36 lines
1.7 KiB
Markdown
36 lines
1.7 KiB
Markdown
# Internal: File Operations
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`internal/fileops` owns the narrow mechanics for durable replacement of one
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byte file. Callers keep ownership of serialization, validation, cancellation,
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and destination-directory policy.
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## Replacement Contract
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`ReplaceFileAtomic` requires an existing destination directory. It creates a
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sibling temporary file, writes the complete byte sequence, applies the
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caller-supplied mode, syncs and closes the file, runs an optional pre-rename
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check, replaces the destination with a rename, then syncs the containing
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directory.
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The pre-rename check is the last point at which a caller can cancel without
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installing a new destination. A failure before the rename leaves the old
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destination unchanged and removes the temporary file; any cleanup failure is
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returned alongside the primary failure. A failure after the rename may leave
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the new file visible, but it is not reported as crash-durable.
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Replacement follows the operating system's same-filesystem rename semantics.
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If a platform cannot replace an existing destination, the operation returns an
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error and never removes the old file as an emulation step.
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## Directory-Sync Support
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Linux and macOS attempt to sync the destination directory. Windows opens the
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directory with backup semantics and flushes its buffers. If either operation
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is unavailable for the platform, directory handle, or filesystem,
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`ErrDirectorySyncUnsupported` is returned. Narratio does not treat that result
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as successful crash-durable replacement.
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`WriteFileAtomic`, copy helpers, and downloaded temporary-file installation
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retain their compatibility behavior of creating the destination parent with
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the repository's workspace permissions before using this contract.
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