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Exploring the pallet template

We will spend most of our time in the pallets/connect folder in the next modules. Upon opening it, there are a few items of interest, mostly with testing, as well as the actual source code of the pallet. Again, as mentioned in the last section of this module, this is just a Rust crate that uses FRAME to generate and implement certain traits and structures to be compatible with the runtime.

Our pallet, called pallet-connect, defines our custom logic that is then enabled by our runtime within the node template.

lib.rs​

lib.rs defines the entry point for the pallet. It contains all the core logic - extrinsics, events, and errors, are all defined by a single struct:

#[pallet::pallet]
pub struct Pallet<T>(_);

We will go into more detail on the structure of lib.rs later but know for now that this makes a FRAME pallet at the most basic level. Pallets, just like this one, are later imported as a crate to the runtime, where the aforementioned construct_runtime! macro is responsible for defining and constructing a runtime based on the collection of pallets and their respective configurations.

mock.rs and tests.rs​

In most pallets, including our template, you will also see the following files: mock.rs and tests.rs. As one may assume, they are used for two purposes:

  • mock.rs is used for configuring a test environment, i.e., a test runtime configured for unit testing.
  • tests.rs is where unit tests reside and act on the values and configuration defined within mock.rs

benchmarking.rs and weights.rs​

Benchmarking and weights measure an extrinsic's performance, or weight. Substrate is built around the concept of weight, which measures how much computation is required to execute it on-chain. Using benchmarking, weight can be assigned to each extrinsic, and the weights.rs file is generated. Often, this weight corresponds to how much a user will pay to execute that state change. Weights also ensure that the transactions within a block can be executed successfully within the block production time window.

Although these two won't be covered in this course in-depth at a technical level, they are both crucial concepts to learn if one wishes to create a production-grade pallet.