From 95f00943106a33112425b69ab61ba0ed8af201ef Mon Sep 17 00:00:00 2001
From: Jordan Whited <jordan@tailscale.com>
Date: Thu, 5 Sep 2024 13:40:12 -0700
Subject: [PATCH] cmd/stunstamp: cleanup timeout and interval constants
 (#13393)

Updates #cleanup

Signed-off-by: Jordan Whited <jordan@tailscale.com>
---
 cmd/stunstamp/stunstamp.go       | 15 ++++++++++++---
 cmd/stunstamp/stunstamp_linux.go | 10 +++++-----
 2 files changed, 17 insertions(+), 8 deletions(-)

diff --git a/cmd/stunstamp/stunstamp.go b/cmd/stunstamp/stunstamp.go
index 1aaa7ced1..7b97a66c5 100644
--- a/cmd/stunstamp/stunstamp.go
+++ b/cmd/stunstamp/stunstamp.go
@@ -53,7 +53,16 @@ var (
 )
 
 const (
-	minInterval       = time.Second
+	// maxTxJitter is the upper bounds for jitter introduced across probes
+	maxTXJitter = time.Millisecond * 400
+	// minInterval is the minimum allowed probe interval/step
+	minInterval = time.Second * 10
+	// txRxTimeout is the timeout value used for kernel timestamping loopback,
+	// and packet receive operations
+	txRxTimeout = time.Second * 2
+	// maxBufferDuration is the maximum duration (maxBufferDuration /
+	// *flagInterval steps worth) of buffered data that can be held in memory
+	// before data loss occurs around prometheus unavailability.
 	maxBufferDuration = time.Hour
 )
 
@@ -322,7 +331,7 @@ func measureSTUNRTT(conn io.ReadWriteCloser, _ string, dst netip.AddrPort) (rtt
 	if !ok {
 		return 0, fmt.Errorf("unexpected conn type: %T", conn)
 	}
-	err = uconn.SetReadDeadline(time.Now().Add(time.Second * 2))
+	err = uconn.SetReadDeadline(time.Now().Add(txRxTimeout))
 	if err != nil {
 		return 0, fmt.Errorf("error setting read deadline: %w", err)
 	}
@@ -380,7 +389,7 @@ func probe(meta nodeMeta, cf *connAndMeasureFn, dstPort int) (*time.Duration, er
 		Port: dstPort,
 	}
 
-	time.Sleep(rand.N(400 * time.Millisecond)) // jitter across tx
+	time.Sleep(rand.N(maxTXJitter)) // jitter across tx
 	rtt, err := cf.fn(cf.conn, meta.hostname, netip.AddrPortFrom(meta.addr, uint16(dstPort)))
 	if err != nil {
 		if isTemporaryOrTimeoutErr(err) {
diff --git a/cmd/stunstamp/stunstamp_linux.go b/cmd/stunstamp/stunstamp_linux.go
index 886f8909a..387805fef 100644
--- a/cmd/stunstamp/stunstamp_linux.go
+++ b/cmd/stunstamp/stunstamp_linux.go
@@ -107,7 +107,7 @@ func measureICMPRTT(source timestampSource, conn io.ReadWriteCloser, _ string, d
 	}
 
 	if source == timestampSourceKernel {
-		txCtx, txCancel := context.WithTimeout(context.Background(), time.Second*2)
+		txCtx, txCancel := context.WithTimeout(context.Background(), txRxTimeout)
 		defer txCancel()
 
 		buf := make([]byte, 1024)
@@ -142,8 +142,8 @@ func measureICMPRTT(source timestampSource, conn io.ReadWriteCloser, _ string, d
 		}
 	}
 
-	rxCtx, txCancel := context.WithTimeout(context.Background(), time.Second*2)
-	defer txCancel()
+	rxCtx, rxCancel := context.WithTimeout(context.Background(), txRxTimeout)
+	defer rxCancel()
 
 	rxBuf := make([]byte, 1024)
 	oob := make([]byte, 1024)
@@ -210,7 +210,7 @@ func measureSTUNRTTKernel(conn io.ReadWriteCloser, _ string, dst netip.AddrPort)
 		return 0, fmt.Errorf("sendto error: %v", err) // don't wrap
 	}
 
-	txCtx, txCancel := context.WithTimeout(context.Background(), time.Second*2)
+	txCtx, txCancel := context.WithTimeout(context.Background(), txRxTimeout)
 	defer txCancel()
 
 	buf := make([]byte, 1024)
@@ -236,7 +236,7 @@ func measureSTUNRTTKernel(conn io.ReadWriteCloser, _ string, dst netip.AddrPort)
 		break
 	}
 
-	rxCtx, rxCancel := context.WithTimeout(context.Background(), time.Second*2)
+	rxCtx, rxCancel := context.WithTimeout(context.Background(), txRxTimeout)
 	defer rxCancel()
 
 	for {