io.go

// +build !windows

/*
   Copyright The containerd Authors.

   Licensed under the Apache License, Version 2.0 (the "License");
   you may not use this file except in compliance with the License.
   You may obtain a copy of the License at

       http://www.apache.org/licenses/LICENSE-2.0

   Unless required by applicable law or agreed to in writing, software
   distributed under the License is distributed on an "AS IS" BASIS,
   WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
   See the License for the specific language governing permissions and
   limitations under the License.
*/

package proc

import (
	"context"
	"fmt"
	"io"
	"os"
	"sync"
	"sync/atomic"
	"syscall"

	"github.com/containerd/containerd/log"
	"github.com/containerd/fifo"
	runc "github.com/containerd/go-runc"
)

var bufPool = sync.Pool{
	New: func() interface{} {
		buffer := make([]byte, 32<<10)
		return &buffer
	},
}

func copyPipes(ctx context.Context, rio runc.IO, stdin, stdout, stderr string, wg, cwg *sync.WaitGroup) error {
	var sameFile *countingWriteCloser
	for _, i := range []struct {
		name string
		dest func(wc io.WriteCloser, rc io.Closer)
	}{
		{
			name: stdout,
			dest: func(wc io.WriteCloser, rc io.Closer) {
				wg.Add(1)
				cwg.Add(1)
				go func() {
					cwg.Done()
					p := bufPool.Get().(*[]byte)
					defer bufPool.Put(p)
					if _, err := io.CopyBuffer(wc, rio.Stdout(), *p); err != nil {
						log.G(ctx).Warn("error copying stdout")
					}
					wg.Done()
					wc.Close()
					if rc != nil {
						rc.Close()
					}
				}()
			},
		}, {
			name: stderr,
			dest: func(wc io.WriteCloser, rc io.Closer) {
				wg.Add(1)
				cwg.Add(1)
				go func() {
					cwg.Done()
					p := bufPool.Get().(*[]byte)
					defer bufPool.Put(p)
					if _, err := io.CopyBuffer(wc, rio.Stderr(), *p); err != nil {
						log.G(ctx).Warn("error copying stderr")
					}
					wg.Done()
					wc.Close()
					if rc != nil {
						rc.Close()
					}
				}()
			},
		},
	} {
		ok, err := isFifo(i.name)
		if err != nil {
			return err
		}
		var (
			fw io.WriteCloser
			fr io.Closer
		)
		if ok {
			if fw, err = fifo.OpenFifo(ctx, i.name, syscall.O_WRONLY, 0); err != nil {
				return fmt.Errorf("containerd-shim: opening %s failed: %s", i.name, err)
			}
			if fr, err = fifo.OpenFifo(ctx, i.name, syscall.O_RDONLY, 0); err != nil {
				return fmt.Errorf("containerd-shim: opening %s failed: %s", i.name, err)
			}
		} else {
			if sameFile != nil {
				sameFile.count++
				i.dest(sameFile, nil)
				continue
			}
			if fw, err = os.OpenFile(i.name, syscall.O_WRONLY|syscall.O_APPEND, 0); err != nil {
				return fmt.Errorf("containerd-shim: opening %s failed: %s", i.name, err)
			}
			if stdout == stderr {
				sameFile = &countingWriteCloser{
					WriteCloser: fw,
					count:       1,
				}
			}
		}
		i.dest(fw, fr)
	}
	if stdin == "" {
		return nil
	}
	f, err := fifo.OpenFifo(context.Background(), stdin, syscall.O_RDONLY|syscall.O_NONBLOCK, 0)
	if err != nil {
		return fmt.Errorf("containerd-shim: opening %s failed: %s", stdin, err)
	}
	cwg.Add(1)
	go func() {
		cwg.Done()
		p := bufPool.Get().(*[]byte)
		defer bufPool.Put(p)

		io.CopyBuffer(rio.Stdin(), f, *p)
		rio.Stdin().Close()
		f.Close()
	}()
	return nil
}

// countingWriteCloser masks io.Closer() until close has been invoked a certain number of times.
type countingWriteCloser struct {
	io.WriteCloser
	count int64
}

func (c *countingWriteCloser) Close() error {
	if atomic.AddInt64(&c.count, -1) > 0 {
		return nil
	}
	return c.WriteCloser.Close()
}

// isFifo checks if a file is a fifo
// if the file does not exist then it returns false
func isFifo(path string) (bool, error) {
	stat, err := os.Stat(path)
	if err != nil {
		if os.IsNotExist(err) {
			return false, nil
		}
		return false, err
	}
	if stat.Mode()&os.ModeNamedPipe == os.ModeNamedPipe {
		return true, nil
	}
	return false, nil
}