perf: avoid string concatenation in loops (#7572)

* perf: avoid string concatenation in loops

Apply perfpsrint linter

Signed-off-by: Philippe Antoine <contact@catenacyber.fr>

* ci: enable perfsprint

Signed-off-by: Philippe Antoine <contact@catenacyber.fr>

---------

Signed-off-by: Philippe Antoine <contact@catenacyber.fr>

.golangci.yml

@@ -15,6 +15,7 @@ linters:
     - intrange
     - nakedret
     - nolintlint
+    - perfsprint
     - prealloc
     - protogetter
     - staticcheck
@@ -31,10 +32,17 @@ linters:
       - common-false-positives
       - legacy
       - std-error-handling
+    rules:
+      # Exclude some linters from running on tests files.
+      - path: _test\.go
+        linters:
+          - perfsprint
   settings:
     govet:
       enable:
         - nilness
+    perfsprint:
+      error-format: false
     revive:
       rules:
         - name: blank-imports

core/dnsserver/onstartup.go

@@ -4,6 +4,7 @@ import (
 	"fmt"
 	"regexp"
 	"sort"
+	"strings"
 
 	"github.com/coredns/coredns/plugin/pkg/dnsutil"
 )
@@ -22,8 +23,6 @@ func checkZoneSyntax(zone string) bool {
 // grpc://example.com.:1055
 // example.com.:1053 on 127.0.0.1
 func startUpZones(protocol, addr string, zones map[string][]*Config) string {
-	s := ""
-
 	keys := make([]string, len(zones))
 	i := 0
 
@@ -33,25 +32,26 @@ func startUpZones(protocol, addr string, zones map[string][]*Config) string {
 	}
 	sort.Strings(keys)
 
+	var sb strings.Builder
 	for _, zone := range keys {
 		if !checkZoneSyntax(zone) {
-			s += fmt.Sprintf("Warning: Domain %q does not follow RFC1035 preferred syntax\n", zone)
+			sb.WriteString(fmt.Sprintf("Warning: Domain %q does not follow RFC1035 preferred syntax\n", zone))
 		}
 		// split addr into protocol, IP and Port
 		_, ip, port, err := SplitProtocolHostPort(addr)
 
 		if err != nil {
 			// this should not happen, but we need to take care of it anyway
-			s += fmt.Sprintln(protocol + zone + ":" + addr)
+			sb.WriteString(fmt.Sprintln(protocol + zone + ":" + addr))
 			continue
 		}
 		if ip == "" {
-			s += fmt.Sprintln(protocol + zone + ":" + port)
+			sb.WriteString(fmt.Sprintln(protocol + zone + ":" + port))
 			continue
 		}
 		// if the server is listening on a specific address let's make it visible in the log,
 		// so one can differentiate between all active listeners
-		s += fmt.Sprintln(protocol + zone + ":" + port + " on " + ip)
+		sb.WriteString(fmt.Sprintln(protocol + zone + ":" + port + " on " + ip))
 	}
-	return s
+	return sb.String()
 }

plugin/auto/regexp.go

@@ -1,5 +1,9 @@
 package auto
 
+import (
+	"strings"
+)
+
 // rewriteToExpand rewrites our template string to one that we can give to regexp.ExpandString. This basically
 // involves prefixing any '{' with a '$'.
 func rewriteToExpand(s string) string {
@@ -7,14 +11,13 @@ func rewriteToExpand(s string) string {
 	// Also wasteful as we build the string with +=. This is OKish
 	// as we do this during config parsing.
 
-	copy := ""
-
+	var copySb strings.Builder
 	for _, c := range s {
 		if c == '{' {
-			copy += "$"
+			copySb.WriteString("$")
 		}
-		copy += string(c)
+		copySb.WriteString(string(c))
 	}
 
-	return copy
+	return copySb.String()
 }

plugin/pkg/doh/doh.go

@@ -29,7 +29,7 @@ func NewRequest(method, url string, m *dns.Msg) (*http.Request, error) {
 	}
 
 	if !strings.HasPrefix(url, "http://") && !strings.HasPrefix(url, "https://") {
-		url = fmt.Sprintf("https://%s", url)
+		url = "https://" + url
 	}
 
 	switch method {

plugin/route53/route53.go

@@ -171,14 +171,14 @@ const escapeSeq = "\\"
 //	`\\052.example.com.` -> `*.example.com`
 //	`\\137.example.com.` -> error ('_' is not valid)
 func maybeUnescape(s string) (string, error) {
-	var out string
+	var outSb strings.Builder
 	for {
 		i := strings.Index(s, escapeSeq)
 		if i < 0 {
-			return out + s, nil
+			return outSb.String() + s, nil
 		}
 
-		out += s[:i]
+		outSb.WriteString(s[:i])
 
 		li, ri := i+len(escapeSeq), i+len(escapeSeq)+3
 		if ri > len(s) {
@@ -196,7 +196,7 @@ func maybeUnescape(s string) (string, error) {
 		case r >= rune('a') && r <= rune('z'): // Route53 converts everything to lowercase.
 		case r >= rune('0') && r <= rune('9'):
 		case r == rune('*'):
-			if out != "" {
+			if outSb.Len() != 0 {
 				return "", errors.New("`*' only supported as wildcard (leftmost label)")
 			}
 		case r == rune('-'):
@@ -205,7 +205,7 @@ func maybeUnescape(s string) (string, error) {
 			return "", fmt.Errorf("invalid character: %s%#03o", escapeSeq, r)
 		}
 
-		out += string(r)
+		outSb.WriteString(string(r))
 
 		s = s[i+len(escapeSeq)+3:]
 	}

plugin/route53/setup.go

@@ -127,7 +127,7 @@ func setup(c *caddy.Controller) error {
 					refreshStr := c.Val()
 					_, err := strconv.Atoi(refreshStr)
 					if err == nil {
-						refreshStr = fmt.Sprintf("%ss", c.Val())
+						refreshStr = c.Val() + "s"
 					}
 					refresh, err = time.ParseDuration(refreshStr)
 					if err != nil {

plugin/sign/keys.go

@@ -111,9 +111,10 @@ func keyTag(ps []Pair) string {
 	if len(ps) == 0 {
 		return ""
 	}
-	s := ""
+	var sb strings.Builder
 	for _, p := range ps {
-		s += strconv.Itoa(int(p.KeyTag)) + ","
+		sb.WriteString(strconv.Itoa(int(p.KeyTag)) + ",")
 	}
+	s := sb.String()
 	return s[:len(s)-1]
 }

plugin/test/scrape.go

@@ -157,14 +157,14 @@ func newMetricFamily(dtoMF *dto.MetricFamily) *MetricFamily {
 			mf.Metrics[i] = summary{
 				Labels:    makeLabels(m),
 				Quantiles: makeQuantiles(m),
-				Count:     fmt.Sprint(m.GetSummary().GetSampleCount()),
+				Count:     strconv.FormatUint(m.GetSummary().GetSampleCount(), 10),
 				Sum:       fmt.Sprint(m.GetSummary().GetSampleSum()),
 			}
 		} else if dtoMF.GetType() == dto.MetricType_HISTOGRAM {
 			mf.Metrics[i] = histogram{
 				Labels:  makeLabels(m),
 				Buckets: makeBuckets(m),
-				Count:   fmt.Sprint(m.GetHistogram().GetSampleCount()),
+				Count:   strconv.FormatUint(m.GetHistogram().GetSampleCount(), 10),
 				Sum:     fmt.Sprint(m.GetSummary().GetSampleSum()),
 			}
 		} else {
@@ -209,7 +209,7 @@ func makeQuantiles(m *dto.Metric) map[string]string {
 func makeBuckets(m *dto.Metric) map[string]string {
 	result := map[string]string{}
 	for _, b := range m.GetHistogram().GetBucket() {
-		result[fmt.Sprint(b.GetUpperBound())] = fmt.Sprint(b.GetCumulativeCount())
+		result[fmt.Sprint(b.GetUpperBound())] = strconv.FormatUint(b.GetCumulativeCount(), 10)
 	}
 	return result
 }