nix-amer/internal/cnf/loader.go

111 lines
2.1 KiB
Go

package cnf
import (
"errors"
"fmt"
"io"
"os"
"path/filepath"
)
// ErrUnknownExtension is raised when encountering an unknown extension
var ErrUnknownExtension = errors.New("unknown extension format")
// ErrUnknownFormat is raised when the format cannot be guessed from the content of the file
var ErrUnknownFormat = errors.New("cannot infer format from content")
// Load the current file and create the configuration format accordingly
func Load(path string) (ConfigurationFormat, error) {
var confFormat ConfigurationFormat
// 1. check file
if _, err := os.Stat(path); os.IsNotExist(err) {
return nil, fmt.Errorf("cannot find file '%s'", path)
}
// 2. Try to load from extension
extension := filepath.Ext(path)
if len(extension) > 0 {
confFormat = loadFromExtension(extension)
if confFormat == nil {
return nil, ErrUnknownExtension
}
// open file
file, err := os.Open(path)
if err != nil {
return nil, err
}
defer file.Close()
// parse
_, err = confFormat.ReadFrom(file)
if err == nil {
return confFormat, nil
}
// return nil, fmt.Errorf("cannot parse file as '%s' | %s", extension, err)
}
// 3. open file
file, err := os.Open(path)
if err != nil {
return nil, err
}
defer file.Close()
// 4. Try to guess from the content
confFormat = loadFromContent(file)
if confFormat == nil {
return nil, ErrUnknownFormat
}
return confFormat, nil
}
func loadFromExtension(ext string) ConfigurationFormat {
// select configuration or fail if not known
switch ext {
case ".json":
return new(json)
case ".ini", ".conf":
return new(ini)
case ".yaml":
return new(yaml)
case ".nginx":
return new(nginx)
default:
return nil
}
}
func loadFromContent(file io.Reader) ConfigurationFormat {
// extensions ordered by unicity of the language's syntax
extensions := []string{".json", ".yaml", ".nginx", ".ini"}
// try to load each available extension
for _, ext := range extensions {
// load parser
c := loadFromExtension(ext)
if c == nil {
continue
}
// parse
_, err := c.ReadFrom(file)
if err == nil {
return c
}
}
return nil
}