client: add external fee estimator as fallback, when feeEstimator fai…

…ls on decred rpcwallets.

client/asset/dcr/config.go

@@ -39,6 +39,7 @@ type walletConfig struct {
 	FeeRateLimit     float64 `ini:"feeratelimit"`
 	RedeemConfTarget uint64  `ini:"redeemconftarget"`
 	ActivelyUsed     bool    `ini:"special:activelyUsed"` //injected by core
+	ApiFeeFallback   bool    `ini:"apifeefallback"`
 }
 
 type rpcConfig struct {

client/asset/dcr/dcr.go

@@ -9,9 +9,12 @@ import (
 	"crypto/sha256"
 	"encoding/binary"
 	"encoding/hex"
+	"encoding/json"
 	"errors"
 	"fmt"
+	"io"
 	"math"
+	"net/http"
 	"path/filepath"
 	"sort"
 	"strconv"
@@ -74,6 +77,12 @@ const (
 	// hierarchical deterministic key derivation for the internal branch of an
 	// account.
 	acctInternalBranch uint32 = 1
+
+	// externalApiUrl is the URL of the external API in case of fallback.
+	externalApiUrl = "https://explorer.dcrdata.org/insight/api"
+	// testnetExternalApiUrl is the URL of the testnet external API in case of
+	// fallback.
+	testnetExternalApiUrl = "https://testnet.dcrdata.org/insight/api"
 )
 
 var (
@@ -172,6 +181,14 @@ var (
 			Description:  "Path to the dcrwallet TLS certificate file",
 			DefaultValue: defaultRPCCert,
 		},
+		{
+			Key:         "apifeefallback",
+			DisplayName: "External fee rate estimates",
+			Description: "Allow fee rate estimation from a block explorer API. " +
+				"This is useful as a fallback for SPV wallets and RPC wallets " +
+				"that have recently been started.",
+			IsBoolean: true,
+		},
 	}
 
 	spvOpts = []*asset.ConfigOption{{
@@ -215,6 +232,7 @@ var (
 	swapFeeBumpKey   = "swapfeebump"
 	splitKey         = "swapsplit"
 	redeemFeeBumpFee = "redeemfeebump"
+	client           http.Client
 )
 
 // outPoint is the hash and output index of a transaction output.
@@ -499,6 +517,8 @@ type ExchangeWallet struct {
 	feeRateLimit     uint64
 	redeemConfTarget uint64
 	useSplitTx       bool
+	ApiFeeFallback   bool
+	Network          dex.Network
 
 	tipMtx     sync.RWMutex
 	currentTip *block
@@ -656,6 +676,8 @@ func unconnectedWallet(cfg *asset.WalletConfig, dcrCfg *walletConfig, chainParam
 		feeRateLimit:        feesLimitPerByte,
 		redeemConfTarget:    redeemConfTarget,
 		useSplitTx:          dcrCfg.UseSplitTx,
+		ApiFeeFallback:      dcrCfg.ApiFeeFallback,
+		Network:             cfg.Network,
 	}, nil
 }
 
@@ -874,7 +896,16 @@ func (dcr *ExchangeWallet) feeRate(confTarget uint64) (uint64, error) {
 	}
 	estimatedFeeRate, err := feeEstimator.EstimateSmartFeeRate(dcr.ctx, int64(confTarget), chainjson.EstimateSmartFeeConservative)
 	if err != nil {
-		return 0, err
+		dcr.log.Errorf("Failed to get fee rate with estimate smart fee rate: %v", err)
+		if !dcr.ApiFeeFallback {
+			return 0, err
+		}
+		dcr.log.Debug("Retrieving fee rate from external API")
+		estimatedFeeRate, err = externalFeeEstimator(dcr.ctx, dcr.Network, confTarget)
+		if err != nil {
+			dcr.log.Errorf("Failed to get fee rate from external API: %v", err)
+			return 0, err
+		}
 	}
 	atomsPerKB, err := dcrutil.NewAmount(estimatedFeeRate) // atomsPerKB is 0 when err != nil
 	if err != nil {
@@ -885,6 +916,39 @@ func (dcr *ExchangeWallet) feeRate(confTarget uint64) (uint64, error) {
 	return 1 + uint64(atomsPerKB)/1000, nil // dcrPerKB * 1e8 / 1e3
 }
 
+// externalFeeEstimator gets the fee rate from the external API
+func externalFeeEstimator(ctx context.Context, net dex.Network, nb uint64) (float64, error) {
+	var url string
+	if net == dex.Testnet {
+		url = testnetExternalApiUrl
+	} else {
+		url = externalApiUrl
+	}
+	url = url + "/utils/estimatefee?nbBlocks=" + strconv.FormatUint(nb, 10)
+	ctx, cancel := context.WithTimeout(ctx, 4*time.Second)
+	defer cancel()
+	r, err := http.NewRequestWithContext(ctx, http.MethodGet, url, nil)
+	if err != nil {
+		return 0, err
+	}
+	httpResponse, err := client.Do(r)
+	if err != nil {
+		return 0, err
+	}
+	c := make(map[uint64]float64)
+	reader := io.LimitReader(httpResponse.Body, 1<<14)
+	err = json.NewDecoder(reader).Decode(&c)
+	httpResponse.Body.Close()
+	if err != nil {
+		return 0, err
+	}
+	estimatedFeeRate, ok := c[nb]
+	if !ok {
+		return 0, errors.New("no fee rate for requested number of blocks")
+	}
+	return estimatedFeeRate, nil
+}
+
 // targetFeeRateWithFallback attempts to get a fresh fee rate for the target
 // number of confirmations, but falls back to the suggestion or fallbackFeeRate
 // via feeRateWithFallback.

client/asset/interface.go

@@ -229,6 +229,8 @@ type WalletConfig struct {
 	// DataDir is a filesystem directory the the wallet may use for persistent
 	// storage.
 	DataDir string
+	// Network flags passed to the wallet representing which network to use.
+	Network dex.Network
 }
 
 // Wallet is a common interface to be implemented by cryptocurrency wallet

client/core/core.go

@@ -1914,6 +1914,7 @@ func (c *Core) loadWallet(dbWallet *db.Wallet) (*xcWallet, error) {
 			}
 		},
 		DataDir: c.assetDataDirectory(assetID),
+		Network: c.Network(),
 	}
 
 	walletCfg.Settings[asset.SpecialSettingActivelyUsed] =