# Integrate a Cosmos-SDK based blockchain as a Service Provider

We define 'service providers' as entities providing services for end-users that involve some form of interaction with a Cosmos-SDK based blockchain (this includes the Cosmos Hub). More specifically, this document will be focused around interactions with tokens.

This section does not concern wallet builders that want to provide [Light-Client](https://github.com/cosmos/cosmos-sdk/tree/develop/docs/light) functionalities. Service providers are expected to act as trusted point of contact to the blockchain for their end-users. 

## High-level description of the architecture

There are three main pieces to consider:

- Full-nodes: To interact with the blockchain. 
- Rest Server: This acts as a relayer for HTTP calls.
- Rest API: Define available endpoints for the Rest Server.

## Running a Full-Node

### Installation and configuration

We will describe the steps to run and interract with a full-node for the Cosmos Hub. For other SDK-based blockchain, the process should be similar. 

First, you need to [install the software](../getting-started/installation.md).

Then, you can start [running a full-node](../getting-started/join-testnet.md).

### Command-Line interface

Next you will find a few useful CLI commands to interact with the Full-Node.

#### Creating a key-pair

To generate a new key (default secp256k1 elliptic curve):

```bash
gaiacli keys add <your_key_name>
```

You will be asked to create a passwords (at least 8 characters) for this key-pair. The command returns 4 informations:

- `NAME`: Name of your key
- `ADDRESS`: Your address. Used to receive funds.
- `PUBKEY`: Your public key. Useful for validators.
- `Seed phrase`: 12-words phrase. **Save this seed phrase somewhere safe**. It is used to recover your private key in case you forget the password.

You can see all your available keys by typing:

```bash
gaiacli keys list
```

#### Checking your balance

After receiving tokens to your address, you can view your account's balance by typing:

```bash
gaiacli account <YOUR_ADDRESS>
```

*Note: When you query an account balance with zero tokens, you will get this error: No account with address <YOUR_ADDRESS> was found in the state. This is expected! We're working on improving our error messages.*

#### Sending coins via the CLI

Here is the command to send coins via the CLI:

```bash
gaiacli send --amount=10faucetToken --chain-id=<name_of_testnet_chain> --from=<key_name> --to=<destination_address>
```

Flags:
- `--amount`: This flag accepts the format `<value|coinName>`.
- `--chain-id`: This flag allows you to specify the id of the chain. There will be different ids for different testnet chains and main chain.
- `--from`: Name of the key of the sending account.
- `--to`: Address of the recipient.

#### Help

If you need to do something else, the best command you can run is:

```bash
gaiacli 
```

It will display all the available commands. For each command, you can use the `--help` flag to get further information. 

## Setting up the Rest Server

The Rest Server acts as an intermediary between the front-end and the full-node. You don't need to run the Rest Server on the same machine as the full-node. If you intend to run the Rest Server on another machine, you need to go through the [Installation and configuration](#installation-and-configuration) again on this machine.

To start the Rest server: 

```bash
gaiacli advanced rest-server --node=<full_node_address:full_node_port>
```

Flags:
- `--trust-node`: A boolean. If `true`, light-client verification is disabled. If `false`, it is disabled. For service providers, this should be set to `true`. By default, it set to `true`. 
- `--node`: This is where you indicate the address and the port of your full-node. The format is <full_node_address:full_node_port>. If the full-node is on the same machine, the address should be `tcp://localhost:26657`.
- `--laddr`: This flag allows you to specify the address and port for the Rest Server (default `1317`). You will mostly use this flag only to specify the port, in which case just input "localhost" for the address. The format is <rest_server_address:port>.


### Listening for incoming transaction

The recommended way to listen for incoming transaction is to periodically query the blockchain through the following endpoint of the LCD:

[`/bank/balance/{account}`](https://cosmos.network/rpc/#/ICS20/get_bank_balances__address_)

## Rest API

The Rest API documents all the available endpoints that you can use to interract with your full node. It can be found [here](https://cosmos.network/rpc/). 

The API is divided into ICS standards for each category of endpoints. For example, the [ICS20](https://cosmos.network/rpc/#/ICS20/) describes the API to interact with tokens. 

To give more flexibility to implementers, we have separated the different steps that are involved in the process of sending transactions. You will be able to generate unsigned transactions (example with [coin transfer](https://cosmos.network/rpc/#/ICS20/post_bank_accounts__address__transfers)), [sign](https://cosmos.network/rpc/#/ICS20/post_tx_sign) and [broadcast](https://cosmos.network/rpc/#/ICS20/post_tx_broadcast) them with different API endpoints. This allows service providers to use their own signing mechanism for instance.