mirror of
https://github.com/restic/restic.git
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97 lines
2.5 KiB
Go
97 lines
2.5 KiB
Go
package fs
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import (
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"bufio"
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"context"
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"fmt"
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"io"
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"os/exec"
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"github.com/restic/restic/internal/errors"
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)
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// CommandReader wrap a command such that its standard output can be read using
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// a io.ReadCloser. Close() waits for the command to terminate, reporting
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// any error back to the caller.
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type CommandReader struct {
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cmd *exec.Cmd
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stdout io.ReadCloser
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// cmd.Wait() must only be called once. Prevent duplicate executions in
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// Read() and Close().
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waitHandled bool
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// alreadyClosedReadErr is the error that we should return if we try to
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// read the pipe again after closing. This works around a Read() call that
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// is issued after a previous Read() with `io.EOF` (but some bytes were
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// read in the past).
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alreadyClosedReadErr error
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}
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func NewCommandReader(ctx context.Context, args []string, logOutput io.Writer) (*CommandReader, error) {
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// Prepare command and stdout
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command := exec.CommandContext(ctx, args[0], args[1:]...)
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stdout, err := command.StdoutPipe()
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if err != nil {
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return nil, fmt.Errorf("failed to setup stdout pipe: %w", err)
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}
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// Use a Go routine to handle the stderr to avoid deadlocks
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stderr, err := command.StderrPipe()
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if err != nil {
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return nil, fmt.Errorf("failed to setup stderr pipe: %w", err)
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}
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go func() {
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sc := bufio.NewScanner(stderr)
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for sc.Scan() {
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_, _ = fmt.Fprintf(logOutput, "subprocess %v: %v\n", command.Args[0], sc.Text())
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}
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}()
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if err := command.Start(); err != nil {
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return nil, fmt.Errorf("failed to start command: %w", err)
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}
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return &CommandReader{
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cmd: command,
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stdout: stdout,
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}, nil
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}
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// Read populate the array with data from the process stdout.
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func (fp *CommandReader) Read(p []byte) (int, error) {
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if fp.alreadyClosedReadErr != nil {
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return 0, fp.alreadyClosedReadErr
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}
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b, err := fp.stdout.Read(p)
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// If the error is io.EOF, the program terminated. We need to check the
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// exit code here because, if the program terminated with no output, the
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// error in `Close()` is ignored.
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if errors.Is(err, io.EOF) {
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fp.waitHandled = true
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// check if the command terminated successfully, If not return the error.
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if errw := fp.wait(); errw != nil {
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err = errw
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}
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}
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fp.alreadyClosedReadErr = err
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return b, err
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}
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func (fp *CommandReader) wait() error {
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err := fp.cmd.Wait()
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if err != nil {
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// Use a fatal error to abort the snapshot.
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return errors.Fatal(err.Error())
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}
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return nil
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}
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func (fp *CommandReader) Close() error {
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if fp.waitHandled {
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return nil
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}
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return fp.wait()
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}
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