WIP: translate: Stub in a translation framework

Add tooling to translate higher-level configs into the basic OCI
config.  On IRC, Julz floated a linux.namespaces[].fromContainer as a
higher-level version of linux.namespaces[].path for emulating exec
[1].  That makes sense to me, and Mrunal is open to something like
[2]:

  $ ocitools generate --template=high-level-config.json --translate=fromContainer --runtime=runc

The interface{} -> rspec.Spec conversion happens through a JSON
serialization trick suggested by 梁辰晔 (Liang Chenye) [3] after the
translations, because before the translations the template may contain
JSON that's not represented in the OCI Spec structure
(e.g. fromContainer in namespace entries).

This commit still needs (marked by FIXMEs):

* Lookup /proc in /proc/self/mounts (recursive?).
* Compare /proc with state JSON namespace [4].
* A way to handle nested definition lists in man pages.  I expect we
  should drop go-md2man in favor of a more established man-page format
  (e.g. AsciiDoc).

[1]: http://ircbot.wl.linuxfoundation.org/eavesdrop/%23opencontainers/%23opencontainers.2016-04-27.log.html#t2016-04-27T20:32:09
[2]: http://ircbot.wl.linuxfoundation.org/eavesdrop/%23opencontainers/%23opencontainers.2016-04-28.log.html#t2016-04-28T16:12:48
[3]: #54 (comment)
[4]: https://groups.google.com/a/opencontainers.org/forum/#!topic/dev/ujtABQoCmgk
     Subject: Linux: Adding the PID namespace inode to state JSON
     Date: Wed, 30 Dec 2015 21:34:57 -0800
     Message-ID: <20151231053457.GG3680@odin.tremily.us>

Signed-off-by: W. Trevor King <wking@tremily.us>

Author: wking

generate.go

@@ -13,6 +13,7 @@ import (
 	"github.com/codegangsta/cli"
 	rspec "github.com/opencontainers/runtime-spec/specs-go"
 	"github.com/syndtr/gocapability/capability"
+	"github.com/opencontainers/ocitools/translate"
 )
 
 var generateFlags = []cli.Flag{
@@ -55,7 +56,9 @@ var generateFlags = []cli.Flag{
 	cli.StringSliceFlag{Name: "seccomp-arch", Usage: "specifies Additional architectures permitted to be used for system calls"},
 	cli.StringSliceFlag{Name: "seccomp-syscalls", Usage: "specifies Additional architectures permitted to be used for system calls, e.g Name:Action:Arg1_index/Arg1_value/Arg1_valuetwo/Arg1_op, Arg2_index/Arg2_value/Arg2_valuetwo/Arg2_op "},
 	cli.StringSliceFlag{Name: "seccomp-allow", Usage: "specifies syscalls to be added to allowed"},
+	cli.StringFlag{Name: "runtime", Usage: "select the runtime command (used for some translations)"},
 	cli.StringFlag{Name: "template", Usage: "base template to use for creating the configuration"},
+	cli.StringSliceFlag{Name: "translate", Usage: "translate higher level constructs"},
 	cli.StringSliceFlag{Name: "label", Usage: "add annotations to the configuration e.g. key=value"},
 }
 
@@ -93,12 +96,35 @@ var generateCommand = cli.Command{
 			}
 		}
 
-		err := modify(spec, context)
+		translations := context.StringSlice("translate")
+		for _, translation := range translations {
+			translator, ok := translate.Translators[translation]
+			if !ok {
+				logrus.Fatalf("unrecognized translation: %s", translation)
+			}
+			var err error
+			spec, err = translator(spec, context)
+			if err != nil {
+				logrus.Fatal(err)
+			}
+		}
+
+		buf, err := json.Marshal(spec)
+		if err != nil {
+			logrus.Fatal(err)
+		}
+		var strictSpec rspec.Spec
+		err = json.Unmarshal(buf, &strictSpec)
+		if err != nil {
+			logrus.Fatal(err)
+		}
+
+		err = modify(&strictSpec, context)
 		if err != nil {
 			logrus.Fatal(err)
 		}
 		cName := "config.json"
-		data, err := json.MarshalIndent(&spec, "", "\t")
+		data, err := json.MarshalIndent(&strictSpec, "", "\t")
 		if err != nil {
 			logrus.Fatal(err)
 		}
@@ -108,7 +134,7 @@ var generateCommand = cli.Command{
 	},
 }
 
-func loadTemplate(path string) (spec *rspec.Spec, err error) {
+func loadTemplate(path string) (spec interface{}, err error) {
 	cf, err := os.Open(path)
 	if err != nil {
 		if os.IsNotExist(err) {
@@ -709,7 +735,7 @@ func removeNamespace(namespaces *[]rspec.Namespace, namespaceType rspec.Namespac
 
 func sPtr(s string) *string { return &s }
 
-func getDefaultTemplate() *rspec.Spec {
+func getDefaultTemplate() interface{} {
 	spec := rspec.Spec{
 		Version: rspec.Version,
 		Platform: rspec.Platform{
@@ -824,5 +850,5 @@ func getDefaultTemplate() *rspec.Spec {
 		},
 	}
 
-	return &spec
+	return spec
 }

man/ocitools-generate.1.md

@@ -147,6 +147,9 @@ inside of the container.
 **--rootfs**=ROOTFSPATH
   Path to the rootfs
 
+**--runtime**=COMMAND
+  Set the runtime command, which is used for state JSON queries in translations like **--translate=fromContainer**.
+
 **--seccomp-arch**=ARCH
   Specifies Additional architectures permitted to be used for system calls.
   By default if you turn on seccomp, only the host architecture will be allowed.
@@ -187,6 +190,16 @@ inside of the container.
     This command mounts a `tmpfs` at `/tmp` within the container.  The supported mount options are the same as the Linux default `mount` flags. If you do not specify any options, the systems uses the following options:
     `rw,noexec,nosuid,nodev,size=65536k`.
 
+**--translate**=TRANSLATION
+  Apply various higher-level spec translations.
+  Available translations:
+
+  **fromContainer**
+    FIXME: This needs to be indented as a sub-definition-list.
+    The base OCI spec requires a namespace path in **`linux.namespaces[].path`** to join a namespace.
+    However, looking up that path in `/proc` can be tedious.
+    With a target container ID in **`linux.namespaces[].fromContainer`**, the **fromContainer** translation will query the runtime (set with **--runtime**) for the state JSON, extract the container PID from that JSON, find the appropriate namespace path for that PID in `/proc`, and insert that path in the translated configuration as **`linux.namespaces[].path`**.
+
 **--uid**=UID
   Sets the UID used within the container.
 

translate/from_container.go

@@ -0,0 +1,95 @@
+package translate
+
+import (
+	"bytes"
+	"encoding/json"
+	"fmt"
+	"os/exec"
+	"path/filepath"
+
+	"github.com/codegangsta/cli"
+	rspec "github.com/opencontainers/runtime-spec/specs-go"
+)
+
+func FromContainer(data interface{}, context *cli.Context) (translated interface{}, err error) {
+	dataMap, ok := data.(map[string]interface{})
+	if !ok {
+		return nil, fmt.Errorf("data is not a map[string]interface{}: %s", data)
+	}
+
+	linuxInterface, ok := dataMap["linux"]
+	if !ok {
+		return data, nil
+	}
+
+	linux, ok := linuxInterface.(map[string]interface{})
+	if !ok {
+		return nil, fmt.Errorf("data.linux is not a map[string]interface{}: %s", linuxInterface)
+	}
+
+	namespacesInterface, ok := linux["namespaces"]
+	if !ok {
+		return data, nil
+	}
+
+	namespaces, ok := namespacesInterface.([]interface{})
+	if !ok {
+		return nil, fmt.Errorf("data.linux.namespaces is not an array: %s", namespacesInterface)
+	}
+
+	for index, namespaceInterface := range namespaces {
+		namespace, ok := namespaceInterface.(map[string]interface{})
+		if !ok {
+			return nil, fmt.Errorf("data.linux.namespaces[%d] is not a map[string]interface{}: %s", index, namespaceInterface)
+		}
+		err := namespaceFromContainer(&namespace, index, context)
+		if err != nil {
+			return nil, err
+		}
+	}
+
+	return data, nil
+}
+
+func namespaceFromContainer(namespace *map[string]interface{}, index int, context *cli.Context) (err error) {
+	fromContainerInterface, ok := (*namespace)["fromContainer"]
+	if ok {
+		fromContainer, ok := fromContainerInterface.(string)
+		if !ok {
+			return fmt.Errorf("data.linux.namespaces[%d].fromContainer is not a string: %s", index, fromContainerInterface)
+		}
+		delete(*namespace, "fromContainer")
+		runtime := context.String("runtime")
+		if (len(runtime) == 0) {
+			return fmt.Errorf("translating fromContainer requires a non-empty --runtime")
+		}
+		command := exec.Command(runtime, "state", fromContainer)
+		var out bytes.Buffer
+		command.Stdout = &out
+		err := command.Run()
+		if err != nil {
+			return err
+		}
+		var state rspec.State
+		err = json.Unmarshal(out.Bytes(), &state)
+		if err != nil {
+			return err
+		}
+		namespaceTypeInterface, ok := (*namespace)["type"]
+		if !ok {
+			return fmt.Errorf("data.linux.namespaces[%d].type is missing: %s", index, fromContainerInterface)
+		}
+		namespaceType, ok := namespaceTypeInterface.(string)
+		if !ok {
+			return fmt.Errorf("data.linux.namespaces[%d].type is not a string: %s", index, namespaceTypeInterface)
+		}
+		switch namespaceType {
+		case "network": namespaceType = "net"
+		case "mount": namespaceType = "mnt"
+		}
+		proc := "/proc"  // FIXME: lookup in /proc/self/mounts, check right namespace
+		path := filepath.Join(proc, fmt.Sprint(state.Pid), "ns", namespaceType)
+		(*namespace)["path"] = path
+	}
+	return nil
+}

translate/translate.go

@@ -0,0 +1,20 @@
+/*
+Package translate handles translation between configuration
+specifications.
+
+For example, it allows you to generate OCI-compliant config.json from
+a higher-level configuration language.
+*/
+package translate
+
+import (
+	"github.com/codegangsta/cli"
+)
+
+// Translate maps JSON from one specification to another.
+type Translate func(data interface{}, context *cli.Context) (translated interface{}, err error)
+
+// Translators is a map from translator names to Translate functions.
+var Translators = map[string]Translate{
+	"fromContainer": FromContainer,
+}