feat: add coder connect exists hidden subcommand (#17418)

Adds a new hidden subcommand `coder connect exists <hostname>` that checks if the name exists via Coder Connect. This will be used in SSH config to match only if Coder Connect is unavailable for the hostname in question, so that the SSH client will directly dial the workspace over an existing Coder Connect tunnel.

Also refactors the way we inject a test DNS resolver into the lookup functions so that we can test from outside the `workspacesdk` package.

codersdk/workspacesdk/workspacesdk_test.go

@@ -1,12 +1,18 @@
 package workspacesdk_test
 
 import (
+	"context"
+	"fmt"
+	"net"
 	"net/http"
 	"net/http/httptest"
 	"net/url"
 	"testing"
 
+	"github.com/stretchr/testify/assert"
 	"github.com/stretchr/testify/require"
+	"golang.org/x/xerrors"
+	"tailscale.com/net/tsaddr"
 	"tailscale.com/tailcfg"
 
 	"github.com/coder/websocket"
@@ -15,6 +21,7 @@ import (
 	"github.com/coder/coder/v2/codersdk"
 	"github.com/coder/coder/v2/codersdk/agentsdk"
 	"github.com/coder/coder/v2/codersdk/workspacesdk"
+	"github.com/coder/coder/v2/tailnet"
 	"github.com/coder/coder/v2/testutil"
 )
 
@@ -72,3 +79,70 @@ func TestWorkspaceDialerFailure(t *testing.T) {
 	// Then: an error indicating a database issue is returned, to conditionalize the behavior of the caller.
 	require.ErrorIs(t, err, codersdk.ErrDatabaseNotReachable)
 }
+
+func TestClient_IsCoderConnectRunning(t *testing.T) {
+	t.Parallel()
+	ctx := testutil.Context(t, testutil.WaitShort)
+
+	srv := httptest.NewServer(http.HandlerFunc(func(rw http.ResponseWriter, r *http.Request) {
+		assert.Equal(t, "/api/v2/workspaceagents/connection", r.URL.Path)
+		httpapi.Write(ctx, rw, http.StatusOK, workspacesdk.AgentConnectionInfo{
+			HostnameSuffix: "test",
+		})
+	}))
+	defer srv.Close()
+
+	apiURL, err := url.Parse(srv.URL)
+	require.NoError(t, err)
+	sdkClient := codersdk.New(apiURL)
+	client := workspacesdk.New(sdkClient)
+
+	// Right name, right IP
+	expectedName := fmt.Sprintf(tailnet.IsCoderConnectEnabledFmtString, "test")
+	ctxResolveExpected := workspacesdk.WithTestOnlyCoderContextResolver(ctx,
+		&fakeResolver{t: t, hostMap: map[string][]net.IP{
+			expectedName: {net.ParseIP(tsaddr.CoderServiceIPv6().String())},
+		}})
+
+	result, err := client.IsCoderConnectRunning(ctxResolveExpected, workspacesdk.CoderConnectQueryOptions{})
+	require.NoError(t, err)
+	require.True(t, result)
+
+	// Wrong name
+	result, err = client.IsCoderConnectRunning(ctxResolveExpected, workspacesdk.CoderConnectQueryOptions{HostnameSuffix: "coder"})
+	require.NoError(t, err)
+	require.False(t, result)
+
+	// Not found
+	ctxResolveNotFound := workspacesdk.WithTestOnlyCoderContextResolver(ctx,
+		&fakeResolver{t: t, err: &net.DNSError{IsNotFound: true}})
+	result, err = client.IsCoderConnectRunning(ctxResolveNotFound, workspacesdk.CoderConnectQueryOptions{})
+	require.NoError(t, err)
+	require.False(t, result)
+
+	// Some other error
+	ctxResolverErr := workspacesdk.WithTestOnlyCoderContextResolver(ctx,
+		&fakeResolver{t: t, err: xerrors.New("a bad thing happened")})
+	_, err = client.IsCoderConnectRunning(ctxResolverErr, workspacesdk.CoderConnectQueryOptions{})
+	require.Error(t, err)
+
+	// Right name, wrong IP
+	ctxResolverWrongIP := workspacesdk.WithTestOnlyCoderContextResolver(ctx,
+		&fakeResolver{t: t, hostMap: map[string][]net.IP{
+			expectedName: {net.ParseIP("2001::34")},
+		}})
+	result, err = client.IsCoderConnectRunning(ctxResolverWrongIP, workspacesdk.CoderConnectQueryOptions{})
+	require.NoError(t, err)
+	require.False(t, result)
+}
+
+type fakeResolver struct {
+	t       testing.TB
+	hostMap map[string][]net.IP
+	err     error
+}
+
+func (f *fakeResolver) LookupIP(_ context.Context, network, host string) ([]net.IP, error) {
+	assert.Equal(f.t, "ip6", network)
+	return f.hostMap[host], f.err
+}