signals.go

/*
   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 containerd

import (
	"context"
	"encoding/json"
	"fmt"
	"strconv"
	"strings"
	"syscall"

	"github.com/containerd/containerd/content"
	"github.com/containerd/containerd/images"
	"github.com/opencontainers/image-spec/specs-go/v1"
)

// StopSignalLabel is a well-known containerd label for storing the stop
// signal specified in the OCI image config
const StopSignalLabel = "io.containerd.image.config.stop-signal"

// GetStopSignal retrieves the container stop signal, specified by the
// well-known containerd label (StopSignalLabel)
func GetStopSignal(ctx context.Context, container Container, defaultSignal syscall.Signal) (syscall.Signal, error) {
	labels, err := container.Labels(ctx)
	if err != nil {
		return -1, err
	}

	if stopSignal, ok := labels[StopSignalLabel]; ok {
		return ParseSignal(stopSignal)
	}

	return defaultSignal, nil
}

// GetOCIStopSignal retrieves the stop signal specified in the OCI image config
func GetOCIStopSignal(ctx context.Context, image Image, defaultSignal string) (string, error) {
	_, err := ParseSignal(defaultSignal)
	if err != nil {
		return "", err
	}
	ic, err := image.Config(ctx)
	if err != nil {
		return "", err
	}
	var (
		ociimage v1.Image
		config   v1.ImageConfig
	)
	switch ic.MediaType {
	case v1.MediaTypeImageConfig, images.MediaTypeDockerSchema2Config:
		p, err := content.ReadBlob(ctx, image.ContentStore(), ic)
		if err != nil {
			return "", err
		}

		if err := json.Unmarshal(p, &ociimage); err != nil {
			return "", err
		}
		config = ociimage.Config
	default:
		return "", fmt.Errorf("unknown image config media type %s", ic.MediaType)
	}

	if config.StopSignal == "" {
		return defaultSignal, nil
	}

	return config.StopSignal, nil
}

// ParseSignal parses a given string into a syscall.Signal
// it checks that the signal exists in the platform-appropriate signalMap
func ParseSignal(rawSignal string) (syscall.Signal, error) {
	s, err := strconv.Atoi(rawSignal)
	if err == nil {
		sig := syscall.Signal(s)
		for _, msig := range signalMap {
			if sig == msig {
				return sig, nil
			}
		}
		return -1, fmt.Errorf("unknown signal %q", rawSignal)
	}
	signal, ok := signalMap[strings.TrimPrefix(strings.ToUpper(rawSignal), "SIG")]
	if !ok {
		return -1, fmt.Errorf("unknown signal %q", rawSignal)
	}
	return signal, nil
}