Test third party repo images for public-ness in the builder. Always clean up private images that we dont know about before build. Pull the base image to refresh before every build.

util/dockerfileparse.py

@@ -17,6 +17,10 @@ class ParsedDockerfile(object):
     if not image_and_tag:
       return None
 
+    return self.base_image_from_repo_identifier(image_and_tag)
+
+  @staticmethod
+  def base_image_from_repo_identifier(image_and_tag):
     # Note:
     # Dockerfile images references can be of multiple forms:
     #   server:port/some/path
@@ -27,8 +31,8 @@ class ParsedDockerfile(object):
     parts = image_and_tag.strip().split(':')
 
     if len(parts) == 1:
-        # somepath
-        return parts[0]
+      # somepath
+      return parts[0]
 
     # Otherwise, determine if the last part is a port
     # or a tag.
@@ -36,33 +40,38 @@ class ParsedDockerfile(object):
       # Last part is part of the hostname.
       return image_and_tag
 
-    return '/'.join(parts[0:-1])
+    # Remaining cases:
+    #   server/some/path:tag
+    #   server:port/some/path:tag    
+    return ':'.join(parts[0:-1])
 
   def get_base_image_and_tag(self):
     from_commands = self.get_commands_of_kind('FROM')
     if not from_commands:
       return None
 
-    return from_commands[0]['parameters']
+    return from_commands[-1]['parameters']
 
 
 def strip_comments(contents):
   lines = [line for line in contents.split('\n') if not line.startswith(COMMENT_CHARACTER)]
   return '\n'.join(lines)
 
+
 def join_continued_lines(contents):
   return LINE_CONTINUATION_REGEX.sub('', contents)
 
+
 def parse_dockerfile(contents):
   contents = join_continued_lines(strip_comments(contents))
   lines = [line for line in contents.split('\n') if len(line) > 0]
 
   commands = []
   for line in lines:
-    m = COMMAND_REGEX.match(line)
-    if m:
-      command = m.group(1)
-      parameters = m.group(2)
+    match_command = COMMAND_REGEX.match(line)
+    if match_command:
+      command = match_command.group(1)
+      parameters = match_command.group(2)
 
       commands.append({
         'command': command,