record diff base profile label key/value constant (#384)

internal/report/report.go

 }
 
 // computeTotal computes the sum of the absolute value of all sample values.
-// If any samples have the label "pprof::base" with value "true", then the total
-// will only include samples with that label.
+// If any samples have label indicating they belong to the diff base, then the
+// total will only include samples with that label.
 func computeTotal(prof *profile.Profile, value, meanDiv func(v []int64) int64) int64 {
 	var div, total, diffDiv, diffTotal int64
 	for _, sample := range prof.Sample {
 		}
 		total += v
 		div += d
-		if sample.HasLabel("pprof::base", "true") {
+		if sample.DiffBaseSample() {
 			diffTotal += v
 			diffDiv += d
 		}

profile/profile.go

 	return false
 }
 
+// DiffBaseSample returns true if a sample belongs to the diff base and false
+// otherwise.
+func (s *Sample) DiffBaseSample() bool {
+	return s.HasLabel("pprof::base", "true")
+}
+
 // Scale multiplies all sample values in a profile by a constant.
 func (p *Profile) Scale(ratio float64) {
 	if ratio == 1 {

profile/profile_test.go

 	}
 }
 
+func TestDiffBaseSample(t *testing.T) {
+	var testcases = []struct {
+		desc               string
+		labels             map[string][]string
+		wantDiffBaseSample bool
+	}{
+		{
+			desc:               "empty label does not have label",
+			labels:             map[string][]string{},
+			wantDiffBaseSample: false,
+		},
+		{
+			desc:               "label with one key and value, including diff base label",
+			labels:             map[string][]string{"pprof::base": {"true"}},
+			wantDiffBaseSample: true,
+		},
+		{
+			desc:               "label with one key and value, not including diff base label",
+			labels:             map[string][]string{"key": {"value"}},
+			wantDiffBaseSample: false,
+		},
+		{
+			desc: "label with many keys and values, including diff base label",
+			labels: map[string][]string{
+				"pprof::base": {"value2", "true"},
+				"key2":        {"true", "value2", "value2"},
+				"key3":        {"true", "value2", "value2"},
+			},
+			wantDiffBaseSample: true,
+		},
+		{
+			desc: "label with many keys and values, not including diff base label",
+			labels: map[string][]string{
+				"key1": {"value2", "value1"},
+				"key2": {"value1", "value2", "value2"},
+				"key3": {"value1", "value2", "value2"},
+			},
+			wantDiffBaseSample: false,
+		},
+	}
+
+	for _, tc := range testcases {
+		t.Run(tc.desc, func(t *testing.T) {
+			sample := &Sample{
+				Label: tc.labels,
+			}
+			if gotHasLabel := sample.DiffBaseSample(); gotHasLabel != tc.wantDiffBaseSample {
+				t.Errorf("sample.DiffBaseSample() got %v, want %v", gotHasLabel, tc.wantDiffBaseSample)
+			}
+		})
+	}
+}
+
 func TestRemove(t *testing.T) {
 	var testcases = []struct {
 		desc       string