Error handling - microsandbox

All SDKs surface typed errors so you can match on specific failure modes instead of parsing strings. Rust has an Error enum, TypeScript exposes a dedicated subclass per variant (use instanceof), Python provides dedicated exception classes, and Go provides an *Error value with an ErrorKind discriminator matched via m.IsKind(err, kind) or errors.As.

Matching errors

use microsandbox::{Sandbox, Error};

async fn get_or_create(name: &str) -> Result<Sandbox, Error> {
    match Sandbox::get(name).await {
        Ok(handle) => handle.start().await,
        Err(Error::SandboxNotFound(_)) => {
            Sandbox::builder(name).image("python").create().await
        }
        Err(e) => Err(e),
    }
}

match sb.exec("python", ["script.py"]).await {
    Ok(output) if output.status().success => {
        println!("{}", output.stdout()?);
    }
    Ok(output) => {
        eprintln!("Exit {}: {}", output.status().code, output.stderr()?);
    }
    Err(Error::ExecTimeout) => eprintln!("Timed out"),
    Err(Error::Runtime(msg)) => eprintln!("Runtime: {msg}"),
    Err(e) => return Err(e),
}

import {
    ExecTimeoutError,
    RuntimeError,
    Sandbox,
    SandboxNotFoundError,
} from "microsandbox";

async function getOrCreate(name: string): Promise<Sandbox> {
    try {
        const handle = await Sandbox.get(name);
        return await handle.start();
    } catch (e) {
        if (e instanceof SandboxNotFoundError) {
            return Sandbox.builder(name).image("python").create();
        }
        throw e;
    }
}

try {
    const output = await sb.exec("python", ["script.py"]);
    if (!output.success) {
        console.error(`Failed (exit ${output.code}):`, output.stderr());
    }
} catch (e) {
    if (e instanceof ExecTimeoutError) {
        console.error(`Timed out after ${e.timeoutMs}ms`);
    } else if (e instanceof RuntimeError) {
        console.error("Runtime:", e.message);
    } else {
        throw e;
    }
}

from microsandbox import (
    ExecTimeoutError, Sandbox, SandboxNotFoundError
)

async def get_or_create(name: str):
    try:
        handle = await Sandbox.get(name)
        return await handle.start()
    except SandboxNotFoundError:
        return await Sandbox.create(name, image="python")

try:
    output = await sb.exec("python", ["script.py"])
    if not output.success:
        print(f"Exit {output.exit_code}: {output.stderr_text}")
except ExecTimeoutError:
    print("Timed out")

import (
    "context"
    "errors"
    "log"

    m "github.com/superradcompany/microsandbox/sdk/go"
)

func getOrCreate(ctx context.Context, name string) (*m.Sandbox, error) {
    handle, err := m.GetSandbox(ctx, name)
    if err != nil {
        if m.IsKind(err, m.ErrSandboxNotFound) {
            return m.CreateSandbox(ctx, name,
                m.WithImage("python"))
        }
        return nil, err
    }
    return handle.Start(ctx)
}

out, err := sb.Exec(ctx, "python", []string{"script.py"})
switch {
case err == nil && !out.Success():
    log.Printf("exit %d: %s", out.ExitCode(), out.Stderr())
case m.IsKind(err, m.ErrExecTimeout):
    log.Println("timed out")
case err != nil:
    // errors.As for deeper inspection.
    var me *m.Error
    if errors.As(err, &me) {
        log.Printf("kind=%s message=%s", me.Kind, me.Message)
    }
}

Spawn-time exec failures

exec() distinguishes between:

A program that ran and exited non-zero: the call returns an ExecOutput with a non-zero code. This is not an error in the SDK sense; it’s a normal result.
A program that never started: the binary doesn’t exist, isn’t executable, the working directory is unreachable, etc. This surfaces as a typed error variant: ExecFailed (Rust), ExecFailedError (TypeScript), ExecFailedError (Python).

The typed error carries a classified kind plus the underlying errno, so callers can branch on the cause and react. Common kinds: NotFound (binary missing on PATH), PermissionDenied, NotExecutable, BadCwd, BadArgs, ResourceLimit, UserSetupFailed, OutOfMemory, PtySetupFailed, Other.

use microsandbox::Error;
use microsandbox_protocol::exec::ExecFailureKind;

match sb.exec("nonexistent", []).await {
    Ok(output) => { /* program ran, check output.status() */ }
    Err(Error::ExecFailed(payload)) => {
        match payload.kind {
            ExecFailureKind::NotFound => {
                eprintln!("Binary not found on PATH: {}", payload.message);
            }
            ExecFailureKind::PermissionDenied => {
                eprintln!("Not executable (chmod +x?): {}", payload.message);
            }
            kind => {
                eprintln!("Spawn failed ({:?}): {}", kind, payload.message);
            }
        }
        // payload.errno, payload.errno_name, payload.stage are also available
    }
    Err(e) => return Err(e),
}

import { ExecFailedError, Sandbox } from "microsandbox";

try {
    const output = await sb.exec("nonexistent");
    // program ran, check output.success / output.code
} catch (e) {
    if (e instanceof ExecFailedError) {
        switch (e.kind) {
            case "not_found":
                console.error("Binary not on PATH:", e.message);
                break;
            case "permission_denied":
                console.error("Not executable (chmod +x?):", e.message);
                break;
            default:
                console.error(`Spawn failed (${e.kind}):`, e.message);
        }
        // e.errno, e.errnoName, e.stage are also available
    } else {
        throw e;
    }
}

from microsandbox import ExecFailedError

try:
    output = await sb.exec("nonexistent")
    # program ran, check output.success / output.exit_code
except ExecFailedError as e:
    if e.kind == "not_found":
        print(f"Binary not on PATH: {e.message}")
    elif e.kind == "permission_denied":
        print(f"Not executable (chmod +x?): {e.message}")
    else:
        print(f"Spawn failed ({e.kind}): {e.message}")
    # e.errno, e.errno_name, e.stage are also available

// Streaming exec surfaces spawn-failure detail via ExecEventFailed.
h, err := sb.ExecStream(ctx, "nonexistent", nil)
if err != nil {
    return err
}
defer h.Close()

for {
    ev, err := h.Recv(ctx)
    if err != nil {
        return err
    }
    switch ev.Kind {
    case m.ExecEventExited:
        // Program ran; inspect ev.ExitCode.
    case m.ExecEventFailed:
        f := ev.Failure // *m.ExecFailure
        switch f.Kind {
        case "not_found":
            log.Printf("Binary not on PATH: %s", f.Message)
        case "permission_denied":
            log.Printf("Not executable (chmod +x?): %s", f.Message)
        default:
            log.Printf("Spawn failed (%s): %s", f.Kind, f.Message)
        }
        // f.Errno (*int), f.ErrnoName, f.Path are also available.
    case m.ExecEventDone:
        return nil
    }
}

The CLI maps these kinds to POSIX-style exit codes: 127 for NotFound, 126 for PermissionDenied and NotExecutable, 1 otherwise. SDK callers reading the error directly don’t need to think about exit codes; branch on kind instead.

Name conflicts

Creating a sandbox with a name that’s already in use (and without replace) surfaces a typed error you can branch on to decide whether to recover (resume the existing one, regenerate the name, etc.).

use microsandbox::Error;

match Sandbox::builder("worker").image("alpine").create().await {
    Ok(sb) => { /* ... */ }
    Err(Error::SandboxAlreadyExists(name)) => {
        eprintln!("sandbox {name} already exists; resume or pass .replace()");
    }
    Err(e) => return Err(e),
}

import { SandboxAlreadyExistsError } from "microsandbox";

try {
    const sb = await Sandbox.builder("worker").image("alpine").create();
} catch (e) {
    if (e instanceof SandboxAlreadyExistsError) {
        console.error("sandbox already exists; resume or pass replace()");
    } else {
        throw e;
    }
}

from microsandbox import SandboxAlreadyExistsError

try:
    sb = await Sandbox.create("worker", image="alpine")
except SandboxAlreadyExistsError:
    print("sandbox already exists; resume or pass replace=True")

sb, err := m.CreateSandbox(ctx, "worker",
    m.WithImage("alpine"))
if m.IsKind(err, m.ErrSandboxAlreadyExists) {
    log.Println("sandbox already exists; resume or pass WithReplace()")
}

Pass replace() / replace=True / --replace / WithReplace() to stop the existing sandbox and recreate it. See Naming conflicts for the grace-period knob.

Sandbox start failures

When a sandbox process exits before the agent relay is ready (mount errors, missing rootfs, network setup failures), the SDK surfaces a typed BootStart / BootStartError. The payload carries the failure stage and errno so callers can recover or report cleanly.

use microsandbox::Error;
use microsandbox_runtime::boot_error::BootErrorStage;

match Sandbox::builder("svc").image("alpine").create().await {
    Ok(sb) => { /* ... */ }
    Err(Error::BootStart { name, err }) => {
        eprintln!("Sandbox {name:?} failed at stage {:?}: {}", err.stage, err.message);
        if matches!(err.stage, BootErrorStage::Mount) {
            eprintln!("Hint: a host volume path may not exist.");
        }
    }
    Err(e) => return Err(e),
}

import { BootStartError } from "microsandbox";

try {
    const sb = await Sandbox.builder("svc").image("alpine").create();
} catch (e) {
    if (e instanceof BootStartError) {
        console.error(`Sandbox "${e.name}" failed at stage ${e.stage}: ${e.message}`);
        if (e.stage === "mount") {
            console.error("Hint: a host volume path may not exist.");
        }
    } else {
        throw e;
    }
}

from microsandbox import BootStartError

try:
    sb = await Sandbox.create("svc", image="alpine")
except BootStartError as e:
    print(f"Sandbox {e.name!r} failed at stage {e.stage}: {e.message}")
    if e.stage == "mount":
        print("Hint: a host volume path may not exist.")

// The Go SDK surfaces boot failures as *m.Error.
// Inspect Kind and Message for the failure details.
_, err := m.CreateSandbox(ctx, "svc", m.WithImage("alpine"))
var me *m.Error
if errors.As(err, &me) {
    log.Printf("sandbox boot failed (kind=%s): %s", me.Kind, me.Message)
}

The CLI prepends the same payload as a styled error: block before any captured log output, so you see “what went wrong + a hint” inline. SDK callers get the structured payload to make their own decisions.

Resource cleanup

Sandboxes hold compute resources, so release them when done. In Rust, Drop handles cleanup when the sandbox goes out of scope. In TypeScript, prefer await using (Node 22+) which calls Sandbox.stop() automatically when the binding leaves scope. In Go, pair every CreateSandbox with a defer that calls Stop + Close.

use microsandbox::Sandbox;

// Sandbox implements Drop, so resources are released when `sb` goes out of scope.
// For explicit control, call stop() or kill().
{
    let sb = Sandbox::builder("temp")
        .image("python")
        .create()
        .await?;

    let output = sb.exec("python", ["-c", "print('hello')"]).await?;
} // sb is dropped here, resources are cleaned up

async function runTemporary(): Promise<string> {
    // `await using` calls Sandbox.stop() when the binding leaves scope.
    await using sb = await Sandbox.builder("temp")
        .image("python")
        .replace()
        .create();

    const out = await sb.exec("python", ["-c", "print('hello')"]);
    return out.stdout();
}

# Use async context manager: auto-kills and removes on exit.
async with await Sandbox.create("temp", image="python") as sb:
    output = await sb.exec("python", ["-c", "print('hello')"])
    print(output.stdout_text)

sb, err := m.CreateSandbox(ctx, "temp",
    m.WithImage("python"),
    m.WithReplace(),
)
if err != nil {
    log.Fatal(err)
}
defer func() {
    stopCtx, cancel := context.WithTimeout(context.Background(), 30*time.Second)
    defer cancel()
    _, _ = sb.Stop(stopCtx)
    _ = sb.Close()
}()

out, _ := sb.Exec(ctx, "python", []string{"-c", "print('hello')"})
fmt.Println(out.Stdout())

​Matching errors

​Spawn-time exec failures

​Name conflicts

​Sandbox start failures

​Resource cleanup

Matching errors

Spawn-time exec failures

Name conflicts

Sandbox start failures

Resource cleanup