Started working on step hashes.

focker-compose.yml

@@ -0,0 +1,15 @@
+defaults:
+  jail:
+    mount.devfs: true
+    interface: lo1
+    exec.start: /bin/sh /etc/rc
+    exec.stop: /bin/sh /etc/rc.shutdown
+
+services:
+  gateway:
+    image: freebsd-12.1
+    jail:
+      ip4.address: 127.0.0.2
+
+volumes:
+  gateway-data: {}

steps.py

@@ -0,0 +1,46 @@
+import hashlib
+import json
+
+
+def filehash(fname):
+    h = hashlib.sha256()
+    with open(fname, 'rb') as f:
+        while True:
+            data = f.read(1024*1024*4)
+            if not data:
+                break
+            h.update(data)
+    res = h.hexdigest()
+    return res
+
+
+class RunStep(object):
+    def __init__(self, base, spec):
+        self.base = base
+        self.spec = spec
+
+    def hash(self):
+        res = hashlib.sha256(
+            json.dumps(( self.base, self.spec ))
+            .encode('utf-8')).hexdigest()
+        return res
+
+
+class CopyStep(object):
+    def __init__(self, base, spec):
+        if not isinstance(spec, list):
+            raise ValueError('CopyStep spec should be a list')
+        self.base = base
+        self.spec = spec
+
+    def hash(self):
+        if len(self.spec) == 0:
+            fh = []
+        elif isinstance(self.spec[0], list):
+            fh = list(map(lambda a: filehash(a[0]), self.spec))
+        else:
+            fh = [ filehash(self.spec[0]) ]
+        res = hashlib.sha256(
+            json.dumps(( self.base, fh, self.spec ))
+            .encode('utf-8')).hexdigest()
+        return res