New Features + Refactoring

1. User can now use image name instead of image uuid when creation vm.
   For Example, now user can create an alpine vm using the following
   command
   ```shell
   ucloud-cli vm create --vm-name myvm --cpu 2 --ram '2GB' \
       --os-ssd '10GB' --image images:alpine
   ```
2. Instead of directly running code, code is now placed under a function
   main and is called using the following code
   ```python
   if __name__ == "__main__":
       main()
   ```
3. Multiprocess (Process) is used instead of threading (Thread) to update
   heart beat of host.
4. IP Address of vm is included in vm's status which is retrieved by the
   following command
   ```shell
   ucloud-cli vm status --vm-name myvm
   ```

filescanner/main.py

@@ -12,6 +12,7 @@ from uuid import uuid4
 
 
 def getxattr(file, attr):
+    """Get specified user extended attribute (arg:attr) of a file (arg:file)"""
     try:
         attr = "user." + attr
         value = sp.check_output(['getfattr', file,
@@ -24,25 +25,39 @@ def getxattr(file, attr):
     
     return value
 
+
 def setxattr(file, attr, value):
+    """Set specified user extended attribute (arg:attr) equal to (arg:value)
+       of a file (arg:file)"""
+
     attr = "user." + attr
     sp.check_output(['setfattr', file,
                         '--name', attr,
                         '--value', str(value)])
 
 
-def sha512sum(filename):
-    _sum = hashlib.sha512()
-    buffer_size = 2**16
-
-    with open(filename, "rb") as f:
-        while True:
-            data = f.read(buffer_size)
-            if not data:
-                break
-            _sum.update(data)
-
-    return _sum.hexdigest()
+def sha512sum(file: str):
+    """Use sha512sum utility to compute sha512 sum of arg:file
+       
+       IF arg:file does not exists:
+        raise FileNotFoundError exception
+       ELSE IF sum successfully computer:
+        return computed sha512 sum
+       ELSE:
+        return None
+    """
+    if not isinstance(file, str): raise TypeError
+    try:
+        output = sp.check_output(["sha512sum", file], stderr=sp.PIPE)
+    except sp.CalledProcessError as e:
+        error = e.stderr.decode("utf-8")
+        if "No such file or directory" in error:
+            raise FileNotFoundError from None
+    else:
+        output = output.decode("utf-8").strip()
+        output = output.split(" ")
+        return output[0]
+    return None
 
 
 try:
@@ -53,57 +68,61 @@ except Exception as e:
     print('Make sure you have getfattr and setfattr available')
     exit(1)
 
+def main():
+    BASE_DIR = config("BASE_DIR")
 
-BASE_DIR = config("BASE_DIR")
+    FILE_PREFIX = config("FILE_PREFIX")
 
-FILE_PREFIX = config("FILE_PREFIX")
+    etcd_client = Etcd3Wrapper(host=config("ETCD_URL"))
 
-etcd_client = Etcd3Wrapper(host=config("ETCD_URL"))
+    # Recursively Get All Files and Folder below BASE_DIR
+    files = glob.glob("{}/**".format(BASE_DIR), recursive=True)
 
-# Recursively Get All Files and Folder below BASE_DIR
-files = glob.glob("{}/**".format(BASE_DIR), recursive=True)
+    # Retain only Files
+    files = list(filter(os.path.isfile, files))
 
-# Retain only Files
-files = list(filter(os.path.isfile, files))
+    untracked_files = list(
+        filter(lambda f: not bool(getxattr(f, "user.utracked")), files)
+    )
 
-untracked_files = list(
-    filter(lambda f: not bool(getxattr(f, "user.utracked")), files)
-)
+    tracked_files = list(
+        filter(lambda f: f not in untracked_files, files)
+    )
+    for file in untracked_files:
+        file_id = uuid4()
 
-tracked_files = list(
-    filter(lambda f: f not in untracked_files, files)
-)
-for file in untracked_files:
-    file_id = uuid4()
+        # Get Username
+        owner = pathlib.Path(file).parts[3]
+        # Get Creation Date of File
+        # Here, we are assuming that ctime is creation time
+        # which is mostly not true.
+        creation_date = time.ctime(os.stat(file).st_ctime)
 
-    # Get Username
-    owner = pathlib.Path(file).parts[3]
-    # Get Creation Date of File
-    # Here, we are assuming that ctime is creation time
-    # which is mostly not true.
-    creation_date = time.ctime(os.stat(file).st_ctime)
+        # Get File Size
+        size = os.path.getsize(file)
 
-    # Get File Size
-    size = os.path.getsize(file)
+        # Compute sha512 sum
+        sha_sum = sha512sum(file)
 
-    # Compute sha512 sum
-    sha_sum = sha512sum(file)
+        # File Path excluding base and username
+        file_path = pathlib.Path(file).parts[4:]
+        file_path = os.path.join(*file_path)
 
-    # File Path excluding base and username
-    file_path = pathlib.Path(file).parts[4:]
-    file_path = os.path.join(*file_path)
+        # Create Entry
+        entry_key = os.path.join(FILE_PREFIX, str(file_id))
+        entry_value = {
+            "filename": file_path,
+            "owner": owner,
+            "sha512sum": sha_sum,
+            "creation_date": creation_date,
+            "size": size
+        }
 
-    # Create Entry
-    entry_key = os.path.join(FILE_PREFIX, str(file_id))
-    entry_value = {
-        "filename": file_path,
-        "owner": owner,
-        "sha512sum": sha_sum,
-        "creation_date": creation_date,
-        "size": size
-    }
+        print("Tracking {}".format(file))
+        # Insert Entry
+        etcd_client.put(entry_key, entry_value, value_in_json=True)
+        setxattr(file, "user.utracked", True)
 
-    print("Tracking {}".format(file))
-    # Insert Entry
-    etcd_client.put(entry_key, entry_value, value_in_json=True)
-    setxattr(file, "user.utracked", True)
+
+if __name__ == "__main__":
+    main()