all: add starting service with Control D config

internal/controld/config.go

@@ -0,0 +1,90 @@
+package controld
+
+import (
+	"bytes"
+	"encoding/json"
+	"errors"
+	"fmt"
+	"net/http"
+	"time"
+)
+
+const resolverDataURL = "https://api.controld.com/utility"
+
+// ResolverConfig represents Control D resolver data.
+type ResolverConfig struct {
+	V4      []string `json:"v4"`
+	V6      []string `json:"v6"`
+	DOH     string   `json:"doh"`
+	Exclude []string `json:"exclude"`
+}
+
+func (r *ResolverConfig) IP(v6 bool) string {
+	ip4 := r.v4()
+	ip6 := r.v6()
+	if v6 && ip6 != "" {
+		return ip6
+	}
+	return ip4
+}
+
+func (r *ResolverConfig) v4() string {
+	for _, ip := range r.V4 {
+		return ip
+	}
+	return ""
+}
+
+func (r *ResolverConfig) v6() string {
+	for _, ip := range r.V6 {
+		return ip
+	}
+	return ""
+}
+
+type utilityResponse struct {
+	Success bool `json:"success"`
+	Body    struct {
+		Resolver ResolverConfig `json:"resolver"`
+	} `json:"body"`
+}
+
+type utilityErrorResponse struct {
+	Error struct {
+		Message string `json:"message"`
+	} `json:"error"`
+}
+
+type utilityRequest struct {
+	UID string `json:"uid"`
+}
+
+// FetchResolverConfig fetch Control D config for given uid.
+func FetchResolverConfig(uid string) (*ResolverConfig, error) {
+	body, _ := json.Marshal(utilityRequest{UID: uid})
+	req, err := http.NewRequest("POST", resolverDataURL, bytes.NewReader(body))
+	if err != nil {
+		return nil, fmt.Errorf("http.NewRequest: %w", err)
+	}
+	req.Header.Add("Content-Type", "application/json")
+	client := http.Client{Timeout: 5 * time.Second}
+	resp, err := client.Do(req)
+	if err != nil {
+		return nil, fmt.Errorf("client.Do: %w", err)
+	}
+	defer resp.Body.Close()
+	d := json.NewDecoder(resp.Body)
+	if resp.StatusCode != http.StatusOK {
+		errResp := &utilityErrorResponse{}
+		if err := d.Decode(errResp); err != nil {
+			return nil, err
+		}
+		return nil, errors.New(errResp.Error.Message)
+	}
+
+	ur := &utilityResponse{}
+	if err := d.Decode(ur); err != nil {
+		return nil, err
+	}
+	return &ur.Body.Resolver, nil
+}

internal/controld/config_test.go

@@ -0,0 +1,33 @@
+//go:build controld
+
+package controld
+
+import (
+	"testing"
+
+	"github.com/stretchr/testify/assert"
+)
+
+const utilityURL = "https://api.controld.com/utility"
+
+func TestFetchResolverConfig(t *testing.T) {
+	tests := []struct {
+		name    string
+		uid     string
+		wantErr bool
+	}{
+		{"valid", "p2", false},
+		{"invalid uid", "abcd1234", true},
+	}
+	for _, tc := range tests {
+		tc := tc
+		t.Run(tc.name, func(t *testing.T) {
+			t.Parallel()
+			got, err := FetchResolverConfig(tc.uid)
+			assert.False(t, (err != nil) != tc.wantErr)
+			if !tc.wantErr {
+				assert.NotEmpty(t, got.DOH)
+			}
+		})
+	}
+}