Resolve [ErrorException: Undefined property] - Return changelly errors

[mattsmithies]

Rationale

The Changelly API returns an error if a request is invalid in particular when trying to request getExchangeAmount. For example when there isn't enough liquidity or there is a minimum amount required for an exchange to take place.

Solution

I've updated src/Changelly.php to check that a result exists from the Changelly API service, if not it reverts to using the error which is returned. The sample code has been updated to illustrate the update.

If you are happy with this PR feel free to merge and update your composer package.

[vittominacori]

What do you think about throwing error instead?

if ($response->code == 200) {
    $body = $response->body;

    if (isset($body->result)) {
        return $body->result;
    }

    throw new \Exception($body->error->message, 400);
} else {
    throw new \Exception($response->body, $response->code);
}

And intercept it in a try catch?

// Throw error when Changelly cannot process the request
try {
    echo json_encode($changelly->getExchangeAmount('btc', 'eth', 22000000)) . PHP_EOL;
} catch (Exception $e) {
    echo $e->getMessage();
}

Otherwise you should check that returned value must not to be an error message.

[mattsmithies]

It would make more sense to use 422 (Unprocessable Entity) and include the full JSON error, as Changelly as provides helpful insight to resolve the situation.

If this was a normal situation I'd stay away from throwing an exception as the design of the Changelly API considers these "warnings" to be a normal part of the exchange flow.

Given that I don't know how many people are using this specific client it is a good compromise to throw an actual exception without breaking anyone's code!