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…dren The worker setup deletes NODE_UNIQUE_ID from process.env so that child processes do not inherit it. Bun.spawn and Bun.spawnSync with no env option copy the native env map, which still had the variable. The child then took itself for a cluster worker, and its net and http listen() never completed. The worker setup now also takes the variable out of the env map. A worker thread's VM reads the OS environment again, so it drops the variable at startup once the main thread took it. Bun.serve keeps its reusePort default in a worker through VirtualMachine::is_cluster_worker.
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WalkthroughWhen the virtual machine detects ChangesChild environment handling
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The title clearly and concisely describes the main change: preventing NODE_UNIQUE_ID from reaching a worker's Bun.spawn children. |
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The description provides a detailed explanation of the problem, fix, scope, tradeoffs, testing, and limitations. It does not use the template headings exactly, but it includes the required information and is complete.
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Status: ready for review. CI passes on How I reproduced it (1.4.3-canary.1+367d939d9 and a debug build of main, Linux x64):
On main each child prints The test is |
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… the env map as it is The env map is shared with a Bun.build that runs on the bundler thread, so a removal at run time can race with it. The map now stays as it is. When the startup environment has NODE_UNIQUE_ID, create_null_delimited_env_map leaves the variable out of every env that it builds for a child process. This also covers a worker that never loads node:cluster and a worker thread that starts early. Bun.serve reads the variable from the map as before, so ServerConfig and the worker setup are back to what main has.
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Updated 9:23 AM PT - Oct 17th, 2026
❌ @robobun, your commit 15ce700 has 1 failures in
🧪 To try this PR locally: bunx bun-pr 43768That installs a local version of the PR into your bun-43768 --bun |
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…er primary A process that starts with NODE_UNIQUE_ID is a worker as far as the fix is concerned, so the tests spawn it directly. They need about 1.5 s on a debug build instead of 3.5 s.
…ter-worker-spawn-env-unique-id
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Merged The one conflict was the re-export list in I did not build this branch by itself. I built it merged with #43821 and #43762 (Linux x64, debug): Why now: #43762 is being reworked to set every cluster worker up before user code, as Node does. With that change a worker's |
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Review comments at @src/dotenv/env_loader.rs:
- Around line 1303-1308: Update write_windows_env_block to skip the map entry at
the omitted index when calculating buffer capacity and writing UTF-16 output, so
NODE_UNIQUE_ID is excluded whenever the child-environment filter is enabled.
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src/dotenv/env_loader.rssrc/dotenv/lib.rssrc/jsc/VirtualMachine.rstest/js/node/cluster.test.ts
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For information, from the review of #43762, which is stacked on this PR.
An empty value gives the same three rows. I measured this on a debug build of #43762, not on this branch alone. I did not change the rule in #43762. If the rule becomes "omit when the worker setup runs", #43762 has one place where that setup runs and deletes the variable: |
…ator Map::write_windows_env_block did not apply the NODE_UNIQUE_ID filter of create_null_delimited_env_map. Its one caller, the .bunx fast path of bun run, runs before a VM exists, so the flag is never set there and its output does not change. Map::child_env_entries now holds the filter, and both builders iterate through it.
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I reviewed the latest push (the shared child_env_entries iterator) and found no bugs; since this flips a process-wide default for every child-spawn path in a VM process, a human look at that design choice is still worthwhile.
What was reviewed:
child_env_entries:get_indexanditerator()both walkinner.keysin insertion order, so the enumerated index matches; the index is taken before the&mutiterator borrow and the lookup goes through the case-insensitive table on Windows.- The flag is set in
load_extra_env_and_source_code_printer, which runs for the main VM and every worker thread, before user code can spawn; all callers of both builders (Bun.spawn/spawnSync, shell fallback,bun test --parallel, cron, webview, lifecycle scripts) are child-env builders, so the filter is not applied anywhere a full env is required. - Tests: the first test fails on main for all four spawn sites (child inherits the variable before
node:clusterloads), pipes are drained concurrently with a combined{stdout, stderr, exitCode}; the reusePort test's EADDRINUSE control relies on the non-worker child not setting SO_REUSEPORT, which is what it checks.
Extended reasoning...
The diff adds a process-global AtomicBool in src/dotenv/env_loader.rs that is set at VM boot when the startup env contains NODE_UNIQUE_ID, and a private filtered iterator that both the POSIX envp builder and the Windows UTF-16 env block builder now use so that spawned children omit the variable; src/jsc/VirtualMachine.rs sets the flag and src/dotenv/lib.rs re-exports the setter, with two new subprocess tests in test/js/node/cluster.test.ts. It touches no auth, crypto, or injection surface; the only sensitive aspect is environment propagation to child processes. It is small and I found no correctness problems, but the global flag affects the default env of every spawn path in a VM process (including bun test --parallel, cron and webview hosts) and is a monotonic process-wide setting rather than per-VM state, which is a design decision a maintainer should weigh; there is also an unresolved coderabbitai inline comment from the previous push whose text I cannot see, though the latest commit plausibly addressed it by routing the Windows builder through the same filter.
Problem
node:clusterworker starts withBun.spawnorBun.spawnSyncand noenvinheritsNODE_UNIQUE_ID. It takes itself for a worker, and itslisten()callback never runs.delete process.env.NODE_UNIQUE_ID(src/js/node/cluster.ts:17). That only changes the JS object.Bun.spawncopies the env map (js_bun_spawn_bindings.rs:920), which keeps it.Fix
NODE_UNIQUE_ID,load_extra_env_and_source_code_printersets a process-wide flag.Map::child_env_entriesskips the variable. Both child env builders ofMapiterate through it.process.envand thereusePortdefault ofBun.serveread the variable from it.node:clusterand for worker threads.test/js/node/cluster.test.ts(two new tests, main fails the first), alltest-cluster-*.jsNode tests,spawn-env.test.ts,worker_threads.test.ts. Self-reviewed: 10 concerns raised, 10 addressed.Background
cluster.fork()setsNODE_UNIQUE_IDfor a worker.node:clusterandnode:netdecide from it if a process is a worker. Node deletes it from the environment at bootstrap, so no child gets it.vm.transpiler.env) is each VM's native copy of the startup environment.Bun.spawnwith noenvpasses it on.process.envchanges do not reach it.Downsides
NODE_UNIQUE_IDno longer passes it to aBun.spawnchild with noenv. Node agrees for a script, but passes it on for-eor an empty value.node:child_processcopiesprocess.env, so it passes the variable untilnode:clusterloads. node: net/tls/http/http2 compat fixes #41400 covers that.Notes
Repro (1.4.3-canary.1+367d939d9, Linux x64). A cluster worker runs:
The child prints nothing and exits with code 0. With this change it prints
listening.Node. Node v26.3.0 decides on the variable alone:
NODE_UNIQUE_ID=1 node -e "require('net').createServer().listen(0, cb)"never callscbeither. Sointernal/cluster/isPrimary.tsstays as it is, and the fix is to not pass the variable on. In Node,delete process.env.Xedits the real environment, so no child inherits the variable. Bun does not edit the OS environment on POSIX.Why a filter and not a removal. The first version of this PR removed the variable from the env map when the worker setup ran. The review found that a
Bun.buildwithenv: "inline"reads the same map on the bundler thread (src/bundler/defines.rs:95) and keeps defines that point into its values. A removal at run time can race with that. The removal also needed a second flag for thereusePortdefault and a second removal at worker thread startup, and it did nothing beforenode:clusterloaded. With the filter nothing writes the map after startup, as on main, andcluster.ts,node_cluster_binding.rsandServerConfig.rsare back to what main has.Why the flag is process-wide. The fact is about the process: it started with
NODE_UNIQUE_ID. Each VM in it, the main thread and every worker thread, has its own env map and builds child envs from it. A flag on oneMapwould have to follow every copy of that map (clone_for_workermakes one for each worker thread). The flag only goes from unset to set.The rule against Node. Node deletes the variable only when it sets a worker up:
process.argv[1]exists (a script, or an argument after-e) and the value is not empty. This PR leaves the variable out of the defaultBun.spawnenv whenever the process starts with it. The table showsNODE_UNIQUE_IDas a child with the default env sees it (node v26.3.0, bun 1.4.3-canary.1+367d939d9, this branch at 8aad2a9, Linux x64).child_processBun.spawnSyncBun.spawnSyncNODE_UNIQUE_ID=5, script5NODE_UNIQUE_ID=5,-e55NODE_UNIQUE_ID=(empty), scriptThe last two processes are not workers: Node and Bun do not run the worker setup for them.
process.envkeeps the variable there, and anode:child_processchild gets it in all three runtimes. The exact rule is "leave it out when the worker setup runs". On main that setup runs only whennode:clusterloads, which is too late for a script that spawns first. #43762 moves the setup to before user code (initializeClusterIPCininternal/process/pre_execution.ts). That is the one place where the exact rule fits.Where the filter applies.
Map::child_env_entriesholds the filter.create_null_delimited_env_mapiterates through it. It builds the default env forBun.spawn,Bun.spawnSync, the Bun shell fallback,bun test --parallelworkers and the WebView host. Only a process that boots a VM sets the flag. Sobun run <script>andbunx, which have no VM, still pass the variable through to a real worker behind them. An explicitenvoption is not filtered. On Windows the lookup uses the case-insensitive map, like every other read of the variable.The Windows
.bunxfast path.write_windows_env_blockis the second child env builder ofMap. It has one caller, the.bunxfast path ofbun run, which runs before a VM exists. So the flag is never set there, and the output of the fast path does not change. It iterates throughchild_env_entriestoo, so the two builders cannot differ. I cannot run Windows here. The crate type-checks forx86_64-pc-windows-msvc.Not covered. A spawn that passes the OS environment and not the env map still gets the variable, as on main. In a VM process I found three: the
crontabtool ofBun.cronon POSIX, the editor ofBun.openInEditor, andgitforbun test --changed.Not changed. The Bun shell and
node:child_processpass the liveprocess.env.bun --watchrestarts from the OS environment (reload_processcopiesenviron), so a watched worker stays a worker.Tests. Both tests start the worker directly: a process that starts with
NODE_UNIQUE_IDand a script file is a worker for Bun and for Node, andcluster.fork()does nothing else to the environment. The first test fails on main for all four spawns (before and after the worker setup,Bun.spawnSync, andBun.spawnSyncin a worker thread): each child prints{"uniqueId":"1","isWorker":true}. ThereusePorttest passes with and without this change. It pins the reason for the filter:Bun.servereads the variable from the env map, so the map has to keep it. Nothing tested that default before. The docs callreusePortLinux only, so that test runs on Linux only. On a debug build the two tests need about 2.4 s and 1.4 s.Related open PRs.
node:child_processfor a worker that has not loadednode:clusteryet. It does not touchBun.spawn.delete process.env.Xreach the env map and the OS environment on POSIX. With it, thedeletein the worker setup removes the variable from the env map, andServerConfig.rsloses thereusePortdefault as soon asnode:clusterloads. The newreusePorttest catches that.process.envof its parent. After the worker setup that object has noNODE_UNIQUE_ID, so aBun.servein a worker thread would lose the default. No test here covers that case.process.envloses the variable before a script runs.Found on the way. A worker thread that starts after
process.env.HTTP_PROXYchanged at run time still uses the value from the OS environment forfetch(). #41932 covers it.Self-review. 10 concerns raised, 10 addressed. In the tests: a hang and a leaked process on the failure paths, a missing
onerrorfor a worker thread, an error without acode, no proof that the port conflict is real, a wrong comment aboutSO_REUSEPORT, and a run time close to the 5 s default of a local debug run (the tests now start the worker directly). In the first design: the run-time write to the env map, the lock question that came with it, a worker thread that starts early, and a flag set for a variable that the map never had. The switch to the filter removed those four.no test proof · iteration 1 · platform-specific test(s) that do not run on this machine, deferring to CI, which covers all platforms: test/js/node/cluster.test.ts