nix-amer/internal/cnf/loader.go

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