Add structcheck, unused, and varcheck linters.

Warn on unused and dead code

Signed-off-by: Daniel Nephin <dnephin@gmail.com>

cmd/ctr/commands/shim/io_windows.go

@@ -1,91 +0,0 @@
-package shim
-
-import (
-	"io"
-	"net"
-	"os"
-	"sync"
-
-	"github.com/Microsoft/go-winio"
-	clog "github.com/containerd/containerd/log"
-	"github.com/pkg/errors"
-)
-
-func prepareStdio(stdin, stdout, stderr string, console bool) (*sync.WaitGroup, error) {
-	var wg sync.WaitGroup
-
-	if stdin != "" {
-		l, err := winio.ListenPipe(stdin, nil)
-		if err != nil {
-			return nil, errors.Wrapf(err, "failed to create stdin pipe %s", stdin)
-		}
-		defer func(l net.Listener) {
-			if err != nil {
-				l.Close()
-			}
-		}(l)
-
-		go func() {
-			c, err := l.Accept()
-			if err != nil {
-				clog.L.WithError(err).Errorf("failed to accept stdin connection on %s", stdin)
-				return
-			}
-			io.Copy(c, os.Stdin)
-			c.Close()
-			l.Close()
-		}()
-	}
-
-	if stdout != "" {
-		l, err := winio.ListenPipe(stdout, nil)
-		if err != nil {
-			return nil, errors.Wrapf(err, "failed to create stdin pipe %s", stdout)
-		}
-		defer func(l net.Listener) {
-			if err != nil {
-				l.Close()
-			}
-		}(l)
-
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			c, err := l.Accept()
-			if err != nil {
-				clog.L.WithError(err).Errorf("failed to accept stdout connection on %s", stdout)
-				return
-			}
-			io.Copy(os.Stdout, c)
-			c.Close()
-			l.Close()
-		}()
-	}
-
-	if !console && stderr != "" {
-		l, err := winio.ListenPipe(stderr, nil)
-		if err != nil {
-			return nil, errors.Wrapf(err, "failed to create stderr pipe %s", stderr)
-		}
-		defer func(l net.Listener) {
-			if err != nil {
-				l.Close()
-			}
-		}(l)
-
-		wg.Add(1)
-		go func() {
-			defer wg.Done()
-			c, err := l.Accept()
-			if err != nil {
-				clog.L.WithError(err).Errorf("failed to accept stderr connection on %s", stderr)
-				return
-			}
-			io.Copy(os.Stderr, c)
-			c.Close()
-			l.Close()
-		}()
-	}
-
-	return &wg, nil
-}