test: Improve layout of helper binaries

This patch moves the test helper binaries to a "one directory per
helper" layout, and also makes them to be ignored in the coverage build
instead of all builds.

With this change, "go build ./..." will build all binaries including the
test helpers, which helps make sure that module manage automation also
considers them. In particular, this makes "go mod tidy" work fine.

test/util/loadgen/loadgen.go

@@ -0,0 +1,208 @@
+//go:build !coverage
+// +build !coverage
+
+// SMTP load generator, for testing purposes.
+package main
+
+import (
+	"flag"
+	"net"
+	"net/http"
+	"net/textproto"
+	"runtime"
+	"sync"
+	"time"
+
+	_ "net/http/pprof"
+
+	"golang.org/x/net/trace"
+
+	"blitiri.com.ar/go/chasquid/internal/smtp"
+	"blitiri.com.ar/go/log"
+)
+
+var (
+	addr = flag.String("addr", "",
+		"server address")
+	httpAddr = flag.String("http_addr", "localhost:8011",
+		"monitoring HTTP server listening address")
+	parallel = flag.Int("parallel", 0,
+		"how many sending loops to run in parallel")
+	runFor = flag.Duration("run_for", 0,
+		"how long to run for (0 = forever)")
+	wait = flag.Bool("wait", false,
+		"don't exit after --run_for has lapsed")
+	noop = flag.Bool("noop", false,
+		"don't send an email, just connect and run a NOOP")
+)
+
+var (
+	host string
+	exit bool
+
+	globalCount   int64 = 0
+	globalRuntime time.Duration
+	globalMu      = &sync.Mutex{}
+)
+
+func main() {
+	var err error
+
+	flag.Parse()
+	log.Init()
+
+	host, _, err = net.SplitHostPort(*addr)
+	if err != nil {
+		log.Fatalf("failed to split --addr=%q: %v", *addr, err)
+	}
+
+	if *wait {
+		go http.ListenAndServe(*httpAddr, nil)
+		log.Infof("monitoring address: http://%v/debug/requests?fam=one&b=11",
+			*httpAddr)
+	}
+
+	if *parallel == 0 {
+		*parallel = runtime.GOMAXPROCS(0)
+	}
+
+	lt := "full"
+	if *noop {
+		lt = "noop"
+	}
+
+	log.Infof("launching %d %s sending loops in parallel", *parallel, lt)
+	for i := 0; i < *parallel; i++ {
+		go serial(i)
+	}
+
+	var totalCount int64
+	var totalRuntime time.Duration
+	start := time.Now()
+	for range time.Tick(1 * time.Second) {
+		globalMu.Lock()
+		totalCount += globalCount
+		totalRuntime += globalRuntime
+		count := globalCount
+		runtime := globalRuntime
+		globalCount = 0
+		globalRuntime = 0
+		globalMu.Unlock()
+
+		if count == 0 {
+			log.Infof("0 ops")
+		} else {
+			log.Infof("%d ops, %v /op", count,
+				time.Duration(runtime.Nanoseconds()/count).Truncate(time.Microsecond))
+		}
+
+		if *runFor > 0 && time.Since(start) > *runFor {
+			exit = true
+			break
+		}
+	}
+
+	end := time.Now()
+	window := end.Sub(start)
+	log.Infof("total: %d ops, %v wall, %v run",
+		totalCount,
+		window.Truncate(time.Millisecond),
+		totalRuntime.Truncate(time.Millisecond))
+
+	avgLat := time.Duration(totalRuntime.Nanoseconds() / totalCount)
+	log.Infof("avg: %v /op, %.0f ops/s",
+		avgLat.Truncate(time.Microsecond),
+		float64(totalCount)/window.Seconds(),
+	)
+
+	if *wait {
+		for {
+			time.Sleep(24 * time.Hour)
+		}
+	}
+}
+
+func serial(id int) {
+	var count int64
+	start := time.Now()
+	for {
+		count += 1
+		err := one()
+		if err != nil {
+			log.Fatalf("%v", err)
+		}
+
+		if count == 5 {
+			globalMu.Lock()
+			globalCount += count
+			globalRuntime += time.Since(start)
+			globalMu.Unlock()
+			count = 0
+			start = time.Now()
+
+			if exit {
+				return
+			}
+		}
+	}
+}
+
+func one() error {
+	tr := trace.New("one", *addr)
+	defer tr.Finish()
+
+	conn, err := net.Dial("tcp", *addr)
+	if err != nil {
+		return err
+	}
+	defer conn.Close()
+
+	client, err := smtp.NewClient(conn, host)
+	if err != nil {
+		return err
+	}
+	defer client.Close()
+
+	if *noop {
+		err = client.Noop()
+		if err != nil {
+			return err
+		}
+	} else {
+		err = client.MailAndRcpt("test@test", "null@testserver")
+		if err != nil {
+			return err
+		}
+
+	retry:
+		w, err := client.Data()
+		if err != nil {
+			return err
+		}
+		_, err = w.Write(body)
+		if err != nil {
+			return err
+		}
+		err = w.Close()
+		if err != nil {
+			// If we are sending too fast we might hit chasquid's queue size
+			// limit. In that case, wait and try again.
+			// We detect it with error code 451 which is used for this
+			// situation.
+			if terr, ok := err.(*textproto.Error); ok {
+				if terr.Code == 451 {
+					time.Sleep(10 * time.Millisecond)
+					goto retry
+				}
+			}
+			return err
+		}
+	}
+
+	return nil
+}
+
+var body = []byte(`Subject: Load test
+
+This is the body of the load test email.
+`)