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config.go
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config.go
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// Copyright (c) 2014 Trygve Aaberge and contributors
// Released under the LGPLv2.1, see LICENSE
// Package itkconfig implements parsing of configuration files through the use
// of reflection.
package itkconfig
import (
"bufio"
"errors"
"fmt"
"os"
"reflect"
"regexp"
"strconv"
"strings"
)
// parseField parses a field based on its field type.
func parseField(key, value string, fieldType reflect.Type) (reflect.Value, error) {
switch fieldType.Kind() {
case reflect.String:
return reflect.ValueOf(value), nil
case reflect.Bool:
v, err := strconv.ParseBool(value)
if err != nil {
return reflect.ValueOf(nil), fmt.Errorf("invalid bool \"%s\" in key \"%s\": %s", value, key, err)
}
return reflect.ValueOf(v), nil
case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
i, err := strconv.ParseInt(value, 10, fieldType.Bits())
if err != nil {
return reflect.ValueOf(nil), fmt.Errorf("invalid int \"%s\" in key \"%s\": %s", value, key, err)
}
return reflect.ValueOf(i).Convert(fieldType), nil
case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64, reflect.Uintptr:
i, err := strconv.ParseUint(value, 10, fieldType.Bits())
if err != nil {
return reflect.ValueOf(nil), fmt.Errorf("invalid uint \"%s\" in key \"%s\": %s", value, key, err)
}
return reflect.ValueOf(i).Convert(fieldType), nil
case reflect.Float32, reflect.Float64:
i, err := strconv.ParseFloat(value, fieldType.Bits())
if err != nil {
return reflect.ValueOf(nil), fmt.Errorf("invalid float \"%s\" in key \"%s\": %s", value, key, err)
}
return reflect.ValueOf(i).Convert(fieldType), nil
default:
return reflect.ValueOf(nil), fmt.Errorf("unsupported type: %s", fieldType.Kind())
}
}
func parseKey(rawKey string) (*string, error) {
key := strings.TrimSpace(rawKey)
if strings.Contains(key, "\"") {
return nil, errors.New("key cannot contain \"")
}
if key == "" {
return nil, errors.New("key cannot be empty")
}
return &key, nil
}
func parseVal(rawVal string) (*string, error) {
val := strings.TrimSpace(rawVal)
quoteCommentGroup := regexp.MustCompile(`^(".*?"|[^"]*?)(\s*#.*)$`)
groups := quoteCommentGroup.FindStringSubmatchIndex(val)
if groups != nil {
val = val[:groups[2*2]]
}
// Remove non-escaped quotes and replace escaped quotes.
var sb strings.Builder
for i, r := range val {
if r == '"' {
continue
}
if val[i] == '\\' && val[i+1] == '"' {
sb.WriteRune('"')
} else {
sb.WriteRune(r)
}
}
val = sb.String()
return &val, nil
}
// LoadConfig loads the provided configuration file and parses it through the
// use of reflection according to the type definition of config, which has to be
// a pointer to a struct.
func LoadConfig(filename string, config interface{}) error {
// Use reflect to place config keys into the right element in the struct
configPtrReflect := reflect.ValueOf(config)
if configPtrReflect.Kind() != reflect.Ptr {
return errors.New("config argument must be a pointer")
}
configReflect := configPtrReflect.Elem()
if configReflect.Kind() != reflect.Struct {
return errors.New("config argument must be a pointer to a struct")
}
lastUpdate := make(map[string]uint)
for _, field := range reflect.VisibleFields(configReflect.Type()) {
lastUpdate[field.Name] = 0
}
f, err := os.Open(filename)
if err != nil {
return err
}
defer f.Close()
fh := bufio.NewScanner(f)
lineNr := uint(0)
syntaxError := func(message string) error {
return fmt.Errorf("syntax error parsing config (%s:%d): %s", filename, lineNr, message)
}
for fh.Scan() {
line := fh.Text()
lineNr++
line = strings.TrimSpace(line)
if line == "" || line[0] == '#' {
continue
}
keyVal := strings.SplitN(line, "=", 2)
if len(keyVal) != 2 {
return syntaxError("line must contain '='")
}
key, err := parseKey(keyVal[0])
if err != nil {
return syntaxError(err.Error())
}
value, err := parseVal(keyVal[1])
if err != nil {
return syntaxError(err.Error())
}
field := configReflect.FieldByName(*key)
if !field.IsValid() {
return syntaxError(fmt.Sprintf("the config key '%s' is not defined", *key))
}
if !field.CanSet() {
return syntaxError(fmt.Sprintf("cannot set unexported field: '%s'", *key))
}
switch field.Kind() {
case reflect.Slice:
if lastUpdate[*key] == 0 {
field.Set(reflect.MakeSlice(field.Type(), 0, 0))
}
v, err := parseField(*key, *value, field.Type().Elem())
if err != nil {
return syntaxError(err.Error())
}
field.Set(reflect.Append(field, v))
default:
if lastUpdate[*key] != 0 {
return syntaxError(fmt.Sprintf("key '%s' was defined multiple times, initially on line %d (did you mean to define a slice?)", *key, lastUpdate[*key]))
}
v, err := parseField(*key, *value, field.Type())
if err != nil {
return syntaxError(err.Error())
}
field.Set(v)
}
lastUpdate[*key] = lineNr
}
return nil
}