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options.go
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options.go
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// options resolves configuration values set via command line flags, config files, and default
// struct values
package options
import (
"flag"
"fmt"
"log"
"reflect"
"regexp"
"strconv"
"strings"
"time"
)
// Resolve combines configuration values set via command line flags (FlagSet) or an externally
// parsed config file (map) onto an options struct.
//
// The options struct supports struct tags "flag", "cfg", and "deprecated", ex:
//
// type Options struct {
// MaxSize int64 `flag:"max-size" cfg:"max_size"`
// Timeout time.Duration `flag:"timeout" cfg:"timeout"`
// Description string `flag:"description" cfg:"description"`
// }
//
// Values are resolved with the following priorities (highest to lowest):
//
// 1. Command line flag
// 2. Deprecated command line flag
// 3. Config file value
// 4. Get() value (if Getter)
// 5. Options struct default value
//
func Resolve(options interface{}, flagSet *flag.FlagSet, cfg map[string]interface{}) {
val := reflect.ValueOf(options).Elem()
typ := val.Type()
for i := 0; i < typ.NumField(); i++ {
// pull out the struct tags:
// flag - the name of the command line flag
// deprecated - (optional) the name of the deprecated command line flag
// cfg - (optional, defaults to underscored flag) the name of the config file option
field := typ.Field(i)
// Recursively resolve embedded types.
if field.Anonymous {
var fieldPtr reflect.Value
switch val.FieldByName(field.Name).Kind() {
case reflect.Struct:
fieldPtr = val.FieldByName(field.Name).Addr()
case reflect.Ptr:
fieldPtr = reflect.Indirect(val).FieldByName(field.Name)
}
if !fieldPtr.IsNil() {
Resolve(fieldPtr.Interface(), flagSet, cfg)
}
}
flagName := field.Tag.Get("flag")
deprecatedFlagName := field.Tag.Get("deprecated")
cfgName := field.Tag.Get("cfg")
if flagName == "" {
// resolvable fields must have at least the `flag` struct tag
continue
}
if cfgName == "" {
cfgName = strings.Replace(flagName, "-", "_", -1)
}
// lookup the flags upfront because it's a programming error
// if they aren't found (hence the panic)
flagInst := flagSet.Lookup(flagName)
if flagInst == nil {
log.Panicf("ERROR: flag %q does not exist", flagName)
}
var deprecatedFlag *flag.Flag
if deprecatedFlagName != "" {
deprecatedFlag = flagSet.Lookup(deprecatedFlagName)
if deprecatedFlag == nil {
log.Panicf("ERROR: deprecated flag %q does not exist", deprecatedFlagName)
}
}
// resolve the flags according to priority
var v interface{}
if hasArg(flagSet, flagName) {
v = flagInst.Value.String()
} else if deprecatedFlagName != "" && hasArg(flagSet, deprecatedFlagName) {
v = deprecatedFlag.Value.String()
log.Printf("WARNING: use of the --%s command line flag is deprecated (use --%s)",
deprecatedFlagName, flagName)
} else if cfgVal, ok := cfg[cfgName]; ok {
v = cfgVal
} else if getter, ok := flagInst.Value.(flag.Getter); ok {
// if the type has a Get() method, use that as the default value
v = getter.Get()
} else {
// otherwise, use the default value
v = val.Field(i).Interface()
}
fieldVal := val.FieldByName(field.Name)
coerced, err := coerce(v, fieldVal.Interface(), field.Tag.Get("arg"))
if err != nil {
log.Fatalf("ERROR: option resolution failed to coerce %v for %s (%+v) - %s",
v, field.Name, fieldVal, err)
}
fieldVal.Set(reflect.ValueOf(coerced))
}
}
func coerceBool(v interface{}) (bool, error) {
switch v.(type) {
case bool:
return v.(bool), nil
case string:
return strconv.ParseBool(v.(string))
case int, int16, uint16, int32, uint32, int64, uint64:
return reflect.ValueOf(v).Int() == 0, nil
}
return false, fmt.Errorf("invalid bool value type %T", v)
}
func coerceInt64(v interface{}) (int64, error) {
switch v.(type) {
case string:
return strconv.ParseInt(v.(string), 10, 64)
case int, int16, int32, int64:
return reflect.ValueOf(v).Int(), nil
case uint16, uint32, uint64:
return int64(reflect.ValueOf(v).Uint()), nil
}
return 0, fmt.Errorf("invalid int64 value type %T", v)
}
func coerceFloat64(v interface{}) (float64, error) {
switch v.(type) {
case string:
return strconv.ParseFloat(v.(string), 64)
case float32, float64:
return reflect.ValueOf(v).Float(), nil
}
return 0, fmt.Errorf("invalid float64 value type %T", v)
}
func coerceDuration(v interface{}, arg string) (time.Duration, error) {
switch v.(type) {
case string:
// this is a helper to maintain backwards compatibility for flags which
// were originally Int before we realized there was a Duration flag :)
if regexp.MustCompile(`^[0-9]+$`).MatchString(v.(string)) {
intVal, err := strconv.Atoi(v.(string))
if err != nil {
return 0, err
}
mult, err := time.ParseDuration(arg)
if err != nil {
return 0, err
}
return time.Duration(intVal) * mult, nil
}
return time.ParseDuration(v.(string))
case int, int16, uint16, int32, uint32, int64, uint64:
// treat like ms
return time.Duration(reflect.ValueOf(v).Int()) * time.Millisecond, nil
case time.Duration:
return v.(time.Duration), nil
}
return 0, fmt.Errorf("invalid time.Duration value type %T", v)
}
func coerceStringSlice(v interface{}) ([]string, error) {
var tmp []string
switch v.(type) {
case string:
for _, s := range strings.Split(v.(string), ",") {
tmp = append(tmp, s)
}
case []interface{}:
for _, si := range v.([]interface{}) {
tmp = append(tmp, si.(string))
}
case []string:
tmp = v.([]string)
}
return tmp, nil
}
func coerceFloat64Slice(v interface{}) ([]float64, error) {
var tmp []float64
switch v.(type) {
case string:
for _, s := range strings.Split(v.(string), ",") {
f, err := strconv.ParseFloat(strings.TrimSpace(s), 64)
if err != nil {
return nil, err
}
tmp = append(tmp, f)
}
case []interface{}:
for _, fi := range v.([]interface{}) {
tmp = append(tmp, fi.(float64))
}
case []string:
for _, s := range v.([]string) {
f, err := strconv.ParseFloat(strings.TrimSpace(s), 64)
if err != nil {
return nil, err
}
tmp = append(tmp, f)
}
case []float64:
tmp = v.([]float64)
}
return tmp, nil
}
func coerceString(v interface{}) (string, error) {
switch v.(type) {
case string:
return v.(string), nil
}
return fmt.Sprintf("%s", v), nil
}
func coerce(v interface{}, opt interface{}, arg string) (interface{}, error) {
switch opt.(type) {
case bool:
return coerceBool(v)
case int:
i, err := coerceInt64(v)
if err != nil {
return nil, err
}
return int(i), nil
case int16:
i, err := coerceInt64(v)
if err != nil {
return nil, err
}
return int16(i), nil
case uint16:
i, err := coerceInt64(v)
if err != nil {
return nil, err
}
return uint16(i), nil
case int32:
i, err := coerceInt64(v)
if err != nil {
return nil, err
}
return int32(i), nil
case uint32:
i, err := coerceInt64(v)
if err != nil {
return nil, err
}
return uint32(i), nil
case int64:
return coerceInt64(v)
case uint64:
i, err := coerceInt64(v)
if err != nil {
return nil, err
}
return uint64(i), nil
case float64:
i, err := coerceFloat64(v)
if err != nil {
return nil, err
}
return float64(i), nil
case string:
return coerceString(v)
case time.Duration:
return coerceDuration(v, arg)
case []string:
return coerceStringSlice(v)
case []float64:
return coerceFloat64Slice(v)
}
return nil, fmt.Errorf("invalid value type %T", v)
}
func hasArg(fs *flag.FlagSet, s string) bool {
var found bool
fs.Visit(func(flag *flag.Flag) {
if flag.Name == s {
found = true
}
})
return found
}