tailscale: support split DNS endpoints (#78)

Support the GET/PATCH/PUT `/api/v2/tailnet/{tailnetID}/dns/split-dns`
endpoints for reading, updating, and replacing split DNS settings for a
given tailnet respectively.

Updates tailscale/corp#19483

Signed-off-by: Mario Minardi <mario@tailscale.com>

tailscale/client.go

@@ -14,7 +14,6 @@ import (
 	"time"
 
 	"github.com/tailscale/hujson"
-
 	"golang.org/x/oauth2/clientcredentials"
 )
 
@@ -333,6 +332,69 @@ func (c *Client) DNSNameservers(ctx context.Context) ([]string, error) {
 	return resp["dns"], nil
 }
 
+// SplitDnsRequest is a map from domain names to a list of nameservers.
+type SplitDnsRequest map[string][]string
+
+// SplitDnsResponse is a map from domain names to a list of nameservers.
+type SplitDnsResponse SplitDnsRequest
+
+// UpdateSplitDNS updates the split DNS settings for a tailnet using the
+// provided SplitDnsRequest object. This is a PATCH operation that performs
+// partial updates of the underlying data structure.
+//
+// Mapping a domain to a nil slice in the request will unset the nameservers
+// associated with that domain. Values provided for domains will overwrite the
+// current value associated with the domain. Domains not included in the request
+// will remain unchanged.
+func (c *Client) UpdateSplitDNS(ctx context.Context, request SplitDnsRequest) (SplitDnsResponse, error) {
+	const uriFmt = "/api/v2/tailnet/%v/dns/split-dns"
+
+	req, err := c.buildRequest(ctx, http.MethodPatch, fmt.Sprintf(uriFmt, c.tailnet), requestBody(request))
+	if err != nil {
+		return nil, err
+	}
+
+	var resp SplitDnsResponse
+	if err = c.performRequest(req, &resp); err != nil {
+		return nil, err
+	}
+
+	return resp, nil
+}
+
+// SetSplitDNS sets the split DNS settings for a tailnet using the provided
+// SplitDnsRequest object. This is a PUT operation that fully replaces the underlying
+// data structure.
+//
+// Passing in an empty SplitDnsRequest will unset all split DNS mappings for the tailnet.
+func (c *Client) SetSplitDNS(ctx context.Context, request SplitDnsRequest) error {
+	const uriFmt = "/api/v2/tailnet/%v/dns/split-dns"
+
+	req, err := c.buildRequest(ctx, http.MethodPut, fmt.Sprintf(uriFmt, c.tailnet), requestBody(request))
+	if err != nil {
+		return err
+	}
+
+	return c.performRequest(req, nil)
+}
+
+// SplitDNS retrieves the split DNS configuration for a tailnet.
+func (c *Client) SplitDNS(ctx context.Context) (SplitDnsResponse, error) {
+	const uriFmt = "/api/v2/tailnet/%v/dns/split-dns"
+
+	req, err := c.buildRequest(ctx, http.MethodGet, fmt.Sprintf(uriFmt, c.tailnet))
+	if err != nil {
+		return nil, err
+	}
+
+	var resp SplitDnsResponse
+	if err = c.performRequest(req, &resp); err != nil {
+		return nil, err
+	}
+
+	return resp, nil
+}
+
 type (
 	// ACL contains the schema for a tailnet policy file. More details: https://tailscale.com/kb/1018/acls/
 	ACL struct {

tailscale/client_test.go

@@ -599,6 +599,24 @@ func TestClient_DNSSearchPaths(t *testing.T) {
 	assert.Equal(t, expectedPaths["searchPaths"], paths)
 }
 
+func TestClient_SplitDNS(t *testing.T) {
+	t.Parallel()
+
+	client, server := NewTestHarness(t)
+	server.ResponseCode = http.StatusOK
+
+	expectedNameservers := tailscale.SplitDnsResponse{
+		"example.com": {"1.1.1.1", "1.2.3.4"},
+	}
+
+	server.ResponseBody = expectedNameservers
+	nameservers, err := client.SplitDNS(context.Background())
+	assert.NoError(t, err)
+	assert.Equal(t, http.MethodGet, server.Method)
+	assert.Equal(t, "/api/v2/tailnet/example.com/dns/split-dns", server.Path)
+	assert.Equal(t, expectedNameservers, nameservers)
+}
+
 func TestClient_SetDNSNameservers(t *testing.T) {
 	t.Parallel()
 
@@ -652,6 +670,53 @@ func TestClient_SetDNSSearchPaths(t *testing.T) {
 	assert.EqualValues(t, paths, body["searchPaths"])
 }
 
+func TestClient_UpdateSplitDNS(t *testing.T) {
+	t.Parallel()
+
+	client, server := NewTestHarness(t)
+	server.ResponseCode = http.StatusOK
+
+	nameservers := []string{"1.1.2.1", "3.3.3.4"}
+	request := tailscale.SplitDnsRequest{
+		"example.com": nameservers,
+	}
+
+	expectedNameservers := tailscale.SplitDnsResponse{
+		"example.com": nameservers,
+	}
+	server.ResponseBody = expectedNameservers
+
+	resp, err := client.UpdateSplitDNS(context.Background(), request)
+	assert.NoError(t, err)
+	assert.Equal(t, http.MethodPatch, server.Method)
+	assert.Equal(t, "/api/v2/tailnet/example.com/dns/split-dns", server.Path)
+
+	body := make(tailscale.SplitDnsResponse)
+	assert.NoError(t, json.Unmarshal(server.Body.Bytes(), &body))
+	assert.EqualValues(t, nameservers, body["example.com"])
+	assert.Equal(t, expectedNameservers, resp)
+}
+
+func TestClient_SetSplitDNS(t *testing.T) {
+	t.Parallel()
+
+	client, server := NewTestHarness(t)
+	server.ResponseCode = http.StatusOK
+
+	nameservers := []string{"1.1.2.1", "3.3.3.4"}
+	request := tailscale.SplitDnsRequest{
+		"example.com": nameservers,
+	}
+
+	assert.NoError(t, client.SetSplitDNS(context.Background(), request))
+	assert.Equal(t, http.MethodPut, server.Method)
+	assert.Equal(t, "/api/v2/tailnet/example.com/dns/split-dns", server.Path)
+
+	body := make(tailscale.SplitDnsResponse)
+	assert.NoError(t, json.Unmarshal(server.Body.Bytes(), &body))
+	assert.EqualValues(t, nameservers, body["example.com"])
+}
+
 func TestClient_AuthorizeDevice(t *testing.T) {
 	t.Parallel()