From 8a8cebd127ba9c955e386c3a2d0b77a0b8cd4582 Mon Sep 17 00:00:00 2001
From: Brian Picciano <mediocregopher@gmail.com>
Date: Fri, 11 Jan 2019 17:47:30 -0500
Subject: [PATCH] mnet: implement ListenerOnStart

---
 mnet/mnet.go      | 34 ++++++++++++++++++++++++++++++++++
 mnet/mnet_test.go | 37 +++++++++++++++++++++++++++++++++++++
 2 files changed, 71 insertions(+)

diff --git a/mnet/mnet.go b/mnet/mnet.go
index c8a4523..33dbe10 100644
--- a/mnet/mnet.go
+++ b/mnet/mnet.go
@@ -4,8 +4,42 @@ package mnet
 
 import (
 	"net"
+
+	"github.com/mediocregopher/mediocre-go-lib/mcfg"
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
+	"github.com/mediocregopher/mediocre-go-lib/mlog"
+	"github.com/mediocregopher/mediocre-go-lib/mrun"
 )
 
+// ListenerOnStart returns a Listener which will be initialized when the start
+// event is triggered on ctx (see mrun.Start).
+//
+// network defaults to "tcp" if empty. defaultAddr defaults to ":0" if empty,
+// and will be configurable via mcfg.
+func ListenerOnStart(ctx mctx.Context, network, defaultAddr string) net.Listener {
+	if network == "" {
+		network = "tcp"
+	}
+	if defaultAddr == "" {
+		defaultAddr = ":0"
+	}
+	addr := mcfg.String(ctx, "addr", defaultAddr, network+" address to listen on in format [host]:port. If port is 0 then a random one will be chosen")
+
+	var l struct{ net.Listener }
+	mrun.OnStart(ctx, func(mctx.Context) error {
+		var err error
+		if l.Listener, err = net.Listen(network, *addr); err != nil {
+			return err
+		}
+		mlog.From(ctx).Info("listening", mlog.KV{"addr": l.Addr()})
+		return nil
+	})
+
+	return &l
+}
+
+////////////////////////////////////////////////////////////////////////////////
+
 func mustGetCIDRNetwork(cidr string) *net.IPNet {
 	_, n, err := net.ParseCIDR(cidr)
 	if err != nil {
diff --git a/mnet/mnet_test.go b/mnet/mnet_test.go
index 64fc7fe..bf878e2 100644
--- a/mnet/mnet_test.go
+++ b/mnet/mnet_test.go
@@ -1,9 +1,14 @@
 package mnet
 
 import (
+	"fmt"
+	"io/ioutil"
 	"net"
 	. "testing"
 
+	"github.com/mediocregopher/mediocre-go-lib/mcfg"
+	"github.com/mediocregopher/mediocre-go-lib/mctx"
+	"github.com/mediocregopher/mediocre-go-lib/mrun"
 	"github.com/mediocregopher/mediocre-go-lib/mtest/massert"
 )
 
@@ -31,3 +36,35 @@ func TestIsReservedIP(t *T) {
 		assertReserved("2600:1700:7580:6e80:21c:25ff:fe97:44df"),
 	))
 }
+
+func TestListen(t *T) {
+	ctx := mctx.New()
+	l := ListenerOnStart(ctx, "", "")
+	if err := mcfg.Populate(ctx, nil); err != nil {
+		t.Fatal(err)
+	} else if err := mrun.Start(ctx); err != nil {
+		t.Fatal(err)
+	}
+
+	go func() {
+		conn, err := net.Dial("tcp", l.Addr().String())
+		if err != nil {
+			t.Fatal(err)
+		} else if _, err = fmt.Fprint(conn, "hello world"); err != nil {
+			t.Fatal(err)
+		}
+		conn.Close()
+	}()
+
+	conn, err := l.Accept()
+	if err != nil {
+		t.Fatal(err)
+	} else if b, err := ioutil.ReadAll(conn); err != nil {
+		t.Fatal(err)
+	} else if string(b) != "hello world" {
+		t.Fatalf("read %q from conn", b)
+	}
+
+	conn.Close()
+	l.Close()
+}