Used subprocess check_output for docker save

The docker save command is what creates the tar of the container
image. For larger images the pipe buffer is too small. So using
subprocess.check_output to get the result of docker save.

- Moved logic to check for sudo use in is_sudo function
- Added function docker_command_check for use of
subprocess.check_output to fork processes
- Used docker_command_check in the extract_image_metadata function

Resolves tern-tools#69

Signed-off-by: Nisha K <[email protected]>

utils/container.py

@@ -43,18 +43,23 @@
 logger = logging.getLogger(logger_name)
 
 
-def docker_command(command, *extra):
-    '''Invoke docker command. If the command fails nothing is returned
-    If it passes then the result is returned'''
-    full_cmd = []
+def is_sudo():
+    '''Check if the user uses sudo for docker commands'''
     sudo = True
     try:
         members = grp.getgrnam('docker').gr_mem
         if pwd.getpwuid(os.getuid()).pw_name in members:
             sudo = False
     except KeyError:
         pass
-    if sudo:
+    return sudo
+
+
+def docker_command(command, *extra):
+    '''Invoke docker command. If the command fails nothing is returned
+    If it passes then the result is returned'''
+    full_cmd = []
+    if is_sudo():
         full_cmd.append('sudo')
     full_cmd.extend(command)
     for arg in extra:
@@ -70,6 +75,23 @@ def docker_command(command, *extra):
         return result
 
 
+def docker_command_check(command, *extra):
+    '''Invoke docker command using subprocess.check_output'''
+    full_cmd = []
+    if is_sudo():
+        full_cmd.append('sudo')
+    full_cmd.extend(command)
+    for arg in extra:
+        full_cmd.append(arg)
+    # invoke
+    logger.debug("Running command: " + ' '.join(full_cmd))
+    try:
+        result = subprocess.check_output(full_cmd)
+        return result
+    except subprocess.CalledProcessError:
+        raise
+
+
 def check_container():
     '''Check if a container exists'''
     is_container = False
@@ -155,7 +177,7 @@ def get_image_id(image_tag_string):
 def extract_image_metadata(image_tag_string):
     '''Run docker save and extract the files in a temporary directory'''
     temp_path = os.path.abspath(temp_folder)
-    result = docker_command(save, image_tag_string)
+    result = docker_command_check(save, image_tag_string)
     with tarfile.open(fileobj=io.BytesIO(result)) as tar:
         tar.extractall(temp_path)
     if not os.path.exists(temp_path):