implement k8s service discovery (#988)

* implement k8s service discovery

* simplify code

* use default namespace if not provided

* disable codecov bot comment

* ignore adhoc dir

* simplify building target in NewClient

* reformat code

* Fix filepath (#990)

* format code, and reorg imports (#991)

* add more unit test

Co-authored-by: anqiansong <anqiansong@gmail.com>

zrpc/internal/resolver/kube/targetparser_test.go

@@ -0,0 +1,83 @@
+package kube
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+	"google.golang.org/grpc/resolver"
+)
+
+func TestParseTarget(t *testing.T) {
+	tests := []struct {
+		name   string
+		input  resolver.Target
+		expect Service
+		hasErr bool
+	}{
+		{
+			name: "normal case",
+			input: resolver.Target{
+				Scheme:    "k8s",
+				Authority: "ns1",
+				Endpoint:  "my-svc:8080",
+			},
+			expect: Service{
+				Namespace: "ns1",
+				Name:      "my-svc",
+				Port:      8080,
+			},
+		},
+		{
+			name: "normal case",
+			input: resolver.Target{
+				Scheme:    "k8s",
+				Authority: "",
+				Endpoint:  "my-svc:8080",
+			},
+			expect: Service{
+				Namespace: defaultNamespace,
+				Name:      "my-svc",
+				Port:      8080,
+			},
+		},
+		{
+			name: "no port",
+			input: resolver.Target{
+				Scheme:    "k8s",
+				Authority: "ns1",
+				Endpoint:  "my-svc:",
+			},
+			hasErr: true,
+		},
+		{
+			name: "no port, no colon",
+			input: resolver.Target{
+				Scheme:    "k8s",
+				Authority: "ns1",
+				Endpoint:  "my-svc",
+			},
+			hasErr: true,
+		},
+		{
+			name: "bad port",
+			input: resolver.Target{
+				Scheme:    "k8s",
+				Authority: "ns1",
+				Endpoint:  "my-svc:800a",
+			},
+			hasErr: true,
+		},
+	}
+
+	for _, test := range tests {
+		t.Run(test.name, func(t *testing.T) {
+			svc, err := ParseTarget(test.input)
+			if test.hasErr {
+				assert.NotNil(t, err)
+			} else {
+				assert.Nil(t, err)
+				assert.Equal(t, test.expect, svc)
+			}
+		})
+	}
+}