Fix up stderr for all external dumpcap routines

Termshark uses a custom approach to capturing, preferring dumpcap but
then launching tshark if dumpcap fails (e.g. on extcap interfaces). This
fixes up stderr for the non-Linux builds so that if capture fails
altogether, the stderr printed out on the terminal is more easily
digestible.

cmd/termshark/termshark.go

@@ -744,7 +744,7 @@ func cmain() int {
 				}
 
 				fmt.Fprintf(os.Stderr, "Standard error stream from %s:\n", cbin)
-				fmt.Fprintf(os.Stderr, "\n%s\n", stderr.String())
+				fmt.Fprintf(os.Stderr, "------\n%s\n------\n", stderr.String())
 			}
 			if runtime.GOOS == "linux" && os.Geteuid() != 0 {
 				fmt.Fprintf(os.Stderr, "You might need: sudo setcap cap_net_raw,cap_net_admin+eip %s\n", termshark.PrivilegedBin())

system/dumpcapext.go

@@ -61,7 +61,7 @@ func DumpcapExt(dumpcapBin string, tsharkBin string, args ...string) error {
 
 	fmt.Fprintf(os.Stderr, "Starting termshark's custom live capture procedure.\n")
 	dumpcapCmd := exec.Command(dumpcapBin, args...)
-	fmt.Fprintf(os.Stderr, "First, trying dumpcap command %v\n", dumpcapCmd)
+	fmt.Fprintf(os.Stderr, "Trying dumpcap command %v\n", dumpcapCmd)
 	dumpcapCmd.Stdin = os.Stdin
 	dumpcapCmd.Stdout = os.Stdout
 	dumpcapCmd.Stderr = os.Stderr

system/dumpcapext_arm64.go

@@ -8,11 +8,10 @@
 package system
 
 import (
+	"fmt"
 	"os"
 	"os/exec"
 	"syscall"
-
-	log "github.com/sirupsen/logrus"
 )
 
 //======================================================================
@@ -26,15 +25,16 @@ func DumpcapExt(dumpcapBin string, tsharkBin string, args ...string) error {
 	var err error
 
 	dumpcapCmd := exec.Command(dumpcapBin, args...)
-	log.Infof("Starting dumpcap command %v", dumpcapCmd)
+	fmt.Fprintf(os.Stderr, "Starting termshark's custom live capture procedure.\n")
+	fmt.Fprintf(os.Stderr, "Trying dumpcap command %v\n", dumpcapCmd)
 	dumpcapCmd.Stdin = os.Stdin
 	dumpcapCmd.Stdout = os.Stdout
 	dumpcapCmd.Stderr = os.Stderr
 	if dumpcapCmd.Run() != nil {
 		var tshark string
 		tshark, err = exec.LookPath(tsharkBin)
 		if err == nil {
-			log.Infof("Retrying with dumpcap command %v", append([]string{tshark}, args...))
+			fmt.Fprintf(os.Stderr, "Retrying with dumpcap command %v\n", append([]string{tshark}, args...))
 			err = syscall.Exec(tshark, append([]string{tshark}, args...), os.Environ())
 		}
 	}

system/dumpcapext_darwin.go

@@ -5,11 +5,10 @@
 package system
 
 import (
+	"fmt"
 	"os"
 	"os/exec"
 	"syscall"
-
-	log "github.com/sirupsen/logrus"
 )
 
 //======================================================================
@@ -23,15 +22,16 @@ func DumpcapExt(dumpcapBin string, tsharkBin string, args ...string) error {
 	var err error
 
 	dumpcapCmd := exec.Command(dumpcapBin, args...)
-	log.Infof("Starting dumpcap command %v", dumpcapCmd)
+	fmt.Fprintf(os.Stderr, "Starting termshark's custom live capture procedure.\n")
+	fmt.Fprintf(os.Stderr, "Trying dumpcap command %v\n", dumpcapCmd)
 	dumpcapCmd.Stdin = os.Stdin
 	dumpcapCmd.Stdout = os.Stdout
 	dumpcapCmd.Stderr = os.Stderr
 	if dumpcapCmd.Run() != nil {
 		var tshark string
 		tshark, err = exec.LookPath(tsharkBin)
 		if err == nil {
-			log.Infof("Retrying with dumpcap command %v", append([]string{tshark}, args...))
+			fmt.Fprintf(os.Stderr, "Retrying with dumpcap command %v\n", append([]string{tshark}, args...))
 			err = syscall.Exec(tshark, append([]string{tshark}, args...), os.Environ())
 		}
 	}

system/dumpcapext_windows.go

@@ -5,10 +5,9 @@
 package system
 
 import (
+	"fmt"
 	"os"
 	"os/exec"
-
-	log "github.com/sirupsen/logrus"
 )
 
 //======================================================================
@@ -20,7 +19,8 @@ import (
 // tshark supports extcap interfaces.
 func DumpcapExt(dumpcapBin string, tsharkBin string, args ...string) error {
 	dumpcapCmd := exec.Command(dumpcapBin, args...)
-	log.Infof("Starting dumpcap command %v", dumpcapCmd)
+	fmt.Fprintf(os.Stderr, "Starting termshark's custom live capture procedure.\n")
+	fmt.Fprintf(os.Stderr, "Trying dumpcap command %v\n", dumpcapCmd)
 	dumpcapCmd.Stdin = os.Stdin
 	dumpcapCmd.Stdout = os.Stdout
 	dumpcapCmd.Stderr = os.Stderr
@@ -29,7 +29,7 @@ func DumpcapExt(dumpcapBin string, tsharkBin string, args ...string) error {
 	}
 
 	tsharkCmd := exec.Command(tsharkBin, args...)
-	log.Infof("Retrying with dumpcap command %v", tsharkCmd)
+	fmt.Fprintf(os.Stderr, "Retrying with dumpcap command %v\n", tsharkCmd)
 	tsharkCmd.Stdin = os.Stdin
 	tsharkCmd.Stdout = os.Stdout
 	tsharkCmd.Stderr = os.Stderr