HKUDS/Vibe-Trading · error · ValueError

unsupported data URL MIME type: {mime}

Error message

unsupported data URL MIME type: {mime}

What it means

After the data URL structure matches, save_base64_data_url extracts the MIME type and looks it up in _EXT_BY_MIME to determine the output file extension. If the MIME type is not in the supported allowlist, the ValueError 'unsupported data URL MIME type: <mime>' is raised, because there is no known extension or sanctioned decoder for that type.

Source

Thrown at agent/src/utils/media_decode.py:51

        data_url: A ``data:<mime>;base64,...`` URL.
        output_dir: Directory where the decoded file should be written.
        max_bytes: Optional maximum decoded byte length. ``0`` disables the
            limit.

    Returns:
        The path of the decoded file.

    Raises:
        FileSizeExceeded: If decoded data exceeds ``max_bytes``.
        ValueError: If the URL is malformed or uses an unsupported MIME type.
    """
    match = _DATA_URL_RE.match(data_url)
    if not match:
        raise ValueError("expected data:<mime>;base64,<payload>")
    mime = match.group(1).strip().lower()
    ext = _EXT_BY_MIME.get(mime)
    if not ext:
        raise ValueError(f"unsupported data URL MIME type: {mime}")

    payload = match.group(3).strip()
    try:
        decoded = base64.b64decode(payload, validate=True)
    except (binascii.Error, ValueError) as exc:
        raise ValueError("invalid base64 payload") from exc

    if max_bytes and len(decoded) > max_bytes:
        raise FileSizeExceeded(f"decoded media exceeds {max_bytes} bytes")

    output_dir.mkdir(parents=True, exist_ok=True)
    path = output_dir / f"{uuid.uuid4().hex}{ext}"
    path.write_bytes(decoded)
    return path

View on GitHub (pinned to 80ffdda44c)

Solutions

  1. Check _EXT_BY_MIME keys for the supported MIME allowlist and convert the media to a supported type before upload
  2. Re-encode the asset (e.g. tiff -> png) client-side
  3. If the type should be supported, extend _EXT_BY_MIME with the mime->extension mapping after security review

Example fix

# before
path = save_base64_data_url("data:image/tiff;base64,...", out_dir)

# after
path = save_base64_data_url("data:image/png;base64,...", out_dir)  # convert to PNG first
Defensive patterns

Strategy: type-guard

Validate before calling

from agent.src.utils.media_decode import _EXT_BY_MIME

def has_supported_mime(data_url: str) -> bool:
    m = _DATA_URL_RE.match(data_url) if _DATA_URL_RE.match(data_url) else None
    return bool(m and m.group(1).strip().lower() in _EXT_BY_MIME)

Type guard

def is_supported_mime(data_url: str) -> bool:
    import re
    m = re.match(r"^data:([^;,]+);base64,", data_url.strip(), re.I)
    return bool(m and m.group(1).lower() in {"image/png", "image/jpeg", "image/gif", "audio/mpeg", "audio/wav", "audio/webm", "video/mp4", "video/webm"})

Try / catch

try:
    path = save_base64_data_url(data_url, out_dir)
except ValueError as e:
    if str(e).startswith("unsupported data URL MIME type"):
        return reject_attachment(f"use a supported type: {sorted(_EXT_BY_MIME)}")
    raise

Prevention

When it happens

Trigger: Passing data URLs with types like 'application/pdf', 'image/tiff', 'video/x-matroska', or even typos like 'image/jpg' (vs 'image/jpeg') when _EXT_BY_MIME only contains allowlisted entries such as image/png, image/jpeg, image/gif, audio/*, etc.

Common situations: Client-side MIME sniffing producing exotic types, uppercase or aliased MIME names, a new media format the allowlist predates, or copy-paste of SVG ('image/svg+xml') which is intentionally excluded for security.

Related errors

AI-assisted analysis of HKUDS/Vibe-Trading@80ffdda44c (2026-08-28). Data as JSON: /api/errors/40b32ec31238e97f. Report an issue: GitHub.