[Feature] Add -extended-stats for *nix platforms

On *nix platforms, there is now a `-extended-stats` option that will
print out some extended statistics for the test. The statistics are
based on information gleaned from the `TCP_INFO` of the underlying TCP
connections. What is implemented so far is just a proof of concept of
the extended stats that could be calculated. Depending on what users
want, we can add additional extended statistics.

1 files changed, 72 insertions, 0 deletions

diff --git a/extendedstats/unix.go b/extendedstats/unix.go
new file mode 100644
index 0000000..e50d719
--- /dev/null
+++ b/extendedstats/unix.go
@@ -0,0 +1,72 @@
+//go:build darwin || dragonfly || freebsd || linux || netbsd || openbsd
+// +build darwin dragonfly freebsd linux netbsd openbsd
+
+package extendedstats
+
+import (
+	"crypto/tls"
+	"fmt"
+	"net"
+
+	"github.com/network-quality/goresponsiveness/utilities"
+	"golang.org/x/sys/unix"
+)
+
+type ExtendedStats struct {
+	MaxPathMtu           uint64
+	TotalRetransmissions uint64
+	AverageRtt           float64
+	rtt_measurements     uint64
+	total_rtt            float64
+}
+
+func ExtendedStatsAvailable() bool {
+	return true
+}
+
+func (es *ExtendedStats) IncorporateConnectionStats(rawConn net.Conn) {
+	tlsConn, ok := rawConn.(*tls.Conn)
+	if !ok {
+		fmt.Printf("OOPS: Could not get the TCP info for the connection (not a TLS connection)!\n")
+	}
+	tcpConn, ok := tlsConn.NetConn().(*net.TCPConn)
+	if !ok {
+		fmt.Printf("OOPS: Could not get the TCP info for the connection (not a TCP connection)!\n")
+	}
+	if info, err := getTCPInfo(tcpConn); err != nil {
+		fmt.Printf("OOPS: Could not get the TCP info for the connection: %v!\n", err)
+	} else {
+		es.MaxPathMtu = utilities.Max(es.MaxPathMtu, uint64(info.Pmtu))
+		// https://lkml.iu.edu/hypermail/linux/kernel/1705.0/01790.html
+		es.TotalRetransmissions += uint64(info.Total_retrans)
+		es.total_rtt += float64(info.Rtt)
+		es.rtt_measurements += 1
+		es.AverageRtt = es.total_rtt / float64(es.rtt_measurements)
+
+	}
+}
+
+func (es *ExtendedStats) Repr() string {
+	return fmt.Sprintf(`Extended Statistics:
+	Maximum Path MTU: %v
+	Total Retransmissions: %v
+	Average RTT: %v
+`, es.MaxPathMtu, es.TotalRetransmissions, es.AverageRtt)
+}
+
+func getTCPInfo(connection net.Conn) (*unix.TCPInfo, error) {
+	tcpConn, ok := connection.(*net.TCPConn)
+	if !ok {
+		return nil, fmt.Errorf("connection is not a net.TCPConn")
+	}
+	rawConn, err := tcpConn.SyscallConn()
+	if err != nil {
+		return nil, err
+	}
+
+	var info *unix.TCPInfo = nil
+	rawConn.Control(func(fd uintptr) {
+		info, err = unix.GetsockoptTCPInfo(int(fd), unix.SOL_TCP, unix.TCP_INFO)
+	})
+	return info, err
+}