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Connect to a node

For a software application to interact with a blockchain (e.g. by sending transactions/data to the network, or even just by reading data), it must connect to a node. This section describes how to connect to your Polygon node.

Backend APIs​

Once a node has been deployed on an EVM (Ethereum Virtual Machine) compatible network, such as Polygon, it can be accessed by different endpoints such as JSON-RPC, JSON-WS or GraphQL. You can connect to your already deployed node using these 3 most common endpoints.

JSON-RPC​

JSON-RPC, is a stateless, light-weight remote procedure call (RPC) protocol. Primarily, the specification defines several data structures and the rules around their processing. By default, the version of the JSON-RPC protocol needs to be 2.0, and you need to provide the node ID as well as a method and parameters.

There are different kinds of methods that can be used: ADMIN methods, DEBUG methods, ETH methods etc.

If you want to correctly connect to your node, you need to respect the right structure for the request, which is always the same:

{
"jsonrpc":"2.0"
"Id": nodeId
"method":"methodName"
"params":{
}
}

If you want to connect to a node deployed on the SettleMint platform, go to the Connect tab on the Node detail page in the Blockchain nodes section of your application. Select JSON-RPC or any other endpoint and click Try it out. You will then be redirected to a new tab where you will be able to test different methods as well as the related Curl command line.

JSON-WS​

To make RPC requests over WebSockets, you can use wscat, which is by definition a Node.js based command-line tool. First you will need to connect to your node’s WebSocket server using wscat, as follows: "wscat -c ws://<JSON-RPC-ws-endpoint:port>". All the credentials are provided in the Connect tab on the Node detail page in the Blockchain nodes section of your application. After you have established a connection, the terminal should display a '>' prompt. You will then be able to send individual requests as a JSON data package, as above, for instance:

{
"jsonrpc":"2.0"
"Id": 1
"method":"eth_blockNumber"
"params":{
}
}

GraphQL​

GraphQL is a query language and server-side runtime for API’s. It is designed to make APIs fast, flexible, and developer-friendly. We have a GraphQL interface that can be used with many different queries. These queries can be tested out in our GraphQL playground. You can also test out the different graphql queries with cURL, those request would look like this:

curl -X POST -H "Content-Type: application/json" -H “x-auth-token: <AUTH_TOKEN>” --data
'{ "query": "{syncing{startingBlock currentBlock highestBlock}}"}' http://<DOMAIN>.settlemint.com/graphql

If you want to connect to a node deployed on the SettleMint platform, go to the Connect tab on the Node detail page in the Blockchain nodes section of your application. Select Graphql and click Try it out. This will bring you to the GraphQL playground where you can use all the different queries.

Javascript API​

If you do not want to use the above endpoints to connect to your node, it is possible to use plain Javascript. Several convenience libraries exist within the different ecosystem which makes connection much easier. With these libraries, developers around the world can write one-line methods to easily initiate requests (still under the hood) that interact with Ethereum or any other EVM compliant network. Note that some libraries might be available for Ethereum but not for the other networks.

These libraries are very helpful and abstract away much of the complexity of interacting directly with your node. Most also provide useful and straightforward functions such as converting ETH to Gwei, so that you can spend less time dealing with decimal issues and more time on the functionality of your underlying application.

One of the most commonly used libraries, Ethers, is extremely easy to use for signing transactions, sending tokens etc. For example:

// If you don't specify a //url//, Ethers connects to the default
// (i.e. ``http:/\/localhost:8545``)
const provider = new ethers.providers.JsonRpcProvider();

// The provider also allows signing transactions to
// send ether and pay to change state within the blockchain.
// For this, we need the account signer...
const signer = provider.getSigner();