vote-validator: Use shutdown context.

Using the shutdown context provided by the internal signal package means
vote-validator can exit cleanly if shutdown is requested by the user.

cmd/vote-validator/dcrdata.go

@@ -6,6 +6,7 @@ package main
 
 import (
 	"bytes"
+	"context"
 	"encoding/json"
 	"fmt"
 	"io"
@@ -46,7 +47,7 @@ type dcrdataClient struct {
 	URL string
 }
 
-func (d *dcrdataClient) txns(txnHashes []string, spends bool) ([]tx, error) {
+func (d *dcrdataClient) txns(ctx context.Context, txnHashes []string, spends bool) ([]tx, error) {
 	jsonData, err := json.Marshal(txns{
 		Transactions: txnHashes,
 	})
@@ -55,7 +56,7 @@ func (d *dcrdataClient) txns(txnHashes []string, spends bool) ([]tx, error) {
 	}
 
 	url := fmt.Sprintf("%s/api/txs?spends=%t", d.URL, spends)
-	request, err := http.NewRequest("POST", url, bytes.NewBuffer(jsonData))
+	request, err := http.NewRequestWithContext(ctx, "POST", url, bytes.NewBuffer(jsonData))
 	if err != nil {
 		return nil, err
 	}

cmd/vote-validator/main.go

@@ -5,6 +5,7 @@
 package main
 
 import (
+	"context"
 	"encoding/binary"
 	"encoding/hex"
 	"errors"
@@ -16,6 +17,7 @@ import (
 
 	"github.com/decred/vspd/database"
 	"github.com/decred/vspd/internal/config"
+	"github.com/decred/vspd/internal/signal"
 )
 
 const (
@@ -79,6 +81,8 @@ func run() int {
 		return 1
 	}
 
+	ctx := signal.ShutdownListener(log)
+
 	// Get all voted tickets from database.
 	dbTickets, err := vdb.GetVotedTickets()
 	if err != nil {
@@ -105,14 +109,22 @@ func run() int {
 	// Use dcrdata to get spender info for voted tickets (dcrd can't do this).
 	log.Infof("Getting vote info from %s", dcrdata.URL)
 	for i := 0; i < numTickets; i += chunkSize {
+		// Stop if shutdown requested.
+		if ctx.Err() != nil {
+			return 0
+		}
+
 		end := i + chunkSize
 		if end > numTickets {
 			end = numTickets
 		}
 
 		// Get the tx info for each ticket.
-		ticketTxns, err := dcrdata.txns(ticketHashes[i:end], true)
+		ticketTxns, err := dcrdata.txns(ctx, ticketHashes[i:end], true)
 		if err != nil {
+			if errors.Is(err, context.Canceled) {
+				return 0
+			}
 			log.Error(err)
 			return 1
 		}
@@ -125,8 +137,11 @@ func run() int {
 			mapSpenderToTicket[spenderHash] = txn.TxID
 		}
 
-		spenderTxns, err := dcrdata.txns(spenderHashes, false)
+		spenderTxns, err := dcrdata.txns(ctx, spenderHashes, false)
 		if err != nil {
+			if errors.Is(err, context.Canceled) {
+				return 0
+			}
 			log.Error(err)
 			return 1
 		}
@@ -193,6 +208,10 @@ func run() int {
 	}
 
 	for _, t := range sorted[0:cfg.ToCheck] {
+		// Stop if shutdown requested.
+		if ctx.Err() != nil {
+			return 0
+		}
 
 		if t.voteVersion != latestVoteVersion {
 			results.wrongVersion = append(results.wrongVersion, t)