BoundaryML/baml · error · BridgeError

call_id must be a nonzero uint64

Error message

call_id must be a nonzero uint64

What it means

FFI argument validation error from the bridge_cffi layer: the call_id passed over the C boundary is zero. Call ids are used to correlate in-flight calls with their results, so zero is reserved/invalid; callers must supply a distinct nonzero uint64 for each call.

Source

Thrown at baml_language/crates/bridge_cffi/src/error.rs:40

    #[error("CallFunctionArgs.call_target must be set")]
    MissingCallTarget,

    #[error("type arguments are not supported when invoking a BAML function handle")]
    FunctionHandleTypeArgs,

    #[error("Function not found: {name}")]
    FunctionNotFound { name: String },

    #[error("Missing argument '{parameter}' for function '{function}'")]
    MissingArgument { function: String, parameter: String },

    #[error("Not implemented: {0}")]
    NotImplemented(String),

    #[error("call_id {0} is already in use by an active call")]
    DuplicateCallId(u64),

    #[error("call_id must be a nonzero uint64")]
    InvalidCallId,

    #[error("Internal error: {0}")]
    Internal(String),

    #[error("{0}")]
    Startup(String),
}

View on GitHub (pinned to bd85ce9dee)

Solutions

1. Assign a nonzero call_id (start counters at 1) before invoking.
2. Validate call_id > 0 client-side before crossing the FFI boundary.
3. Check integer width conversions so the value fits in uint64.
4. Explicitly initialize ctypes structs instead of relying on zeroed memory.

Example fix

// before
args.call_id = 0;
// after
args.call_id = next_id(); // guaranteed >= 1

if not (0 < call_id <= 2**64 - 1):
    raise ValueError('call_id must be a nonzero uint64')

def valid_call_id(v) -> bool:
    return isinstance(v, int) and 0 < v < 2**64

try:
    bridge.call_start(args)
except BridgeError as e:
    if e is BridgeError.InvalidCallId:
        args.call_id = next_id()  # starts at 1
        bridge.call_start(args)

When it happens

Trigger: Passing call_id = 0 (or an unset/default-initialized field) to a call_start or call-related bridge function; passing a value that overflows u64 from a wider client-side integer.

Common situations: Zero-initialized C structs in ctypes users who never assign call_id; languages where the default integer is 0; sign/overflow issues when converting from i64 or arbitrary-precision ints.

Understand the failure class

Background: "value must be between 0 and 1" / "out of range" / "must not be negative" errors: fixing range-validation failures across open-source libraries — this error's family across 42 libraries.

Related errors

• CallFunctionArgs.call_target must be set
• Missing argument '{parameter}' for function '{function}'
• call_id {0} is already in use by an active call
• {0}
• Invalid bigint hex string ({len} bytes)

AI-assisted analysis of BoundaryML/baml@bd85ce9dee (2026-09-12). Data as JSON: /api/errors/b3e89fb84c0342c8. Report an issue: GitHub.