feat(webui): support image uploads in composer and message bubbles

nanobot/utils/media_decode.py

@@ -0,0 +1,55 @@
+"""Shared helpers for decoding ``data:...;base64,...`` URLs to disk.
+
+Historically lived in ``nanobot.api.server``; now shared by the WebSocket
+channel so the ``api`` + ``websocket`` ingress paths apply the same parsing,
+size guard, and filesystem layout.
+"""
+
+from __future__ import annotations
+
+import base64
+import mimetypes
+import re
+import uuid
+from pathlib import Path
+
+from nanobot.utils.helpers import safe_filename
+
+DEFAULT_MAX_BYTES = 10 * 1024 * 1024
+MAX_FILE_SIZE = DEFAULT_MAX_BYTES
+
+_DATA_URL_RE = re.compile(r"^data:([^;]+);base64,(.+)$", re.DOTALL)
+
+
+class FileSizeExceeded(Exception):
+    """Raised when a decoded payload exceeds the caller's size limit."""
+
+
+def save_base64_data_url(
+    data_url: str,
+    media_dir: Path,
+    *,
+    max_bytes: int | None = None,
+) -> str | None:
+    """Decode a ``data:<mime>;base64,<payload>`` URL and persist it.
+
+    Returns the absolute path on success, ``None`` when the URL shape or the
+    base64 payload itself is malformed. Raises :class:`FileSizeExceeded`
+    when the decoded payload is larger than ``max_bytes`` (default 10 MB).
+    """
+    m = _DATA_URL_RE.match(data_url)
+    if not m:
+        return None
+    mime_type, b64_payload = m.group(1), m.group(2)
+    try:
+        raw = base64.b64decode(b64_payload)
+    except Exception:
+        return None
+    limit = DEFAULT_MAX_BYTES if max_bytes is None else max_bytes
+    if len(raw) > limit:
+        raise FileSizeExceeded(f"File exceeds {limit // (1024 * 1024)}MB limit")
+    ext = mimetypes.guess_extension(mime_type) or ".bin"
+    filename = f"{uuid.uuid4().hex[:12]}{ext}"
+    dest = media_dir / safe_filename(filename)
+    dest.write_bytes(raw)
+    return str(dest)