Close #360 : Revert to IPv4 debug port binding if IPv6 fails

* use "/sys/module/ipv6/parameters/disable"

helper/debug_9.go

@@ -18,15 +18,19 @@ package helper
 
 import (
 	"fmt"
-	"strings"
-
 	"github.com/paketo-buildpacks/libpak/sherpa"
+	"io"
+	"os"
+	"strings"
 
 	"github.com/paketo-buildpacks/libpak/bard"
 )
 
+const DefaultIPv6CheckPath = "/sys/module/ipv6/parameters/disable"
+
 type Debug9 struct {
-	Logger bard.Logger
+	Logger              bard.Logger
+	CustomIPv6CheckPath string
 }
 
 func (d Debug9) Execute() (map[string]string, error) {
@@ -43,11 +47,24 @@ func (d Debug9) Execute() (map[string]string, error) {
 		return nil, nil
 	}
 
-	port := "*:" + sherpa.GetEnvWithDefault("BPL_DEBUG_PORT", "8000")
+	port := sherpa.GetEnvWithDefault("BPL_DEBUG_PORT", "8000")
+	var host = "*"
+	var iPv6CheckPath string
+	if d.CustomIPv6CheckPath != "" {
+		iPv6CheckPath = d.CustomIPv6CheckPath
+	} else {
+		iPv6CheckPath = DefaultIPv6CheckPath
+	}
+	if !IPv6Enabled(iPv6CheckPath) {
+		d.Logger.Infof("IPv6 does not seem to be enabled in the container, configuring debug agent with 0.0.0.0\n")
+		host = "0.0.0.0"
+	}
+
+	address := host + ":" + port
 
 	suspend := sherpa.ResolveBool("BPL_DEBUG_SUSPEND")
 
-	s := fmt.Sprintf("Debugging enabled on port %s", port)
+	s := fmt.Sprintf("Debugging enabled on address %s", address)
 	if suspend {
 		s = fmt.Sprintf("%s, suspended on start", s)
 	}
@@ -59,7 +76,27 @@ func (d Debug9) Execute() (map[string]string, error) {
 		s = "n"
 	}
 
-	opts = sherpa.AppendToEnvVar("JAVA_TOOL_OPTIONS", " ", fmt.Sprintf("-agentlib:jdwp=transport=dt_socket,server=y,address=%s,suspend=%s", port, s))
+	opts = sherpa.AppendToEnvVar("JAVA_TOOL_OPTIONS", " ", fmt.Sprintf("-agentlib:jdwp=transport=dt_socket,server=y,address=%s,suspend=%s", address, s))
 
 	return map[string]string{"JAVA_TOOL_OPTIONS": opts}, nil
 }
+
+func IPv6Enabled(iPv6CheckPath string) bool {
+	in, err := os.Open(iPv6CheckPath)
+
+	if err != nil {
+		return false
+	}
+	defer func(in *os.File) {
+		_ = in.Close()
+	}(in)
+
+	b, err := io.ReadAll(in)
+	value := string(b[0:1])
+
+	if err != nil || value == "1" {
+		return false
+	} else {
+		return true
+	}
+}

helper/debug_9_test.go

@@ -17,6 +17,7 @@
 package helper_test
 
 import (
+	"log"
 	"os"
 	"testing"
 
@@ -36,14 +37,23 @@ func testDebug9(t *testing.T, context spec.G, it spec.S) {
 	})
 
 	context("$BPL_DEBUG_ENABLED", func() {
-
+		var fakeIPv6File *os.File
 		it.Before(func() {
 			Expect(os.Setenv("BPL_DEBUG_ENABLED", "true")).
 				To(Succeed())
+
+			var fakeIPv6FileErr error
+			fakeIPv6File, fakeIPv6FileErr = os.CreateTemp("", "IPv6Test")
+			if fakeIPv6FileErr != nil {
+				log.Fatal(fakeIPv6FileErr)
+			}
+			fakeIPv6File.WriteString("0\n")
+			d.CustomIPv6CheckPath = fakeIPv6File.Name()
 		})
 
 		it.After(func() {
 			Expect(os.Unsetenv("BPL_DEBUG_ENABLED")).To(Succeed())
+			os.Remove(fakeIPv6File.Name())
 		})
 
 		it("contributes configuration", func() {
@@ -114,5 +124,39 @@ func testDebug9(t *testing.T, context spec.G, it spec.S) {
 			})
 		})
 
+		context("IPv6 is not present", func() {
+			it.Before(func() {
+				d1 := []byte("1\n")
+				os.WriteFile(fakeIPv6File.Name(), d1, 0644)
+			})
+
+			it.After(func() {
+				d1 := []byte("0\n")
+				os.WriteFile(fakeIPv6File.Name(), d1, 0644)
+			})
+
+			it("replaces '*' host with IPv4 0.0.0.0", func() {
+				Expect(d.Execute()).To(Equal(map[string]string{
+					"JAVA_TOOL_OPTIONS": "-agentlib:jdwp=transport=dt_socket,server=y,address=0.0.0.0:8000,suspend=n",
+				}))
+			})
+		})
+
+		context("IPv6 kernel module file not there", func() {
+			it.Before(func() {
+				d.CustomIPv6CheckPath = "/does/not/exist"
+			})
+
+			it.After(func() {
+				d.CustomIPv6CheckPath = fakeIPv6File.Name()
+			})
+
+			it("replaces '*' host with IPv4 0.0.0.0", func() {
+				Expect(d.Execute()).To(Equal(map[string]string{
+					"JAVA_TOOL_OPTIONS": "-agentlib:jdwp=transport=dt_socket,server=y,address=0.0.0.0:8000,suspend=n",
+				}))
+			})
+		})
+
 	})
 }