CertifiedData

The Internet Computer allows canister smart contracts to store a small amount of data during update method processing so that during query call processing, the canister can obtain a certificate about that data.

:::info Intended audience

This module provides a low-level interface to this API, aimed at advanced users and library implementors. See the Internet Computer interface specification and corresponding documentation for how to use this to make query calls to your canister tamperproof. :::

`public func set(data : Blob) : ()`

Set the certified data.

:::note Usage constraints

Must be called from an update method, else traps. Must be passed a blob of at most 32 bytes, else traps. :::

Example:

motoko no-repl
import CertifiedData "mo:base/CertifiedData";
import Blob "mo:base/Blob";

// Must be in an update call

let array : [Nat8] = [1, 2, 3];
let blob = Blob.fromArray(array);
CertifiedData.set(blob);

:::info See a full example on how to use certified variables. :::

`public func getCertificate() : ?Blob`

Gets a certificate.

:::note When available

Returns null if no certificate is available, e.g. when processing an update call or inter-canister call. This returns a non-null value only when processing a query call. :::

Example:

motoko no-repl
import CertifiedData "mo:base/CertifiedData";
// Must be in a query call

CertifiedData.getCertificate();

:::info See a full example on how to use certified variables. :::