HKUDS/Vibe-Trading · error · ValueError

invalid base64 payload

Error message

invalid base64 payload

What it means

save_base64_data_url decodes the payload with base64.b64decode(payload, validate=True), which rejects any non-alphabet characters. binascii.Error (or ValueError) from the decoder is re-raised as ValueError('invalid base64 payload'), preserving the original as __cause__.

Source

Thrown at agent/src/utils/media_decode.py:57

        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. Validate/normalize the payload: strip whitespace, restore padding with '=' to a multiple of 4
2. If the source uses URL-safe alphabet, translate '-_' to '+/' before passing
3. Send base64 in the request body (not query params) so '+' survives transport
4. Check payload length % 4 == 0 before calling

Example fix

# before
path = save_base64_data_url(data_url, out_dir)  # URL-safe base64 payload

# after
import re
header, _, payload = data_url.partition(',')
payload = payload.strip().replace('-', '+').replace('_', '/')
payload += '=' * (-len(payload) % 4)
path = save_base64_data_url(f"{header},{payload}", out_dir)

import base64

def is_valid_base64_payload(data_url: str) -> bool:
    payload = data_url.split(",", 1)[1].strip() if "," in data_url else ""
    if not payload or len(payload) % 4 != 0:
        return False
    try:
        base64.b64decode(payload, validate=True)
        return True
    except Exception:
        return False

def is_standard_base64(payload: str) -> bool:
    import re
    p = payload.strip()
    return bool(re.fullmatch(r"[A-Za-z0-9+/]+={0,2}", p)) and len(p) % 4 == 0

try:
    path = save_base64_data_url(data_url, out_dir)
except ValueError as e:
    if str(e) == "invalid base64 payload":
        return reject_attachment("attachment data corrupted in transit")
    raise

When it happens

Trigger: Payloads containing URL-safe characters ('-','_') instead of standard base64, missing '=' padding, embedded newlines/whitespace in the middle, corrupted transfer truncating the string, or '+' or '/' mangled to spaces by URL form encoding.

Common situations: Base64 passed through a query string unescaped ( '+' becomes ' '), URL-safe base64 from another library, JSON truncation of very large payloads, or copy-paste artifacts (smart quotes, ellipses).

Related errors

• expected data:<mime>;base64,<payload>
• invalid alpha_id
• alpha_id not found
• invalid period: {exc}
• too many running benches; wait for one to finish

AI-assisted analysis of HKUDS/Vibe-Trading@80ffdda44c (2026-08-28). Data as JSON: /api/errors/5f37299fa8c87a8a. Report an issue: GitHub.