wip: add approve filter (untested)

go.sum

@@ -267,8 +267,6 @@ github.com/gorilla/mux v1.8.0/go.mod h1:DVbg23sWSpFRCP0SfiEN6jmj59UnW/n46BH5rLB7
 github.com/gorilla/websocket v1.4.2 h1:+/TMaTYc4QFitKJxsQ7Yye35DkWvkdLcvGKqM+x0Ufc=
 github.com/gorilla/websocket v1.4.2/go.mod h1:YR8l580nyteQvAITg2hZ9XVh4b55+EU/adAjf1fMHhE=
 github.com/graph-gophers/graphql-go v1.3.0/go.mod h1:9CQHMSxwO4MprSdzoIEobiHpoLtHm77vfxsvsIN5Vuc=
-github.com/grassrootseconomics/celoutils v1.1.1 h1:REsndvfBkPN8UKOoQFNEGm/sCwKtTm+woYtgMl3bfZ0=
-github.com/grassrootseconomics/celoutils v1.1.1/go.mod h1:Uo5YRy6AGLAHDZj9jaOI+AWoQ1H3L0v79728pPMkm9Q=
 github.com/grassrootseconomics/celoutils v1.2.1 h1:ndM4h7Df0d57m2kdRXRStrnunqOL61wQ51rnOanX1KI=
 github.com/grassrootseconomics/celoutils v1.2.1/go.mod h1:Uo5YRy6AGLAHDZj9jaOI+AWoQ1H3L0v79728pPMkm9Q=
 github.com/grassrootseconomics/w3-celo-patch v0.2.0 h1:YqibbPzX0tQKmxU1nUGzThPKk/fiYeYZY6Aif3eyu8U=

internal/filter/approve_filter.go

@@ -0,0 +1,84 @@
+package filter
+
+import (
+	"context"
+	"math/big"
+
+	"github.com/celo-org/celo-blockchain/common"
+	"github.com/celo-org/celo-blockchain/common/hexutil"
+	"github.com/grassrootseconomics/celoutils"
+	"github.com/grassrootseconomics/cic-chain-events/internal/pub"
+	"github.com/grassrootseconomics/cic-chain-events/pkg/fetch"
+	"github.com/grassrootseconomics/w3-celo-patch"
+	"github.com/zerodha/logf"
+)
+
+type (
+	ApproveFilterOpts struct {
+		Logg logf.Logger
+		Pub  *pub.Pub
+	}
+
+	ApproveFilter struct {
+		logg logf.Logger
+		pub  *pub.Pub
+	}
+)
+
+const (
+	approveEventSubject = "CHAIN.approve"
+)
+
+var (
+	approveSig = w3.MustNewFunc("approve(address, uint256)", "bool")
+)
+
+func NewApproveFilter(o ApproveFilterOpts) Filter {
+	return &ApproveFilter{
+		logg: o.Logg,
+		pub:  o.Pub,
+	}
+}
+
+func (f *ApproveFilter) Execute(_ context.Context, transaction *fetch.Transaction) (bool, error) {
+	if len(transaction.InputData) < 10 {
+		return true, nil
+	}
+
+	if transaction.InputData[:10] == "0x095ea7b3" {
+		var (
+			address common.Address
+			value   big.Int
+		)
+
+		if err := approveSig.DecodeArgs(w3.B(transaction.InputData), &address, &value); err != nil {
+			return false, err
+		}
+
+		approveEvent := &pub.MinimalTxInfo{
+			Block:           transaction.Block.Number,
+			ContractAddress: celoutils.ChecksumAddress(transaction.To.Address),
+			Timestamp:       hexutil.MustDecodeUint64(transaction.Block.Timestamp),
+			To:              address.Hex(),
+			TxHash:          transaction.Hash,
+			TxIndex:         transaction.Index,
+			TXType:          "approve",
+		}
+
+		if transaction.Status == 1 {
+			approveEvent.Success = true
+		}
+
+		if err := f.pub.Publish(
+			approveEventSubject,
+			transaction.Hash,
+			approveEvent,
+		); err != nil {
+			return false, err
+		}
+
+		return true, nil
+	}
+
+	return true, nil
+}