Sketched step execution implementation

Fockerfile

@@ -1,14 +1,6 @@
-from: freebsd-12.1
+base: freebsd-12.1
 
 steps:
   - run: |
       pkg install python3 && \
       pkg install py37-pip
-
-jail:
-  name: xxx
-  mount.devfs: true
-  ip4.address: 127.0.0.2
-  interface: lo1
-  exec.start: /bin/sh /etc/rc
-  exec.stop: /bin/sh /etc/rc.shutdown

jail.py

@@ -0,0 +1,4 @@
+import subprocess
+
+def jail_run(path, command):
+    subprocess.check_output(['jail', '-c', 'path=' + path, 'command', '/bin/sh', '-c', command)

steps.py

@@ -1,5 +1,7 @@
 import hashlib
 import json
+from jail import jail_run
+import shutil
 
 
 def filehash(fname):
@@ -15,25 +17,32 @@ def filehash(fname):
 
 
 class RunStep(object):
-    def __init__(self, base, spec):
-        self.base = base
+    def __init__(self, spec):
+        if not isinstance(spec, list) and \
+            not isinstance(spec, str):
+            raise ValueError('Run spec must be a list or a string')
         self.spec = spec
 
-    def hash(self):
+    def hash(self, base):
         res = hashlib.sha256(
-            json.dumps(( self.base, self.spec ))
+            json.dumps(( base, self.spec ))
             .encode('utf-8')).hexdigest()
         return res
 
+    def execute(self, path):
+        spec = self.spec
+        if isinstance(spec, list)
+            spec = ' && ' .join(self.spec)
+        jail_run(path, spec)
+
 
 class CopyStep(object):
-    def __init__(self, base, spec):
+    def __init__(self, spec):
         if not isinstance(spec, list):
             raise ValueError('CopyStep spec should be a list')
-        self.base = base
         self.spec = spec
 
-    def hash(self):
+    def hash(self, base):
         if len(self.spec) == 0:
             fh = []
         elif isinstance(self.spec[0], list):
@@ -41,6 +50,23 @@ class CopyStep(object):
         else:
             fh = [ filehash(self.spec[0]) ]
         res = hashlib.sha256(
-            json.dumps(( self.base, fh, self.spec ))
+            json.dumps(( base, fh, self.spec ))
             .encode('utf-8')).hexdigest()
         return res
+
+    def execute(self, path):
+        lst = [ self.spec ] \
+            if not isinstance(self.spec[0], list) \
+            else self.spec
+        for a in lst:
+            shutil.copyfile(a[0], os.path.join(path, a[1]))
+
+
+def create_step(spec):
+    if not isinstance(spec, dict):
+        raise ValueError('Step specification must be a dictionary')
+    if 'copy' in spec:
+        return CopyStep(spec['copy'])
+    elif 'run' in spec:
+        return RunStep(spec['run'])
+    raise ValueError('Unrecognized step spec: ' + json.dumps(spec))