From 7172fd77848522a29b4894ea3c5c8d8702941a98 Mon Sep 17 00:00:00 2001
From: Wen Bo Li <50884368+wenovus@users.noreply.github.com>
Date: Mon, 6 Nov 2023 22:05:21 -0500
Subject: [PATCH] ygot.FormatDiff (#929)

* ygot.FormatDiff

* Add sanity test

* add test
---
 ygot/diff.go      | 36 ++++++++++++++++++++++++++++++++++
 ygot/diff_test.go | 50 +++++++++++++++++++++++++++++++++++++++++++++++
 2 files changed, 86 insertions(+)

diff --git a/ygot/diff.go b/ygot/diff.go
index f35a2587..3cec08c3 100644
--- a/ygot/diff.go
+++ b/ygot/diff.go
@@ -24,6 +24,7 @@ import (
 	"github.com/openconfig/gnmi/errlist"
 	"github.com/openconfig/ygot/internal/yreflect"
 	"github.com/openconfig/ygot/util"
+	"google.golang.org/protobuf/encoding/prototext"
 	"google.golang.org/protobuf/proto"
 
 	gnmipb "github.com/openconfig/gnmi/proto/gnmi"
@@ -488,6 +489,41 @@ func Diff(original, modified GoStruct, opts ...DiffOpt) (*gnmipb.Notification, e
 	}
 }
 
+// FormatDiff formats the output of ygot.Diff as a multiline string. This
+// function is only intended for human consumption and ignores errors. Do not
+// depend on the output being stable. It may change over time across different
+// versions of the program.
+func FormatDiff(n *gnmipb.Notification) string {
+	if n == nil {
+		return "<nil> Notification"
+	}
+	var build strings.Builder
+	for _, d := range n.Delete {
+		path, err := PathToString(d)
+		if err != nil {
+			path = prototext.Format(d)
+		}
+		if build.Len() != 0 {
+			build.WriteRune('\n')
+		}
+		build.WriteString(fmt.Sprintf("deleted: %s", path))
+	}
+	for _, u := range n.Update {
+		path, err := PathToString(u.GetPath())
+		if err != nil {
+			path = prototext.Format(u.GetPath())
+		}
+		if build.Len() != 0 {
+			build.WriteRune('\n')
+		}
+		build.WriteString(fmt.Sprintf("new/updated %s: %v", path, u.GetVal()))
+	}
+	if build.Len() == 0 {
+		return "no diff"
+	}
+	return build.String()
+}
+
 // DiffWithAtomic takes an original and modified GoStruct, which must be of the same
 // type and returns a slice of gNMI Notifications that represents the diff
 // between them in a way that can be used to update a local gNMI.Subscribe
diff --git a/ygot/diff_test.go b/ygot/diff_test.go
index 70c7b968..628fe542 100644
--- a/ygot/diff_test.go
+++ b/ygot/diff_test.go
@@ -1576,6 +1576,9 @@ func TestDiff(t *testing.T) {
 		t.Run(tt.desc+"Diff", func(t *testing.T) {
 			got, err := Diff(tt.inOrig, tt.inMod, tt.inOpts...)
 			testDiffSingleNotif(t, "Diff", got, err)
+			if diffout := FormatDiff(got); diffout == "" {
+				t.Errorf("FormatDiff returned empty")
+			}
 		})
 		t.Run(tt.desc+"DiffWithAtomic", func(t *testing.T) {
 			var got *gnmipb.Notification
@@ -1589,6 +1592,53 @@ func TestDiff(t *testing.T) {
 				t.Fatalf("Got multiple Notifications for DiffWithAtomic: %d, this is not expected.", len(gots))
 			}
 			testDiffSingleNotif(t, "DiffWithAtomic", got, err)
+			if diffout := FormatDiff(got); diffout == "" {
+				t.Errorf("FormatDiff returned empty")
+			}
+		})
+	}
+}
+
+func TestFormatDiff(t *testing.T) {
+	tests := []struct {
+		desc    string
+		inNotif *gnmipb.Notification
+		want    string
+	}{{
+		desc: "basic",
+		inNotif: &gnmipb.Notification{
+			Delete: []*gnmipb.Path{{
+				Elem: []*gnmipb.PathElem{{
+					Name: "floatval",
+				}},
+			}},
+			Update: []*gnmipb.Update{{
+				Path: &gnmipb.Path{
+					Elem: []*gnmipb.PathElem{{
+						Name: "int-val",
+					}},
+				},
+				Val: &gnmipb.TypedValue{Value: &gnmipb.TypedValue_IntVal{10}},
+			}},
+		},
+		want: `deleted: /floatval
+new/updated /int-val: int_val:10`,
+	}, {
+		desc:    "empty",
+		inNotif: &gnmipb.Notification{},
+		want:    `no diff`,
+	}, {
+		desc:    "nil",
+		inNotif: nil,
+		want:    `<nil> Notification`,
+	}}
+
+	for _, tt := range tests {
+		t.Run(tt.desc, func(t *testing.T) {
+			got := FormatDiff(tt.inNotif)
+			if diff := cmp.Diff(tt.want, got); diff != "" {
+				t.Errorf("(-want, +got):\n%s", diff)
+			}
 		})
 	}
 }