。

backend/app/services/image_security.py

@@ -0,0 +1,117 @@
+"""
+Copyright 2024-2026 ReplyPier
+
+Licensed under the Apache License, Version 2.0 (the "License");
+you may not use this file except in compliance with the License.
+You may obtain a copy of the License at
+
+    http://www.apache.org/licenses/LICENSE-2.0
+
+Unless required by applicable law or agreed to in writing, software
+distributed under the License is distributed on an "AS IS" BASIS,
+WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+See the License for the specific language governing permissions and
+limitations under the License.
+
+Hardening for user-uploaded images (help-center logo + article images). Every
+uploaded raster is:
+  - size-capped (bytes),
+  - checked for a real, decodable image (not a polyglot / renamed file),
+  - guarded against decompression bombs (pixel-count cap read from the header
+    BEFORE the full image is decoded),
+  - re-encoded from decoded pixels — which strips EXIF/metadata, trailing bytes
+    and any appended payload, and normalises the stored format.
+
+SVG is intentionally NOT accepted here: it is active markup and would be stored
+XSS on the public help center. Callers that previously took SVG rasterise on the
+client (the cropper) or drop it.
+"""
+
+import io
+
+from fastapi import HTTPException
+from PIL import Image
+
+# Refuse absurd pixel counts before decoding — a few-KB file can claim to be
+# tens of thousands of pixels per side and exhaust memory on decode.
+_MAX_PIXELS = 40_000_000  # 40 MP
+Image.MAX_IMAGE_PIXELS = _MAX_PIXELS
+
+# PIL format -> (content type, extension) for the formats we re-encode to.
+_PNG = ("image/png", ".png")
+_JPEG = ("image/jpeg", ".jpg")
+
+_FORMAT_CONTENT_TYPE = {
+    "PNG": "image/png",
+    "JPEG": "image/jpeg",
+    "WEBP": "image/webp",
+    "GIF": "image/gif",
+}
+
+
+def _open_validated(content: bytes, *, max_bytes: int, max_dim: int) -> Image.Image:
+    """Open bytes as an image, enforcing byte size, decodability and a pixel /
+    dimension cap (bomb guard) — all before the pixels are fully decoded."""
+    if not content:
+        raise HTTPException(status_code=400, detail="Empty image file.")
+    if len(content) > max_bytes:
+        raise HTTPException(status_code=400, detail=f"Image must be {max_bytes // (1024 * 1024)} MB or smaller.")
+    try:
+        img = Image.open(io.BytesIO(content))
+        width, height = img.size  # header only; no full decode yet
+    except HTTPException:
+        raise
+    except Exception:
+        raise HTTPException(status_code=400, detail="Invalid or corrupt image file.")
+    if width <= 0 or height <= 0:
+        raise HTTPException(status_code=400, detail="Invalid image dimensions.")
+    if width > max_dim or height > max_dim or width * height > _MAX_PIXELS:
+        raise HTTPException(
+            status_code=400,
+            detail=f"Image is too large — keep it within {max_dim}×{max_dim} pixels.",
+        )
+    try:
+        img.load()  # dimensions are now known-safe, so decoding is bounded
+    except Exception:
+        raise HTTPException(status_code=400, detail="Invalid or corrupt image file.")
+    return img
+
+
+def sanitize_image(
+    content: bytes,
+    *,
+    allowed_content_types: set[str],
+    max_bytes: int,
+    max_dim: int,
+    fit: int | None = None,
+) -> tuple[bytes, str, str]:
+    """Validate and re-encode an uploaded raster image.
+
+    Returns (safe_bytes, content_type, extension). Raises HTTPException(400) on
+    anything that is not a clean, in-policy raster image. `fit`, when given,
+    downscales the longest side to at most `fit` px (aspect preserved).
+
+    JPEG re-encodes to JPEG (keeps photos small); everything else re-encodes to
+    PNG (keeps transparency). Either path strips metadata and any non-pixel
+    payload because the output is built from decoded pixels only.
+    """
+    img = _open_validated(content, max_bytes=max_bytes, max_dim=max_dim)
+
+    detected = _FORMAT_CONTENT_TYPE.get((img.format or "").upper())
+    if detected is None or detected not in allowed_content_types:
+        raise HTTPException(
+            status_code=400,
+            detail="Unsupported image type. Use PNG, JPEG or WebP.",
+        )
+
+    if fit and max(img.size) > fit:
+        img.thumbnail((fit, fit), Image.LANCZOS)
+
+    out = io.BytesIO()
+    if detected == "image/jpeg":
+        img.convert("RGB").save(out, format="JPEG", quality=85, optimize=True)
+        content_type, ext = _JPEG
+    else:
+        img.convert("RGBA").save(out, format="PNG", optimize=True)
+        content_type, ext = _PNG
+    return out.getvalue(), content_type, ext