Documentation

Creates a DataSourceFactory which uses the configured file data sources.

This allows you to use local files as a source of feature flag state, instead of using an actual LaunchDarkly connection.

To use the file dataSource you can add it to the Config using configSetDataSourceFactory

let config = configSetDataSourceFactory (FileData.dataSourceFactory [".testDataflags.json"]) $
             makeConfig "sdk-key"
client <- makeClient config

This will cause the client not to connect to LaunchDarkly to get feature flags. The client may still make network connections to send analytics events, unless you have disabled this with configSetSendEvents to False. IMPORTANT: Do not set configSetOffline to True; doing so would not just put the SDK "offline" with regard to LaunchDarkly, but will completely turn off all flag data sources to the SDK /including the file data source/.

Flag data files can be either JSON or YAML. They contain an object with three possible properties:

flags

Feature flag definitions.

flagValues

Simplified feature flags that contain only a value.

segments

Context segment definitions.

The format of the data in flags and segments is defined by the LaunchDarkly application and is subject to change. Rather than trying to construct these objects yourself, it is simpler to request existing flags directly from the LaunchDarkly server in JSON format, and use this output as the starting point for your file. In Linux you would do this:

curl -H "Authorization: {your sdk key}" https://sdk.launchdarkly.com/sdk/latest-all

The output will look something like this (but with many more properties):

{
    "flags": {
        "flag-key-1": {
            "key": "flag-key-1",
            "on": true,
            "variations": [ "a", "b" ]
        },
        "flag-key-2": {
            "key": "flag-key-2",
            "on": true,
            "variations": [ "c", "d" ]
        }
    },
    "segments": {
        "segment-key-1": {
            "key": "segment-key-1",
            "includes": [ "user-key-1" ]
        }
    }
}

Data in this format allows the SDK to exactly duplicate all the kinds of flag behavior supported by LaunchDarkly. However, in many cases you will not need this complexity, but will just want to set specific flag keys to specific values. For that, you can use a much simpler format:

{
    "flagValues": {
        "my-string-flag-key": "value-1",
        "my-boolean-flag-key": true,
        "my-integer-flag-key": 3
    }
}

Or, in YAML:

flagValues:
  my-string-flag-key: "value-1"
  my-boolean-flag-key: true

It is also possible to specify both flags and flagValues, if you want some flags to have simple values and others to have complex behavior. However, it is an error to use the same flag key or segment key more than once, either in a single file or across multiple files.

If the data source encounters any error in any file(malformed content, a missing file) it will not load flags from that file. If the data source encounters a duplicate key it will ignore that duplicate entry.

Since: 2.2.1