conf

Overview ¶

Package conf is an extensible solution for cascading configuration of application. Package conf provides configuration processor, that can load configuration layers from different sources and merges them into the one configuration tree. In addition configuration processor can expand variables in string values and process _var and _include directives in resulting configuration tree (see below). Package conf comes with built-in configuration loaders: fileconf and envconf, and can be extended by third-party configuration loaders. Package conf do not watch for configuration changes, but you can implement this feature in the custom configuration loader.

Configuration processor can expand variables in string values (if you need alias for complex structures see _var directive). Variable names can be absolute or relative. Relative variable names begins with "." (dot). The section, in which a value of relative variable will be searched, determines by number of dots in variable name. For example, we have a YAML file:

myapp:
  mediaFormats: ["images", "audio", "video"]

  dirs:
    rootDir: "/myapp"
    templatesDir: "${myapp.dirs.rootDir}/templates"
    sessionsDir: "${.rootDir}/sessions"

    mediaDirs:
      - "${..rootDir}/media/${myapp.mediaFormats.0}"
      - "${..rootDir}/media/${myapp.mediaFormats.1}"
      - "${..rootDir}/media/${myapp.mediaFormats.2}"

After processing of the file we will get a map:

"myapp": map[string]interface{}{
  "mediaFormats": []interface{}{"images", "audio", "video"},

  "dirs": map[string]interface{}{
    "rootDir":      "/myapp",
    "templatesDir": "/myapp/templates",
    "sessionsDir": "/myapp/sessions",

    "mediaDirs": []interface{}{
      "/myapp/media/images",
      "/myapp/media/audio",
      "/myapp/media/video",
    },
  },
}

To escape variable expansion add one more "$" symbol before variable name.

templatesDir: "$${myapp.dirs.rootDir}/templates"

After processing we will get:

templatesDir: "${myapp.dirs.rootDir}/templates"

Package conf supports two special directives in configuration layers: _var and _include. _var directive assigns configuration parameter value to another configuration parameter. Argument of the _var directive is a variabale name, absolute or relative. Here some example:

myapp:
  db:
    defaultOptions:
      PrintWarn: 0
      PrintError: 0
      RaiseError: 1

    connectors:
      stat:
        host: "stat.mydb.com"
        port: "1234"
        dbname: "stat"
        username: "stat_writer"
        password: "stat_writer_pass"
        options: {_var: "myapp.db.defaultOptions"}

      metrics:
        host: "metrics.mydb.com"
        port: "1234"
        dbname: "metrics"
        username: "metrics_writer"
        password: "metrics_writer_pass"
        options: {_var: "...defaultOptions"}

_include directive loads configuration layer from external sources and assigns it to configuration parameter. Argument of the _include directive is a list of configuration locators.

myapp:
  db:
    defaultOptions:
      PrintWarn:  0
      PrintError: 0
      RaiseError: 1

  connectors: {_include: ["file:connector.yml"]}

You can find full example in repository.