Allow for pull as an option to docker build

Signed-off-by: Derek Hammer <derek.r.hammer@gmail.com>

docker/client.py

@@ -408,7 +408,7 @@ class Client(requests.Session):
 
     def build(self, path=None, tag=None, quiet=False, fileobj=None,
               nocache=False, rm=False, stream=False, timeout=None,
-              custom_context=False, encoding=None):
+              pull=False, custom_context=False, encoding=None):
         remote = context = headers = None
         if path is None and fileobj is None:
             raise TypeError("Either path or fileobj needs to be provided.")
@@ -439,6 +439,7 @@ class Client(requests.Session):
         params = {
             't': tag,
             'remote': remote,
+            'pull': pull,
             'q': quiet,
             'nocache': nocache,
             'rm': rm

docs/api.md

@@ -56,6 +56,7 @@ correct value (e.g `gzip`).
 * stream (bool): Return a blocking generator you can iterate over to retrieve
 build output as it happens
 * timeout (int): HTTP timeout
+* pull (bool): Downloads any updates to the FROM image in Dockerfiles
 * custom_context (bool): Optional if using `fileobj`
 * encoding (str): The encoding for a stream. Set to `gzip` for compressing
 

tests/test.py

@@ -1677,6 +1677,20 @@ class DockerClientTest(Cleanup, unittest.TestCase):
         except Exception as e:
             self.fail('Command should not raise exception: {0}'.format(e))
 
+    def test_build_container_pull(self):
+        script = io.BytesIO('\n'.join([
+            'FROM busybox',
+            'MAINTAINER docker-py',
+            'RUN mkdir -p /tmp/test',
+            'EXPOSE 8080',
+            'ADD https://dl.dropboxusercontent.com/u/20637798/silence.tar.gz'
+            ' /tmp/silence.tar.gz'
+        ]).encode('ascii'))
+        try:
+            self.client.build(fileobj=script, pull=True)
+        except Exception as e:
+            self.fail('Command should not raise exception: {0}'.format(e))
+
     def test_build_container_stream(self):
         script = io.BytesIO('\n'.join([
             'FROM busybox',