hamlab/internal/incus/vga.go

package incus

// The graphical console. Incus exposes a VM's SPICE display as a websocket: POST to the
// instance's console endpoint with type vga and it answers an operation with two secrets,
// one for the display stream and one for a control channel. Ham Lab dials both over Incus's
// unix socket and hands the display stream to the browser, where spice-html5 draws it.

import (
	"bytes"
	"context"
	"encoding/json"
	"errors"
	"fmt"
	"net"
	"net/http"
	"os"
	"time"

	"github.com/coder/websocket"
)

// SocketPath is where Incus's API listens; the daemon's account reaches it by being in
// incus-admin, which Install arranges.
func SocketPath() string {
	if p := os.Getenv("INCUS_SOCKET"); p != "" {
		return p
	}
	for _, p := range []string{"/var/lib/incus/unix.socket", "/run/incus/unix.socket"} {
		if _, err := os.Stat(p); err == nil {
			return p
		}
	}
	return "/var/lib/incus/unix.socket"
}

func (m *Manager) apiClient() *http.Client {
	sock := SocketPath()
	return &http.Client{Transport: &http.Transport{
		DialContext: func(ctx context.Context, _, _ string) (net.Conn, error) {
			var d net.Dialer
			return d.DialContext(ctx, "unix", sock)
		},
		ForceAttemptHTTP2: false,
	}}
}

// VGA opens the display and control websockets for a running VM. The caller closes both.
func (m *Manager) VGA(ctx context.Context, name string) (display, control *websocket.Conn, err error) {
	if !ValidName(name) {
		return nil, nil, errors.New("bad name")
	}
	client := m.apiClient()
	body, _ := json.Marshal(map[string]any{"type": "vga", "width": 0, "height": 0})
	c, cancel := context.WithTimeout(ctx, 20*time.Second)
	defer cancel()
	req, _ := http.NewRequestWithContext(c, "POST", "http://incus/1.0/instances/"+name+"/console", bytes.NewReader(body))
	req.Header.Set("Content-Type", "application/json")
	resp, err := client.Do(req)
	if err != nil {
		if os.IsPermission(errors.Unwrap(err)) || isPermission(err) {
			return nil, nil, errors.New("Ham Lab's account can't reach Incus's socket; Finish setup on the Virtualization tab puts it in incus-admin")
		}
		return nil, nil, err
	}
	defer resp.Body.Close()
	var op struct {
		Error     string `json:"error"`
		Operation string `json:"operation"`
		Metadata  struct {
			ID       string `json:"id"`
			Metadata struct {
				FDs map[string]string `json:"fds"`
			} `json:"metadata"`
		} `json:"metadata"`
	}
	if err := json.NewDecoder(resp.Body).Decode(&op); err != nil {
		return nil, nil, errors.New("unreadable answer from incus")
	}
	if op.Error != "" {
		return nil, nil, errors.New(op.Error)
	}
	data, control0 := op.Metadata.Metadata.FDs["0"], op.Metadata.Metadata.FDs["control"]
	if op.Metadata.ID == "" || data == "" {
		return nil, nil, errors.New("incus gave no console; is the VM running?")
	}
	dial := func(secret string) (*websocket.Conn, error) {
		u := fmt.Sprintf("ws://incus/1.0/operations/%s/websocket?secret=%s", op.Metadata.ID, secret)
		ws, _, err := websocket.Dial(ctx, u, &websocket.DialOptions{HTTPClient: client, CompressionMode: websocket.CompressionDisabled})
		return ws, err
	}
	if control0 != "" {
		if control, err = dial(control0); err != nil {
			return nil, nil, err
		}
	}
	if display, err = dial(data); err != nil {
		if control != nil {
			control.Close(websocket.StatusInternalError, "")
		}
		return nil, nil, err
	}
	display.SetReadLimit(64 << 20) // a SPICE frame can carry a whole screen
	return display, control, nil
}

func isPermission(err error) bool {
	var pe *os.PathError
	if errors.As(err, &pe) {
		return os.IsPermission(pe)
	}
	var oe *net.OpError
	if errors.As(err, &oe) {
		return os.IsPermission(oe.Err) || isPermission(oe.Err)
	}
	return false
}