ccon-oci: Stub in initial support for hooks

ccon doesn't believe in container IDs, so this still needs some work
before it will feed OCI-specified state JSON into the hook's stdin.

The hook syntax (with argv[0] in args) doesn't quite match the v0.1.0
docs [1,2], but it does match the phrasing from
opencontainers/runtime-spec#255 which was claimed to "clarify, but not
change" the semantics [3,4].  I think that the v0.1.0 phrasing wasn't
clear enough to decide if #255 was a change or not, but since it
wasn't clear, there's no more harm in just going with Qiang and
Mrunal's interpretation.

[1]: https://github.com/opencontainers/specs/blob/v0.1.1/runtime.md#post-stop
[2]: https://groups.google.com/a/opencontainers.org/forum/#!topic/dev/luaaorsya10
     Subject: Explicit args[0] for hooks?
     Date: Sat, 15 Aug 2015 12:15:23 -0700
     Message-ID: <[email protected]>
[3]: opencontainers/runtime-spec#255 (comment)
[4]: opencontainers/runtime-spec#255 (comment)

Author: wking

ccon-oci

@@ -153,6 +153,17 @@ def _convert_root(basedir, root):
     ]
 
 
+def _convert_hook(hook):
+    h = {
+        'args': hook.pop('args', [hook['path']]),
+    }
+    if hook['path'] != h['args'][0]:
+        h['path'] = hook['path']
+    if 'env' in hook:
+        h['env'] = hook.pop('env')
+    return h
+
+
 def convert_config(basedir, config, runtime):
     version = config.pop('version')
     if version not in ['0.1.0']:
@@ -217,6 +228,21 @@ def convert_config(basedir, config, runtime):
         capabilities = config.get('linux', {}).pop('capabilities', None)
         if capabilities:
             c['process']['capabilities'] = capabilities
+    hooks = runtime.pop('hooks', None)
+    if hooks:
+        pre_start = hooks.pop('prestart', None)
+        if pre_start:
+            c['hooks'] = {
+                'pre-start': [_convert_hook(hook=h) for h in pre_start],
+            }
+        post_stop = hooks.pop('poststop', None)
+        if post_stop:
+            if 'hooks' not in c:
+                c['hooks'] = {}
+            c['hooks']['post-stop'] = [_convert_hook(hook=h) for h in post_stop]
+        if hooks:
+            raise NotImplementedError(
+                'unparsed config.json hooks: {}'.format(hooks))
     hostname = config.pop('hostname', None)
     # TODO: inject hostname-setting hook
     if 'linux' in config and not config['linux']:

examples/good/oci/0.1.0/runtime.json

@@ -6,6 +6,28 @@
 			"options": ["rbind", "rw"]
 		}
 	},
+	"hooks": {
+		"prestart": [
+			{
+				"path": "/bin/sh",
+				"args": ["/bin/sh", "-c", "echo 'pre-start'; env; cat"],
+				"env": [
+					"PATH=/bin",
+					"PAGER=less"
+				]
+			}
+		],
+		"poststop": [
+			{
+				"path": "/bin/sh",
+				"args": ["sh", "-c", "echo 'post-stop'; env;"],
+				"env": [
+					"PATH=/bin",
+					"PAGER=less"
+				]
+			}
+		]
+	},
 	"linux": {
 		"namespaces": [
 			{