Add `target` argument to image building

This is related to the multi-stage image building
that was introduced in 17.05 (API 1.29).

This allows a user to specify the stage of a multi-stage
Dockerfile to build for, rather than the final stage.
Signed-off-by: Yong Wen Chua <me@yongwen.xyz>

docker/api/build.py

@@ -18,7 +18,7 @@ class BuildApiMixin(object):
               custom_context=False, encoding=None, pull=False,
               forcerm=False, dockerfile=None, container_limits=None,
               decode=False, buildargs=None, gzip=False, shmsize=None,
-              labels=None, cache_from=None):
+              labels=None, cache_from=None, target=None):
         """
         Similar to the ``docker build`` command. Either ``path`` or ``fileobj``
         needs to be set. ``path`` can be a local path (to a directory
@@ -94,6 +94,8 @@ class BuildApiMixin(object):
             labels (dict): A dictionary of labels to set on the image.
             cache_from (list): A list of images used for build cache
                 resolution.
+            target (str): Name of the build-stage to build in a multi-stage
+                Dockerfile.
 
         Returns:
             A generator for the build output.
@@ -198,6 +200,14 @@ class BuildApiMixin(object):
                     'cache_from was only introduced in API version 1.25'
                 )
 
+        if target:
+            if utils.version_gte(self._version, '1.29'):
+                params.update({'target': target})
+            else:
+                raise errors.InvalidVersion(
+                    'target was only introduced in API version 1.29'
+                )
+
         if context is not None:
             headers = {'Content-Type': 'application/tar'}
             if encoding:

docker/models/images.py

@@ -151,6 +151,8 @@ class ImageCollection(Collection):
                 decoded into dicts on the fly. Default ``False``.
             cache_from (list): A list of images used for build cache
                 resolution.
+            target (str): Name of the build-stage to build in a multi-stage
+                Dockerfile.
 
         Returns:
             (:py:class:`Image`): The built image.

tests/integration/api_build_test.py

@@ -189,6 +189,28 @@ class BuildTest(BaseAPIIntegrationTest):
                 counter += 1
         assert counter == 0
 
+    @requires_api_version('1.29')
+    def test_build_container_with_target(self):
+        script = io.BytesIO('\n'.join([
+            'FROM busybox as first',
+            'RUN mkdir -p /tmp/test',
+            'RUN touch /tmp/silence.tar.gz',
+            'FROM alpine:latest',
+            'WORKDIR /root/'
+            'COPY --from=first /tmp/silence.tar.gz .',
+            'ONBUILD RUN echo "This should not be in the final image"'
+        ]).encode('ascii'))
+
+        stream = self.client.build(
+            fileobj=script, target='first', tag='build1'
+        )
+        self.tmp_imgs.append('build1')
+        for chunk in stream:
+            pass
+
+        info = self.client.inspect_image('build1')
+        self.assertEqual(info['Config']['OnBuild'], [])
+
     def test_build_stderr_data(self):
         control_chars = ['\x1b[91m', '\x1b[0m']
         snippet = 'Ancient Temple (Mystic Oriental Dream ~ Ancient Temple)'