core: Refactor listeners; use SO_REUSEPORT on Unix (#4705)

* core: Refactor listeners; use SO_REUSEPORT on Unix

Just an experiment for now

* Fix lint by logging error

* TCP Keepalive configuration (#4865)

* initial attempt at TCP Keepalive configuration

* core: implement tcp-keepalive for linux

* move canSetKeepAlive interface

* Godoc for keepalive server parameter

* handle return values

* log keepalive errors

* Clean up after bad merge

* Merge in pluggable network types

From 1edc1a45e3aee1f7d86b68c3ddaf2fd16ba8ab73

* Slight refactor, fix from recent merge conflict

Co-authored-by: Karmanyaah Malhotra <karmanyaah.gh@malhotra.cc>

1 files changed, 34 insertions, 0 deletions

diff --git a/listen_linux.go b/listen_linux.go
new file mode 100644
index 0000000..b1220ce
--- /dev/null
+++ b/listen_linux.go
@@ -0,0 +1,34 @@
+package caddy
+
+import (
+	"context"
+	"net"
+	"syscall"
+	"time"
+
+	"go.uber.org/zap"
+	"golang.org/x/sys/unix"
+)
+
+// ListenTimeout is the same as Listen, but with a configurable keep-alive timeout duration.
+func ListenTimeout(network, addr string, keepalivePeriod time.Duration) (net.Listener, error) {
+	// check to see if plugin provides listener
+	if ln, err := getListenerFromPlugin(network, addr); err != nil || ln != nil {
+		return ln, err
+	}
+
+	config := &net.ListenConfig{Control: reusePort, KeepAlive: keepalivePeriod}
+	return config.Listen(context.Background(), network, addr)
+}
+
+func reusePort(network, address string, conn syscall.RawConn) error {
+	return conn.Control(func(descriptor uintptr) {
+		if err := unix.SetsockoptInt(int(descriptor), unix.SOL_SOCKET, unix.SO_REUSEPORT, 1); err != nil {
+			Log().Error("setting SO_REUSEPORT",
+				zap.String("network", network),
+				zap.String("address", address),
+				zap.Uintptr("descriptor", descriptor),
+				zap.Error(err))
+		}
+	})
+}