Add current gas price resolver to API server.

Makefile

@@ -0,0 +1,26 @@
+# --------------------------------------------------------------------------
+# Makefile for the Fantom API GaphQL Server
+#
+# v0.1 (2020/03/09)  - Initial version, base API server build.
+# (c) Fantom Foundation, 2020
+# --------------------------------------------------------------------------
+
+# project related vars
+PROJECT := $(shell basename "$(PWD)")
+
+# go related vars
+GOBASE := $(shell pwd)
+GOBIN=$(CURDIR)/build
+
+## server: Make the API server as bin/frd
+server:
+	go build -o $(GOBIN)/apiserver ./cmd/apiserver
+
+.PHONY: help
+all: help
+help: Makefile
+	@echo
+	@echo "Choose a make command in "$(PROJECT)":"
+	@echo
+	@sed -n 's/^##//p' $< | column -t -s ':' |  sed -e 's/^/ /'
+	@echo

internal/graphql/resolvers/root.go

@@ -81,6 +81,9 @@ type ApiResolver interface {
 	// Price resolves price details of the Opera blockchain token for the given target symbols.
 	Price(*struct{ To string }) (types.Price, error)
 
+	// GasPrice resolves the current amount of WEI for single Gas.
+	GasPrice() (hexutil.Uint64, error)
+
 	// Close terminates resolver broadcast management.
 	Close()
 }

internal/graphql/resolvers/util.go → internal/graphql/resolvers/utils.go

@@ -5,6 +5,7 @@ import (
 	"crypto/rand"
 	"fantom-api-graphql/internal/types"
 	"fmt"
+	"github.com/ethereum/go-ethereum/common/hexutil"
 	"io"
 )
 
@@ -13,6 +14,11 @@ func (rs *rootResolver) Price(args *struct{ To string }) (types.Price, error) {
 	return rs.repo.Price(args.To)
 }
 
+// GasPrice resolves the current amount of WEI for single Gas.
+func (rs *rootResolver) GasPrice() (hexutil.Uint64, error) {
+	return rs.repo.GasPrice()
+}
+
 // uuid generates new random subscription UUID
 func uuid() (string, error) {
 	// prep container

internal/graphql/schema/bundle.go

@@ -1,6 +1,6 @@
 package gqlschema
 
-// Auto generated GraphQL schema bundle; created 2020-03-20 23:21
+// Auto generated GraphQL schema bundle; created 2020-04-16 18:29
 const schema = `
 # StakerInfo represents extended staker information from smart contract.
 type StakerInfo {
@@ -474,6 +474,9 @@ type Query {
     "Get the details of a delegator by it's address."
     delegation(address:Address!): Delegator
 
+    "Returns the current price per gas in WEI units."
+    gasPrice: Long!
+
     "Get price details of the Opera blockchain token for the given target symbols."
     price(to:String!):Price!
 }

internal/graphql/schema/definition/schema.graphql

@@ -60,6 +60,9 @@ type Query {
     "Get the details of a delegator by it's address."
     delegation(address:Address!): Delegator
 
+    "Returns the current price per gas in WEI units."
+    gasPrice: Long!
+
     "Get price details of the Opera blockchain token for the given target symbols."
     price(to:String!):Price!
 }

internal/repository/repository.go

@@ -116,6 +116,9 @@ type Repository interface {
 	// Price returns a price information for the given target symbol.
 	Price(sym string) (types.Price, error)
 
+	// GasPrice resolves the current amount of WEI for single Gas.
+	GasPrice() (hexutil.Uint64, error)
+
 	// FtmConnection returns open connection to Opera/Lachesis full node.
 	FtmConnection() *ftm.Client
 

internal/repository/rpc/utils.go

@@ -0,0 +1,40 @@
+/*
+Package rpc implements bridge to Lachesis full node API interface.
+
+We recommend using local IPC for fast and the most efficient inter-process communication between the API server
+and an Opera/Lachesis node. Any remote RPC connection will work, but the performance may be significantly degraded
+by extra networking overhead of remote RPC calls.
+
+You should also consider security implications of opening Lachesis RPC interface for a remote access.
+If you considering it as your deployment strategy, you should establish encrypted channel between the API server
+and Lachesis RPC interface with connection limited to specified endpoints.
+
+We strongly discourage opening Lachesis RPC interface for unrestricted Internet access.
+*/
+package rpc
+
+import "github.com/ethereum/go-ethereum/common/hexutil"
+
+// GasPrice resolves the current amount of WEI for single Gas.
+func (ftm *FtmBridge) GasPrice() (hexutil.Uint64, error) {
+	// keep track of the operation
+	ftm.log.Debugf("checking current gas price")
+
+	// call for data
+	var price hexutil.Big
+	err := ftm.rpc.Call(&price, "ftm_gasPrice")
+	if err != nil {
+		ftm.log.Error("current gas price could not be obtained")
+		return hexutil.Uint64(0), err
+	}
+
+	// if the price safely within the range
+	if !price.ToInt().IsUint64() {
+		ftm.log.Error("current gas price is too high and can not be extracted")
+		return hexutil.Uint64(0), err
+	}
+
+	// inform and return
+	ftm.log.Debugf("current gas price is %d", uint64(price.ToInt().Uint64()))
+	return hexutil.Uint64(price.ToInt().Uint64()), nil
+}

internal/repository/utils.go

@@ -25,6 +25,11 @@ const (
 	priceApiTargetSymbolVar = "tsyms="
 )
 
+// GasPrice resolves the current amount of WEI for single Gas.
+func (p *proxy) GasPrice() (hexutil.Uint64, error) {
+	return p.rpc.GasPrice()
+}
+
 // Price returns a price information for the given target symbol.
 func (p *proxy) Price(sym string) (types.Price, error) {
 	// inform what we do