fiatrates: Implement a fiat rate oracle for tatanka

dex/fiatrates/fiatrates.go

@@ -91,11 +91,22 @@ func FetchCoinpaprikaRates(ctx context.Context, assets []*CoinpaprikaAsset, log
 }
 
 func getRates(ctx context.Context, url string, thing any) error {
+	return getRatesWithHeader(ctx, url, thing, nil)
+}
+
+func getRatesWithHeader(ctx context.Context, url string, thing any, header map[string]string) error {
+	ctx, cancel := context.WithTimeout(ctx, fiatRequestTimeout)
+	defer cancel()
+
 	req, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
 	if err != nil {
 		return err
 	}
 
+	for key, value := range header {
+		req.Header.Add(key, value)
+	}
+
 	resp, err := http.DefaultClient.Do(req)
 	if err != nil {
 		return err

dex/fiatrates/oracle.go

@@ -0,0 +1,239 @@
+package fiatrates
+
+import (
+	"context"
+	"fmt"
+	"strings"
+	"sync"
+	"time"
+
+	"decred.org/dcrdex/dex"
+)
+
+const (
+	// FiatRateDataExpiry : Any data older than FiatRateDataExpiry will be
+	// discarded.
+	FiatRateDataExpiry = 60 * time.Minute
+
+	// averageRateRefreshInterval is how long it'll take before a fresh fiat
+	// average rate is calculated.
+	averageRateRefreshInterval = defaultRefreshInterval + time.Minute
+)
+
+// Oracle manages and retrieves fiat rate information from all enabled rate
+// sources.
+type Oracle struct {
+	sources  []*source
+	ratesMtx sync.RWMutex
+	rates    map[string]*FiatRateInfo
+}
+
+func NewFiatOracle(cfg Config) (*Oracle, error) {
+	fiatOracle := &Oracle{
+		rates:   make(map[string]*FiatRateInfo),
+		sources: fiatSources(cfg),
+	}
+
+	assets := strings.Split(cfg.Assets, ",")
+	for _, asset := range assets {
+		_, ok := dex.BipSymbolID(strings.ToLower(asset))
+		if !ok {
+			return nil, fmt.Errorf("unknown asset %s", asset)
+		}
+
+		// Initialize entry for this asset.
+		fiatOracle.rates[parseSymbol(asset)] = new(FiatRateInfo)
+	}
+
+	return fiatOracle, nil
+}
+
+// Rate returns the current fiat rate information for the provided symbol.
+// Returns zero if there are no rates for the provided symbol yet.
+func (o *Oracle) Rate(symbol string) float64 {
+	o.ratesMtx.Lock()
+	defer o.ratesMtx.Unlock()
+
+	symbol = parseSymbol(symbol)
+	rateInfo := o.rates[symbol]
+	hasRateInfo := rateInfo != nil
+	if hasRateInfo && time.Since(rateInfo.LastUpdate) < FiatRateDataExpiry && rateInfo.Rate > 0 {
+		return rateInfo.Rate
+	}
+
+	if !hasRateInfo {
+		// Initiate an entry for this asset. Data for this asset will be fetched
+		// in the next refresh cycle.
+		o.rates[symbol] = new(FiatRateInfo)
+	}
+
+	return 0
+}
+
+// assets retrieves all assets that data can be fetched for.
+func (o *Oracle) assets() []string {
+	o.ratesMtx.RLock()
+	defer o.ratesMtx.RUnlock()
+	var assets []string
+	for sym := range o.rates {
+		assets = append(assets, sym)
+	}
+	return assets
+}
+
+// Run starts goroutines that refresh fiat rates every source.refreshInterval.
+// This should be called in a goroutine as it's blocking.
+func (o *Oracle) Run(ctx context.Context, log dex.Logger) {
+	var wg sync.WaitGroup
+	var sourcesEnabled int
+	initializedWithAssets := o.hasAssets()
+	for i := range o.sources {
+		fiatSource := o.sources[i]
+		if fiatSource.isDisabled() {
+			log.Infof("Fiat rate source %q is disabled...", fiatSource.name)
+			continue
+		}
+
+		o.fetchFromSource(ctx, fiatSource, &wg, log)
+		sourcesEnabled++
+
+		if !initializedWithAssets {
+			continue
+		}
+
+		// Fetch rates now.
+		newRates, err := fiatSource.getRates(ctx, o.assets(), log)
+		if err != nil {
+			log.Errorf("failed to retrieve rate from %s: %v", fiatSource.name, err)
+			continue
+		}
+
+		fiatSource.mtx.Lock()
+		fiatSource.rates = newRates
+		fiatSource.lastRefresh = time.Now()
+		fiatSource.mtx.Unlock()
+	}
+
+	if initializedWithAssets {
+		// Calculate average fiat rate now.
+		o.calculateAverageRate(ctx, &wg, log)
+	}
+
+	if sourcesEnabled > 0 {
+		// Start a goroutine to generate an average fiat rate based on fresh
+		// data from all enabled sources. This is done every
+		// averageRateRefreshInterval.
+		wg.Add(1)
+		go func() {
+			defer wg.Done()
+			ticker := time.NewTicker(averageRateRefreshInterval)
+			defer ticker.Stop()
+
+			for {
+				select {
+				case <-ctx.Done():
+					return
+				case <-ticker.C:
+					if !o.hasAssets() {
+						continue // nothing to do
+					}
+
+					o.calculateAverageRate(ctx, &wg, log)
+				}
+			}
+		}()
+	}
+
+	wg.Wait()
+}
+
+// calculateAverageRate is a shared function to support fiat average rate
+// calculations before and after averageRateRefreshInterval.
+func (o *Oracle) calculateAverageRate(ctx context.Context, wg *sync.WaitGroup, log dex.Logger) {
+	newRatesInfo := make(map[string]*fiatRateAndSourceCount)
+	for i := range o.sources {
+		s := o.sources[i]
+		if s.isDisabled() {
+			if s.checkIfSourceCanReactivate() {
+				// Start a new goroutine for this source.
+				o.fetchFromSource(ctx, s, wg, log)
+			}
+			continue
+		}
+
+		s.mtx.RLock()
+		sourceRates := s.rates
+		s.mtx.RUnlock()
+
+		for sym, rate := range sourceRates {
+			if rate == 0 {
+				continue
+			}
+
+			info, ok := newRatesInfo[sym]
+			if !ok {
+				info = new(fiatRateAndSourceCount)
+				newRatesInfo[sym] = info
+			}
+
+			info.sources++
+			info.totalFiatRate += rate
+		}
+	}
+
+	now := time.Now()
+	o.ratesMtx.Lock()
+	for sym := range o.rates {
+		rateInfo := newRatesInfo[sym]
+		if rateInfo != nil {
+			o.rates[sym].Rate = rateInfo.totalFiatRate / float64(rateInfo.sources)
+			o.rates[sym].LastUpdate = now
+		}
+	}
+	o.ratesMtx.Unlock()
+}
+
+func (o *Oracle) hasAssets() bool {
+	o.ratesMtx.RLock()
+	defer o.ratesMtx.RUnlock()
+	return len(o.rates) != 0
+}
+
+// fetchFromSource starts a goroutine that retrieves fiat rate from the provided
+// source.
+func (o *Oracle) fetchFromSource(ctx context.Context, s *source, wg *sync.WaitGroup, log dex.Logger) {
+	wg.Add(1)
+	go func(s *source) {
+		defer wg.Done()
+		ticker := time.NewTicker(s.requestInterval)
+		defer ticker.Stop()
+
+		for {
+			select {
+			case <-ctx.Done():
+				return
+			case <-ticker.C:
+				if !o.hasAssets() || s.isDisabled() { // nothing to fetch.
+					continue
+				}
+
+				if s.hasAssets() && s.isExpired() {
+					s.deactivate()
+					log.Errorf("Fiat rate source %q has been disabled due to lack of fresh data. It will be re-enabled after %d hours.", s.name, reactivateDuration.Hours())
+					return
+				}
+
+				newRates, err := s.getRates(ctx, o.assets(), log)
+				if err != nil {
+					log.Errorf("%s.getRates error: %v", s.name, err)
+					continue
+				}
+
+				s.mtx.Lock()
+				s.rates = newRates
+				s.lastRefresh = time.Now()
+				s.mtx.Unlock()
+			}
+		}
+	}(s)
+}