Add hooks support to podman

Signed-off-by: Daniel J Walsh <dwalsh@redhat.com>

Closes: #155
Approved by: mheon

pkg/hooks/hooks.go

@@ -0,0 +1,141 @@
+package hooks
+
+import (
+	"encoding/json"
+	"fmt"
+	"io/ioutil"
+	"os"
+	"path/filepath"
+	"regexp"
+	"strings"
+	"syscall"
+
+	spec "github.com/opencontainers/runtime-spec/specs-go"
+	"github.com/opencontainers/runtime-tools/generate"
+	"github.com/pkg/errors"
+	"github.com/sirupsen/logrus"
+)
+
+const (
+	// DefaultHooksDir Default directory containing hooks config files
+	DefaultHooksDir = "/usr/share/containers/oci/hooks.d"
+	// OverrideHooksDir Directory where admin can override the default configuration
+	OverrideHooksDir = "/etc/containers/oci/hooks.d"
+)
+
+// HookParams is the structure returned from read the hooks configuration
+type HookParams struct {
+	Hook          string   `json:"hook"`
+	Stage         []string `json:"stage"`
+	Cmds          []string `json:"cmd"`
+	Annotations   []string `json:"annotation"`
+	HasBindMounts bool     `json:"hasbindmounts"`
+	Arguments     []string `json:"arguments"`
+}
+
+// readHook reads hooks json files, verifies it and returns the json config
+func readHook(hookPath string) (HookParams, error) {
+	var hook HookParams
+	raw, err := ioutil.ReadFile(hookPath)
+	if err != nil {
+		return hook, errors.Wrapf(err, "error Reading hook %q", hookPath)
+	}
+	if err := json.Unmarshal(raw, &hook); err != nil {
+		return hook, errors.Wrapf(err, "error Unmarshalling JSON for %q", hookPath)
+	}
+	if _, err := os.Stat(hook.Hook); err != nil {
+		return hook, errors.Wrapf(err, "unable to stat hook %q in hook config %q", hook.Hook, hookPath)
+	}
+	validStage := map[string]bool{"prestart": true, "poststart": true, "poststop": true}
+	for _, cmd := range hook.Cmds {
+		if _, err = regexp.Compile(cmd); err != nil {
+			return hook, errors.Wrapf(err, "invalid cmd regular expression %q defined in hook config %q", cmd, hookPath)
+		}
+	}
+	for _, cmd := range hook.Annotations {
+		if _, err = regexp.Compile(cmd); err != nil {
+			return hook, errors.Wrapf(err, "invalid cmd regular expression %q defined in hook config %q", cmd, hookPath)
+		}
+	}
+	for _, stage := range hook.Stage {
+		if !validStage[stage] {
+			return hook, errors.Wrapf(err, "unknown stage %q defined in hook config %q", stage, hookPath)
+		}
+	}
+	return hook, nil
+}
+
+// readHooks reads hooks json files in directory to setup OCI Hooks
+// adding hooks to the passedin hooks map.
+func readHooks(hooksPath string, hooks map[string]HookParams) error {
+	if _, err := os.Stat(hooksPath); err != nil {
+		if os.IsNotExist(err) {
+			logrus.Warnf("hooks path: %q does not exist", hooksPath)
+			return nil
+		}
+		return errors.Wrapf(err, "unable to stat hooks path %q", hooksPath)
+	}
+
+	files, err := ioutil.ReadDir(hooksPath)
+	if err != nil {
+		return err
+	}
+
+	for _, file := range files {
+		if !strings.HasSuffix(file.Name(), ".json") {
+			continue
+		}
+		hook, err := readHook(filepath.Join(hooksPath, file.Name()))
+		if err != nil {
+			return err
+		}
+		for key, h := range hooks {
+			// hook.Hook can only be defined in one hook file, unless it has the
+			// same name in the override path.
+			if hook.Hook == h.Hook && key != file.Name() {
+				return errors.Wrapf(syscall.EINVAL, "duplicate path,  hook %q from %q already defined in %q", hook.Hook, hooksPath, key)
+			}
+		}
+		hooks[file.Name()] = hook
+	}
+	return nil
+}
+
+// SetupHooks takes a hookspath and reads all of the hooks in that directory.
+// returning a map of the configured hooks
+func SetupHooks(hooksPath string) (map[string]HookParams, error) {
+	hooksMap := make(map[string]HookParams)
+	if err := readHooks(hooksPath, hooksMap); err != nil {
+		return nil, err
+	}
+	if hooksPath == DefaultHooksDir {
+		if err := readHooks(OverrideHooksDir, hooksMap); err != nil {
+			return nil, err
+		}
+	}
+
+	return hooksMap, nil
+}
+
+// AddOCIHook generates OCI specification using the included hook
+func AddOCIHook(g *generate.Generator, hook HookParams) error {
+	for _, stage := range hook.Stage {
+		h := spec.Hook{
+			Path: hook.Hook,
+			Args: append([]string{hook.Hook}, hook.Arguments...),
+			Env:  []string{fmt.Sprintf("stage=%s", stage)},
+		}
+		logrus.Debugf("AddOCIHook", h)
+		switch stage {
+		case "prestart":
+			g.AddPreStartHook(h)
+
+		case "poststart":
+			g.AddPostStartHook(h)
+
+		case "poststop":
+			g.AddPostStopHook(h)
+		}
+	}
+	return nil
+}