[Bubblewrap] Make Bubblewrap the default Linux backend by SohamDas2021 · Pull Request #368 · microsoft/mxc

SohamDas2021 · 2026-05-21T03:48:00Z

📖 Description

Makes Bubblewrap the default Linux process-sandbox backend. Callers that omit containment, or set the abstract containment: "process", now get Bubblewrap instead of LXC. Explicit containment: "lxc" and explicit containment: "bubblewrap" continue to work as before.

Linux containment resolution matrix

`containment`	SDK gate	Native dispatcher resolves to
(omitted)	none	Bubblewrap
`"process"`	none	Bubblewrap
`"lxc"`	none	LXC
`"bubblewrap"`	requires `experimental: true` (SDK only)	Bubblewrap
`"processcontainer"`	none	LXC (catch-all fallback)

Note: the experimental gate on explicit "bubblewrap" is enforced at the SDK layer only (helper.ts ExperimentalBackends`); the native binary does not re-check it. This is the same behavior as the original Bubblewrap PR (#314) and is unchanged here.

🔗 References

🔍 Validation

✅ Checklist

Signed the Contributor License Agreement
Linked to an issue
Updated documentation (if applicable)
Updated Copilot instructions (if build, architecture, or conventions changed)

📋 Issue Type

Bug fix
Feature
Task

Microsoft Reviewers: Open in CodeFlow

Copilot

Pull request overview

Updates MXC’s Linux containment resolution so the abstract “process” intent (and omitted containment) routes to Bubblewrap by default, while keeping explicit containment: "lxc" working as an opt-in path. This fits into the codebase’s “abstract intent → per-OS concrete backend” design in wxc_common::config_parser.

Changes:

Change Rust config parsing so omitted containment and containment: "process" resolve to ContainmentBackend::Bubblewrap on Linux.
Add/adjust SDK unit + integration tests to exercise the new default and to keep explicit LXC coverage via an explicit containment: "lxc" config.
Add CLI-level test configs + scripts to validate default Linux process behavior.

Reviewed changes

Copilot reviewed 11 out of 11 changed files in this pull request and generated 5 comments.

Show a summary per file

File	Description
`test_scripts/run_linux_process_default_test.sh`	New script to run configs that exercise Linux default/abstract process containment resolution.
`test_scripts/run_bwrap_all_tests.sh`	Includes the new default-process test script and line-ending checks for it.
`test_configs/linux_process_default.json`	New config to validate “containment omitted” Linux default behavior.
`test_configs/linux_process_abstract.json`	New config to validate `containment: "process"` behavior on Linux.
`src/wxc_common/src/config_parser.rs`	Core behavior change: Linux default + `"process"` resolve to Bubblewrap; adds parser tests/regressions.
`src/lxc/src/main.rs`	Updates dispatch comment to reflect Bubblewrap being the Linux default for abstract intents.
`sdk/tests/unit/sandbox.test.ts`	Adds unit coverage for Bubblewrap mapping and explicit LXC opt-in behavior.
`sdk/tests/integration/test-helpers.ts`	Adds a helper to run `spawnSandboxFromConfig` as a Promise for tests.
`sdk/tests/integration/linux-process-container.test.ts`	Routes these tests through explicit `containment: "lxc"` to keep exercising LXC.
`sdk/tests/integration/linux-bubblewrap.test.ts`	New integration coverage for Bubblewrap as the silent default and for explicit selection.
`sdk/src/sandbox.ts`	Adds explicit `containment === 'lxc'` handling; updates Linux `'process'` diagnostic logging.

Six proxy tests omitted containment and relied on the previous unconditional ProcessContainer default to satisfy the proxy guard (proxy is only valid with processcontainer). After this PR the default resolves to Seatbelt on macOS, causing those six tests to fail in the arm64 MAC CI job. Make each test explicit by setting containment: "processcontainer" in the JSON — they are testing proxy parsing behavior, not the OS-default resolution. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Agent-Logs-Url: https://github.com/microsoft/mxc/sessions/81dc5e19-9e89-4a1a-a005-6633f4ffbfe8 Co-authored-by: huzaifa-d <16077119+huzaifa-d@users.noreply.github.com>

PR 368 introduces SDK integration tests that exercise the Bubblewrap backend (the new Linux default for `containment: "process"` / omitted). Those tests skip unless `bwrap` is installed on the runner; the Linux integration job previously only installed `lxc`, so the new bwrap tests failed under sudo. Add `bubblewrap` to the apt-get install line alongside `lxc lxc-utils dnsmasq-base iptables` so both backends are present and both test suites can run. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

huzaifa-d · 2026-05-22T16:28:43Z

+// Async spawn from a pre-built ContainerConfig (no per-call containment arg on
+// spawnSandboxAsync, so tests that need a specific backend build the config
+// directly and run it through this helper).
+export function spawnFromConfigAsync(


Suggestion - Don't ignore stderr. Consider a timeout too. And have a on error handler.

This helper emulates the SDK's spawnSandboxAsync; the SDK doesn't expose an async wrapper around spawnSandboxFromConfig. Goal is parity with spawnSandboxAsync.

stderr- not ignored. wxc-exec runs under node-pty (single PTY), so stdout/stderr are merged at the OS level. node-pty only exposes one onData. The SDK does the same thing and comments it on sandbox.ts:666. I'll mirror that comment here.

timeout- spawnSandboxAsync doesn't have one either. node --test enforces per-test timeouts, and the config's process.timeout is enforced by the native runner.

onError- node-pty's IPty has no onError event. Sync spawn failures hit the existing try/catch; post-spawn failures surface as a non-zero exitCode via onExit

huzaifa-d · 2026-05-22T16:32:19Z

 * Containment values (abstract intent or concrete backend) that require
 * the `--experimental` flag.
 */
 export const ExperimentalBackends: readonly (ContainmentType | ContainmentBackend)[] = ['microvm', 'wslc', 'seatbelt', 'bubblewrap'];


Now that bubblewrap is default, should it still need experimental? If yes, do the default process paths check/throw if not experimental?

Once we promote bubblewrap to stable, this will be cleaned up. Currently default process paths do not check for experimental. This are the scenarios:

Linux containment resolution matrix

containment SDK gate Native dispatcher resolves to

(omitted) none Bubblewrap

"process" none Bubblewrap

"lxc" none LXC

"bubblewrap" requires experimental: true (SDK only) Bubblewrap

"processcontainer" none LXC (catch-all fallback)

…411) * Fix: exempt abstract 'process' on macOS from allowOutbound precheck On macOS, the abstract containment 'process' resolves to the seatbelt backend, which supports per-host network filtering natively via sandbox-exec profiles. The SDK precheck incorrectly required allowOutbound=true for allowedHosts/blockedHosts when using the default 'process' containment on macOS, despite the explicit 'seatbelt' backend being correctly exempted. Add 'darwin' platform check to resolvesToHostFilteringBackend alongside the existing 'linux' check (which maps to bubblewrap). Add unit tests mirroring the Linux coverage from PR #368. Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> * Fix blockedHosts test: remove allowOutbound to actually test the precheck waiver --------- Co-authored-by: Richie Gomez <richiegomez@Richies-Mac-mini.local> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Make Bubblewrap the silent default Linux process-sandbox backen

ef031a3

Copilot AI review requested due to automatic review settings May 21, 2026 03:48

Copilot started reviewing on behalf of SohamDas2021 May 21, 2026 03:48 View session

Copilot AI reviewed May 21, 2026

View reviewed changes

Comment thread sdk/tests/integration/linux-bubblewrap.test.ts

Comment thread test_configs/linux_process_default.json

Comment thread test_configs/linux_process_abstract.json

Comment thread src/lxc/src/main.rs

Comment thread sdk/src/sandbox.ts Outdated

SohamDas2021 changed the title ~~[Bubblewrap] Make Bubblewrap the silent default Linux process-sandbox backend~~ [Bubblewrap] Make Bubblewrap the default Linux backend May 21, 2026

Addressed PR comments

25bb4dd

SohamDas2021 requested review from a team and shschaefer May 21, 2026 04:30

Update ContainmentType JSDoc to reflect bubblewrap as Linux default

c824a36

SohamDas2021 marked this pull request as ready for review May 21, 2026 16:58

huzaifa-d approved these changes May 21, 2026

View reviewed changes

Copilot started work on behalf of huzaifa-d May 21, 2026 19:26 View session

Fix MicroVM workflow cache permissions

13b6f46

Agent-Logs-Url: https://github.com/microsoft/mxc/sessions/81dc5e19-9e89-4a1a-a005-6633f4ffbfe8 Co-authored-by: huzaifa-d <16077119+huzaifa-d@users.noreply.github.com>

Copilot finished work on behalf of huzaifa-d May 21, 2026 19:37

Copilot AI requested a review from huzaifa-d May 21, 2026 19:37

huzaifa-d requested changes May 21, 2026

View reviewed changes

Comment thread sdk/src/sandbox.ts Outdated

Comment thread sdk/src/sandbox.ts

Comment thread src/wxc_common/src/config_parser.rs

microsoft-github-policy-service Bot assigned SohamDas2021 May 21, 2026

microsoft-github-policy-service Bot added Needs-Author-Feedback Issue needs attention from issue or PR author Needs-Attention Issue needs attention from Microsoft and removed Needs-Author-Feedback Issue needs attention from issue or PR author labels May 21, 2026

SohamDas2021 added 2 commits May 21, 2026 18:15

Addressed PR comments

be21417

More fixes to LXC

a830520

huzaifa-d reviewed May 22, 2026

View reviewed changes

huzaifa-d approved these changes May 22, 2026

View reviewed changes

Comment clarification

59e4c6d

huzaifa-d approved these changes May 22, 2026

View reviewed changes

huzaifa-d merged commit b82cd9c into main May 22, 2026
18 checks passed

huzaifa-d deleted the user/sodas/MakeBubblewrapDefault branch May 22, 2026 19:55

microsoft-github-policy-service Bot removed the Needs-Attention Issue needs attention from Microsoft label May 22, 2026

richiemsft mentioned this pull request May 26, 2026

Fix: exempt abstract 'process' on macOS from allowOutbound precheck #411

Merged

7 tasks

SohamDas2021 mentioned this pull request May 30, 2026

Publish 0.6.0-alpha as the new stable schema (strict surface) #455

Merged

5 tasks

Provide feedback

Saved searches

Use saved searches to filter your results more quickly

Uh oh!

[Bubblewrap] Make Bubblewrap the default Linux backend#368

[Bubblewrap] Make Bubblewrap the default Linux backend#368
huzaifa-d merged 9 commits into
mainfrom
user/sodas/MakeBubblewrapDefault

SohamDas2021 commented May 21, 2026 •

edited

Loading

Uh oh!

Copilot AI left a comment

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

huzaifa-d May 22, 2026

Uh oh!

SohamDas2021 May 22, 2026

Uh oh!

huzaifa-d May 22, 2026

Uh oh!

SohamDas2021 May 22, 2026

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

Uh oh!

Conversation

SohamDas2021 commented May 21, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

Uh oh!

📖 Description

Linux containment resolution matrix

🔗 References

🔍 Validation

✅ Checklist

📋 Issue Type

Microsoft Reviewers: Open in CodeFlow

Uh oh!

Copilot AI left a comment

Choose a reason for hiding this comment

Pull request overview

Reviewed changes

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

Uh oh!

huzaifa-d May 22, 2026

Choose a reason for hiding this comment

Uh oh!

SohamDas2021 May 22, 2026

Choose a reason for hiding this comment

Uh oh!

huzaifa-d May 22, 2026

Choose a reason for hiding this comment

Uh oh!

SohamDas2021 May 22, 2026

Choose a reason for hiding this comment

Linux containment resolution matrix

Uh oh!

Uh oh!

Reviewers

Assignees

Labels

Projects

Milestone

Development

Uh oh!

4 participants

SohamDas2021 commented May 21, 2026 •

edited

Loading