chore: Fix linter findings for prealloc (part2) (#12242)

plugins/inputs/nfsclient/nfsclient.go

@@ -33,7 +33,7 @@ type NFSClient struct {
 func convertToUint64(line []string) ([]uint64, error) {
 	/* A "line" of input data (a pre-split array of strings) is
 	   processed one field at a time.  Each field is converted to
-	   an uint64 value, and appened to an array of return values.
+	   an uint64 value, and appended to an array of return values.
 	   On an error, check for ErrRange, and returns an error
 	   if found.  This situation indicates a pretty major issue in
 	   the /proc/self/mountstats file, and returning faulty data
@@ -41,12 +41,11 @@ func convertToUint64(line []string) ([]uint64, error) {
 	   whatever we got in the first place (probably 0).
 	   Yes, this is ugly. */
 
-	var nline []uint64
-
 	if len(line) < 2 {
-		return nline, nil
+		return nil, nil
 	}
 
+	nline := make([]uint64, 0, len(line[1:]))
 	// Skip the first field; it's handled specially as the "first" variable
 	for _, l := range line[1:] {
 		val, err := strconv.ParseUint(l, 10, 64)

plugins/inputs/procstat/procstat.go

@@ -412,14 +412,14 @@ func (p *Procstat) systemdUnitPIDs() []PidsTags {
 }
 
 func (p *Procstat) simpleSystemdUnitPIDs() ([]PID, error) {
-	var pids []PID
+	out, err := execCommand("systemctl", "show", p.SystemdUnit).Output()
-
-	cmd := execCommand("systemctl", "show", p.SystemdUnit)
-	out, err := cmd.Output()
 	if err != nil {
 		return nil, err
 	}
-	for _, line := range bytes.Split(out, []byte{'\n'}) {
+
+	lines := bytes.Split(out, []byte{'\n'})
+	pids := make([]PID, 0, len(lines))
+	for _, line := range lines {
 		kv := bytes.SplitN(line, []byte{'='}, 2)
 		if len(kv) != 2 {
 			continue
@@ -441,17 +441,17 @@ func (p *Procstat) simpleSystemdUnitPIDs() ([]PID, error) {
 }
 
 func (p *Procstat) cgroupPIDs() []PidsTags {
-	var pidTags []PidsTags
-
 	procsPath := p.CGroup
 	if procsPath[0] != '/' {
 		procsPath = "/sys/fs/cgroup/" + procsPath
 	}
+
 	items, err := filepath.Glob(procsPath)
 	if err != nil {
-		pidTags = append(pidTags, PidsTags{nil, nil, fmt.Errorf("glob failed '%s'", err)})
+		return []PidsTags{{nil, nil, fmt.Errorf("glob failed '%s'", err)}}
-		return pidTags
 	}
+
+	pidTags := make([]PidsTags, 0, len(items))
 	for _, item := range items {
 		pids, err := p.singleCgroupPIDs(item)
 		tags := map[string]string{"cgroup": p.CGroup, "cgroup_full": item}
@@ -462,8 +462,6 @@ func (p *Procstat) cgroupPIDs() []PidsTags {
 }
 
 func (p *Procstat) singleCgroupPIDs(path string) ([]PID, error) {
-	var pids []PID
-
 	ok, err := isDir(path)
 	if err != nil {
 		return nil, err
@@ -476,7 +474,10 @@ func (p *Procstat) singleCgroupPIDs(path string) ([]PID, error) {
 	if err != nil {
 		return nil, err
 	}
-	for _, pidBS := range bytes.Split(out, []byte{'\n'}) {
+
+	lines := bytes.Split(out, []byte{'\n'})
+	pids := make([]PID, 0, len(lines))
+	for _, pidBS := range lines {
 		if len(pidBS) == 0 {
 			continue
 		}

plugins/inputs/procstat/procstat_test.go

@@ -27,7 +27,7 @@ func mockExecCommand(arg0 string, args ...string) *exec.Cmd {
 	return cmd
 }
 func TestMockExecCommand(_ *testing.T) {
-	var cmd []string
+	var cmd []string //nolint:prealloc // Pre-allocated this slice would break the algorithm
 	for _, arg := range os.Args {
 		if arg == "--" {
 			cmd = []string{}

plugins/inputs/smart/smart.go

@@ -587,8 +587,7 @@ func (m *Smart) getVendorNVMeAttributes(acc telegraf.Accumulator, devices []stri
 }
 
 func getDeviceInfoForNVMeDisks(acc telegraf.Accumulator, devices []string, nvme string, timeout config.Duration, useSudo bool) []nvmeDevice {
-	var nvmeDevices []nvmeDevice
+	nvmeDevices := make([]nvmeDevice, 0, len(devices))
-
 	for _, device := range devices {
 		newDevice, err := gatherNVMeDeviceInfo(nvme, device, timeout, useSudo)
 		if err != nil {

plugins/inputs/snmp/snmp_mocks_test.go

@@ -25,7 +25,7 @@ func mockExecCommand(arg0 string, args ...string) *exec.Cmd {
 //
 // Idea based on https://github.com/golang/go/blob/7c31043/src/os/exec/exec_test.go#L568
 func TestMockExecCommand(_ *testing.T) {
-	var cmd []string
+	var cmd []string //nolint:prealloc // Pre-allocated this slice would break the algorithm
 	for _, arg := range os.Args {
 		if arg == "--" {
 			cmd = []string{}

plugins/inputs/sqlserver/sqlserver.go

@@ -179,11 +179,11 @@ func (s *SQLServer) initQueries() error {
 		}
 	}
 
-	var querylist []string
+	queryList := make([]string, 0, len(queries))
 	for query := range queries {
-		querylist = append(querylist, query)
+		queryList = append(queryList, query)
 	}
-	s.Log.Infof("Config: Effective Queries: %#v\n", querylist)
+	s.Log.Infof("Config: Effective Queries: %#v\n", queryList)
 
 	return nil
 }

plugins/inputs/tcp_listener/tcp_listener.go

@@ -133,10 +133,10 @@ func (t *TCPListener) Stop() {
 
 	// Close all open TCP connections
 	//  - get all conns from the t.conns map and put into slice
-	//  - this is so the forget() function doesnt conflict with looping
+	//  - this is so the forget() function doesn't conflict with looping
 	//    over the t.conns map
-	var conns []*net.TCPConn
 	t.cleanup.Lock()
+	conns := make([]*net.TCPConn, 0, len(t.conns))
 	for _, conn := range t.conns {
 		conns = append(conns, conn)
 	}

plugins/inputs/varnish/varnish.go

@@ -103,7 +103,7 @@ func (*Varnish) SampleConfig() string {
 }
 
 func (s *Varnish) Init() error {
-	var customRegexps []*regexp.Regexp
+	customRegexps := make([]*regexp.Regexp, 0, len(s.Regexps))
 	for _, re := range s.Regexps {
 		compiled, err := regexp.Compile(re)
 		if err != nil {

plugins/inputs/wireguard/wireguard.go

@@ -67,8 +67,6 @@ func (wg *Wireguard) Gather(acc telegraf.Accumulator) error {
 }
 
 func (wg *Wireguard) enumerateDevices() ([]*wgtypes.Device, error) {
-	var devices []*wgtypes.Device
-
 	// If no device names are specified, defer to the library to enumerate
 	// all of them
 	if len(wg.Devices) == 0 {
@@ -76,6 +74,7 @@ func (wg *Wireguard) enumerateDevices() ([]*wgtypes.Device, error) {
 	}
 
 	// Otherwise, explicitly populate only device names specified in config
+	devices := make([]*wgtypes.Device, 0, len(wg.Devices))
 	for _, name := range wg.Devices {
 		dev, err := wg.client.Device(name)
 		if err != nil {

plugins/outputs/azure_monitor/azure_monitor.go

@@ -277,7 +277,7 @@ func (a *AzureMonitor) Write(metrics []telegraf.Metric) error {
 		return nil
 	}
 
-	var body []byte
+	var body []byte //nolint:prealloc // There is no point in guessing the final capacity of this slice
 	for _, m := range azmetrics {
 		// Azure Monitor accepts new batches of points in new-line delimited
 		// JSON, following RFC 4288 (see https://github.com/ndjson/ndjson-spec).
@@ -364,8 +364,8 @@ func hashIDWithTagKeysOnly(m telegraf.Metric) uint64 {
 }
 
 func translate(m telegraf.Metric, prefix string) (*azureMonitorMetric, error) {
-	var dimensionNames []string
+	dimensionNames := make([]string, 0, len(m.TagList()))
-	var dimensionValues []string
+	dimensionValues := make([]string, 0, len(m.TagList()))
 	for _, tag := range m.TagList() {
 		// Azure custom metrics service supports up to 10 dimensions
 		if len(dimensionNames) >= 10 {

plugins/outputs/event_hubs/event_hubs.go

@@ -109,8 +109,7 @@ func (e *EventHubs) SetSerializer(serializer serializers.Serializer) {
 }
 
 func (e *EventHubs) Write(metrics []telegraf.Metric) error {
-	var events []*eventhub.Event
+	events := make([]*eventhub.Event, 0, len(metrics))
-
 	for _, metric := range metrics {
 		payload, err := e.serializer.Serialize(metric)
 

plugins/outputs/graylog/graylog.go

@@ -327,7 +327,6 @@ func (*Graylog) SampleConfig() string {
 }
 
 func (g *Graylog) Connect() error {
-	var writers []io.Writer
 	dialer := &net.Dialer{Timeout: time.Duration(g.Timeout)}
 
 	if len(g.Servers) == 0 {
@@ -339,6 +338,7 @@ func (g *Graylog) Connect() error {
 		return err
 	}
 
+	writers := make([]io.Writer, 0, len(g.Servers))
 	for _, server := range g.Servers {
 		w := newGelfWriter(gelfConfig{Endpoint: server}, dialer, tlsCfg)
 		err := w.Connect()

plugins/outputs/groundwork/groundwork.go

@@ -149,7 +149,7 @@ func (g *Groundwork) Write(metrics []telegraf.Metric) error {
 		})
 	}
 
-	var resources []transit.MonitoredResource
+	resources := make([]transit.MonitoredResource, 0, len(resourceToServicesMap))
 	for resourceName, services := range resourceToServicesMap {
 		resources = append(resources, transit.MonitoredResource{
 			BaseResource: transit.BaseResource{

plugins/outputs/iotdb/iotdb.go

@@ -158,12 +158,12 @@ func (s *IoTDB) convertTimestampOfMetric(m telegraf.Metric) (int64, error) {
 
 // convert Metrics to Records with tags
 func (s *IoTDB) convertMetricsToRecordsWithTags(metrics []telegraf.Metric) (*recordsWithTags, error) {
-	var deviceidList []string
+	timestampList := make([]int64, 0, len(metrics))
-	var measurementsList [][]string
+	deviceidList := make([]string, 0, len(metrics))
-	var valuesList [][]interface{}
+	measurementsList := make([][]string, 0, len(metrics))
-	var dataTypesList [][]client.TSDataType
+	valuesList := make([][]interface{}, 0, len(metrics))
-	var timestampList []int64
+	dataTypesList := make([][]client.TSDataType, 0, len(metrics))
-	var tagsList [][]*telegraf.Tag
+	tagsList := make([][]*telegraf.Tag, 0, len(metrics))
 
 	for _, metric := range metrics {
 		// write `metric` to the output sink here

plugins/outputs/loki/stream_test.go

@@ -3,8 +3,9 @@ package loki
 import (
 	"testing"
 
-	"github.com/influxdata/telegraf"
 	"github.com/stretchr/testify/require"
+
+	"github.com/influxdata/telegraf"
 )
 
 type tuple struct {
@@ -13,8 +14,7 @@ type tuple struct {
 
 func generateLabelsAndTag(tt ...tuple) (map[string]string, []*telegraf.Tag) {
 	labels := map[string]string{}
-	var tags []*telegraf.Tag
+	tags := make([]*telegraf.Tag, 0, len(tt))
-
 	for _, t := range tt {
 		labels[t.key] = t.value
 		tags = append(tags, &telegraf.Tag{Key: t.key, Value: t.value})

plugins/outputs/postgresql/table_manager.go

@@ -179,7 +179,7 @@ func (tm *TableManager) EnsureStructure(
 
 	// check that the missing columns are columns that can be added
 	addColumns := make([]utils.Column, 0, len(missingCols))
-	var invalidColumns []utils.Column
+	invalidColumns := make([]utils.Column, 0, len(missingCols))
 	for _, col := range missingCols {
 		if tm.validateColumnName(col.Name) {
 			addColumns = append(addColumns, col)

plugins/outputs/riemann/riemann.go

@@ -169,7 +169,7 @@ func (r *Riemann) tags(tags map[string]string) []string {
 	}
 
 	// otherwise add all values from telegraf tag key/value pairs
-	var keys []string
+	keys := make([]string, 0, len(tags))
 	for key := range tags {
 		keys = append(keys, key)
 	}

plugins/outputs/sql/sql.go

@@ -141,7 +141,7 @@ func (p *SQL) deriveDatatype(value interface{}) string {
 }
 
 func (p *SQL) generateCreateTable(metric telegraf.Metric) string {
-	var columns []string
+	columns := make([]string, 0, len(metric.TagList())+len(metric.FieldList())+1)
 	//  ##  {KEY_COLUMNS} is a comma-separated list of key columns (timestamp and tags)
 	//var pk []string
 
@@ -171,7 +171,8 @@ func (p *SQL) generateCreateTable(metric telegraf.Metric) string {
 }
 
 func (p *SQL) generateInsert(tablename string, columns []string) string {
-	var placeholders, quotedColumns []string
+	placeholders := make([]string, 0, len(columns))
+	quotedColumns := make([]string, 0, len(columns))
 	for _, column := range columns {
 		quotedColumns = append(quotedColumns, quoteIdent(column))
 	}

plugins/outputs/stackdriver/counter_cache.go

@@ -7,10 +7,10 @@ import (
 	"sync"
 	"time"
 
-	"github.com/influxdata/telegraf"
-
 	monpb "google.golang.org/genproto/googleapis/monitoring/v3"
 	tspb "google.golang.org/protobuf/types/known/timestamppb"
+
+	"github.com/influxdata/telegraf"
 )
 
 type counterCache struct {
@@ -87,7 +87,7 @@ func NewCounterCacheEntry(value *monpb.TypedValue, ts *tspb.Timestamp) *counterC
 
 func GetCounterCacheKey(m telegraf.Metric, f *telegraf.Field) string {
 	// normalize tag list to form a predictable key
-	var tags []string
+	tags := make([]string, 0, len(m.TagList()))
 	for _, t := range m.TagList() {
 		tags = append(tags, strings.Join([]string{t.Key, t.Value}, "="))
 	}