Make generate-secrets script use existing values.

Fixes #1035

scripts/setup/generate_secrets.py

@@ -8,6 +8,8 @@ sys.path.insert(0, os.path.join(os.path.dirname(__file__), '..', '..'))
 os.environ['DJANGO_SETTINGS_MODULE'] = 'zproject.settings'
 
 from django.utils.crypto import get_random_string
+import six
+
 from zerver.lib.utils import generate_random_token
 
 os.chdir(os.path.join(os.path.dirname(__file__), '..', '..'))
@@ -31,6 +33,21 @@ def generate_django_secretkey():
     chars = 'abcdefghijklmnopqrstuvwxyz0123456789!@#$%^&*(-_=+)'
     return get_random_string(50, chars)
 
+def get_old_conf(output_filename):
+    if not os.path.exists(output_filename):
+        return {}
+
+    secrets_file = six.moves.configparser.RawConfigParser()
+    secrets_file.read(output_filename)
+
+    def get_secret(key):
+        if secrets_file.has_option('secrets', key):
+            return secrets_file.get('secrets', key)
+        return None
+
+    fields = AUTOGENERATED_SETTINGS + ['secret_key', 'camo_key']
+    return {name: get_secret(name) for name in fields}
+
 def generate_secrets(development=False):
     if development:
         OUTPUT_SETTINGS_FILENAME = "zproject/dev-secrets.conf"
@@ -42,12 +59,16 @@ def generate_secrets(development=False):
     def config_line(var, value):
         return "%s = %s\n" % (var, value)
 
+    old_conf = get_old_conf(OUTPUT_SETTINGS_FILENAME)
     for name in AUTOGENERATED_SETTINGS:
-        lines.append(config_line(name, generate_random_token(64)))
+        lines.append(config_line(name, old_conf.get(name, generate_random_token(64))))
 
-    lines.append(config_line('secret_key', generate_django_secretkey()))
-    camo_key = get_random_string(64)
+    secret_key = old_conf.get('secret_key', generate_django_secretkey())
+    lines.append(config_line('secret_key', secret_key))
+
+    camo_key = old_conf.get('camo_key', get_random_string(64))
     lines.append(config_line('camo_key', camo_key))
+
     if not development:
         # Write the Camo config file directly
         generate_camo_config_file(camo_key)