Golang FlagSet.Lookup方法代码示例

// getConflictFreeConfiguration loads the configuration from a JSON file.
// It compares that configuration with the one provided by the flags,
// and returns an error if there are conflicts.
func getConflictFreeConfiguration(configFile string, flags *flag.FlagSet) (*Config, error) {
	b, err := ioutil.ReadFile(configFile)
	if err != nil {
		return nil, err
	}

	var config Config
	var reader io.Reader
	if flags != nil {
		var jsonConfig map[string]interface{}
		reader = bytes.NewReader(b)
		if err := json.NewDecoder(reader).Decode(&jsonConfig); err != nil {
			return nil, err
		}

		configSet := configValuesSet(jsonConfig)

		if err := findConfigurationConflicts(configSet, flags); err != nil {
			return nil, err
		}

		// Override flag values to make sure the values set in the config file with nullable values, like `false`,
		// are not overriden by default truthy values from the flags that were not explicitly set.
		// See https://github.com/docker/docker/issues/20289 for an example.
		//
		// TODO: Rewrite configuration logic to avoid same issue with other nullable values, like numbers.
		namedOptions := make(map[string]interface{})
		for key, value := range configSet {
			f := flags.Lookup("-" + key)
			if f == nil { // ignore named flags that don't match
				namedOptions[key] = value
				continue
			}

			if _, ok := f.Value.(boolValue); ok {
				f.Value.Set(fmt.Sprintf("%v", value))
			}
		}
		if len(namedOptions) > 0 {
			// set also default for mergeVal flags that are boolValue at the same time.
			flags.VisitAll(func(f *flag.Flag) {
				if opt, named := f.Value.(opts.NamedOption); named {
					v, set := namedOptions[opt.Name()]
					_, boolean := f.Value.(boolValue)
					if set && boolean {
						f.Value.Set(fmt.Sprintf("%v", v))
					}
				}
			})
		}

		config.valuesSet = configSet
	}

	reader = bytes.NewReader(b)
	err = json.NewDecoder(reader).Decode(&config)
	return &config, err
}

// findConfigurationConflicts iterates over the provided flags searching for
// duplicated configurations and unknown keys. It returns an error with all the conflicts if
// it finds any.
func findConfigurationConflicts(config map[string]interface{}, flags *flag.FlagSet) error {
	// 1. Search keys from the file that we don't recognize as flags.
	unknownKeys := make(map[string]interface{})
	for key, value := range config {
		flagName := "-" + key
		if flag := flags.Lookup(flagName); flag == nil {
			unknownKeys[key] = value
		}
	}

	// 2. Discard values that implement NamedOption.
	// Their configuration name differs from their flag name, like `labels` and `label`.
	if len(unknownKeys) > 0 {
		unknownNamedConflicts := func(f *flag.Flag) {
			if namedOption, ok := f.Value.(opts.NamedOption); ok {
				if _, valid := unknownKeys[namedOption.Name()]; valid {
					delete(unknownKeys, namedOption.Name())
				}
			}
		}
		flags.VisitAll(unknownNamedConflicts)
	}

	if len(unknownKeys) > 0 {
		var unknown []string
		for key := range unknownKeys {
			unknown = append(unknown, key)
		}
		return fmt.Errorf("the following directives don't match any configuration option: %s", strings.Join(unknown, ", "))
	}

	var conflicts []string
	printConflict := func(name string, flagValue, fileValue interface{}) string {
		return fmt.Sprintf("%s: (from flag: %v, from file: %v)", name, flagValue, fileValue)
	}

	// 3. Search keys that are present as a flag and as a file option.
	duplicatedConflicts := func(f *flag.Flag) {
		// search option name in the json configuration payload if the value is a named option
		if namedOption, ok := f.Value.(opts.NamedOption); ok {
			if optsValue, ok := config[namedOption.Name()]; ok {
				conflicts = append(conflicts, printConflict(namedOption.Name(), f.Value.String(), optsValue))
			}
		} else {
			// search flag name in the json configuration payload without trailing dashes
			for _, name := range f.Names {
				name = strings.TrimLeft(name, "-")

				if value, ok := config[name]; ok {
					conflicts = append(conflicts, printConflict(name, f.Value.String(), value))
					break
				}
			}
		}
	}

	flags.Visit(duplicatedConflicts)

	if len(conflicts) > 0 {
		return fmt.Errorf("the following directives are specified both as a flag and in the configuration file: %s", strings.Join(conflicts, ", "))
	}
	return nil
}