Write a generic script signing utility

Signed-off-by: Thomas Nagy <tnagy2pow10@gmail.com>

utils/sign_file.py

@@ -0,0 +1,118 @@
+#! /usr/bin/env python
+
+"""
+A script that creates signed Python files.
+
+Distributing detached signatures is boring.
+"""
+
+
+from __future__ import print_function
+
+import os
+import argparse
+import subprocess
+
+
+def get_file_encoding(filename):
+    """
+    Get the file encoding for the file with the given filename
+    """
+
+    with open(filename, 'rb') as fp:
+        # The encoding is usually specified on the second line
+        txt = fp.read().splitlines()[1]
+        txt = txt.decode('utf-8')
+        if 'encoding' in txt:
+            encoding = txt.split()[-1]
+        else:
+            encoding = 'utf-8' # default
+
+    return str(encoding)
+
+
+def sign_file_and_get_sig(filename, encoding):
+    """
+    Sign the file and get the signature
+    """
+
+    cmd = 'gpg -bass {}'.format(filename)
+    ret = subprocess.Popen(cmd, shell=True).wait()
+    print ('-> %r' % cmd)
+
+    if ret:
+        raise ValueError('Could not sign the file!')
+
+    with open('{}.asc'.format(filename), 'rb') as fp:
+        sig = fp.read()
+
+    try:
+        os.remove('{}.asc'.format(filename))
+    except OSError:
+        pass
+
+    sig = sig.decode(encoding)
+    sig = sig.replace('\r', '').replace('\n', '\\n')
+    sig = sig.encode(encoding)
+
+    return sig
+
+
+def sign_original_file(filename, encoding):
+    """
+    Sign the original file
+    """
+
+    sig = sign_file_and_get_sig(filename, encoding)
+
+    with open(filename, 'ab') as outfile:
+        outfile.write('#'.encode(encoding))
+        outfile.write(sig)
+        outfile.write('\n'.encode(encoding))
+
+
+def create_signed_file(filename, encoding):
+    """
+    Create a signed file
+    """
+
+    sig = sign_file_and_get_sig(filename, encoding)
+    name, extension = os.path.splitext(filename)
+
+    new_file_name = '{}_signed{}'.format(name, extension)
+
+    with open(new_file_name, 'wb') as outfile, \
+         open(filename, 'rb') as infile:
+        txt = infile.read()
+        outfile.write(txt)
+        outfile.write('#'.encode(encoding))
+        outfile.write(sig)
+        outfile.write('\n'.encode(encoding))
+
+
+def parse_args():
+    parser = argparse.ArgumentParser()
+
+    parser.add_argument('filenames', action='store', nargs='+',
+                        help='Files you wish to sign')
+
+    parser.add_argument('--overwrite', action='store_true',
+                        dest='overwrite', default=False, 
+                        help='Overwrite the original file'
+                             ' (sign the original file)')
+
+    opts = parser.parse_args()
+
+    return opts
+
+
+if __name__ == '__main__':
+    opts = parse_args()
+
+    for filename in opts.filenames:
+        encoding = get_file_encoding(filename)
+        if opts.overwrite:
+            sign_original_file(filename, encoding)
+        else:
+            create_signed_file(filename, encoding)
+