BabylonJS/Babylon.js · error · Error

Truncated binary FBX header

Error message

Truncated binary FBX header

What it means

A binary FBX file must contain at least a 27-byte header (21-byte magic, 2 padding bytes, 4-byte version uint32). If the ArrayBuffer is shorter than HEADER_SIZE the file is truncated and no version or node data can be read, so the parser throws.

Source

Thrown at packages/dev/loaders/src/FBX/parsers/fbxBinaryParser.ts:22

const FBX_MAGIC = "Kaydara FBX Binary  \0";
const HEADER_SIZE = 27; // 21 magic + 2 padding + 4 version uint32

/**
 * Parse a binary FBX file into an FBXDocument.
 * Supports FBX versions 7.0–7.7 (v7.5+ uses 64-bit node headers).
 */
export function parseBinaryFBX(buffer: ArrayBuffer): FBXDocument {
    const view = new DataView(buffer);
    const bytes = new Uint8Array(buffer);

    // Validate magic
    const magic = decodeASCII(bytes, 0, 21);
    if (magic !== FBX_MAGIC) {
        throw new Error("Not a valid binary FBX file");
    }
    if (buffer.byteLength < HEADER_SIZE) {
        throw new Error("Truncated binary FBX header");
    }

    const version = view.getUint32(23, true);
    // v7.5+ uses 64-bit offsets in node records
    const is64Bit = version >= 7500;

    const nodes: FBXNode[] = [];
    let offset = HEADER_SIZE;

    while (offset < buffer.byteLength) {
        const result = parseNode(view, bytes, offset, is64Bit, buffer.byteLength);
        if (result === null) {
            break; // null sentinel node
        }
        nodes.push(result.node);
        offset = result.endOffset;
    }

View on GitHub (pinned to 0592b347b8)

Solutions

1. Check `buffer.byteLength >= 27` before parsing; re-fetch the file if shorter
2. Re-download/re-upload the asset — the file on disk may itself be truncated
3. Ensure the whole file is read into the buffer (await full read, use Blob.arrayBuffer()/fs full read)
4. If handling untrusted input, treat this as invalid input and surface a user-facing 'corrupt file' message

Example fix

// before
parseBinaryFBX(await partialChunk.arrayBuffer());
// after
const buf = await file.arrayBuffer();
if (buf.byteLength < 27) throw new Error("FBX file is truncated");
parseBinaryFBX(buf);

function hasFbxHeader(buf) {
  return buf instanceof ArrayBuffer && buf.byteLength >= 27;
}
if (!hasFbxHeader(buffer)) throw new Error("FBX buffer too small/truncated");

function isPlausibleFbxBuffer(buf) {
  return buf instanceof ArrayBuffer && buf.byteLength >= 27;
}

try {
  const doc = parseBinaryFBX(buffer);
} catch (e) {
  if (e.message === "Truncated binary FBX header") {
    console.error(`Buffer is ${buffer.byteLength} bytes; need ≥27 — re-fetch the file`);
  } else throw e;
}

When it happens

Trigger: Calling the binary FBX parse (via `_parseFromArrayBuffer`/`doc`) with an ArrayBuffer of byteLength < 27 — e.g. an empty buffer, a partially downloaded file, or a tiny placeholder file.

Common situations: Incomplete uploads/downloads; file reads aborted mid-way producing zero-length buffers; test fixtures containing stub files; streaming code that passes a partial chunk instead of the whole file.

Related errors

• ASCII FBX array declared ${count} values but parsed ${values
• Not a valid binary FBX file
• Invalid FBX node end offset ${endOffset} at offset ${offset}
• Invalid FBX property list length for node '${name}' at offse
• Invalid FBX child node end offset ${child.endOffset} at offs

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/f6b8447e4afc3950. Report an issue: GitHub.