Resolver Package

The resolver package provides a flexible and extensible way to resolve configuration values from various sources including environment variables, files, JSON, YAML, INI, and key-value files. It uses a prefix-based system to identify which resolver to use and returns the resolved value or an error if something goes wrong.

Installation

go get github.com/yourusername/yourrepo/resolver

Usage

The primary entry point is the ResolveVariable function. It takes a single string and attempts to resolve it based on its prefix:

• env: – Resolves environment variables. Example: env:PATH returns the value of the PATH environment variable.
• file: – Resolves values from a simple key-value file. Example: file:/config/app.txt//KeyName returns the value associated with KeyName in app.txt.
• json: – Resolves values from a JSON file. Supports dot notation for nested keys. Example: json:/config/app.json//database.host returns host field under database in app.json. It is also possible to indexing into arrays (e.g., json:/config/app.json//servers.0.host).
• yaml: – Resolves values from a YAML file. Supports dot notation for nested keys. Example: yaml:/config/app.yaml//server.port returns port under server in app.yaml.It is also possible to indexing into arrays (e.g., yaml:/config/app.yaml//servers.0.host).
• ini: – Resolves values from an INI file. Can specify a section and key, or just a key in the default section. Example: ini:/config/app.ini//Section.Key returns the value of Key under Section.
• No prefix – Returns the value as-is, unchanged.

Example

package main

import (
    "fmt"
    "log"
    "os"

    "github.com/containeroo/portpatrol/resolver"
)

func main() {
    os.Setenv("MY_VAR", "HelloWorld")

    val, err := resolver.ResolveVariable("env:MY_VAR")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(val) // Output: HelloWorld

    // Resolve a JSON key:
    // Given a JSON file: /config/app.json
    // {
    //   "server": {
    //     "host": "localhost",
    //     "port": 8080
    //   }
    // }
    jsonVal, err := resolver.ResolveVariable("json:/config/app.json//server.host")
    if err != nil {
        log.Fatal(err)
    }
    fmt.Println(jsonVal) // Output: localhost
}