55 lines
2.6 KiB
Markdown
55 lines
2.6 KiB
Markdown
# Internal: File Operations
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`internal/fileops` owns the narrow mechanics for atomically visible 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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## Destination Paths
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Ordinary workspace replacement uses standard operating-system path semantics.
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Callers with a root-scoped safety contract own that validation at their boundary.
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Remote object acquisition uses a writer supplied by the storage owner. The
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writer receives a `fileops`-owned, already-open sibling temporary file rather
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than a mutable destination path. Callers still own remote object selection,
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validation, conflict handling, and final mode.
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Directory promotion keeps the verified destination parent open while it creates
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the temporary tree, copies regular source entries, and performs the platform
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no-replace rename. Platforms without a verified handle-relative atomic
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no-replace primitive reject promotion before writing a temporary tree.
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## Cleanup Contract
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`RemoveAllUnderRoot` accepts an explicit root and a proper descendant. It opens
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the root and each target ancestor without following symlinks, then removes the
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tree through those directory handles. It rejects root deletion and any symlink
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encountered in the target path or tree; repeated removal of a missing target is
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successful. Command and post-publish policy remains owned by `internal/app`.
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## Bounded Reads
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`ReadFileBounded` opens a normal path and reads at most its caller-supplied
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limit. Credential mode policy and environment precedence remain owned by
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`internal/app`.
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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, closes the file, runs an optional pre-rename check, and
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replaces the destination with a rename.
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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. Successful replacement
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provides atomic visibility; it makes no crash- or power-loss durability claim.
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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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`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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