Initial manifest parsing

fetcher.py

@@ -0,0 +1,55 @@
+#!/usr/bin/python3
+# coding=utf8
+
+import argparse
+import json
+import hashlib
+import socket
+import struct
+import urllib.request
+
+
+parser = argparse.ArgumentParser(description='iconograph fetcher')
+parser.add_argument(
+	'--base-url',
+	dest='base_url',
+	action='store',
+	required=True)
+parser.add_argument(
+	'--image-type',
+	dest='image_type',
+	action='store',
+	required=True)
+FLAGS = parser.parse_args()
+
+
+class Fetcher(object):
+
+  _MAX_BP = 10000
+
+  def __init__(self, base_url, image_type):
+    self._base_url = base_url
+    self._image_type = image_type
+
+  def _GetManifest(self):
+    url = '%s/%s.manifest.json' % (self._base_url, self._image_type)
+    return json.loads(urllib.request.urlopen(url).read().decode('utf8'))
+
+  def _ChooseImage(self, manifest):
+    hostname = socket.gethostname()
+    hash_base = hashlib.sha256(hostname.encode('ascii'))
+    for image in manifest:
+      hashobj = hash_base.copy()
+      hashobj.update(struct.pack('!L', image['timestamp']))
+      my_bp = struct.unpack('!I', hashobj.digest()[-4:])[0] % self._MAX_BP
+      if my_bp < image['rollout_‱']:
+        return image
+
+  def Fetch(self):
+    manifest = self._GetManifest()
+    image = self._ChooseImage(manifest)
+    print(image)
+
+
+fetcher = Fetcher(FLAGS.base_url, FLAGS.image_type)
+fetcher.Fetch()