Ansible module that takes in a target Java .properties file, and patches in any arbitrary key-value properties specified in a JSON hash format

properties.py

#!/usr/local/python/bin/python
"""
Ansible module that takes in a target Java .properties file, and patches in any
arbitrary key-value properties specified in a JSON hash format. This module is
expected to be used alongside the `properties` Ansible action module.

Examples:
    - properties:
        dest: ~/dists/cluster/ix/ZookeeperIndexMerger.properties
        props:
          helloStr: Hello world!

@author: Jerry Chong <jchong@netbase.com>
@tags: WANT_JSON
"""

from __future__ import print_function
import json
import os
import re
import sys
from six import StringIO


def decode(path):
    """Load a JSON file from the given path"""
    jsonfile = open(path)
    return json.load(jsonfile)


def process(target, properties):
    """
    Performs simple string replacements to generate a new .properties file at
    the `target` path, using the `properties` key-value mapping
    """

    # shallow copy since we will need to modify this dict later
    src_dict = properties.copy()
    buffer = StringIO()
    keys = src_dict.keys()
    prop_re = re.compile(r"^(?P<comment>#*\s*)(?P<key>[\w.]+)\s*=\s*(?P<val>.*?)?;?\s*$")

    with open(target, "r+") as propfile:
        for line in propfile.readlines():
            line = line.strip()
            match = prop_re.match(line)

            # if line does have key=value pattern, otherwise simply write it
            if match:
                commented, key, val = match.groups(default='')
                # replace in target INI file if replacement value is defined
                if key in keys:
                    line = "{}{}={}".format(commented, key, str(src_dict[key]))
                    src_dict.pop(key)
            buffer.write(line + "\n")

        # append any unreplaced key/values in as extra lines
        for key in sorted(src_dict.keys()):
            buffer.write(key + "=" + str(src_dict[key]) + "\n")

        # write to disk
        propfile.seek(0)
        propfile.write(buffer.getvalue())


def main():
    """Main function"""
    data = decode(sys.argv[1])
    result = {"msg": "OK"}

    # basic checking
    try:
        if not data:
            raise Exception("JSON data not loaded!")

        target = data.get("target") or data.get("dest")
        props = data.get("props")

        if target is None or props is None:
            raise Exception("JSON data is missing 'target' or 'props' attributes!")
        elif not isinstance(props, dict):
            raise Exception("'props' is not a dict!")
        elif not os.path.exists(target):
            raise Exception("Target %s does not exist!" % target)

        process(target, props)
        result["msg"] = "Finished replacing " + target
    except Exception as e:
        result['failed'] = True
        result['msg'] = str(e)

    print(json.dumps(result))


if __name__ == "__main__":
    main()