test: Add stress tests

This patch introduces stress tests, which put load on the daemon to help
sanity check its behaviour under stress.

They are separate from the existing integration tests, which focus on
correctness.

Two tests are included here: a load test, which sends emails repeatedly;
and a connection test which opens as many conections as possible.

test/util/conngen.go

@@ -0,0 +1,109 @@
+// +build ignore
+
+// SMTP connection generator, for testing purposes.
+package main
+
+import (
+	"flag"
+	"net"
+	"net/http"
+	"net/smtp"
+	"time"
+
+	"golang.org/x/net/trace"
+
+	_ "net/http/pprof"
+
+	"blitiri.com.ar/go/log"
+)
+
+var (
+	addr = flag.String("addr", "",
+		"server address")
+	httpAddr = flag.String("http_addr", "localhost:8011",
+		"monitoring HTTP server listening address")
+	wait = flag.Bool("wait", false,
+		"don't exit after --run_for has lapsed")
+	count = flag.Int("count", 1000,
+		"how many connections to open")
+)
+
+var (
+	host string
+	exit bool
+)
+
+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)
+	}
+
+	log.Infof("creating %d simultaneous connections", *count)
+	conns := []*C{}
+	for i := 0; i < *count; i++ {
+		c, err := newC()
+		if err != nil {
+			log.Fatalf("failed to connect #%d: %v", i, err)
+		}
+
+		conns = append(conns, c)
+
+		if i%200 == 0 {
+			log.Infof("  ... %d connections", i)
+
+		}
+	}
+	log.Infof("done, created %d simultaneous connections", *count)
+
+	if *wait {
+		for {
+			time.Sleep(24 * time.Hour)
+		}
+	}
+}
+
+type C struct {
+	tr trace.Trace
+	n  net.Conn
+	s  *smtp.Client
+}
+
+func newC() (*C, error) {
+	tr := trace.New("conn", *addr)
+
+	conn, err := net.Dial("tcp", *addr)
+	if err != nil {
+		return nil, err
+	}
+
+	client, err := smtp.NewClient(conn, host)
+	if err != nil {
+		conn.Close()
+		return nil, err
+	}
+
+	err = client.Hello(host)
+	if err != nil {
+		return nil, err
+	}
+
+	return &C{tr: tr, n: conn, s: client}, nil
+}
+
+func (c *C) close() {
+	c.tr.Finish()
+	c.s.Close()
+	c.n.Close()
+}