resource_dns_configuration: create resource for managing entire DNS configuration at once

This resource uses the new `/tailnet/-/dns/configuration` endpoint to manage the
complete DNS configuration for a tailnet.

Updates tailscale/corp#32130

Signed-off-by: Percy Wegmann <percy@tailscale.com>

Author: oxtoacart

dns.go

@@ -147,3 +147,42 @@ func (dr *DNSResource) SetPreferences(ctx context.Context, preferences DNSPrefer
 
 	return dr.do(req, nil)
 }
+
+type DNSConfiguration struct {
+	Nameservers []DNSConfigurationResolver            `json:"nameservers,omitempty"`
+	SplitDNS    map[string][]DNSConfigurationResolver `json:"splitDNS,omitempty"`
+	SearchPaths []string                              `json:"searchPaths,omitempty"`
+	Preferences DNSConfigurationPreferences           `json:"preferences,omitempty"`
+}
+
+type DNSConfigurationResolver struct {
+	Address         string `json:"address,omitempty"`
+	UseWithExitNode bool   `json:"useWithExitNode,omitempty"`
+}
+
+type DNSConfigurationPreferences struct {
+	OverrideLocalDNS bool `json:"overrideLocalDNS,omitempty"`
+	MagicDNS         bool `json:"magicDNS,omitempty"`
+}
+
+// Configuration retrieves the tailnet's complete DNS configuration.
+// WARNING - this is currently in alpha and subject to change.
+func (dr *DNSResource) Configuration(ctx context.Context) (*DNSConfiguration, error) {
+	req, err := dr.buildRequest(ctx, http.MethodGet, dr.buildTailnetURL("dns", "configuration"))
+	if err != nil {
+		return nil, err
+	}
+
+	return body[DNSConfiguration](dr, req)
+}
+
+// SetConfiguration sets the tailnet's complete DNS configuration.
+// WARNING - this is currently in alpha and subject to change.
+func (dr *DNSResource) SetConfiguration(ctx context.Context, configuration DNSConfiguration) error {
+	req, err := dr.buildRequest(ctx, http.MethodPost, dr.buildTailnetURL("dns", "configuration"), requestBody(configuration))
+	if err != nil {
+		return nil
+	}
+
+	return dr.do(req, nil)
+}

dns_test.go

@@ -182,3 +182,72 @@ func TestClient_SetSplitDNS(t *testing.T) {
 	assert.NoError(t, json.Unmarshal(server.Body.Bytes(), &body))
 	assert.EqualValues(t, nameservers, body["example.com"])
 }
+
+func TestClient_DNSConfiguration(t *testing.T) {
+	t.Parallel()
+
+	client, server := NewTestHarness(t)
+	server.ResponseCode = http.StatusOK
+	server.ResponseBody = &DNSConfiguration{
+		Nameservers: []DNSConfigurationResolver{
+			{
+				Address:         "8.8.8.8",
+				UseWithExitNode: true,
+			},
+		},
+		SplitDNS: map[string][]DNSConfigurationResolver{
+			"example.com": []DNSConfigurationResolver{
+				{
+					Address:         "4.4.4.4",
+					UseWithExitNode: true,
+				},
+			},
+		},
+		Preferences: DNSConfigurationPreferences{
+			OverrideLocalDNS: true,
+			MagicDNS:         true,
+		},
+	}
+
+	configuration, err := client.DNS().Configuration(context.Background())
+	assert.NoError(t, err)
+	assert.Equal(t, http.MethodGet, server.Method)
+	assert.Equal(t, "/api/v2/tailnet/example.com/dns/configuration", server.Path)
+	assert.Equal(t, server.ResponseBody, configuration)
+}
+
+func TestClient_SetDNSConfiguration(t *testing.T) {
+	t.Parallel()
+
+	client, server := NewTestHarness(t)
+	server.ResponseCode = http.StatusOK
+
+	configuration := DNSConfiguration{
+		Nameservers: []DNSConfigurationResolver{
+			{
+				Address:         "8.8.8.8",
+				UseWithExitNode: true,
+			},
+		},
+		SplitDNS: map[string][]DNSConfigurationResolver{
+			"example.com": {
+				{
+					Address:         "4.4.4.4",
+					UseWithExitNode: true,
+				},
+			},
+		},
+		Preferences: DNSConfigurationPreferences{
+			OverrideLocalDNS: true,
+			MagicDNS:         true,
+		},
+	}
+
+	assert.NoError(t, client.DNS().SetConfiguration(context.Background(), configuration))
+	assert.Equal(t, http.MethodPost, server.Method)
+	assert.Equal(t, "/api/v2/tailnet/example.com/dns/configuration", server.Path)
+
+	var body DNSConfiguration
+	assert.NoError(t, json.Unmarshal(server.Body.Bytes(), &body))
+	assert.EqualValues(t, configuration, body)
+}