(ctx context.Context, args StartProcessConfig)
| 35 | } |
| 36 | |
| 37 | func StartProcess(ctx context.Context, args StartProcessConfig) (*Process, error) { |
| 38 | logger := logctx.From(ctx) |
| 39 | clock := args.Clock |
| 40 | if clock == nil { |
| 41 | clock = quartz.NewReal() |
| 42 | } |
| 43 | xp, err := xpty.New(args.TerminalWidth, args.TerminalHeight, false) |
| 44 | if err != nil { |
| 45 | return nil, err |
| 46 | } |
| 47 | execCmd := exec.Command(args.Program, args.Args...) |
| 48 | // vt100 is the terminal type that the vt10x library emulates. |
| 49 | // Setting this signals to the process that it should only use compatible |
| 50 | // escape sequences. |
| 51 | execCmd.Env = append(os.Environ(), "TERM=vt100") |
| 52 | if err := xp.StartProcessInTerminal(execCmd); err != nil { |
| 53 | return nil, err |
| 54 | } |
| 55 | |
| 56 | process := &Process{xp: xp, execCmd: execCmd, clock: clock} |
| 57 | |
| 58 | go func() { |
| 59 | // HACK: Working around xpty concurrency limitations |
| 60 | // |
| 61 | // Problem: |
| 62 | // 1. We need to track when the terminal screen was last updated (for ReadScreen) |
| 63 | // 2. xpty only updates terminal state through xp.ReadRune() |
| 64 | // 3. xp.ReadRune() has a bug - it panics when SetReadDeadline is used |
| 65 | // 4. Without deadlines, ReadRune blocks until the process outputs data |
| 66 | // |
| 67 | // Why this matters: |
| 68 | // If we wrapped ReadRune + lastScreenUpdate in a mutex, this goroutine would |
| 69 | // hold the lock while waiting for process output. Since ReadRune blocks indefinitely, |
| 70 | // ReadScreen callers would be locked out until new output arrives. Even worse, |
| 71 | // after output arrives, this goroutine could immediately reacquire the lock |
| 72 | // for the next ReadRune call, potentially starving ReadScreen callers indefinitely. |
| 73 | // |
| 74 | // Solution: |
| 75 | // Instead of using xp.ReadRune(), we directly use its internal components: |
| 76 | // - pp.ReadRune() - handles the blocking read from the process |
| 77 | // - xp.Term.WriteRune() - updates the terminal state |
| 78 | // |
| 79 | // This lets us apply the mutex only around the terminal update and timestamp, |
| 80 | // keeping reads non-blocking while maintaining thread safety. |
| 81 | // |
| 82 | // Warning: This depends on xpty internals and may break if xpty changes. |
| 83 | // A proper fix would require forking xpty or getting upstream changes. |
| 84 | pp := util.GetUnexportedField(xp, "pp").(*xpty.PassthroughPipe) |
| 85 | for { |
| 86 | r, _, err := pp.ReadRune() |
| 87 | if err != nil { |
| 88 | if err != io.EOF { |
| 89 | logger.Error("Error reading from pseudo terminal", "error", err) |
| 90 | } |
| 91 | // TODO: handle this error better. if this happens, the terminal |
| 92 | // state will never be updated anymore and the process will appear |
| 93 | // unresponsive. |
| 94 | return |
no test coverage detected