From bbdd1a57efaf35167262f1e985a3770fab8e47a3 Mon Sep 17 00:00:00 2001
From: Marco Munizaga <marco@marcopolo.io>
Date: Wed, 17 Jul 2024 04:12:53 -0700
Subject: [PATCH] check for nil interfaces (#251)

---
 component.go      |  3 +++
 multiaddr.go      |  7 +++++++
 multiaddr_test.go | 22 ++++++++++++++++++++++
 util.go           | 16 ++++++++++++++++
 4 files changed, 48 insertions(+)

diff --git a/component.go b/component.go
index 490b8ac..4ee6809 100644
--- a/component.go
+++ b/component.go
@@ -70,6 +70,9 @@ func (m *Component) UnmarshalJSON(data []byte) error {
 }
 
 func (c *Component) Equal(o Multiaddr) bool {
+	if o == nil {
+		return false
+	}
 	return bytes.Equal(c.bytes, o.Bytes())
 }
 
diff --git a/multiaddr.go b/multiaddr.go
index 4b3a360..5e60780 100644
--- a/multiaddr.go
+++ b/multiaddr.go
@@ -48,6 +48,9 @@ func NewMultiaddrBytes(b []byte) (a Multiaddr, err error) {
 
 // Equal tests whether two multiaddrs are equal
 func (m *multiaddr) Equal(m2 Multiaddr) bool {
+	if m2 == nil {
+		return false
+	}
 	return bytes.Equal(m.bytes, m2.Bytes())
 }
 
@@ -139,6 +142,10 @@ func (m *multiaddr) Protocols() []Protocol {
 
 // Encapsulate wraps a given Multiaddr, returning the resulting joined Multiaddr
 func (m *multiaddr) Encapsulate(o Multiaddr) Multiaddr {
+	if o == nil {
+		return m
+	}
+
 	mb := m.bytes
 	ob := o.Bytes()
 
diff --git a/multiaddr_test.go b/multiaddr_test.go
index eda478f..37e825c 100644
--- a/multiaddr_test.go
+++ b/multiaddr_test.go
@@ -242,6 +242,28 @@ func TestEqual(t *testing.T) {
 	}
 }
 
+// TestNilInterface makes sure funcs that accept a multiaddr interface don't
+// panic if it's passed a nil interface.
+func TestNilInterface(t *testing.T) {
+	m1 := newMultiaddr(t, "/ip4/127.0.0.1/udp/1234")
+	var m2 Multiaddr
+	m1.Equal(m2)
+	m1.Encapsulate(m2)
+	m1.Decapsulate(m2)
+
+	// Test components
+	c, _ := SplitFirst(m1)
+	c.Equal(m2)
+	c.Encapsulate(m2)
+	c.Decapsulate(m2)
+
+	// Util funcs
+	_ = Split(m2)
+	_, _ = SplitFirst(m2)
+	_, _ = SplitLast(m2)
+	ForEach(m2, func(c Component) bool { return true })
+}
+
 func TestStringToBytes(t *testing.T) {
 
 	testString := func(s string, h string) {
diff --git a/util.go b/util.go
index 63abbcc..16a347c 100644
--- a/util.go
+++ b/util.go
@@ -45,6 +45,9 @@ func Join(ms ...Multiaddr) Multiaddr {
 		}
 		bidx += copy(b[bidx:], mb.Bytes())
 	}
+	if length == 0 {
+		return nil
+	}
 	return &multiaddr{bytes: b}
 }
 
@@ -68,6 +71,9 @@ func StringCast(s string) Multiaddr {
 
 // SplitFirst returns the first component and the rest of the multiaddr.
 func SplitFirst(m Multiaddr) (*Component, Multiaddr) {
+	if m == nil {
+		return nil, nil
+	}
 	// Shortcut if we already have a component
 	if c, ok := m.(*Component); ok {
 		return c, nil
@@ -89,6 +95,10 @@ func SplitFirst(m Multiaddr) (*Component, Multiaddr) {
 
 // SplitLast returns the rest of the multiaddr and the last component.
 func SplitLast(m Multiaddr) (Multiaddr, *Component) {
+	if m == nil {
+		return nil, nil
+	}
+
 	// Shortcut if we already have a component
 	if c, ok := m.(*Component); ok {
 		return nil, c
@@ -126,6 +136,9 @@ func SplitLast(m Multiaddr) (Multiaddr, *Component) {
 // component on which the callback first returns will be included in the
 // *second* multiaddr.
 func SplitFunc(m Multiaddr, cb func(Component) bool) (Multiaddr, Multiaddr) {
+	if m == nil {
+		return nil, nil
+	}
 	// Shortcut if we already have a component
 	if c, ok := m.(*Component); ok {
 		if cb(*c) {
@@ -168,6 +181,9 @@ func SplitFunc(m Multiaddr, cb func(Component) bool) (Multiaddr, Multiaddr) {
 // This function iterates over components *by value* to avoid allocating.
 // Return true to continue iteration, false to stop.
 func ForEach(m Multiaddr, cb func(c Component) bool) {
+	if m == nil {
+		return
+	}
 	// Shortcut if we already have a component
 	if c, ok := m.(*Component); ok {
 		cb(*c)