SeleniumHQ/selenium · error · anyhow::Error

Payload is not a pbzx stream

Error message

Payload is not a pbzx stream

What it means

Raised by decode_pbzx() (files.rs:253) when the first 4 bytes of a .pkg Payload are not the ASCII magic 'pbzx'. Apple's modern .pkg Payload files are pbzx-wrapped cpio archives; a missing magic means the file is either an older format, corrupt, or not a Payload at all. decode_pbzx is called during macOS .pkg extraction.

Source

Thrown at rust/src/files.rs:253

    move_dir(source, target, &options)?;
    Ok(())
}

const PBZX_MAGIC: [u8; 4] = *b"pbzx";
const XZ_MAGIC: [u8; 6] = [0xfd, 0x37, 0x7a, 0x58, 0x5a, 0x00];

/// Decode a `pbzx` stream into the raw cpio archive it wraps.
///
/// `pbzx` is Apple's block-based container used for newer `.pkg` Payloads. It
/// consists of a `pbzx` magic, an 8-byte flags field, then a sequence of chunks
/// each prefixed by its big-endian decompressed and compressed sizes. A chunk is
/// xz-compressed unless its bytes are stored verbatim.
fn decode_pbzx(data: &[u8]) -> Result<Vec<u8>, Error> {
    let mut cursor = Cursor::new(data);
    let mut magic = [0u8; 4];
    cursor.read_exact(&mut magic)?;
    if magic != PBZX_MAGIC {
        return Err(anyhow!("Payload is not a pbzx stream"));
    }
    // The 8-byte flags field is not needed to walk the chunks.
    cursor.read_exact(&mut [0u8; 8])?;

    let mut output = Vec::new();
    let mut sizes = [0u8; 8];
    loop {
        match cursor.read_exact(&mut sizes) {
            Ok(()) => {}
            Err(err) if err.kind() == io::ErrorKind::UnexpectedEof => break,
            Err(err) => return Err(err.into()),
        }
        // Decompressed size is recorded but not required to read the chunk.
        cursor.read_exact(&mut sizes)?;
        let compressed_size = u64::from_be_bytes(sizes) as usize;
        let mut chunk = vec![0u8; compressed_size];
        cursor.read_exact(&mut chunk)?;

View on GitHub (pinned to aa36b38e69)

Solutions

1. Verify the .pkg is a modern Apple installer (use `xar -tf <pkg>` to list contents).
2. Re-download the driver .pkg to rule out truncation.
3. If the Payload is raw cpio, extend decode_pbzx to fall back to direct cpio handling.
4. Run the extraction on genuine macOS where pkgutil handles all formats.

# Bash: verify the .pkg Payload is a pbzx stream before decode
PAYLOAD=$(xar -tf "$PKG" | grep -i Payload | head -1)
xar -xf "$PKG" "$PAYLOAD" 2>/dev/null
if [ "$(head -c4 "$PAYLOAD" 2>/dev/null)" != "pbzx" ]; then
  echo "Payload is not pbzx; may be legacy cpio or corrupt"; exit 1
fi

match decode_pbzx(&data) {
    Ok(cpio) => cpio,
    Err(e) if e.to_string().contains("not a pbzx stream") => {
        eprintln!("Payload magic mismatch; re-download .pkg or handle legacy cpio");
        return Err(e);
    }
    Err(e) => return Err(e),
}

When it happens

Trigger: uncompress_pkg reads the Payload file and passes its bytes to decode_pbzx. cursor.read_exact(&mut magic) succeeds but magic != PBZX_MAGIC ('pbzx'). Typical when the .pkg uses a legacy uncompressed cpio Payload, the file is truncated, or a non-Payload was read.

Common situations: An older .pkg whose Payload is raw cpio (no pbzx wrapper); a corrupted/truncated download; the wrong file inside the .pkg was selected as Payload; a third-party packaging tool emits a different Payload format.

Related errors

• {} files are only supported in macOS
• Unsafe entry (path traversal): {:?}
• Format for file {} cannot be inferred
• Wrong browser/driver version
• Downloaded file cannot be uncompressed ({} extension)

AI-assisted analysis of SeleniumHQ/selenium@aa36b38e69 (2026-08-14). Data as JSON: /api/errors/e8433f15445a3465. Report an issue: GitHub.