From f85651f2c4515451b64ef10138fc964ff75dbf79 Mon Sep 17 00:00:00 2001
From: Kiril Vladimirov <kiril@vladimiroff.org>
Date: Fri, 22 Jan 2021 16:29:36 +0200
Subject: [PATCH] Marshal Matcher to JSON for API v1 compatibility

Signed-off-by: Kiril Vladimirov <kiril@vladimiroff.org>
---
 pkg/labels/matcher.go      | 44 +++++++++++++++++++++++++
 pkg/labels/matcher_test.go | 66 +++++++++++++++++++++++++++++++++++++-
 2 files changed, 109 insertions(+), 1 deletion(-)

diff --git a/pkg/labels/matcher.go b/pkg/labels/matcher.go
index a0f97413..308ed9d4 100644
--- a/pkg/labels/matcher.go
+++ b/pkg/labels/matcher.go
@@ -15,6 +15,7 @@ package labels
 
 import (
 	"bytes"
+	"encoding/json"
 	"fmt"
 	"regexp"
 	"strings"
@@ -91,6 +92,49 @@ func (m *Matcher) Matches(s string) bool {
 	panic("labels.Matcher.Matches: invalid match type")
 }
 
+type apiV1Matcher struct {
+	Name    string `json:"name"`
+	Value   string `json:"value"`
+	IsRegex bool   `json:"isRegex"`
+	IsEqual bool   `json:"isEqual"`
+}
+
+// MarshalJSON retains backwards compatibility with types.Matcher for the v1 API.
+func (m Matcher) MarshalJSON() ([]byte, error) {
+	return json.Marshal(apiV1Matcher{
+		Name:    m.Name,
+		Value:   m.Value,
+		IsRegex: m.Type == MatchRegexp || m.Type == MatchNotRegexp,
+		IsEqual: m.Type == MatchRegexp || m.Type == MatchEqual,
+	})
+}
+
+func (m *Matcher) UnmarshalJSON(data []byte) error {
+	var v1m apiV1Matcher
+	if err := json.Unmarshal(data, &v1m); err != nil {
+		return err
+	}
+
+	var t MatchType
+	switch {
+	case v1m.IsEqual && !v1m.IsRegex:
+		t = MatchEqual
+	case !v1m.IsEqual && !v1m.IsRegex:
+		t = MatchNotEqual
+	case v1m.IsEqual && v1m.IsRegex:
+		t = MatchRegexp
+	case !v1m.IsEqual && v1m.IsRegex:
+		t = MatchNotRegexp
+	}
+
+	matcher, err := NewMatcher(t, v1m.Name, v1m.Value)
+	if err != nil {
+		return err
+	}
+	*m = *matcher
+	return nil
+}
+
 // openMetricsEscape is similar to the usual string escaping, but more
 // restricted. It merely replaces a new-line character with '\n', a double-quote
 // character with '\"', and a backslash with '\\', which is the escaping used by
diff --git a/pkg/labels/matcher_test.go b/pkg/labels/matcher_test.go
index 95e643c2..a645f9d6 100644
--- a/pkg/labels/matcher_test.go
+++ b/pkg/labels/matcher_test.go
@@ -13,7 +13,10 @@
 
 package labels
 
-import "testing"
+import (
+	"encoding/json"
+	"testing"
+)
 
 func mustNewMatcher(t *testing.T, mType MatchType, value string) *Matcher {
 	m, err := NewMatcher(mType, "", value)
@@ -191,3 +194,64 @@ line`,
 		}
 	}
 }
+
+func TestMatcherJSON(t *testing.T) {
+	tests := []struct {
+		name  string
+		op    MatchType
+		value string
+		want  string
+	}{
+		{
+			name:  `foo`,
+			op:    MatchEqual,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":false,"isEqual":true}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchNotEqual,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":false,"isEqual":false}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchRegexp,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":true,"isEqual":true}`,
+		},
+		{
+			name:  `foo`,
+			op:    MatchNotRegexp,
+			value: `bar`,
+			want:  `{"name":"foo","value":"bar","isRegex":true,"isEqual":false}`,
+		},
+	}
+
+	cmp := func(m1, m2 Matcher) bool {
+		return m1.Name == m2.Name && m1.Value == m2.Value && m1.Type == m2.Type
+	}
+
+	for _, test := range tests {
+		m, err := NewMatcher(test.op, test.name, test.value)
+		if err != nil {
+			t.Fatal(err)
+		}
+
+		b, err := json.Marshal(m)
+		if err != nil {
+			t.Fatal(err)
+		}
+		if got := string(b); got != test.want {
+			t.Errorf("Unexpected JSON representation of matcher:\nwant:\t%v\ngot:\t%v", test.want, got)
+		}
+
+		var m2 Matcher
+		if err := json.Unmarshal(b, &m2); err != nil {
+			t.Fatal(err)
+		}
+		if !cmp(*m, m2) {
+			t.Errorf("Doing Marshal and Unmarshal seems to be losing data; before %#v, after %#v", m, m2)
+		}
+	}
+}