coder/agent/agent_test.go

package agent_test

import (
	"bufio"
	"context"
	"encoding/json"
	"fmt"
	"io"
	"net"
	"net/netip"
	"os"
	"os/exec"
	"os/user"
	"path"
	"path/filepath"
	"runtime"
	"strconv"
	"strings"
	"sync"
	"sync/atomic"
	"testing"
	"time"

	"golang.org/x/xerrors"
	"tailscale.com/net/speedtest"
	"tailscale.com/tailcfg"

	scp "github.com/bramvdbogaerde/go-scp"
	"github.com/google/uuid"
	"github.com/pion/udp"
	"github.com/pkg/sftp"
	"github.com/spf13/afero"
	"github.com/stretchr/testify/assert"
	"github.com/stretchr/testify/require"
	"go.uber.org/goleak"
	"golang.org/x/crypto/ssh"
	"golang.org/x/text/encoding/unicode"
	"golang.org/x/text/transform"

	"cdr.dev/slog"
	"cdr.dev/slog/sloggers/slogtest"
	"github.com/coder/coder/agent"
	"github.com/coder/coder/codersdk"
	"github.com/coder/coder/pty/ptytest"
	"github.com/coder/coder/tailnet"
	"github.com/coder/coder/tailnet/tailnettest"
	"github.com/coder/coder/testutil"
)

func TestMain(m *testing.M) {
	goleak.VerifyTestMain(m)
}

func TestAgent(t *testing.T) {
	t.Parallel()
	t.Run("Stats", func(t *testing.T) {
		t.Parallel()

		t.Run("SSH", func(t *testing.T) {
			t.Parallel()
			ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
			defer cancel()

			conn, stats, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)

			sshClient, err := conn.SSHClient(ctx)
			require.NoError(t, err)
			defer sshClient.Close()
			session, err := sshClient.NewSession()
			require.NoError(t, err)
			defer session.Close()
			require.NoError(t, session.Run("echo test"))

			var s *codersdk.AgentStats
			require.Eventuallyf(t, func() bool {
				var ok bool
				s, ok = <-stats
				return ok && s.NumConns > 0 && s.RxBytes > 0 && s.TxBytes > 0
			}, testutil.WaitLong, testutil.IntervalFast,
				"never saw stats: %+v", s,
			)
		})

		t.Run("ReconnectingPTY", func(t *testing.T) {
			t.Parallel()

			ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
			defer cancel()

			conn, stats, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)

			ptyConn, err := conn.ReconnectingPTY(ctx, uuid.New(), 128, 128, "/bin/bash")
			require.NoError(t, err)
			defer ptyConn.Close()

			data, err := json.Marshal(codersdk.ReconnectingPTYRequest{
				Data: "echo test\r\n",
			})
			require.NoError(t, err)
			_, err = ptyConn.Write(data)
			require.NoError(t, err)

			var s *codersdk.AgentStats
			require.Eventuallyf(t, func() bool {
				var ok bool
				s, ok = <-stats
				return ok && s.NumConns > 0 && s.RxBytes > 0 && s.TxBytes > 0
			}, testutil.WaitLong, testutil.IntervalFast,
				"never saw stats: %+v", s,
			)
		})
	})

	t.Run("SessionExec", func(t *testing.T) {
		t.Parallel()
		session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{})

		command := "echo test"
		if runtime.GOOS == "windows" {
			command = "cmd.exe /c echo test"
		}
		output, err := session.Output(command)
		require.NoError(t, err)
		require.Equal(t, "test", strings.TrimSpace(string(output)))
	})

	t.Run("GitSSH", func(t *testing.T) {
		t.Parallel()
		session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{})
		command := "sh -c 'echo $GIT_SSH_COMMAND'"
		if runtime.GOOS == "windows" {
			command = "cmd.exe /c echo %GIT_SSH_COMMAND%"
		}
		output, err := session.Output(command)
		require.NoError(t, err)
		require.True(t, strings.HasSuffix(strings.TrimSpace(string(output)), "gitssh --"))
	})

	t.Run("SessionTTYShell", func(t *testing.T) {
		t.Parallel()
		if runtime.GOOS == "windows" {
			// This might be our implementation, or ConPTY itself.
			// It's difficult to find extensive tests for it, so
			// it seems like it could be either.
			t.Skip("ConPTY appears to be inconsistent on Windows.")
		}
		session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{})
		command := "bash"
		if runtime.GOOS == "windows" {
			command = "cmd.exe"
		}
		err := session.RequestPty("xterm", 128, 128, ssh.TerminalModes{})
		require.NoError(t, err)
		ptty := ptytest.New(t)
		require.NoError(t, err)
		session.Stdout = ptty.Output()
		session.Stderr = ptty.Output()
		session.Stdin = ptty.Input()
		err = session.Start(command)
		require.NoError(t, err)
		caret := "$"
		if runtime.GOOS == "windows" {
			caret = ">"
		}
		ptty.ExpectMatch(caret)
		ptty.WriteLine("echo test")
		ptty.ExpectMatch("test")
		ptty.WriteLine("exit")
		err = session.Wait()
		require.NoError(t, err)
	})

	t.Run("SessionTTYExitCode", func(t *testing.T) {
		t.Parallel()
		session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{})
		command := "areallynotrealcommand"
		err := session.RequestPty("xterm", 128, 128, ssh.TerminalModes{})
		require.NoError(t, err)
		ptty := ptytest.New(t)
		require.NoError(t, err)
		session.Stdout = ptty.Output()
		session.Stderr = ptty.Output()
		session.Stdin = ptty.Input()
		err = session.Start(command)
		require.NoError(t, err)
		err = session.Wait()
		exitErr := &ssh.ExitError{}
		require.True(t, xerrors.As(err, &exitErr))
		if runtime.GOOS == "windows" {
			assert.Equal(t, 1, exitErr.ExitStatus())
		} else {
			assert.Equal(t, 127, exitErr.ExitStatus())
		}
	})

	t.Run("LocalForwarding", func(t *testing.T) {
		t.Parallel()
		random, err := net.Listen("tcp", "127.0.0.1:0")
		require.NoError(t, err)
		_ = random.Close()
		tcpAddr, valid := random.Addr().(*net.TCPAddr)
		require.True(t, valid)
		randomPort := tcpAddr.Port

		local, err := net.Listen("tcp", "127.0.0.1:0")
		require.NoError(t, err)
		defer local.Close()
		tcpAddr, valid = local.Addr().(*net.TCPAddr)
		require.True(t, valid)
		localPort := tcpAddr.Port
		done := make(chan struct{})
		go func() {
			defer close(done)
			conn, err := local.Accept()
			if !assert.NoError(t, err) {
				return
			}
			_ = conn.Close()
		}()

		err = setupSSHCommand(t, []string{"-L", fmt.Sprintf("%d:127.0.0.1:%d", randomPort, localPort)}, []string{"echo", "test"}).Start()
		require.NoError(t, err)

		conn, err := net.Dial("tcp", "127.0.0.1:"+strconv.Itoa(localPort))
		require.NoError(t, err)
		conn.Close()
		<-done
	})

	t.Run("SFTP", func(t *testing.T) {
		t.Parallel()
		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
		defer cancel()
		u, err := user.Current()
		require.NoError(t, err, "get current user")
		home := u.HomeDir
		if runtime.GOOS == "windows" {
			home = "/" + strings.ReplaceAll(home, "\\", "/")
		}
		conn, _, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)
		sshClient, err := conn.SSHClient(ctx)
		require.NoError(t, err)
		defer sshClient.Close()
		client, err := sftp.NewClient(sshClient)
		require.NoError(t, err)
		wd, err := client.Getwd()
		require.NoError(t, err, "get working directory")
		require.Equal(t, home, wd, "working directory should be home user home")
		tempFile := filepath.Join(t.TempDir(), "sftp")
		// SFTP only accepts unix-y paths.
		remoteFile := filepath.ToSlash(tempFile)
		if !path.IsAbs(remoteFile) {
			// On Windows, e.g. "/C:/Users/...".
			remoteFile = path.Join("/", remoteFile)
		}
		file, err := client.Create(remoteFile)
		require.NoError(t, err)
		err = file.Close()
		require.NoError(t, err)
		_, err = os.Stat(tempFile)
		require.NoError(t, err)
	})

	t.Run("SCP", func(t *testing.T) {
		t.Parallel()

		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
		defer cancel()

		conn, _, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)
		sshClient, err := conn.SSHClient(ctx)
		require.NoError(t, err)
		defer sshClient.Close()
		scpClient, err := scp.NewClientBySSH(sshClient)
		require.NoError(t, err)
		tempFile := filepath.Join(t.TempDir(), "scp")
		content := "hello world"
		err = scpClient.CopyFile(context.Background(), strings.NewReader(content), tempFile, "0755")
		require.NoError(t, err)
		_, err = os.Stat(tempFile)
		require.NoError(t, err)
	})

	t.Run("EnvironmentVariables", func(t *testing.T) {
		t.Parallel()
		key := "EXAMPLE"
		value := "value"
		session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{
			EnvironmentVariables: map[string]string{
				key: value,
			},
		})
		command := "sh -c 'echo $" + key + "'"
		if runtime.GOOS == "windows" {
			command = "cmd.exe /c echo %" + key + "%"
		}
		output, err := session.Output(command)
		require.NoError(t, err)
		require.Equal(t, value, strings.TrimSpace(string(output)))
	})

	t.Run("EnvironmentVariableExpansion", func(t *testing.T) {
		t.Parallel()
		key := "EXAMPLE"
		session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{
			EnvironmentVariables: map[string]string{
				key: "$SOMETHINGNOTSET",
			},
		})
		command := "sh -c 'echo $" + key + "'"
		if runtime.GOOS == "windows" {
			command = "cmd.exe /c echo %" + key + "%"
		}
		output, err := session.Output(command)
		require.NoError(t, err)
		expect := ""
		if runtime.GOOS == "windows" {
			expect = "%EXAMPLE%"
		}
		// Output should be empty, because the variable is not set!
		require.Equal(t, expect, strings.TrimSpace(string(output)))
	})

	t.Run("Coder env vars", func(t *testing.T) {
		t.Parallel()

		for _, key := range []string{"CODER"} {
			key := key
			t.Run(key, func(t *testing.T) {
				t.Parallel()

				session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{})
				command := "sh -c 'echo $" + key + "'"
				if runtime.GOOS == "windows" {
					command = "cmd.exe /c echo %" + key + "%"
				}
				output, err := session.Output(command)
				require.NoError(t, err)
				require.NotEmpty(t, strings.TrimSpace(string(output)))
			})
		}
	})

	t.Run("SSH connection env vars", func(t *testing.T) {
		t.Parallel()

		// Note: the SSH_TTY environment variable should only be set for TTYs.
		// For some reason this test produces a TTY locally and a non-TTY in CI
		// so we don't test for the absence of SSH_TTY.
		for _, key := range []string{"SSH_CONNECTION", "SSH_CLIENT"} {
			key := key
			t.Run(key, func(t *testing.T) {
				t.Parallel()

				session := setupSSHSession(t, codersdk.WorkspaceAgentMetadata{})
				command := "sh -c 'echo $" + key + "'"
				if runtime.GOOS == "windows" {
					command = "cmd.exe /c echo %" + key + "%"
				}
				output, err := session.Output(command)
				require.NoError(t, err)
				require.NotEmpty(t, strings.TrimSpace(string(output)))
			})
		}
	})

	t.Run("StartupScript", func(t *testing.T) {
		t.Parallel()
		if runtime.GOOS == "windows" {
			t.Skip("This test doesn't work on Windows for some reason...")
		}
		content := "output"
		_, _, fs := setupAgent(t, codersdk.WorkspaceAgentMetadata{
			StartupScript: "echo " + content,
		}, 0)
		var gotContent string
		require.Eventually(t, func() bool {
			outputPath := filepath.Join(os.TempDir(), "coder-startup-script.log")
			content, err := afero.ReadFile(fs, outputPath)
			if err != nil {
				t.Logf("read file %q: %s", outputPath, err)
				return false
			}
			if len(content) == 0 {
				t.Logf("no content in %q", outputPath)
				return false
			}
			if runtime.GOOS == "windows" {
				// Windows uses UTF16! 🪟🪟🪟
				content, _, err = transform.Bytes(unicode.UTF16(unicode.LittleEndian, unicode.UseBOM).NewDecoder(), content)
				if !assert.NoError(t, err) {
					return false
				}
			}
			gotContent = string(content)
			return true
		}, testutil.WaitShort, testutil.IntervalMedium)
		require.Equal(t, content, strings.TrimSpace(gotContent))
	})

	t.Run("ReconnectingPTY", func(t *testing.T) {
		t.Parallel()
		if runtime.GOOS == "windows" {
			// This might be our implementation, or ConPTY itself.
			// It's difficult to find extensive tests for it, so
			// it seems like it could be either.
			t.Skip("ConPTY appears to be inconsistent on Windows.")
		}

		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
		defer cancel()

		conn, _, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)
		id := uuid.New()
		netConn, err := conn.ReconnectingPTY(ctx, id, 100, 100, "/bin/bash")
		require.NoError(t, err)
		bufRead := bufio.NewReader(netConn)

		// Brief pause to reduce the likelihood that we send keystrokes while
		// the shell is simultaneously sending a prompt.
		time.Sleep(100 * time.Millisecond)

		data, err := json.Marshal(codersdk.ReconnectingPTYRequest{
			Data: "echo test\r\n",
		})
		require.NoError(t, err)
		_, err = netConn.Write(data)
		require.NoError(t, err)

		expectLine := func(matcher func(string) bool) {
			for {
				line, err := bufRead.ReadString('\n')
				require.NoError(t, err)
				if matcher(line) {
					break
				}
			}
		}

		matchEchoCommand := func(line string) bool {
			return strings.Contains(line, "echo test")
		}
		matchEchoOutput := func(line string) bool {
			return strings.Contains(line, "test") && !strings.Contains(line, "echo")
		}

		// Once for typing the command...
		expectLine(matchEchoCommand)
		// And another time for the actual output.
		expectLine(matchEchoOutput)

		_ = netConn.Close()
		netConn, err = conn.ReconnectingPTY(ctx, id, 100, 100, "/bin/bash")
		require.NoError(t, err)
		bufRead = bufio.NewReader(netConn)

		// Same output again!
		expectLine(matchEchoCommand)
		expectLine(matchEchoOutput)
	})

	t.Run("Dial", func(t *testing.T) {
		t.Parallel()

		cases := []struct {
			name  string
			setup func(t *testing.T) net.Listener
		}{
			{
				name: "TCP",
				setup: func(t *testing.T) net.Listener {
					l, err := net.Listen("tcp", "127.0.0.1:0")
					require.NoError(t, err, "create TCP listener")
					return l
				},
			},
			{
				name: "UDP",
				setup: func(t *testing.T) net.Listener {
					addr := net.UDPAddr{
						IP:   net.ParseIP("127.0.0.1"),
						Port: 0,
					}
					l, err := udp.Listen("udp", &addr)
					require.NoError(t, err, "create UDP listener")
					return l
				},
			},
		}

		for _, c := range cases {
			c := c
			t.Run(c.name, func(t *testing.T) {
				t.Parallel()

				// Setup listener
				l := c.setup(t)
				defer l.Close()
				go func() {
					for {
						c, err := l.Accept()
						if err != nil {
							return
						}

						go testAccept(t, c)
					}
				}()

				conn, _, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)
				require.True(t, conn.AwaitReachable(context.Background()))
				conn1, err := conn.DialContext(context.Background(), l.Addr().Network(), l.Addr().String())
				require.NoError(t, err)
				defer conn1.Close()
				conn2, err := conn.DialContext(context.Background(), l.Addr().Network(), l.Addr().String())
				require.NoError(t, err)
				defer conn2.Close()
				testDial(t, conn2)
				testDial(t, conn1)
				time.Sleep(150 * time.Millisecond)
			})
		}
	})

	t.Run("Speedtest", func(t *testing.T) {
		t.Parallel()
		t.Skip("This test is relatively flakey because of Tailscale's speedtest code...")
		ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
		defer cancel()
		derpMap := tailnettest.RunDERPAndSTUN(t)
		conn, _, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{
			DERPMap: derpMap,
		}, 0)
		defer conn.Close()
		res, err := conn.Speedtest(ctx, speedtest.Upload, 250*time.Millisecond)
		require.NoError(t, err)
		t.Logf("%.2f MBits/s", res[len(res)-1].MBitsPerSecond())
	})

	t.Run("Reconnect", func(t *testing.T) {
		t.Parallel()
		// After the agent is disconnected from a coordinator, it's supposed
		// to reconnect!
		coordinator := tailnet.NewCoordinator()
		agentID := uuid.New()
		statsCh := make(chan *codersdk.AgentStats)
		derpMap := tailnettest.RunDERPAndSTUN(t)
		client := &client{
			t:       t,
			agentID: agentID,
			metadata: codersdk.WorkspaceAgentMetadata{
				DERPMap: derpMap,
			},
			statsChan:   statsCh,
			coordinator: coordinator,
		}
		initialized := atomic.Int32{}
		closer := agent.New(agent.Options{
			ExchangeToken: func(ctx context.Context) (string, error) {
				initialized.Add(1)
				return "", nil
			},
			Client: client,
			Logger: slogtest.Make(t, nil).Leveled(slog.LevelInfo),
		})
		t.Cleanup(func() {
			_ = closer.Close()
		})

		require.Eventually(t, func() bool {
			return coordinator.Node(agentID) != nil
		}, testutil.WaitShort, testutil.IntervalFast)
		client.lastWorkspaceAgent()
		require.Eventually(t, func() bool {
			return initialized.Load() == 2
		}, testutil.WaitShort, testutil.IntervalFast)
	})

	t.Run("WriteVSCodeConfigs", func(t *testing.T) {
		t.Parallel()
		client := &client{
			t:       t,
			agentID: uuid.New(),
			metadata: codersdk.WorkspaceAgentMetadata{
				GitAuthConfigs: 1,
				DERPMap:        &tailcfg.DERPMap{},
			},
			statsChan:   make(chan *codersdk.AgentStats),
			coordinator: tailnet.NewCoordinator(),
		}
		filesystem := afero.NewMemMapFs()
		closer := agent.New(agent.Options{
			ExchangeToken: func(ctx context.Context) (string, error) {
				return "", nil
			},
			Client:     client,
			Logger:     slogtest.Make(t, nil).Leveled(slog.LevelInfo),
			Filesystem: filesystem,
		})
		t.Cleanup(func() {
			_ = closer.Close()
		})
		home, err := os.UserHomeDir()
		require.NoError(t, err)
		path := filepath.Join(home, ".vscode-server", "data", "Machine", "settings.json")
		require.Eventually(t, func() bool {
			_, err := filesystem.Stat(path)
			return err == nil
		}, testutil.WaitShort, testutil.IntervalFast)
	})
}

func setupSSHCommand(t *testing.T, beforeArgs []string, afterArgs []string) *exec.Cmd {
	agentConn, _, _ := setupAgent(t, codersdk.WorkspaceAgentMetadata{}, 0)
	listener, err := net.Listen("tcp", "127.0.0.1:0")
	require.NoError(t, err)
	waitGroup := sync.WaitGroup{}
	go func() {
		defer listener.Close()
		for {
			conn, err := listener.Accept()
			if err != nil {
				return
			}

			ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
			ssh, err := agentConn.SSH(ctx)
			cancel()
			if err != nil {
				_ = conn.Close()
				return
			}
			waitGroup.Add(1)
			go func() {
				agent.Bicopy(context.Background(), conn, ssh)
				waitGroup.Done()
			}()
		}
	}()
	t.Cleanup(func() {
		_ = listener.Close()
		waitGroup.Wait()
	})
	tcpAddr, valid := listener.Addr().(*net.TCPAddr)
	require.True(t, valid)
	args := append(beforeArgs,
		"-o", "HostName "+tcpAddr.IP.String(),
		"-o", "Port "+strconv.Itoa(tcpAddr.Port),
		"-o", "StrictHostKeyChecking=no", "host")
	args = append(args, afterArgs...)
	return exec.Command("ssh", args...)
}

func setupSSHSession(t *testing.T, options codersdk.WorkspaceAgentMetadata) *ssh.Session {
	ctx, cancel := context.WithTimeout(context.Background(), testutil.WaitLong)
	defer cancel()
	conn, _, _ := setupAgent(t, options, 0)
	sshClient, err := conn.SSHClient(ctx)
	require.NoError(t, err)
	t.Cleanup(func() {
		_ = sshClient.Close()
	})
	session, err := sshClient.NewSession()
	require.NoError(t, err)
	return session
}

type closeFunc func() error

func (c closeFunc) Close() error {
	return c()
}

func setupAgent(t *testing.T, metadata codersdk.WorkspaceAgentMetadata, ptyTimeout time.Duration) (
	*codersdk.AgentConn,
	<-chan *codersdk.AgentStats,
	afero.Fs,
) {
	if metadata.DERPMap == nil {
		metadata.DERPMap = tailnettest.RunDERPAndSTUN(t)
	}
	coordinator := tailnet.NewCoordinator()
	agentID := uuid.New()
	statsCh := make(chan *codersdk.AgentStats, 50)
	fs := afero.NewMemMapFs()
	closer := agent.New(agent.Options{
		Client: &client{
			t:           t,
			agentID:     agentID,
			metadata:    metadata,
			statsChan:   statsCh,
			coordinator: coordinator,
		},
		Filesystem:             fs,
		Logger:                 slogtest.Make(t, nil).Leveled(slog.LevelDebug),
		ReconnectingPTYTimeout: ptyTimeout,
	})
	t.Cleanup(func() {
		_ = closer.Close()
	})
	conn, err := tailnet.NewConn(&tailnet.Options{
		Addresses:          []netip.Prefix{netip.PrefixFrom(tailnet.IP(), 128)},
		DERPMap:            metadata.DERPMap,
		Logger:             slogtest.Make(t, nil).Named("client").Leveled(slog.LevelDebug),
		EnableTrafficStats: true,
	})
	require.NoError(t, err)
	clientConn, serverConn := net.Pipe()
	t.Cleanup(func() {
		_ = clientConn.Close()
		_ = serverConn.Close()
		_ = conn.Close()
	})
	go coordinator.ServeClient(serverConn, uuid.New(), agentID)
	sendNode, _ := tailnet.ServeCoordinator(clientConn, func(node []*tailnet.Node) error {
		return conn.UpdateNodes(node)
	})
	conn.SetNodeCallback(sendNode)
	return &codersdk.AgentConn{
		Conn: conn,
	}, statsCh, fs
}

var dialTestPayload = []byte("dean-was-here123")

func testDial(t *testing.T, c net.Conn) {
	t.Helper()

	assertWritePayload(t, c, dialTestPayload)
	assertReadPayload(t, c, dialTestPayload)
}

func testAccept(t *testing.T, c net.Conn) {
	t.Helper()
	defer c.Close()

	assertReadPayload(t, c, dialTestPayload)
	assertWritePayload(t, c, dialTestPayload)
}

func assertReadPayload(t *testing.T, r io.Reader, payload []byte) {
	b := make([]byte, len(payload)+16)
	n, err := r.Read(b)
	assert.NoError(t, err, "read payload")
	assert.Equal(t, len(payload), n, "read payload length does not match")
	assert.Equal(t, payload, b[:n])
}

func assertWritePayload(t *testing.T, w io.Writer, payload []byte) {
	n, err := w.Write(payload)
	assert.NoError(t, err, "write payload")
	assert.Equal(t, len(payload), n, "payload length does not match")
}

type client struct {
	t                  *testing.T
	agentID            uuid.UUID
	metadata           codersdk.WorkspaceAgentMetadata
	statsChan          chan *codersdk.AgentStats
	coordinator        tailnet.Coordinator
	lastWorkspaceAgent func()
}

func (c *client) WorkspaceAgentMetadata(_ context.Context) (codersdk.WorkspaceAgentMetadata, error) {
	return c.metadata, nil
}

func (c *client) ListenWorkspaceAgent(_ context.Context) (net.Conn, error) {
	clientConn, serverConn := net.Pipe()
	closed := make(chan struct{})
	c.lastWorkspaceAgent = func() {
		_ = serverConn.Close()
		_ = clientConn.Close()
		<-closed
	}
	c.t.Cleanup(c.lastWorkspaceAgent)
	go func() {
		_ = c.coordinator.ServeAgent(serverConn, c.agentID)
		close(closed)
	}()
	return clientConn, nil
}

func (c *client) AgentReportStats(ctx context.Context, _ slog.Logger, stats func() *codersdk.AgentStats) (io.Closer, error) {
	doneCh := make(chan struct{})
	ctx, cancel := context.WithCancel(ctx)

	go func() {
		defer close(doneCh)

		t := time.NewTicker(500 * time.Millisecond)
		defer t.Stop()
		for {
			select {
			case <-ctx.Done():
				return
			case <-t.C:
			}
			select {
			case c.statsChan <- stats():
			case <-ctx.Done():
				return
			default:
				// We don't want to send old stats.
				continue
			}
		}
	}()
	return closeFunc(func() error {
		cancel()
		<-doneCh
		close(c.statsChan)
		return nil
	}), nil
}

func (*client) PostWorkspaceAgentAppHealth(_ context.Context, _ codersdk.PostWorkspaceAppHealthsRequest) error {
	return nil
}

func (*client) PostWorkspaceAgentVersion(_ context.Context, _ string) error {
	return nil
}