Add flag to Docker pull_image to know when the image is already latest (#21508)

* Add flag to Docker pull_image to know when the image is already latest

Whenever the flag pull is set to 'yes' the resource is always defined
as 'changed'. That is not true in case the image is already at the
latest version.

Related to ansible/ansible#19549

* Docker pull_image does not change status if the image is latest

lib/ansible/module_utils/docker_common.py

@@ -430,9 +430,13 @@ class AnsibleDockerClient(Client):
         Pull an image
         '''
         self.log("Pulling image %s:%s" % (name, tag))
+        alreadyToLatest = False
         try:
             for line in self.pull(name, tag=tag, stream=True, decode=True):
                 self.log(line, pretty_print=True)
+                if line.get('status'):
+                    if line.get('status').startswith('Status: Image is up to date for'):
+                        alreadyToLatest = True
                 if line.get('error'):
                     if line.get('errorDetail'):
                         error_detail = line.get('errorDetail')
@@ -444,6 +448,6 @@ class AnsibleDockerClient(Client):
         except Exception as exc:
             self.fail("Error pulling image %s:%s - %s" % (name, tag, str(exc)))
 
-        return self.find_image(name, tag)
+        return self.find_image(name, tag), alreadyToLatest
 
 

lib/ansible/modules/cloud/docker/docker_container.py

@@ -1748,9 +1748,12 @@ class ContainerManager(DockerBaseClass):
         if not self.check_mode:
             if not image or self.parameters.pull:
                 self.log("Pull the image.")
-                image = self.client.pull_image(repository, tag)
-                self.results['actions'].append(dict(pulled_image="%s:%s" % (repository, tag)))
-                self.results['changed'] = True
+                image, alreadyToLatest = self.client.pull_image(repository, tag)
+                if alreadyToLatest:
+                    self.results['changed'] = False
+                else:
+                    self.results['changed'] = True
+                    self.results['actions'].append(dict(pulled_image="%s:%s" % (repository, tag)))
         self.log("image")
         self.log(image, pretty_print=True)
         return image