Add equality functions.

CHANGELOG.md

@@ -12,6 +12,12 @@ The format is based on [Keep a Changelog], and this project adheres to
 
 ## [Unreleased]
 
+### Added
+
+- Added `dnssd.ServiceInstance.Equal()` method
+- Added `dnssd.Attributes.Equal()` method
+- Added `dnssd.AttributeCollectionsEqual()` function
+
 ### Changed
 
 - **[BC]** Renamed `dnssd.ServiceInstance.Instance` to `Name`

dnssd/attributes.go

@@ -1,6 +1,7 @@
 package dnssd
 
 import (
+	"bytes"
 	"errors"
 	"fmt"
 	"strings"
@@ -239,6 +240,20 @@ func (a Attributes) ToTXT() []string {
 	return result
 }
 
+// Equal returns true if the attributes are equal.
+func (a Attributes) Equal(attr Attributes) bool {
+	return maps.EqualFunc(
+		a.m,
+		attr.m,
+		func(v1, v2 []byte) bool {
+			isFlag1 := v1 == nil
+			isFlag2 := v2 == nil
+
+			return isFlag1 == isFlag2 && bytes.Equal(v1, v2)
+		},
+	)
+}
+
 // mustNormalizeAttributeKey normalizes the DNS-SD TXT key, k, or panics if it
 // can not be normalized.
 //
@@ -289,3 +304,31 @@ func normalizeAttributeKey(k string) (string, error) {
 
 	return w.String(), nil
 }
+
+// AttributeCollectionsEqual returns true if lhs and rhs contain the same sets
+// of attributes, in any order.
+func AttributeCollectionsEqual(lhs, rhs []Attributes) bool {
+	if len(lhs) != len(rhs) {
+		return false
+	}
+
+	visited := make([]bool, len(rhs))
+
+left:
+	for _, l := range lhs {
+		for i, r := range rhs {
+			if visited[i] {
+				continue
+			}
+
+			if l.Equal(r) {
+				visited[i] = true
+				continue left
+			}
+		}
+
+		return false
+	}
+
+	return true
+}

dnssd/instance.go

@@ -86,6 +86,19 @@ type ServiceInstance struct {
 	TTL time.Duration
 }
 
+// Equal returns true if i and inst are equal.
+func (i ServiceInstance) Equal(inst ServiceInstance) bool {
+	return i.Name == inst.Name &&
+		i.ServiceType == inst.ServiceType &&
+		i.Domain == inst.Domain &&
+		i.TargetHost == inst.TargetHost &&
+		i.TargetPort == inst.TargetPort &&
+		i.Priority == inst.Priority &&
+		i.Weight == inst.Weight &&
+		AttributeCollectionsEqual(i.Attributes, inst.Attributes) &&
+		i.TTL == inst.TTL
+}
+
 // ServiceInstanceName returns the fully-qualfied DNS domain name that is
 // queried to lookup records about a single service instance.
 //

dnssd/instance_test.go

@@ -1,11 +1,214 @@
 package dnssd_test
 
 import (
+	"time"
+
 	. "github.com/dogmatiq/dissolve/dnssd"
 	. "github.com/onsi/ginkgo/v2"
 	. "github.com/onsi/gomega"
 )
 
+var _ = Describe("type ServiceInstance", func() {
+	Describe("func Equal()", func() {
+		DescribeTable(
+			"it returns true if the instances are equal",
+			func(a, b ServiceInstance) {
+				Expect(a.Equal(b)).To(BeTrue())
+			},
+			Entry(
+				"zero-value",
+				ServiceInstance{},
+				ServiceInstance{},
+			),
+			Entry(
+				"fully populated",
+				ServiceInstance{
+					Name:        "Boardroom Printer",
+					ServiceType: "_http._tcp",
+					Domain:      "example.org",
+					TargetHost:  "boardroom-printer.example.org",
+					TargetPort:  80,
+					Priority:    10,
+					Weight:      20,
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}).
+							WithFlag("default"),
+					},
+					TTL: 30 * time.Second,
+				},
+				ServiceInstance{
+					Name:        "Boardroom Printer",
+					ServiceType: "_http._tcp",
+					Domain:      "example.org",
+					TargetHost:  "boardroom-printer.example.org",
+					TargetPort:  80,
+					Priority:    10,
+					Weight:      20,
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}).
+							WithFlag("default"),
+					},
+					TTL: 30 * time.Second,
+				},
+			),
+			Entry(
+				"attributes in a different order",
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}).
+							WithFlag("default"),
+						NewAttributes().
+							WithPair("txtvers", []byte{2}),
+					},
+				},
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{2}),
+						NewAttributes().
+							WithFlag("default").
+							WithPair("txtvers", []byte{1}),
+					},
+				},
+			),
+			Entry(
+				"multiple copies of the same set of attributes",
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}),
+						NewAttributes().
+							WithPair("txtvers", []byte{1}),
+					},
+				},
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}),
+						NewAttributes().
+							WithPair("txtvers", []byte{1}),
+					},
+				},
+			),
+		)
+		DescribeTable(
+			"it returns false if the instances are not equal",
+			func(a, b ServiceInstance) {
+				Expect(a.Equal(b)).To(BeFalse())
+			},
+			Entry(
+				"different name",
+				ServiceInstance{Name: "Boardroom Printer"},
+				ServiceInstance{Name: "Boardroom Printer 2"},
+			),
+			Entry(
+				"different service type",
+				ServiceInstance{ServiceType: "_http._tcp"},
+				ServiceInstance{ServiceType: "_other._udp"},
+			),
+			Entry(
+				"different domain",
+				ServiceInstance{Domain: "example.org"},
+				ServiceInstance{Domain: "example.com"},
+			),
+			Entry(
+				"different target host",
+				ServiceInstance{TargetHost: "boardroom-printer.example.org"},
+				ServiceInstance{TargetHost: "boardroom-printer-2.example.org"},
+			),
+			Entry(
+				"different target port",
+				ServiceInstance{TargetPort: 80},
+				ServiceInstance{TargetPort: 8080},
+			),
+			Entry(
+				"different priority",
+				ServiceInstance{Priority: 10},
+				ServiceInstance{Priority: 20},
+			),
+			Entry(
+				"different weight",
+				ServiceInstance{Weight: 20},
+				ServiceInstance{Weight: 30},
+			),
+			Entry(
+				"different TTL",
+				ServiceInstance{TTL: 30 * time.Second},
+				ServiceInstance{TTL: 60 * time.Second},
+			),
+			Entry(
+				"different attributes",
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}),
+					},
+				},
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{2}),
+					},
+				},
+			),
+			Entry(
+				"different attributes - flag vs empty value",
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("flag", nil),
+					},
+				},
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithFlag("flag"),
+					},
+				},
+			),
+			Entry(
+				"different attributes - subset",
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}),
+					},
+				},
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}), // <-- same
+						NewAttributes().
+							WithPair("txtvers", []byte{2}), // <-- different
+					},
+				},
+			),
+			Entry(
+				"different attributes - multiple copies of the same set of attributes",
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}), // <-- same
+						NewAttributes().
+							WithPair("txtvers", []byte{1}), // <-- same
+					},
+				},
+				ServiceInstance{
+					Attributes: []Attributes{
+						NewAttributes().
+							WithPair("txtvers", []byte{1}), // <-- same
+						NewAttributes().
+							WithPair("txtvers", []byte{2}), // <-- different
+					},
+				},
+			),
+		)
+	})
+})
+
 var _ = Describe("func ServiceInstanceName()", func() {
 	It("returns the fully-qualified name, with appropriate escaping", func() {
 		d := ServiceInstanceName("Boardroom Printer.", "_http._tcp", "example.org")