feat(lint): Fix golangci-lint warnings

This commit addresses a large number of golangci-lint warnings across
the codebase. The fixes span multiple categories of linters.

Key changes include:

- Error Handling: Ensured that all error return values are checked,
  particularly from `io.Copy` and `flag.Value.Set`.
- Code Formatting: Corrected formatting issues with `gofumpt`.
- Vet and Staticcheck:
    - Resolved a potential context leak in the GCS output by
      ensuring the cancel function is always called.
    - Replaced deprecated `io/ioutil` with `io` and `os` packages.
    - Replaced deprecated `zap.OnFatal` with `zap.WithFatalHook`.
    - Fixed an issue in TCP and TLS outputs where the write buffer was being
      modified, which is unsafe. A new buffer is now used.
    - Simplified various struct field selectors and boolean expressions.
- Revive Linter:
    - Added comments to numerous exported functions, types, and methods to improve documentation.
    - Removed unused function parameters and variables.
    - Corrected function signatures to place `context.Context` as the first argument.
- Code Organization:
    - Added package-level comments to all packages.
    - Renamed the `internal/output/tls` and `internal/output/udp` packages to match their dir names.
    - Added go-licenser and golangci-lint as go.mod tool dependencies. Removed tools.go.

The only remaining linter warning is for the TODO in the udp output.

Author: andrewkroh

.changelog/158.txt

@@ -0,0 +1,7 @@
+```release-note:bug
+Fixes a bug in the webhook output where an error when reading the response body was ignored.
+```
+
+```release-note:bug
+Resolved a potential context leak in the GCS output by ensuring the cancel function is always called.
+```

.golangci.yml

@@ -63,6 +63,7 @@ linters:
     staticcheck:
       checks:
         - all
+        - '-QF1008' # https://staticcheck.dev/docs/checks/#QF1008
   exclusions:
     generated: lax
     presets:

Makefile

@@ -1,18 +1,21 @@
 LICENSE := ASL2-Short
 VERSION ?= local
 
-GOIMPORTS := go run golang.org/x/tools/cmd/goimports
+GOLANGCI_LINT:= go run github.com/golangci/golangci-lint/v2/cmd/golangci-lint
 GOLICENSER := go run github.com/elastic/go-licenser
 
 check-fmt:
 	@${GOLICENSER} -d -license ${LICENSE}
-	@${GOIMPORTS} -l -e -local github.com/elastic . | read && echo "Code differs from gofmt's style. Run 'gofmt -w .'" 1>&2 && exit 1 || true
+	@${GOLANGCI_LINT} fmt --diff > /dev/null || (echo "Please run 'make fmt' to fix the formatting issues" 1>&2 && exit 1)
 
 docker:
 	docker build -t docker.elastic.co/observability/stream:${VERSION} .
 
 fmt:
 	${GOLICENSER} -license ${LICENSE}
-	${GOIMPORTS} -l -w -local github.com/elastic .
+	${GOLANGCI_LINT} fmt ./...
 
-.PHONY: check-fmt docker fmt
+lint:
+	@${GOLANGCI_LINT} run ./...
+
+.PHONY: check-fmt docker fmt lint

go.mod

@@ -2,6 +2,9 @@
 // Elasticsearch B.V. licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information.
 
+// Package cmdutil provides utility functions and argument validators
+// to facilitate the creation and validation of CLI command arguments
+// when using the spf13/cobra library.
 package cmdutil
 
 import (
@@ -42,6 +45,10 @@ func RegularFiles(_ *cobra.Command, args []string) error {
 	return nil
 }
 
+// ExpandGlobPatternsFromArgs expands each argument in args as a glob pattern,
+// returning a slice containing all matching file paths. If any pattern is
+// invalid, an error is returned. Patterns that do not match any files are
+// silently ignored.
 func ExpandGlobPatternsFromArgs(args []string) ([]string, error) {
 	var paths []string
 	for _, pat := range args {

go.sum

@@ -26,14 +26,15 @@ func newHTTPServerRunner(options *httpserver.Options, logger *zap.Logger) *cobra
 		},
 	}
 
-	r.cmd.RunE = func(_ *cobra.Command, args []string) error {
+	r.cmd.RunE = func(_ *cobra.Command, _ []string) error {
 		r.logger = logger.Sugar().With("address", options.Addr)
 		return r.Run()
 	}
 
 	return r.cmd
 }
 
+// Run executes the http-server command.
 func (r *httpServerRunner) Run() error {
 	r.logger.Debug("mock server running...")
 	server, err := httpserver.New(r.opts, r.logger)

internal/cmdutil/validate.go

@@ -39,8 +39,9 @@ func newLogRunner(options *output.Options, logger *zap.Logger) *cobra.Command {
 	return r.cmd
 }
 
+// Run executes the log command.
 func (r *logRunner) Run(args []string) error {
-	out, err := output.Initialize(r.out, r.logger, r.cmd.Context())
+	out, err := output.Initialize(r.cmd.Context(), r.out, r.logger)
 	if err != nil {
 		return err
 	}

internal/command/httpserver.go

@@ -38,8 +38,9 @@ func newPCAPRunner(options *output.Options, logger *zap.Logger) *cobra.Command {
 	return r.cmd
 }
 
+// Run executes the pcap command.
 func (r *pcapRunner) Run(files []string) error {
-	out, err := output.Initialize(r.out, r.logger, r.cmd.Context())
+	out, err := output.Initialize(r.cmd.Context(), r.out, r.logger)
 	if err != nil {
 		return err
 	}

internal/command/log.go

@@ -2,6 +2,10 @@
 // Elasticsearch B.V. licenses this file to you under the Apache 2.0 License.
 // See the LICENSE file in the project root for more information.
 
+// Package command provides the CLI interface and subcommands for the stream
+// utility. It defines the root command and all supported subcommands,
+// configuring command-line flags, argument validation, and the main entry point
+// for invoking stream's features.
 package command
 
 import (
@@ -38,6 +42,8 @@ import (
 	_ "github.com/elastic/stream/internal/output/webhook"
 )
 
+// Execute calls ExecuteContext with a context that is cancelled when
+// SIGINT is received.
 func Execute() error {
 	c := make(chan os.Signal, 1)
 	signal.Notify(c, os.Interrupt)
@@ -50,6 +56,9 @@ func Execute() error {
 	return ExecuteContext(ctx)
 }
 
+// ExecuteContext executes the stream command. It sets up the command-line
+// flags and initializes them with data from environment variables, before
+// executing the command.
 func ExecuteContext(ctx context.Context) error {
 	logger, err := log.NewLogger()
 	if err != nil {
@@ -97,10 +106,10 @@ func ExecuteContext(ctx context.Context) error {
 	rootCmd.PersistentFlags().StringVar(&opts.KafkaOptions.Topic, "kafka-topic", "test", "Kafka topic name")
 
 	// GCS output flags.
-	rootCmd.PersistentFlags().StringVar(&opts.GcsOptions.Bucket, "gcs-bucket", "testbucket", "GCS Bucket name")
-	rootCmd.PersistentFlags().StringVar(&opts.GcsOptions.Object, "gcs-object", "testobject", "GCS Object name")
-	rootCmd.PersistentFlags().StringVar(&opts.GcsOptions.ObjectContentType, "gcs-content-type", "application/json", "The Content type of the object to be uploaded to GCS.")
-	rootCmd.PersistentFlags().StringVar(&opts.GcsOptions.ProjectID, "gcs-projectid", "testproject", "GCS Project name")
+	rootCmd.PersistentFlags().StringVar(&opts.GCSOptions.Bucket, "gcs-bucket", "testbucket", "GCS Bucket name")
+	rootCmd.PersistentFlags().StringVar(&opts.GCSOptions.Object, "gcs-object", "testobject", "GCS Object name")
+	rootCmd.PersistentFlags().StringVar(&opts.GCSOptions.ObjectContentType, "gcs-content-type", "application/json", "The Content type of the object to be uploaded to GCS.")
+	rootCmd.PersistentFlags().StringVar(&opts.GCSOptions.ProjectID, "gcs-projectid", "testproject", "GCS Project name")
 
 	// Lumberjack output flags.
 	rootCmd.PersistentFlags().BoolVar(&opts.LumberjackOptions.ParseJSON, "lumberjack-parse-json", false, "Parse the input data as JSON and send the structured data as a Lumberjack batch.")
@@ -122,20 +131,20 @@ func ExecuteContext(ctx context.Context) error {
 	rootCmd.AddCommand(versionCmd)
 
 	// Add common start-up delay logic.
-	rootCmd.PersistentPreRunE = func(cmd *cobra.Command, args []string) error {
+	rootCmd.PersistentPreRunE = func(cmd *cobra.Command, _ []string) error {
 		return multierr.Combine(
-			waitForStartSignal(&opts, cmd.Context(), logger),
-			waitForDelay(&opts, cmd.Context(), logger),
+			waitForStartSignal(cmd.Context(), &opts, logger),
+			waitForDelay(cmd.Context(), &opts, logger),
 		)
 	}
 
 	// Automatically set flags based on environment variables.
-	rootCmd.PersistentFlags().VisitAll(setFlagFromEnv)
+	rootCmd.PersistentFlags().VisitAll(setFlagFromEnv(logger))
 
 	return rootCmd.ExecuteContext(ctx)
 }
 
-func waitForStartSignal(opts *output.Options, parent context.Context, logger *zap.Logger) error {
+func waitForStartSignal(ctx context.Context, opts *output.Options, logger *zap.Logger) error {
 	if opts.StartSignal == "" {
 		return nil
 	}
@@ -147,30 +156,34 @@ func waitForStartSignal(opts *output.Options, parent context.Context, logger *za
 
 	// Wait for the signal or the command context to be done.
 	logger.Sugar().Infow("Waiting for signal.", "start-signal", opts.StartSignal)
-	startCtx, _ := osctx.WithSignal(parent, os.Signal(num))
+	startCtx, _ := osctx.WithSignal(ctx, os.Signal(num))
 	<-startCtx.Done()
 	return nil
 }
 
-func waitForDelay(opts *output.Options, parent context.Context, logger *zap.Logger) error {
+func waitForDelay(ctx context.Context, opts *output.Options, logger *zap.Logger) error {
 	if opts.Delay <= 0 {
 		return nil
 	}
 
 	logger.Sugar().Infow("Delaying connection.", "delay", opts.Delay)
-	if err := timed.Wait(parent, opts.Delay); err != nil {
+	if err := timed.Wait(ctx, opts.Delay); err != nil {
 		return fmt.Errorf("delay waiting period was interrupted: %w", err)
 	}
 	return nil
 }
 
-func setFlagFromEnv(flag *pflag.Flag) {
-	envVar := strings.ToUpper(flag.Name)
-	envVar = strings.ReplaceAll(envVar, "-", "_")
-	envVar = "STREAM_" + envVar
-
-	flag.Usage = fmt.Sprintf("%v [env %v]", flag.Usage, envVar)
-	if value := os.Getenv(envVar); value != "" {
-		flag.Value.Set(value)
+func setFlagFromEnv(l *zap.Logger) func(*pflag.Flag) {
+	return func(flag *pflag.Flag) {
+		envVar := strings.ToUpper(flag.Name)
+		envVar = strings.ReplaceAll(envVar, "-", "_")
+		envVar = "STREAM_" + envVar
+
+		flag.Usage = fmt.Sprintf("%v [env %v]", flag.Usage, envVar)
+		if value := os.Getenv(envVar); value != "" {
+			if err := flag.Value.Set(value); err != nil {
+				l.Error("Failed to set flag from env", zap.String("env", envVar), zap.Error(err))
+			}
+		}
 	}
 }