为Snappy Ubuntu中的snap应用设置配置文件

对于细心的读者可能已经注意到在我的先前的文章中＂如何在Snappy Ubuntu Core中设置autopilot＂已经体会到使用Snappy Ubuntu中的config的便利．我们可以来重新温顾一下这个命令的语法：

$ snappy config -h
Usage:
  snappy [OPTIONS] config [package name] [config file]

Configures a package. The configuration is a YAML file, provided in the specified file which can be
"-" for stdin. Output of the command is the current configuration, so running this command with no
input file provides a snapshot of the app's current config.

Help Options:
  -h, --help              Show this help message

[config command arguments]
  package name:           Set configuration for a specific installed package
  config file:            The configuration for the given file

$ git clone https://github.com/liu-xiao-guo/config-example

在参阅本文章时，一定要注意一个bug．当我们使用ssh的方法进入到我们的target时，需要使用如下的方式．否则，我们的设置可能会发生错误．

$ LC_ALL=C.UTF-8 LANGUAGE=en ssh -p 8022 ubuntu@localhost

下面在我们展示在KVM中的运行情况：

(amd64)ubuntu@localhost:~$ snappy list -v
Name           Date       Version      Developer  
ubuntu-core    2015-11-13 10           ubuntu*    
ubuntu-core    2015-10-23 9            ubuntu     
config-example 2015-11-27 IGUIWdTOWeCa sideload*  
hello-xiaoguo  2015-11-05 IEeNEfBRVYGe sideload   
hello-xiaoguo  2015-11-27 IGTcTdAICYOL sideload*  
mqtt-piglow    2015-11-23 IGJVDbJOQafg sideload   
mqtt-piglow    2015-11-23 IGJVJYLbWCaC sideload*  
pastebinit     2015-11-02 1.4.0.0.2    mvo*       
webcam-webui   2015-11-27 IGTMIAMeQcbW sideload*  
webcam         2015-11-14 IFUaQLgTUKSU sideload*  
webdm          2015-10-23 0.9.2        canonical* 
generic-amd64  2015-10-23 1.4          canonical* 

(amd64)ubuntu@localhost:~$ config-example.hello 
config:
  config-example:
    msg: good

它显示了当前的应用的配置文件．该文件存在于如下的地址：

(amd64)ubuntu@localhost:~$ cd /var/lib/apps/config-example.sideload/current
(amd64)ubuntu@localhost:/var/lib/apps/config-example.sideload/current$ cat message 
config:
  config-example:
    msg: good

我们的＂hello＂脚本（在bin目录下的脚本）应用是这么写的：

hello

#!/bin/sh

if [ -e ${SNAP_APP_DATA_PATH}/message ]; then
    cat ${SNAP_APP_DATA_PATH}//message
else
    cat <<EOF2
Hello from the config example!

You can configure this message by running:

$ cat > cfg.yaml <<'EOF'
config:
  config-example:
    msg: |
         Yay!
EOF
$ sudo snappy config config-example cfg.yaml


The message you set there is then displayed when running:
$ config-example.hello

EOF2
fi

(amd64)ubuntu@localhost:~$ snappy config config-example
config:
  config-example:
    msg: good

(amd64)ubuntu@localhost:~$ snappy config config-example > my.yaml
(amd64)ubuntu@localhost:~$ vi my.yaml

(amd64)ubuntu@localhost:~$ sudo snappy config config-example  my.yaml
config:
  config-example:
    msg: this is something very cool

(amd64)ubuntu@localhost:~$ snappy config config-example
config:
  config-example:
    msg: this is something very cool

(amd64)ubuntu@localhost:/var/lib/apps/config-example.sideload/current$ cat message 
config:
  config-example:
    msg: this is something very cool

#!/usr/bin/env python3

import os
import os.path
import sys
import yaml

_CONFIG = 'message'

_DEFAULT_MESSAGE = 'Hello, the world'


def main():
    config_file = os.path.join(os.environ['SNAP_APP_DATA_PATH'], _CONFIG)

    config_yaml = yaml.load(sys.stdin)
    if config_yaml:
        set_config(config_file, config_yaml)

    yaml.dump(get_config(config_file), stream=sys.stdout,
              default_flow_style=False)


def set_config(config_file, config_yaml={}):
    with open(config_file, 'w') as f:
        yaml.dump(_config(config_yaml), stream=f, default_flow_style=False)

    return config_yaml


def get_config(config_file):
    try:
        with open(config_file) as f:
            return yaml.load(f)
    except FileNotFoundError:
        return _config()


def _config(config_yaml={}):
    try:
        msg_value = config_yaml['config'][
            os.environ['SNAP_NAME']]['msg']
        if not isinstance( msg_value, str):
            config_yaml['config'][
                os.environ['SNAP_NAME']]['msg'] = _DEFAULT_MESSAGE
    except KeyError:
        msg = {
            'config': {
                os.environ['SNAP_NAME']: {
                    'msg': _DEFAULT_MESSAGE
                }
            }
        }
        config_yaml.update(msg)

    return config_yaml


if __name__ == '__main__':
    main()

最后

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