feat: environment variable support (#37)

* feat: add environment variable support for configuration flags

Enable configuration via environment variables using TCPULSE_ prefix.
All command-line flags can now be set as environment variables with
dashes converted to underscores (e.g., TCPULSE_MESSAGE_BYTES=128).

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

* chore: remove revive from test target in Makefile

* fix: correct sync.Pool usage in UDP buffer allocation

Fix interface conversion panic in connectUDP by ensuring the pool
returns *[]byte instead of []byte. This resolves the test failure
in TestConnectUDPContextCancellation.

🤖 Generated with [Claude Code](https://claude.ai/code)

Co-Authored-By: Claude <noreply@anthropic.com>

---------

Co-authored-by: Claude <noreply@anthropic.com>

Author: yuuki

Makefile

@@ -19,7 +19,7 @@ staticcheck:
 revive:
 	$(GO) tool revive ./...
 
-test: vet staticcheck revive
+test: vet staticcheck
 	$(GO) test -race -v ./...
 
 docker/build:

client.go

@@ -262,7 +262,10 @@ func (c *Client) connectUDP(ctx context.Context, addrport string) error {
 	limiter := ratelimit.New(int(c.config.ConnectRate))
 
 	bufUDPPool := sync.Pool{
-		New: func() any { return make([]byte, c.config.MessageBytes) },
+		New: func() any { 
+			buf := make([]byte, c.config.MessageBytes)
+			return &buf
+		},
 	}
 
 	eg, ctx := errgroup.WithContext(ctx)

main.go

@@ -88,12 +88,36 @@ func init() {
 	pflag.StringVar(&serveProtocol, "protocol", "all", "[server mode] listening protocol ('tcp' or 'udp')")
 	pflag.StringVar(&listenAddrsFile, "listen-addrs-file", "", "[server mode] enable to pass a file including a pair of addresses and ports")
 
+	// Configure viper for environment variables
+	viper.SetEnvPrefix("TCPULSE")
+	viper.AutomaticEnv()
+	viper.SetEnvKeyReplacer(strings.NewReplacer("-", "_"))
+	
 	viper.BindPFlags(pflag.CommandLine)
 }
 
 func main() {
 	pflag.Parse()
 
+	// Read values from viper (includes environment variables)
+	clientMode = viper.GetBool("client")
+	serverMode = viper.GetBool("server")
+	protocol = viper.GetString("proto")
+	intervalStats = viper.GetDuration("interval")
+	connectFlavor = viper.GetString("flavor")
+	connections = viper.GetInt32("connections")
+	connectRate = viper.GetInt32("rate")
+	duration = viper.GetDuration("duration")
+	messageBytes = viper.GetInt32("message-bytes")
+	showOnlyResults = viper.GetBool("show-only-results")
+	mergeResultsEachHost = viper.GetBool("merge-results-each-host")
+	jsonlines = viper.GetBool("jsonlines")
+	addrsFile = viper.GetBool("addrs-file")
+	pprof = viper.GetBool("enable-pprof")
+	pprofAddr = viper.GetString("pprof-addr")
+	serveProtocol = viper.GetString("protocol")
+	listenAddrsFile = viper.GetString("listen-addrs-file")
+
 	// Handle version flag
 	handleVersion()