brain-of-reese/app/api/chat_images.py

"""Question-image upload/serve pair (phase 123, TODO L6 — attach an
image to a question).

A user attaches ONE image to a chat question (LOCKED A5): the bytes are
stored server-side under ``chat_image_dir/<uuid4().hex>.<ext>`` — NOT
base64 in saved/shared chats. ``POST /api/chat-images`` answers
``{"path": "/api/chat-images/<uuid>.<ext>"}`` and that path is what
``ChatRequest.image`` / ``ChatMessage.image`` carry (a stored PATH,
never a data URL — the upload endpoint owns the size/mime
enforcement). ``GET /api/chat-images/{filename}`` serves the bytes back
so the user bubble, the refreshed page, and the shared chat can render
the attachment. A question image is NEVER indexed as a document (no
importer call) — it is turn-local storage, not a source.

Auth posture: the upload is user-gated exactly like the chat turn it
feeds (``require_user`` — the question itself is user-gated, and an
anonymous 10 MiB disk-fill would be a DoS); the serve route is PUBLIC
like saved-chat content (phase 55 A1 — a saved chat's id is already its
credential, and the image is part of that content; the filename is an
unguessable ``uuid4().hex`` — no enumeration value).

The extension is the source of truth (the Content-Type header is a
hint — the archive-uploader precedent): it must be in the phase-122
image set (``settings.image_extension_set`` — the same frozenset the
image-document walk uses), lowercased; total bytes are streamed with a
``chat_image_max_mb`` cap (413, fixed detail naming the cap — never
echoing the filename).
"""
from __future__ import annotations

import logging
import re
import uuid
from pathlib import Path

from fastapi import APIRouter, Depends, File, HTTPException, UploadFile
from fastapi.responses import FileResponse

from app.config import get_settings
from app.core.auth import require_user
from app.rag.summarizer import IMAGE_FALLBACK_MIME, IMAGE_MIMES

logger = logging.getLogger(__name__)

router = APIRouter(tags=["chat-images"])

#: Stream receive chunk (the git-sources upload's 1 MiB pattern).
_STREAM_CHUNK = 1 << 20

#: Stored question-image filename guard: ``<uuid4().hex>.<ext>`` — 32
#: hex chars + one of the six image extensions (the ``ChatRequest.image``
#: path pattern's filename part, kept in lockstep with it). Anything
#: else 404s — no path traversal by construction (the route parameter
#: cannot carry a ``/`` and the regex rejects everything but the
#: upload endpoint's own naming).
_CHAT_IMAGE_FILENAME_RE = re.compile(r"^[0-9a-fA-F]{32}\.(png|jpe?g|webp|gif|bmp)$")


@router.post("/chat-images")
async def upload_chat_image(
    file: UploadFile = File(...),  # noqa: B008
    _user: None = Depends(require_user),  # noqa: B008
) -> dict[str, str]:
    """Store one question image (phase 123, task 01; LOCKED A5).

    Gates, in order:

    1. **extension** — the file name's extension (lowercased) must be in
       the phase-122 image set (``settings.image_extension_set``); the
       Content-Type header is a hint, never a source of truth (the
       archive-uploader precedent). A missing/unknown extension is a
       422 naming the accepted set — a fixed detail, no filename echo.
    2. **size** — the bytes are streamed (1 MiB chunks) with the
       ``chat_image_max_mb`` cap; over-cap is a 413 naming the cap
       (fixed detail — never echoing the filename), the temp file is
       removed, and nothing is stored.

    The file lands as ``<uuid4().hex>.<ext>`` in ``chat_image_dir``
    (created on demand; a dotfile temp is renamed into place, so a
    failed/partial receive never leaves a servable-looking file). The
    response is the served path — ``{"path":
    "/api/chat-images/<uuid>.<ext>"}`` — the value ``ChatRequest.image``
    accepts (never a data URL, never the on-disk location).
    """
    settings = get_settings()
    filename = file.filename or ""
    ext = Path(filename).suffix.lower()
    if ext not in settings.image_extension_set:
        accepted = ", ".join(sorted(settings.image_extension_set))
        raise HTTPException(
            status_code=422, detail=f"only {accepted} images are accepted"
        )

    root = Path(settings.chat_image_dir).expanduser()
    root.mkdir(parents=True, exist_ok=True)
    name = f"{uuid.uuid4().hex}{ext}"
    temp = root / f".{name}.upload"
    max_bytes = settings.chat_image_max_mb * 1024 * 1024
    total = 0
    try:
        # Stream with the cap — the dotfile temp is hidden from any
        # listing of the store dir (the git-sources upload pattern).
        with open(temp, "wb") as out:
            while chunk := await file.read(_STREAM_CHUNK):
                total += len(chunk)
                if total > max_bytes:
                    raise HTTPException(
                        status_code=413,
                        detail=(
                            f"the image exceeds the "
                            f"{settings.chat_image_max_mb} MB limit"
                        ),
                    )
                out.write(chunk)
        temp.rename(root / name)
    except BaseException:
        # A failed receive (413, broken pipe, cancellation) leaves no
        # file behind — the final name was never created.
        temp.unlink(missing_ok=True)
        raise
    logger.info(
        "chat-image: uploaded name=%s bytes=%d", name, total
    )
    return {"path": f"/api/chat-images/{name}"}


@router.get("/chat-images/{filename}", response_class=FileResponse)
def serve_chat_image(filename: str) -> FileResponse:
    """Serve one stored question image (phase 123, task 01).

    PUBLIC (no auth dependency) — like saved-chat content: the saved
    chat's id is already its credential (phase 55 A1), the image is part
    of that content, and the filename is an unguessable ``uuid4().hex``
    (no enumeration value).

    Every non-servable case is a 404 with the same fixed detail — a
    filename that does not match ``<uuid-hex>.<ext>`` (the regex guard:
    no path traversal by construction, no 422 that would hint at
    accepted shapes) and a matching name whose file is missing (the
    stale-path edge — the file was deleted out-of-band). Servable files
    stream the exact bytes with the phase-122 ``IMAGE_MIMES``
    ``Content-Type`` (one map, one truth with the describe call's
    data-URL mime; the six-extension guard makes the fallback
    unreachable) and ``Cache-Control: private, max-age=3600`` (the
    phase-122 serve-route convention — the bytes are content-hashed
    uuids, bustable by re-upload).
    """
    if _CHAT_IMAGE_FILENAME_RE.fullmatch(filename) is None:
        raise HTTPException(status_code=404, detail="chat image not found")
    path = Path(get_settings().chat_image_dir).expanduser() / filename
    if not path.is_file():
        raise HTTPException(status_code=404, detail="chat image not found")
    media_type = IMAGE_MIMES.get(path.suffix.lower(), IMAGE_FALLBACK_MIME)
    return FileResponse(
        path,
        media_type=media_type,
        headers={"Cache-Control": "private, max-age=3600"},
    )