Pumpkin-MC/Pumpkin · error

unknown stack request item descriptor type

Error message

unknown stack request item descriptor type {descriptor_type}

What it means

Thrown when decoding an ItemStackRequest item descriptor whose descriptor_type VarUInt is neither 0 (invalid/none descriptor) nor 1 (string identifier with metadata). The wire format only defines these two variants, so any other value means the stream is not a valid descriptor. Parsing aborts with an InvalidData error.

Solutions

1. Align client and server Bedrock protocol versions
2. Decode the packet manually (offsets before the descriptor) to confirm which bytes were read as descriptor_type
3. Add support for the new descriptor type in the decoder if a newer protocol defines it

Example fix

// before (crafting a descriptor)
let descriptor_type: VarUInt = VarUInt(2);
// after
let descriptor_type: VarUInt = VarUInt(1); // 0 or 1 only

fn is_valid_descriptor_type(t: u32) -> bool { matches!(t, 0 | 1) }

fn known_descriptor_type(t: u32) -> Option<DescriptorType> { match t { 0 => Some(DescriptorType::None), 1 => Some(DescriptorType::Item), _ => None } }

match read_item_descriptor(reader) {
    Err(e) if e.to_string().contains("unknown stack request item descriptor") => log_malformed(peer, e),
    Err(e) => return Err(e),
    Ok(d) => Ok(d),
}

When it happens

Trigger: A client sends an ItemStackRequest containing an item descriptor with descriptor_type >= 2, usually due to a protocol version mismatch, corrupted stream, or a crafted packet.

Common situations: Mismatched Bedrock protocol versions after a game update, modified clients, or packet fuzzing hitting the item-stack-request route.

Understand the failure class

Background: Invalid enum value errors: "Unknown type", "Invalid scope", "must be one of" — when a string is not on the library's allowed list — this error's family across 23 libraries.

Related errors

• Unknown ItemStackRequestAction ID
• unknown item descriptor type
• invalid player input flag
• user_data_len exceeds 1MB limit
• extra_data_len exceeds 1MB limit

AI-assisted analysis of Pumpkin-MC/Pumpkin@8d4639e25a (2026-09-09). Data as JSON: /api/errors/7f30cb3302499c93. Report an issue: GitHub.

Appendix: source

Thrown at crates/pumpkin-protocol/src/bedrock/server/item_stack_request.rs:47

#[derive(Debug)]
pub struct StackRequestItem {
    pub identifier: Option<String>,
    pub metadata_value: VarInt,
    pub count: u16,
    pub block_runtime_id: VarUInt,
    pub extra_data: Vec<u8>,
}

impl PacketRead for StackRequestItem {
    fn read<R: Read>(reader: &mut R) -> Result<Self, Error> {
        let descriptor_type = VarUInt::read(reader)?.0;
        let _legacy_type = u8::read(reader)?;
        let (identifier, metadata_value) = match descriptor_type {
            0 => (None, VarInt(0)),
            1 => (Some(String::read(reader)?), VarInt::read(reader)?),
            _ => {
                return Err(Error::new(
                    ErrorKind::InvalidData,
                    format!("unknown stack request item descriptor type {descriptor_type}"),
                ));
            }
        };
        let count = i16::read(reader)? as u16;
        let block_runtime_id = VarUInt::read(reader)?;
        let data_len = VarUInt::read(reader)?.0 as usize;
        if data_len > 1_048_576 {
            return Err(Error::new(
                ErrorKind::InvalidData,
                "extra_data length exceeds limit",
            ));
        }
        let mut extra_data = vec![0; data_len];
        reader.read_exact(&mut extra_data)?;
        Ok(Self {
            identifier,

View on GitHub (pinned to 8d4639e25a)