76 lines
2.1 KiB
Go
76 lines
2.1 KiB
Go
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// SPDX-License-Identifier: MIT
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// Package fsx provides small filesystem helpers with atomic, durable writes.
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//
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// prx persists configuration and runtime state that must never be observed in a
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// partially written form, so every write goes through WriteFileAtomic.
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package fsx
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import (
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"fmt"
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"os"
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"path/filepath"
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)
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// WriteFileAtomic writes data to path atomically and durably.
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//
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// It creates any missing parent directories, writes to a temporary file in the
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// destination directory, flushes it to stable storage, renames it over path and
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// finally flushes the directory. Concurrent readers therefore either see the
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// previous contents or the complete new contents, never a partial file.
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func WriteFileAtomic(path string, data []byte, perm os.FileMode) error {
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dir := filepath.Dir(path)
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if err := os.MkdirAll(dir, 0o755); err != nil {
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return fmt.Errorf("create %s: %w", dir, err)
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}
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tmp, err := os.CreateTemp(dir, ".prx-*.tmp")
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if err != nil {
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return fmt.Errorf("create temporary file in %s: %w", dir, err)
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}
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tmpName := tmp.Name()
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// Remove the temporary file unless it has been renamed into place.
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committed := false
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defer func() {
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if !committed {
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_ = os.Remove(tmpName)
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}
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}()
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if _, err := tmp.Write(data); err != nil {
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_ = tmp.Close()
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return fmt.Errorf("write %s: %w", tmpName, err)
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}
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if err := tmp.Chmod(perm); err != nil {
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_ = tmp.Close()
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return fmt.Errorf("chmod %s: %w", tmpName, err)
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}
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if err := tmp.Sync(); err != nil {
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_ = tmp.Close()
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return fmt.Errorf("sync %s: %w", tmpName, err)
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}
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if err := tmp.Close(); err != nil {
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return fmt.Errorf("close %s: %w", tmpName, err)
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}
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if err := os.Rename(tmpName, path); err != nil {
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return fmt.Errorf("replace %s: %w", path, err)
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}
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committed = true
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// Flush the directory so the rename itself survives a crash. Failure to
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// sync a directory is tolerated because some filesystems do not support it.
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syncDir(dir)
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return nil
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}
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// syncDir flushes directory metadata to stable storage, ignoring filesystems
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// that do not support directory fsync.
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func syncDir(dir string) {
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f, err := os.Open(dir)
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if err != nil {
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return
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}
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defer f.Close()
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_ = f.Sync()
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}
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