npm package: @mavrykdynamics/taquito-tzip16
Description: Tzip16
Author: Roxane Letourneau
Latest version: 20.1.0

# Taquito TZIP-016 package
*Documentation can be found [here](https://taquito.mavryk.org/docs/metadata-tzip16/)*  
*TypeDoc style documentation is available on-line [here](https://taquito.mavryk.org/typedoc/modules/_taquito_tzip16.html)*

`@mavrykdynamics/taquito-tzip16` is an npm package that provides developers with TZIP-016 functionality for Taquito. TZIP-016 is a standard for encoding access to smart contract metadata either on-chain or off-chain. The `@mavrykdynamics/taquito-tzip16` package allows developers to retrieve the metadata associated with a smart contract and execute the off-chain views found in the metadata.

## General Information

Contract metadata gathers valuable information about the contract that is not directly used for its operation. According to TZIP-016, a contract with metadata must include in its storage a big_map named `%metadata` of the following type: `(big_map %metadata string bytes)`. The big_map must have an empty string as a key where its value is a byte-encoded URI representing the metadata location. Contract metadata can be located on-chain or off-chain (web services or IPFS). Please refer to the following link for complete documentation on [TZIP-016](https://gitlab.com/tezos/tzip/-/blob/master/proposals/tzip-16/tzip-16.md#introduction).

When using the `@mavrykdynamics/taquito-tzip16` package, developers can retrieve metadata of a contract based on its address. The underlying steps performed by Taquito are to find the URI in the contract storage, decode it, extract the metadata depending on the protocol (mavryk-storage, HTTP(S) or IPFS), perform an integrity check if the URI contains a sha256 hash, and return the metadata to the user.

Another functionality of the `@mavrykdynamics/taquito-tzip16` package allows executing off-chain views. If a contract contains views in its metadata, Taquito builds an ordinary JavaScript object with methods corresponding to the views name.

## Install

The package can be used to extend the well-known Taquito contract abstraction. The `@mavrykdynamics/taquito-tzip16` and the `@mavrykdynamics/taquito` packages need to be installed as follows:
```
npm i --save @mavrykdynamics/taquito-tzip16
npm i --save @mavrykdynamics/taquito
```

## Usage

**Create an instance of the `Tzip16Module` and add it as an extension to the `MavrykToolkit`**

The constructor of the `Tzip16Module` takes an optional `MetadataProvider` as a parameter. When none is passed, the default `MetadataProvider` of Taquito is instantiated, and the default handlers (`HttpHandler`, `IpfsHandler`, and `MavrykStorageHandler`) are used. 
The `MetadataProvider` can be customized by the user if needed.

**Use the `tzip16` function to extend a contract abstraction**

```js
import { MavrykToolkit } from '@mavrykdynamics/taquito';
import { Tzip16Module } from '@mavrykdynamics/taquito-tzip16';
import { tzip16 } from '@mavrykdynamics/taquito-tzip16';

const Mavryk = new MavrykToolkit('https://YOUR_PREFERRED_RPC_URL');
Mavryk.addExtension(new Tzip16Module());

const contract = await Mavryk.contract.at("contractAddress", tzip16)
```

### Get the contract metadata

```ts
const metadata = await contract.tzip16().getMetadata();
```

The `getMetadata` method returns an object which contains the URI, the metadata in JSON format, an optional SHA256 hash of the metadata, and an optional integrity check result.

### Execute off-chain views

```ts
// Initialize off-chain views
const metadataViews = await contractAbstraction.tzip16().metadataViews();
const viewResult = await metadataViews.nameOfTheView().executeView(paramOfTheView);
```

## Additional info

See the top-level [https://github.com/ecadlabs/taquito](https://github.com/ecadlabs/taquito) file for details on reporting issues, contributing, and versioning.

## Disclaimer

THIS SOFTWARE IS PROVIDED "AS IS" AND ANY EXPRESSED OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE REGENTS OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.