Do a conntrack -L before -E to capture existing connections.

probe/endpoint/conntrack.go

@@ -8,6 +8,7 @@ import (
 	"os"
 	"strings"
 	"sync"
+	"io"
 
 	"github.com/weaveworks/scope/common/exec"
 )
@@ -59,6 +60,11 @@ type Flow struct {
 	Original, Reply, Independent *Meta `xml:"-"`
 }
 
+type conntrack struct {
+	XMLName xml.Name `xml:"conntrack"`
+	Flows   []Flow   `xml:"flow"`
+}
+
 // Conntracker uses the conntrack command to track network connections
 type Conntracker struct {
 	sync.Mutex
@@ -105,7 +111,18 @@ var ConntrackModulePresent = func() bool {
 
 // NB this is not re-entrant!
 func (c *Conntracker) run(args ...string) {
-	args = append([]string{"-E", "-o", "xml"}, args...)
+	// Fork another conntrack, just to capture existing connections
+	// for which we don't get events
+	existingFlows, err := c.existingConnections(args...)
+	if err != nil {
+		log.Printf("conntrack existingConnections error: %v", err)
+		return
+	}
+	for _, flow := range existingFlows {
+		c.handleFlow(flow)
+	}
+
+	args = append([]string{"-E", "-o", "xml", "-p", "tcp"}, args...)
 	cmd := exec.Command("conntrack", args...)
 	stdout, err := cmd.StdoutPipe()
 	if err != nil {
@@ -154,6 +171,31 @@ func (c *Conntracker) run(args ...string) {
 	}
 }
 
+func (c *Conntracker) existingConnections(args ...string) ([]Flow, error) {
+	var conntrack conntrack
+	args = append([]string{"-L", "-o", "xml", "-p", "tcp"}, args...)
+	cmd := exec.Command("conntrack", args...)
+	stdout, err := cmd.StdoutPipe()
+	if err != nil {
+		return conntrack.Flows, err
+	}
+	if err := cmd.Start(); err != nil {
+		return conntrack.Flows, err
+	}
+	defer func() {
+		if err := cmd.Wait(); err != nil {
+			log.Printf("conntrack existingConnections exit error: %v", err)
+		}
+	}()
+	if err := xml.NewDecoder(stdout).Decode(&conntrack); err != nil {
+		if err == io.EOF {
+			return conntrack.Flows, err
+		}
+		return conntrack.Flows, err
+	}
+	return conntrack.Flows, nil
+}
+
 // Stop stop stop
 func (c *Conntracker) Stop() {
 	c.Lock()