Execution - microsandbox

Run commands inside a running sandbox, collect their output, stream events live, or drive an interactive pseudo-terminal programmatically. See Commands for usage examples. The exec API mirrors os/exec conventions: a non-zero exit code is not a Go error. Transport, timeout, and spawn-failure paths return an error; a program that ran and exited non-zero is a normal *ExecOutput result, inspect Success() or ExitCode().

Sandbox methods

The exec entry points live on *Sandbox.

sb.Exec()

func (s *Sandbox) Exec(ctx context.Context, cmd string, args []string, opts ...ExecOption) (*ExecOutput, error)

Example

out, err := sb.Exec(ctx, "make", []string{"build"},
    m.WithExecCwd("/app"),
    m.WithExecEnv(map[string]string{"DEBUG": "1"}),
)

Run a command in the sandbox and return its collected output. Blocks until the command exits. The returned error is non-nil only on transport or runtime failures; a non-zero exit code is reported via ExecOutput.ExitCode, not as an error.

Parameters

ctxcontext.Context

Cancels the wait. The guest process may continue in the background.

cmdstring

Program to run. Passed literally to the guest agent (the image ENTRYPOINT is not consulted).

args[]string

Command arguments. May be nil.

opts…ExecOption

Per-command cwd, timeout, TTY allocation, user, and env.

Returns

*ExecOutput

Collected stdout, stderr, and exit code.

sb.Shell()

func (s *Sandbox) Shell(ctx context.Context, command string, opts ...ExecOption) (*ExecOutput, error)

Example

out, err := sb.Shell(ctx, "echo $HOME && ls /tmp")
if err != nil {
    return err
}
fmt.Print(out.Stdout())

Run /bin/sh -c command in the sandbox and collect its output. Blocks until the command exits. A convenience wrapper over Exec for shell one-liners.

Parameters

ctxcontext.Context

Cancels the wait.

commandstring

Shell command line passed to /bin/sh -c.

opts…ExecOption

Per-command cwd, timeout, TTY allocation, user, and env.

Returns

*ExecOutput

Collected stdout, stderr, and exit code.

sb.ExecStream()

func (s *Sandbox) ExecStream(ctx context.Context, cmd string, args []string, opts ...ExecOption) (*ExecHandle, error)

Example

h, err := sb.ExecStream(ctx, "cat", nil, m.WithExecStdinPipe())
if err != nil {
    return err
}
defer h.Close()

Start a streaming exec session and return an *ExecHandle. The handle MUST be closed with Close when the stream is no longer needed. Nonblocking: the handle returns immediately and the stream starts in the background. ctx controls only the start handshake; individual Recv calls take their own ctx. Non-zero exit codes are not errors, inspect ExecEventExited.

Parameters

ctxcontext.Context

Controls the start handshake only.

cmdstring

Program to run.

args[]string

Command arguments. May be nil.

opts…ExecOption

Per-command options; add WithExecStdinPipe() to enable stdin and WithExecTTY(true) to allocate a pseudo-terminal.

Returns

*ExecHandle

Live exec session. Close it when done.

sb.ShellStream()

func (s *Sandbox) ShellStream(ctx context.Context, command string, opts ...ExecOption) (*ExecHandle, error)

Example

h, err := sb.ShellStream(ctx, "tail -f /var/log/app.log")
if err != nil {
    return err
}
defer h.Close()

for {
    ev, err := h.Recv(ctx)
    if err != nil {
        return err
    }
    switch ev.Kind {
    case m.ExecEventStdout:
        os.Stdout.Write(ev.Data)
    case m.ExecEventDone:
        return nil
    }
}

Run /bin/sh -c command with streaming output. A convenience wrapper over ExecStream. Nonblocking: the handle returns immediately and the stream starts in the background.

Parameters

ctxcontext.Context

Controls the start handshake only.

commandstring

Shell command line passed to /bin/sh -c.

opts…ExecOption

Per-command options.

Returns

*ExecHandle

Live exec session. Close it when done.

ExecHandle methods

A live streaming exec session returned by ExecStream and ShellStream. Signal, Kill, and Resize may be called concurrently with Recv, allowing a control goroutine to act while another goroutine waits for terminal output. Other method combinations, including concurrent Recv calls, are not supported.

h.ID()

func (h *ExecHandle) ID() (string, error)

Return the unique identifier for this exec session, assigned by the guest agent. Useful for correlating log entries or referencing the session from external tooling.

Returns

string

Session correlation id.

h.TakeStdin()

func (h *ExecHandle) TakeStdin() *ExecSink

Example

sink := h.TakeStdin()
sink.Write([]byte("hello\n"))
sink.Close()

Return the stdin sink for this exec session. Single-take: returns nil if the session was not started with WithExecStdinPipe, or if TakeStdin was already called on this handle (matching the Node and Python SDKs). The caller is responsible for closing the sink when done writing; closing the sink without closing the exec handle is fine, they own different Rust-side resources.

Returns

*ExecSink

Stdin writer, or nil if unavailable.

h.Recv()

func (h *ExecHandle) Recv(ctx context.Context) (*ExecEvent, error)

Example

for {
    ev, err := h.Recv(ctx)
    if err != nil {
        return err
    }
    switch ev.Kind {
    case m.ExecEventStarted:
        fmt.Printf("started pid=%d\n", ev.PID)
    case m.ExecEventStdout:
        os.Stdout.Write(ev.Data)
    case m.ExecEventStderr:
        os.Stderr.Write(ev.Data)
    case m.ExecEventExited:
        fmt.Printf("exited code=%d\n", ev.ExitCode)
    case m.ExecEventDone:
        return nil
    }
}

Block until the next event arrives or the stream ends. Returns an event with Kind == ExecEventDone when all events have been consumed. ctx controls the wait; cancellation causes Recv to return ctx.Err() immediately. The underlying Rust call may continue to completion in the background.

Parameters

ctxcontext.Context

Cancels the wait for the next event.

Returns

*ExecEvent

The next streamed event.

h.Collect()

func (h *ExecHandle) Collect(ctx context.Context) (*ExecOutput, error)

Example

out, err := h.Collect(ctx)
if err != nil {
    return err
}
fmt.Print(out.Stdout())

Drain the stream, accumulate all output, and return it as an *ExecOutput. Equivalent to calling Recv in a loop and assembling the result. The handle should be closed after Collect returns.

Parameters

ctxcontext.Context

Cancels the drain.

Returns

*ExecOutput

Collected stdout, stderr, and exit code.

h.Wait()

func (h *ExecHandle) Wait(ctx context.Context) (int, error)

Block until the process exits and return its exit code. Unlike Collect, stdout and stderr are discarded. The handle should be closed after Wait returns.

Parameters

ctxcontext.Context

Cancels the wait.

Returns

int

Process exit code.

h.Kill()

func (h *ExecHandle) Kill(ctx context.Context) error

Send SIGKILL to the running process.

Parameters

ctxcontext.Context

Cancels the call.

h.Signal()

func (h *ExecHandle) Signal(ctx context.Context, signal int) error

Example

import "syscall"

if err := h.Signal(ctx, int(syscall.SIGTERM)); err != nil {
    return err
}

Send a Unix signal to the running process. Pass values from syscall (e.g. int(syscall.SIGTERM)).

Parameters

ctxcontext.Context

Cancels the call.

signalint

Signal number, e.g. int(syscall.SIGTERM).

h.Resize()

func (h *ExecHandle) Resize(ctx context.Context, rows, cols uint16) error

Example

if err := h.Resize(ctx, 40, 120); err != nil {
    return err
}

Resize the pseudo-terminal for this exec session. Use with a session started with WithExecTTY(true), typically when relaying a terminal-size change from a remote client. Resize may be called concurrently while another goroutine is blocked in Recv.

Parameters

ctxcontext.Context

Cancels the resize call.

rowsuint16

New terminal height in character cells.

colsuint16

New terminal width in character cells.

h.Close()

func (h *ExecHandle) Close() error

Example

defer h.Close()

Release the Rust-side exec handle. Does not kill the running process; call Signal or Kill first if you need to terminate it. Safe to call after ExecEventDone has been received.

ExecOutput methods

The collected result of a completed command execution, returned by Exec, Shell, and Collect.

out.Stdout()

func (e *ExecOutput) Stdout() string

Captured standard output as a string.

Returns

string

Collected stdout.

out.StdoutBytes()

func (e *ExecOutput) StdoutBytes() []byte

Captured standard output as raw bytes. Use when the output may not be valid UTF-8.

Returns

[]byte

Raw stdout bytes.

out.Stderr()

func (e *ExecOutput) Stderr() string

Captured standard error as a string.

Returns

string

Collected stderr.

out.StderrBytes()

func (e *ExecOutput) StderrBytes() []byte

Captured standard error as raw bytes.

Returns

[]byte

Raw stderr bytes.

out.ExitCode()

func (e *ExecOutput) ExitCode() int

The process’s exit code, or -1 if the guest did not report one (e.g. the process was killed by a signal).

Returns

int

Exit code, or -1.

out.Success()

func (e *ExecOutput) Success() bool

Reports whether the command exited with code 0.

Returns

bool

true if ExitCode() is 0.

ExecSink methods

A write-only pipe to a running process’s stdin, obtained from ExecHandle.TakeStdin. Implements io.WriteCloser. Write and Close use context.Background() under the hood; for caller-controlled cancellation use WriteCtx, or tear the session down via ExecHandle.Kill / Close.

sink.Write()

func (sk *ExecSink) Write(p []byte) (int, error)

Example

h, err := sb.ExecStream(ctx, "cat", nil, m.WithExecStdinPipe())
if err != nil {
    return err
}
defer h.Close()

sink := h.TakeStdin()
sink.Write([]byte("hello\n"))
sink.Close()

out, _ := h.Collect(ctx)
fmt.Print(out.Stdout()) // "hello\n"

Send data to the process stdin. Implements io.Writer. Uses context.Background() internally, there is no way to cancel a stuck write through this method alone.

Parameters

p[]byte

Bytes to write to stdin.

Returns

int

Number of bytes written.

sink.WriteCtx()

func (sk *ExecSink) WriteCtx(ctx context.Context, p []byte) (int, error)

Like Write, but with a caller-controlled context, so a stuck stdin write can be cancelled.

Parameters

ctxcontext.Context

Cancels the write.

p[]byte

Bytes to write to stdin.

Returns

int

Number of bytes written.

sink.Close()

func (sk *ExecSink) Close() error

Example

sink.Close()

Close the stdin sink. In non-TTY pipe mode this sends EOF to the process. In TTY mode it prevents further writes through this sink, but the guest PTY remains open; send the terminal’s EOF control character (usually \x04 in canonical mode) when the interactive program needs one. Implements io.Closer.

Types

ExecOutput

Returned by sb.Exec() · sb.Shell() · h.Collect()

The collected result of a command execution. A non-zero ExitCode is not treated as a Go error, callers inspect Success or ExitCode explicitly, matching how os/exec.Cmd.Output works against a script that exits non-zero. In TTY mode, Stdout contains the combined terminal output and Stderr is empty because a PTY cannot preserve separate stdout and stderr streams.

Method	Returns	Description
`Stdout()`	`string`	Captured stdout as a string
`StdoutBytes()`	`[]byte`	Raw stdout bytes
`Stderr()`	`string`	Captured stderr as a string
`StderrBytes()`	`[]byte`	Raw stderr bytes
`ExitCode()`	`int`	Exit code, or `-1` if the guest did not report one
`Success()`	`bool`	`true` if `ExitCode()` is `0`

ExecHandle

Returned by sb.ExecStream() · sb.ShellStream()

A live streaming exec session. Must be closed with Close when done to release Rust-side resources. Signal, Kill, and Resize may run concurrently with Recv; other method combinations, including multiple concurrent Recv calls, are not supported.

Method	Returns	Description
`ID()`	`(string, error)`	Session correlation id assigned by the guest agent
`TakeStdin()`	`*ExecSink`	Take the stdin writer (single-take; only with `WithExecStdinPipe`)
`Recv(ctx)`	`(*ExecEvent, error)`	Block until the next event arrives
`Collect(ctx)`	`(*ExecOutput, error)`	Drain remaining output into an `ExecOutput`
`Wait(ctx)`	`(int, error)`	Wait for exit, discarding output; returns the exit code
`Kill(ctx)`	`error`	Send SIGKILL
`Signal(ctx, signal)`	`error`	Send a Unix signal
`Resize(ctx, rows, cols)`	`error`	Resize the pseudo-terminal
`Close()`	`error`	Release the Rust-side handle

ExecSink

Returned by h.TakeStdin()

type ExecSink = ffi.ExecSink

A write-only pipe to a running process’s stdin. Implements io.WriteCloser.

Method	Returns	Description
`Write(p)`	`(int, error)`	Implements `io.Writer`
`WriteCtx(ctx, p)`	`(int, error)`	Write with explicit context
`Close()`	`error`	Close the sink; sends EOF in non-TTY pipe mode

ExecEvent

Returned by h.Recv()

One event from a streaming exec session. Kind identifies which fields are populated.

Field	Type	Description
`Kind`	`ExecEventKind`	Identifies which fields are populated
`PID`	`uint32`	Guest process id, set on `ExecEventStarted`
`Data`	`[]byte`	Chunk of stdout or stderr, set on `ExecEventStdout` / `ExecEventStderr`
`ExitCode`	`int`	Process exit code, set on `ExecEventExited`
`Failure`	`*ExecFailure`	Failure detail, set on `ExecEventFailed` and `ExecEventStdinError`

ExecEventKind

Field of ExecEvent

type ExecEventKind = ffi.ExecEventKind

Identifies what an ExecEvent carries.

Constant	Description
`ExecEventStarted`	Sent once when the guest process starts; `PID` is valid
`ExecEventStdout`	A chunk of stdout; in TTY mode, carries the combined terminal output stream. `Data` is valid
`ExecEventStderr`	A chunk of stderr; not emitted separately in TTY mode. `Data` is valid
`ExecEventExited`	The process exited; `ExitCode` is valid
`ExecEventFailed`	The user program never started (binary missing, permission denied, …); `Failure` is valid and `ExitCode` is not meaningful
`ExecEventStdinError`	A stdin write failed; `Failure` is valid. Non-terminal: the process may still exit normally
`ExecEventDone`	All events have been consumed

ExecFailure

Field of ExecEvent

type ExecFailure = ffi.ExecFailure

Structured detail about a failed-to-start exec, populated on ExecEventFailed and ExecEventStdinError. See Error Handling for the kinds it carries (not_found, permission_denied, etc.) and how to branch on them.

Field	Type	Description
`Kind`	`string`	Failure category, e.g. `not_found`, `permission_denied`
`Errno`	`*int`	Underlying errno, if known
`ErrnoName`	`string`	Symbolic errno name, if known
`Message`	`string`	Human-readable failure message
`Path`	`string`	Offending path, if applicable

ExecConfig

Populated by ExecOption

Configures a single Exec or ExecStream call. Most callers set fields through the WithExec* functional options; ExecConfig is exported for parity with the other SDKs’ config types.

Field	Type	Description
`Cwd`	`string`	Working directory inside the guest
`Timeout`	`time.Duration`	Kill the process after this duration; sub-second precision is rounded up
`StdinPipe`	`bool`	Enable a stdin pipe; required for `TakeStdin`
`TTY`	`bool`	Allocate a pseudo-terminal; default `false`
`User`	`string`	Guest user (UID or name)
`Env`	`map[string]string`	Per-command environment variables

ExecOption

Accepted by sb.Exec() · sb.Shell() · sb.ExecStream() · sb.ShellStream()

type ExecOption func(*ExecConfig)

A functional option that mutates an ExecConfig. Construct them with the WithExec* functions below.

WithExecCwd()

func WithExecCwd(path string) ExecOption

Set the working directory for a single command.

Parameters

pathstring

Absolute path inside the guest.

WithExecTimeout()

func WithExecTimeout(d time.Duration) ExecOption

Example

out, err := sb.Shell(ctx, "long-running-task",
    m.WithExecTimeout(30*time.Second))
if m.IsKind(err, m.ErrExecTimeout) {
    log.Println("timed out")
}

Set a per-command timeout. When exceeded, the guest terminates the process and the call returns an error with Kind == ErrExecTimeout. Sub-second precision rounds up to whole seconds; pass at least 1 second.

Parameters

dtime.Duration

Timeout duration, rounded up to whole seconds.

WithExecStdinPipe()

func WithExecStdinPipe() ExecOption

Enable a stdin pipe for the exec session, allowing data to be written via ExecHandle.TakeStdin.

WithExecTTY()

func WithExecTTY(enabled bool) ExecOption

Example

h, err := sb.ExecStream(ctx, "/bin/bash", nil,
    m.WithExecStdinPipe(),
    m.WithExecTTY(true),
)
if err != nil {
    return err
}
defer h.Close()

stdin := h.TakeStdin()
if stdin == nil {
    return errors.New("stdin pipe is unavailable")
}

if err := h.Resize(ctx, 40, 120); err != nil {
    return err
}
if _, err := stdin.Write([]byte("echo hello\n")); err != nil {
    return err
}

Control whether the command runs inside a pseudo-terminal. Enable it for interactive programs such as shells, editors, REPLs, and top. Default: false. When enabled, the guest process runs with its stdin, stdout, and stderr connected to the PTY. Streaming sessions expose the combined terminal output through ExecEventStdout; they do not emit a separately attributable stderr stream. Collected output similarly places the combined stream in Stdout and leaves Stderr empty. Add WithExecStdinPipe() to write to the terminal programmatically, and use Resize to update its dimensions after the session starts.

Parameters

enabledbool

true to allocate a pseudo-terminal.

WithExecUser()

func WithExecUser(user string) ExecOption

Run the command as the given guest user (UID or name).

Parameters

userstring

Guest user, as a UID or name.

WithExecEnv()

func WithExecEnv(env map[string]string) ExecOption

Example

out, err := sb.Exec(ctx, "make", []string{"build"},
    m.WithExecCwd("/app"),
    m.WithExecEnv(map[string]string{"DEBUG": "1"}),
)

Add per-command environment variables. Called repeatedly, maps merge; later keys overwrite earlier ones.

Parameters

envmap[string]string

Environment variables for this command.

​Sandbox methods

​sb.Exec()

​sb.Shell()

​sb.ExecStream()

​sb.ShellStream()

​ExecHandle methods

​h.ID()

​h.TakeStdin()

​h.Recv()

​h.Collect()

​h.Wait()

​h.Kill()

​h.Signal()

​h.Resize()

​h.Close()

​ExecOutput methods

​out.Stdout()

​out.StdoutBytes()

​out.Stderr()

​out.StderrBytes()

​out.ExitCode()

​out.Success()

​ExecSink methods

​sink.Write()

​sink.WriteCtx()

​sink.Close()

​Types

​ExecOutput

​ExecHandle

​ExecSink

​ExecEvent

​ExecEventKind

​ExecFailure

​ExecConfig

​ExecOption

​WithExecCwd()

​WithExecTimeout()

​WithExecStdinPipe()

​WithExecTTY()

​WithExecUser()

​WithExecEnv()

Sandbox methods

sb.Exec()

sb.Shell()

sb.ExecStream()

sb.ShellStream()

ExecHandle methods

h.ID()

h.TakeStdin()

h.Recv()

h.Collect()

h.Wait()

h.Kill()

h.Signal()

h.Resize()

h.Close()

ExecOutput methods

out.Stdout()

out.StdoutBytes()

out.Stderr()

out.StderrBytes()

out.ExitCode()

out.Success()

ExecSink methods

sink.Write()

sink.WriteCtx()

sink.Close()

Types

ExecOutput

ExecHandle

ExecSink

ExecEvent

ExecEventKind

ExecFailure

ExecConfig

ExecOption

WithExecCwd()

WithExecTimeout()

WithExecStdinPipe()

WithExecTTY()

WithExecUser()

WithExecEnv()