Yichen Jiang
ba37180946
writeFileAtomic: exclusive-create random-suffix temp + rename carrying the caller-stated mode; settings-local persistSection now consumes it. The credentials-local store shares it next.
31 lines
1.7 KiB
Markdown
31 lines
1.7 KiB
Markdown
# dsh-atomic-write
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English | [中文](README.zh.md)
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Zero-dependency atomic file replacement shared by file-backed stores that must never leave partial, symlink-hijacked, or wider-than-intended content on disk — the user-settings document (`dsh-settings-local`) and the credentials store (`dsh-credentials-local`).
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## Surface
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```ts
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import { writeFileAtomic } from '@deepseek-ai/dsh-atomic-write'
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await writeFileAtomic('/home/u/.dsh/settings.yaml', text, { mode: 0o600 })
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```
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One export. The contract, in the order failures would exploit it:
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- **Exclusive-create temp** (`wx`, random suffix): the open refuses to follow a symlink planted at a guessable temp path.
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- **The fresh inode carries `mode` through the rename**: replacing a wider-permission file narrows it without a chmod race. `mode` is required so the permission decision stays visible at every call site (subject to the process umask, like every fresh inode).
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- **`rename` replaces a symlinked target itself**, never writing through to its referent.
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- **Same-directory sibling** keeps the rename on one filesystem, so the swap stays atomic.
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- Parent directories are created; on any failure the temp is removed and the failure rethrown; readers observe either the old or the new complete content.
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## Model Experience
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None, as this is a pure filesystem primitive; nothing here reaches a model request.
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## Known Limitations and Deferred Work
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- **Atomic, not durable** — no `fsync` of the file or its directory, so after a crash the rename may be observed unwound. The file-backed stores here re-read and republish on boot, keeping durability the caller's policy.
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- **String content only** — no `Buffer` or stream form until a consumer needs one.
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