[AVLE] Handling CORS issue for Release

One issue to release the AVLE dapp is CORS (Cross-Origin Resource Sharing).

The request has been blocked by CORS policy

A request to get Tron data from steemwallet.com is blocked by this CORS policy.
It simply means the browser does not allow to fetch data from different domain which is 'avle.io' in this case.

Other than Tron related APIs have no CORS issue, meaning that steemapi.com allows access from different domain. I guess Tron APIs should allow it too.

There is a workaround for this issue, which is to use a proxy server. User's request from AVLE dapp to Tron api server is proxied in the middle. The CORS issue occurs only in a browser. So requesting from not a browser does not violet CORS policy.

Firebase Functions

Firebase provides cloud functions which act as a backend server (it is called serverless computing).

The followings are functions to handle requests from the AVLE dapp:

// fetch tron reward
exports.tronRewardRequest = functions.https.onCall((async (data) => {
    console.log('[tronBalanceRequest] input data', data);
    const { account } = data;
    const tronRewardEndpoint = `https://steemitwallet.com/api/v1/tron/tron_user?username=${account}`;
    let result = null;
    try {
        console.log('[tronBalanceRequest] tronRewardEndpoint', tronRewardEndpoint);
        await axios.get(tronRewardEndpoint).then(
            (response) => {
                console.log('[tronRewardRequest] res.data', response.data);
                result = response.data;
            })
            .catch((error) => console.log('failed to get tron reward. error', error));
    } catch (error) {
        console.log('failed to get tron reward, error', error);
        return null;
    }
    return result;
}));

// fetch tron account data
exports.tronAccountRequest = functions.https.onCall(async (data) => {
    console.log('[tronAccountRequest] input data', data);
    const { address } = data;
    const options = { 'address': address };
    const tronAccountEndpoint =
        'https://api.trongrid.io/walletsolidity/getaccount';
    let result = null;
    try {
        const response =
            await axios.post(tronAccountEndpoint, options);
        console.log('[tronAccountRequest] response', response);
        result = response.data;
    } catch (error) {
        console.log('failed to get tron account. error', error);
        return null;
    }
    return result;
});

Now test this with release build

$ flutter run --release -d chrome

When we check the logs in Firebase Functions, it shows correct messages.

On step closer to the Release!

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