Settings and configurations for golang application

• Easy to learn and easy to use settings for golang libraries and applications.
• Settings object is represented as map[string]interface{} object.
• Settings can be marshalled to JSON or un-marshalled from JSON.
• Possible to add more formats for marshalling and un-marshalling settings.
• All methods exported on settings object are immutable, except Mixin.
• Stable APIs, existing APIs are not going to change.

Settings as Key value pairs

Golang map is the chosen structure for passing around settings, holding them within components and interpret them when ever needed. To create new settings object:

setts := make(Settings)

Subsequently setts can be populated with {key,value} pairs, where each {key,value} pair correspond to a single configuration parameter. To make most out of Settings it is better to avoid nested values, as in:

// not recommended
setts["llrb"] = Settings{
    "maxkeylen": 1024,
    "maxvallen": 1024,
}

Instead compose settings as:

    // recommended
    setts := make(Settings)
    setts["llrb.maxkeylen"] = 1024
    setts["llrb.maxvallen"] = 1024

Although the former style is quite natural to manage a tree of settings at component and sub-component level, it can quickly become complex when we start passing settings object around the application. While the later style encourages flat map of {key,value} pairs, we can still preserve the topology of settings by using the dot-separated namespaces. There are three APIs available to filter out component level settings and merge it with container namespace, Section, Trim, and AddPrefix:

    setts := make(Settings)
    setts["numvbuckets"] = 8
    setts["memalloc"] = 1000000
    setts["llrb.maxkeylen"] = 1024
    setts["llrb.maxvallen"] = 1024

    llrbsetts := setts.Section("llrb.") // Section

setts.Section API will filter out setting keys that are prefixed by llrb., it will look-like:

llrbsetts <==> Settings{"llrb.maxkeylen": 1024, "llrb.maxvallen": 1024}

While passing llrbsettings to the llrb component, it may not expect the llrb. prefixed to its settings key-name. To trim them away:

llrbsettings := setts.Section("llrb.").Trim("llrb.") // Trim away "llrb."

Now, llrbsettings will just be:

llrbsetts <==> Settings{"maxkeylen": 1024, "maxvallen": 1024}

In case, the llrb component is going to provide default set of configuration parameters, and we want to merge them with our application-level settings object, then, use AddPrefix:

appsetts := llrbsetts.AddPrefix("llrb.")

appsetts will look like:

appsetts <==> Settings{"llrb.maxkeylen": 1024, "llrb.maxvallen": 1024}

Settings from json

Most often, settings are obtained from JSON text. One of the reason for using map[string]interface{} as the underlying data-structure is to keep it friendly for JSON. To initialize Settings from JSON:

var setts Settings
json.Unmarshal(data, &setts)

Can't get simpler than that !

Accessors

With map[string]interface{}, settings value are resolved only during run time. There are several helper functions that type check and extract the settings value.

• Bool(key string), return the boolean value for key.
• Float64(key string), return the float64 value for key.
• Int64(key string) return the int64 value for key.
• Uint64(key string) return the uint64 value for key.
• String(key string) return the string value for key.
• Strings(key string) shall parse value as comma separated string items.

NOTE: To encode large numbers that can fit within int64 and uint64, settings value can be encoded as decimal strings Eg: {"epoch": "1125899906842624"}.

Panic and Recovery

Settings API don't return error, instead it creates panic. This is because settings are mostly part of bootstrapping process and are expected to be clean and suggested by developers. If panics become un-avoidable please use panic/recover. We are listing some of the cases when panic can happened.

• When accessing a settings key which is not present in the map.
• When using one of the typed accessors, if underlying value does not match the accessor type.

How to contribute

• Pick an issue, or create an new issue. Provide adequate documentation for the issue.
• Assign the issue or get it assigned.
• Work on the code, once finished, raise a pull request.
• Gosettings is written in golang, hence expected to follow the global guidelines for writing go programs.
• As of now, branch master is the development branch.