refactor exchange rates data backend, supports multi data source, supports timeout

pkg/exchangerates/exchange_rates_datasource.go

@@ -0,0 +1,15 @@
+package exchangerates
+
+import (
+	"github.com/mayswind/lab/pkg/core"
+	"github.com/mayswind/lab/pkg/models"
+)
+
+// ExchangeRatesDataSource defines the structure of exchange rates data source
+type ExchangeRatesDataSource interface {
+	// GetRequestUrl returns the data source url
+	GetRequestUrl() string
+
+	// Parse returns the common response entity according to the data source raw response
+	Parse(c *core.Context, content []byte) (*models.LatestExchangeRateResponse, error)
+}