Crate sp_io

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§Substrate Primitives: IO

This crate contains interfaces for the runtime to communicate with the outside world, ergo io. In other context, such interfaces are referred to as “host functions”.

Each set of host functions are defined with an instance of the sp_runtime_interface::runtime_interface macro.

Most notably, this crate contains host functions for:

All of the default host functions provided by this crate, and by default contained in all substrate-based clients are amalgamated in SubstrateHostFunctions.


Host functions go hand in hand with the concept of externalities. Externalities are an environment in which host functions are provided, and thus can be accessed. Some host functions are only accessible in an externality environment that provides it.

A typical error for substrate developers is the following:

use sp_io::storage::get;
let data = get(b"hello world");

This code will panic with the following error:

thread 'main' panicked at '`get_version_1` called outside of an Externalities-provided environment.'

Such error messages should always be interpreted as “code accessing host functions accessed outside of externalities”.

An externality is any type that implements sp_externalities::Externalities. A simple example of which is TestExternalities, which is commonly used in tests and is exported from this crate.

use sp_io::{storage::get, TestExternalities};
TestExternalities::default().execute_with(|| {
	let data = get(b"hello world");


  • Wasm only interface that provides functions for calling into the allocator.
  • Interfaces for working with crypto related types from within the runtime.
  • Interface for accessing the child storage for default child trie, from within the runtime.
  • Interface that provides functions for hashing with different algorithms.
  • Interface that provides functions for logging from within the runtime.
  • Interface that provides miscellaneous functions for communicating between the runtime and the node.
  • Interface that provides functions to access the offchain functionality.
  • Interface that provides functions to access the Offchain DB.
  • WASM-only interface which allows for aborting the execution in case of an unrecoverable error.
  • Interface for accessing the storage from within the runtime.
  • Interface that provides transaction indexing API.
  • Interface that provides trie related functionality.
  • Interface to provide tracing facilities for wasm. Modelled after tokios tracing-crate interfaces. See sp-tracing for more information.


  • Crossing is a helper wrapping any Encode-Decodeable type for transferring over the wasm barrier.
  • Results concerning an operation to remove many keys.
  • Extension to signal to [crypt::ed25519_verify] to use the dalek crate.


  • Error verifying ECDSA signature
  • The outcome of calling storage_kill. Returned value is the number of storage items removed from the backend from making the storage_kill call.


  • Initialize tracing of sp_tracing not necessary – noop. To enable build without std and with the with-tracing-feature.
  • Crashes the execution of the program.

Type Aliases§