clockworklabs/SpacetimeDB · critical

unsupported type for :sender: {ty:?}

Error message

unsupported type for :sender: {ty:?}

What it means

When executing a physical plan, ExecutionParams::resolve_param binds implicit parameter slots: PARAM_SENDER can bind only to parameters declared as Identity or as bytes (sender passed as big-endian bytes); the view-arg-hash slots only to U256; any unknown slot panics too. If the module's declared type for the :sender slot is anything else, resolve_param panics with the offending AlgebraicType. This is a module-ABI constraint: the caller identity can only be supplied to Identity- or bytes-typed parameters.

Source

Thrown at crates/execution/src/lib.rs:47

    pub fn from_sender(sender: Identity) -> Self {
        Self {
            sender,
            empty_view_arg_hash: hash_empty_view_args().to_u256(),
            sender_view_arg_hash: hash_sender_view_args(sender).to_u256(),
        }
    }

    pub fn from_auth(auth: &AuthCtx) -> Self {
        Self::from_sender(auth.caller())
    }
}

impl ParamResolver for ExecutionParams {
    fn resolve_param(&self, param: ParamSlot, ty: &AlgebraicType) -> AlgebraicValue {
        match param {
            PARAM_SENDER if ty.is_identity() => self.sender.into(),
            PARAM_SENDER if ty.is_bytes() => AlgebraicValue::Bytes(self.sender.to_be_byte_array().into()),
            PARAM_SENDER => panic!("unsupported type for :sender: {ty:?}"),
            PARAM_VIEW_ARG_HASH_EMPTY if matches!(ty, AlgebraicType::U256) => {
                AlgebraicValue::U256(self.empty_view_arg_hash.into())
            }
            PARAM_VIEW_ARG_HASH_EMPTY => panic!("unsupported type for empty view arg hash: {ty:?}"),
            PARAM_VIEW_ARG_HASH_SENDER if matches!(ty, AlgebraicType::U256) => {
                AlgebraicValue::U256(self.sender_view_arg_hash.into())
            }
            PARAM_VIEW_ARG_HASH_SENDER => panic!("unsupported type for sender view arg hash: {ty:?}"),
            ParamSlot(slot) => panic!("unknown physical plan parameter slot: {slot}"),
        }
    }
}

pub trait Datastore {
    /// Iterator type for table scans
    type TableIter<'a>: Iterator<Item = RowRef<'a>> + 'a
    where
        Self: 'a;

View on GitHub (pinned to 6dee26c6ef)

Solutions

1. Rebuild and republish the module with an SDK matching the server so the sender parameter is typed Identity.
2. In module code, use ctx.sender (ReducerContext) or declare the parameter as Identity, not Address/String/custom types.
3. If a bytes parameter is acceptable, declare it bytes and convert from the identity's big-endian byte array in module code.

Example fix

// before (older SDK ABI): sender parameter declared as Address
#[reducer]
fn tick(ctx: &ReducerContext, sender: Address) { /* ... */ }

// after: read the caller from the context as Identity
#[reducer]
fn tick(ctx: &ReducerContext) {
    let sender: Identity = ctx.sender;
    /* ... */
}

// before publishing, verify the sender slot's declared type
// (adapt to however you introspect the module; the host allows only these two)
fn sender_type_supported(ty: &AlgebraicType) -> bool {
    ty.is_identity() || ty.is_bytes()
}
// in your build/publish checks: reject modules whose sender param fails this predicate

fn sender_type_supported(ty: &AlgebraicType) -> bool { ty.is_identity() || ty.is_bytes() }

When it happens

Trigger: Executing a plan whose :sender implicit parameter is declared with a non-Identity, non-bytes type — typically a module compiled with an SDK whose caller parameter used a different type (e.g. Address), resolved when the plan binds PARAM_SENDER.

Common situations: SDK/server version skew across releases that changed the sender representation; hand-written wasm declaring the sender param as String or a custom type; porting modules between breaking ABI versions.

Related errors

• reducer ran out of energy
• cannot deserialize refs without a typespace
• There is already a reducer, procedure, or view with the name
• Table ${tableName} defines a schedule, but it seems like the
• Table ${tableName} defines multiple schedules: ${existingFun

AI-assisted analysis of clockworklabs/SpacetimeDB@6dee26c6ef (2026-08-20). Data as JSON: /api/errors/233b8435fa7540b7. Report an issue: GitHub.