[GNC-dev] Robust error handling and respecting the Apha Vantage API limits in gnc-fq-helper.

[Mike Alexander]

On 11 Feb 2020, at 3:59, Edward d'Auvergne wrote:

> F::Q uses this URL for all queries:
>
> https://www.alphavantage.co/query?function=GLOBAL_QUOTE&datatype=json&symbol=IDRUSD&apikey=$MY_KEY
>
> The result I see is:
>
> {
>     "Global Quote": {
>         "01. symbol": "IDRUSD",
>         "02. open": "0.0001",
>         "03. high": "0.0001",
>         "04. low": "0.0001",
>         "05. price": "0.0001",
>         "06. volume": "0",
>         "07. latest trading day": "2020-02-10",
>         "08. previous close": "0.0001",
>         "09. change": "0.0000",
>         "10. change percent": "0.0000%"
>     }
> }

It doesn't use that URL for currency exchange rates.  It uses

https://www.alphavantage.co/query?function=CURRENCY_EXCHANGE_RATE&from_currency=IDR&to_currency=USD&apikey=xxx

which returns

{
     "Realtime Currency Exchange Rate": {
         "1. From_Currency Code": "IDR",
         "2. From_Currency Name": "Indonesian Rupiah",
         "3. To_Currency Code": "USD",
         "4. To_Currency Name": "United States Dollar",
         "5. Exchange Rate": "0.00007297",
         "6. Last Refreshed": "2020-02-12 06:30:18",
         "7. Time Zone": "UTC",
         "8. Bid Price": "-",
         "9. Ask Price": "-"
     }
}

> It looks like this code then kicks in, from the "currency" subroutine
> in lib/Finance/Quote.pm:
>
> """
> if ( $exchange_rate < 0.001 ) {
>     # exchange_rate is too little. we'll get more accuracy by using
>     # the inverse rate and inverse it
>     my $inverse_rate = $this->currency( $to, $from );
>     {
>         local $^W = 0;
>         return undef unless ( $exchange_rate + 0 );
>     }
>     $exchange_rate = int( 100000000 / $inverse_rate + .5 ) / 
> 100000000;
> }
> """
>

That code should be removed.  It actually gets the same accuracy and it 
gets a different answer.  The reverse quote is 13683.5.  This inverts to 
a rate of 0.00007308 which is not the same as 0.00007297.  That's a 
trivial difference, but F::Q should really return the quote it was asked 
for if possible.

I noticed that there was some action on my pull request after you 
rattled their cage.  Thanks for doing that.  That may make this 
discussion largely irrelevant.

    Mike