Decapsulate by component rather than string

multiaddr.go

@@ -5,7 +5,6 @@ import (
 	"encoding/json"
 	"fmt"
 	"log"
-	"strings"
 
 	"golang.org/x/exp/slices"
 )
@@ -150,26 +149,41 @@ func (m *multiaddr) Encapsulate(o Multiaddr) Multiaddr {
 }
 
 // Decapsulate unwraps Multiaddr up until the given Multiaddr is found.
-func (m *multiaddr) Decapsulate(o Multiaddr) Multiaddr {
-	s1 := m.String()
-	s2 := o.String()
-	i := strings.LastIndex(s1, s2)
-	if i < 0 {
-		// if multiaddr not contained, returns a copy.
-		cpy := make([]byte, len(m.bytes))
-		copy(cpy, m.bytes)
-		return &multiaddr{bytes: cpy}
+func (m *multiaddr) Decapsulate(right Multiaddr) Multiaddr {
+	if right == nil {
+		return m
 	}
 
-	if i == 0 {
+	leftParts := Split(m)
+	rightParts := Split(right)
+
+	lastIndex := -1
+	for i := range leftParts {
+		foundMatch := false
+		for j, rightC := range rightParts {
+			foundMatch = rightC.Equal(leftParts[i+j])
+			if !foundMatch {
+				break
+			}
+		}
+
+		if foundMatch {
+			lastIndex = i
+		}
+	}
+
+	if lastIndex == 0 {
 		return nil
 	}
 
-	ma, err := NewMultiaddr(s1[:i])
-	if err != nil {
-		panic("Multiaddr.Decapsulate incorrect byte boundaries.")
+	if lastIndex < 0 {
+		// if multiaddr not contained, returns a copy.
+		cpy := make([]byte, len(m.bytes))
+		copy(cpy, m.bytes)
+		return &multiaddr{bytes: cpy}
 	}
-	return ma
+
+	return Join(leftParts[:lastIndex]...)
 }
 
 var ErrProtocolNotFound = fmt.Errorf("protocol not found in multiaddr")

multiaddr_test.go

@@ -454,6 +454,46 @@ func TestDecapsulateComment(t *testing.T) {
 	require.Nil(t, rest, "expected a nil multiaddr if we decapsulate everything")
 }
 
+func TestDecapsulate(t *testing.T) {
+	t.Run("right is nil", func(t *testing.T) {
+		left := StringCast("/ip4/1.2.3.4/tcp/1")
+		var right Multiaddr
+		left.Decapsulate(right)
+	})
+
+	testcases := []struct {
+		left, right, expected string
+	}{
+		{"/ip4/1.2.3.4/tcp/1234", "/ip4/1.2.3.4", ""},
+		{"/ip4/1.2.3.5/tcp/1234", "/ip4/5.3.2.1", "/ip4/1.2.3.5/tcp/1234"},
+		{"/ip4/1.2.3.5/udp/1234/quic-v1", "/udp/1234", "/ip4/1.2.3.5"},
+		{"/ip4/1.2.3.6/udp/1234/quic-v1", "/udp/1234/quic-v1", "/ip4/1.2.3.6"},
+		{"/ip4/1.2.3.7/tcp/1234", "/ws", "/ip4/1.2.3.7/tcp/1234"},
+		{"/dnsaddr/wss.com/tcp/4001", "/ws", "/dnsaddr/wss.com/tcp/4001"},
+		{"/dnsaddr/wss.com/tcp/4001/ws", "/wss", "/dnsaddr/wss.com/tcp/4001/ws"},
+		{"/dnsaddr/wss.com/ws", "/wss", "/dnsaddr/wss.com/ws"},
+		{"/dnsaddr/wss.com/ws", "/dnsaddr/wss.com", ""},
+		{"/dnsaddr/wss.com/tcp/4001/wss", "/wss", "/dnsaddr/wss.com/tcp/4001"},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.left, func(t *testing.T) {
+			left := StringCast(tc.left)
+			right := StringCast(tc.right)
+			actualMa := left.Decapsulate(right)
+
+			if tc.expected == "" {
+				require.Nil(t, actualMa, "expected nil")
+				return
+			}
+
+			actual := actualMa.String()
+			expected := StringCast(tc.expected).String()
+			require.Equal(t, expected, actual)
+		})
+	}
+}
+
 func assertValueForProto(t *testing.T, a Multiaddr, p int, exp string) {
 	t.Logf("checking for %s in %s", ProtocolWithCode(p).Name, a)
 	fv, err := a.ValueForProtocol(p)