mod_exchange_rates

Fetch currency exchange rates from the ECB daily XML feed and expose them through m_exchange_rates, the exchange_rates template filter and Erlang functions. Enable mod_exchange_rates with its dependency mod_tkvstore. There are no module configuration keys or API credentials.

Updates and rate units

A per-site server fetches rates asynchronously at startup and on tick_12h. update(Context) requests another asynchronous fetch and returns ok before it finishes. Rates are normalized to USD: a rate is the number of units of that currency per US dollar, with USD fixed at 1.0.

After fetching, the server merges in-memory and persisted rates, then writes the result to mod_tkvstore. Fresh values override stored values. Handled fetch failures retain previous currencies; rates have no exposed timestamp or expiry check. Before the initial update finishes, the rates map is empty.

Erlang interface

mod_exchange_rates:rate(<<"EUR">>, Context).
mod_exchange_rates:convert(100, <<"USD">>, <<"EUR">>, Context).

base_currency/1 returns <<"USD">>. rates/1 returns {ok, Map} and currencies/1 returns {ok, SortedCurrencyCodes}. rate/2 normalizes the currency code to uppercase and returns {ok, Rate} or {error, unknown_currency}. USD always has rate 1.0.

convert/4 computes Amount / FromRate * ToRate, rounded using the module's currency exponent table (two decimal places by default). It returns {ok, Amount} or {error, currency_from | currency_to} for a missing or unavailable currency. Identical source and destination values bypass rate lookup and return the input as a float without currency rounding. These data-access functions do not perform ACL checks.