How can I set the max byte size extrinsic/transaction?

Question

I will like to play with limiting the max size of transactions? I cannot find in substrate where those configurations go.

Answer 1

FRAME does not have a limit on a single transaction, but does have a limit for a single block. Then any transaction would be limited to the size limit of that block.

You can find those settings in the frame_system::Config configuration, specifically the BlockLength configuration:

/// System configuration trait. Implemented by runtime.
#[pallet::config]
#[pallet::disable_frame_system_supertrait_check]
pub trait Config: 'static + Eq + Clone {
    /// The basic call filter to use in Origin. All origins are built with this filter as base,
    /// except Root.
    type BaseCallFilter: Contains<Self::Call>;

    /// Block & extrinsics weights: base values and limits.
    #[pallet::constant]
    type BlockWeights: Get<limits::BlockWeights>;

    /// The maximum length of a block (in bytes).
    #[pallet::constant]
    type BlockLength: Get<limits::BlockLength>;

    /// -- snip --
}

The structure here: https://github.com/paritytech/substrate/blob/master/frame/system/src/limits.rs

If you wanted to create some logic which rejects transactions based on their individual length, you could create a SignedExtension.

An example of that can be found in the example pallet: https://github.com/paritytech/substrate/blob/master/frame/examples/basic/src/lib.rs#L674