Move image existence check to a separate repo

repo2docker/app.py

@@ -32,7 +32,7 @@ class Repo2Docker(Application):
     name = 'jupyter-repo2docker'
     version = __version__
     description = __doc__
-    
+
     config_file = Unicode(
         'repo2docker_config.py',
         config=True,
@@ -216,49 +216,37 @@ class Repo2Docker(Application):
             container.kill()
             container.remove()
 
-    def start(self):
+    def image_exists(self):
+        client = docker.from_env(version='auto')
         # HACK: Try to just pull this and see if that works.
         # if it does, then just bail.
         # WHAT WE REALLY WANT IS TO NOT DO ANY WORK IF THE IMAGE EXISTS
-        client = docker.APIClient(version='auto', **kwargs_from_env())
-
-        repo, tag = self.output_image_spec.split(':')
         try:
-            for line in client.pull(
-                    repository=repo,
-                    tag=tag,
-                    stream=True,
-            ):
-                progress = json.loads(line.decode('utf-8'))
-                if 'error' in progress:
-                    # pull failed, proceed to build
+            image = client.images.pull(self.output_image_spec)
+            return True
+        except docker.errors.ImageNotFound:
+            return False
+
+    def start(self):
+        if not self.image_exists():
+            checkout_path = os.path.join(self.git_workdir, str(uuid.uuid4()))
+            self.fetch(
+                self.repo,
+                self.ref,
+                checkout_path
+            )
+            for bp_class in self.buildpacks:
+                bp = bp_class()
+                if bp.detect(checkout_path):
+                    self.log.info('Using %s builder', bp.name, extra=dict(phase='building'))
+                    bp.build(checkout_path, self.ref, self.output_image_spec)
                     break
             else:
-                # image exists, nothing to build
-                return
-        except docker.errors.ImageNotFound:
-            # image not found, proceed to build
-            pass
+                self.log.error('Could not figure out how to build this repository! Tell us?', extra=dict(phase='failed'))
+                sys.exit(1)
 
-
-        checkout_path = os.path.join(self.git_workdir, str(uuid.uuid4()))
-        self.fetch(
-            self.repo,
-            self.ref,
-            checkout_path
-        )
-        for bp_class in self.buildpacks:
-            bp = bp_class()
-            if bp.detect(checkout_path):
-                self.log.info('Using %s builder', bp.name, extra=dict(phase='building'))
-                bp.build(checkout_path, self.ref, self.output_image_spec)
-                break
-        else:
-            self.log.error('Could not figure out how to build this repository! Tell us?', extra=dict(phase='failed'))
-            sys.exit(1)
-
-        if self.cleanup_checkout:
-            shutil.rmtree(checkout_path)
+            if self.cleanup_checkout:
+                shutil.rmtree(checkout_path)
 
         if self.push:
             self.push_image()