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https://blitiri.com.ar/repos/chasquid
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3be7cd5160
This patch adds tests to verify how safeio behaves when *os.File operations return various errors. To do this, we allow the possibility of wrapping os.CreateTemp, so we can simulate the errors during testing. This is not pretty, but the code is small enough that the readability overhead is minimal, and we get a lot of tests from it.
98 lines
2.4 KiB
Go
98 lines
2.4 KiB
Go
// Package safeio implements convenient I/O routines that provide additional
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// levels of safety in the presence of unexpected failures.
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package safeio
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import (
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"os"
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"path"
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"syscall"
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)
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// osFile is an interface to the methods of os.File that we need, so we can
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// simulate failures in tests.
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type osFile interface {
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Name() string
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Chmod(os.FileMode) error
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Chown(int, int) error
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Write([]byte) (int, error)
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Close() error
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}
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var createTemp func(dir, pattern string) (osFile, error) = func(
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dir, pattern string) (osFile, error) {
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return os.CreateTemp(dir, pattern)
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}
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// FileOp represents an operation on a file (passed by its name).
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type FileOp func(fname string) error
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// WriteFile writes data to a file named by filename, atomically.
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//
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// It's a wrapper to os.WriteFile, but provides atomicity (and increased
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// safety) by writing to a temporary file and renaming it at the end.
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//
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// Before the final rename, the given ops (if any) are called. They can be
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// used to manipulate the file before it is atomically renamed.
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// If any operation fails, the file is removed and the error is returned.
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//
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// Note this relies on same-directory Rename being atomic, which holds in most
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// reasonably modern filesystems.
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func WriteFile(filename string, data []byte, perm os.FileMode, ops ...FileOp) error {
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// Note we create the temporary file in the same directory, otherwise we
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// would have no expectation of Rename being atomic.
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// We make the file names start with "." so there's no confusion with the
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// originals.
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tmpf, err := createTemp(path.Dir(filename), "."+path.Base(filename))
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if err != nil {
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return err
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}
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if err = tmpf.Chmod(perm); err != nil {
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tmpf.Close()
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os.Remove(tmpf.Name())
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return err
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}
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if uid, gid := getOwner(filename); uid >= 0 {
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if err = tmpf.Chown(uid, gid); err != nil {
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tmpf.Close()
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os.Remove(tmpf.Name())
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return err
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}
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}
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if _, err = tmpf.Write(data); err != nil {
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tmpf.Close()
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os.Remove(tmpf.Name())
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return err
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}
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if err = tmpf.Close(); err != nil {
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os.Remove(tmpf.Name())
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return err
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}
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for _, op := range ops {
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if err = op(tmpf.Name()); err != nil {
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os.Remove(tmpf.Name())
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return err
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}
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}
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return os.Rename(tmpf.Name(), filename)
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}
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func getOwner(fname string) (uid, gid int) {
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uid = -1
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gid = -1
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stat, err := os.Stat(fname)
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if err == nil {
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if sysstat, ok := stat.Sys().(*syscall.Stat_t); ok {
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uid = int(sysstat.Uid)
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gid = int(sysstat.Gid)
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}
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}
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return
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}
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