BabylonJS/Babylon.js · error

zlib: trailing deflate data

Error message

zlib: trailing deflate data

What it means

After the final deflate block, inflateZlib expects the reader to sit exactly at the 4-byte Adler-32 trailer (input.byteLength - 4). If bytes remain before the trailer, it throws 'zlib: trailing deflate data' — the stream contains more compressed blocks than needed for the declared expected length, indicating concatenated streams or junk data.

Source

Thrown at packages/dev/loaders/src/FBX/parsers/zlibInflate.ts:59

        switch (blockType) {
            case 0:
                inflateStoredBlock(reader, output);
                break;
            case 1:
                inflateCompressedBlock(reader, output, getFixedLiteralLengthTree(), getFixedDistanceTree());
                break;
            case 2: {
                const { literalLengthTree, distanceTree } = readDynamicTrees(reader);
                inflateCompressedBlock(reader, output, literalLengthTree, distanceTree);
                break;
            }
            default:
                throw new Error("deflate: invalid block type");
        }
    }

    if (reader.byteOffset < input.byteLength - 4) {
        throw new Error("zlib: trailing deflate data");
    }

    output.finish();
    const expectedAdler = ((input[input.byteLength - 4] << 24) | (input[input.byteLength - 3] << 16) | (input[input.byteLength - 2] << 8) | input[input.byteLength - 1]) >>> 0;
    if (output.adler32() !== expectedAdler) {
        throw new Error("zlib: adler32 mismatch");
    }

    return output.bytes;
}

class BitReader {
    private bitBuffer = 0;
    private bitCount = 0;

    public constructor(
        private readonly input: Uint8Array,
        public byteOffset: number,

View on GitHub (pinned to 0592b347b8)

Solutions

  1. Re-export or re-compress the FBX payload as a single zlib stream
  2. Check that the record's compressedLength exactly matches one zlib stream (header + deflate + 4-byte adler)
  3. If you control the pipeline, avoid concatenating streams — compress once
  4. Trim any junk bytes between the deflate end and the trailer if you can regenerate the file
Defensive patterns

Strategy: validation

Validate before calling

// exactly one zlib stream: header + payload + 4-byte adler
if (compressed.byteLength !== expectedStreamLength(compressed, expectedLength)) {
  throw new Error('FBX compressed array length does not match a single zlib stream');
}

Try / catch

try {
  return inflateZlib(compressed, expectedLength);
} catch (e) {
  if ((e as Error).message === 'zlib: trailing deflate data') {
    throw new Error('FBX array contains concatenated or padded zlib data — re-export', { cause: e });
  }
  throw e;
}

Prevention

When it happens

Trigger: A compressed FBX array payload containing concatenated zlib streams, extra bytes appended between the deflate stream and the Adler trailer, or a compressedLength field larger than the actual single stream.

Common situations: Custom exporters concatenating compressed chunks; files post-processed by scripts that append data; mismatched length fields after byte-level edits.

Related errors

AI-assisted analysis of BabylonJS/Babylon.js@0592b347b8 (2026-08-30). Data as JSON: /api/errors/04e0d181312da82d. Report an issue: GitHub.