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.

Externalities

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");
});

Modules

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

Structs

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

Enums

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

Functions

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

Type Aliases