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alligotor.go
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alligotor.go
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package alligotor
import (
"encoding"
"encoding/json"
"errors"
"fmt"
"io/ioutil"
"os"
"path"
"reflect"
"strconv"
"strings"
"time"
"github.com/mitchellh/mapstructure"
"github.com/spf13/pflag"
"gopkg.in/yaml.v3"
)
var (
ErrMalformedFlagConfig = errors.New("malformed flag config strings")
ErrFileTypeNotSupported = errors.New("could not unmarshal file, file type not supported")
ErrPointerExpected = errors.New("expected a pointer as input")
ErrNoFileFound = errors.New("no config file could be found")
ErrUnsupportedType = errors.New("invalid type")
ErrCantSet = errors.New("can't set value")
)
const (
tag = "config"
envKey = "env"
flagKey = "flag"
fileKey = "file"
flagConfigSeparator = " "
defaultEnvSeparator = "_"
defaultFileSeparator = "."
defaultFlagSeparator = "-"
)
// DefaultCollector is the default Collector and is used by Get.
var DefaultCollector = &Collector{ // nolint: gochecknoglobals // usage just like in http package
Files: FilesConfig{
Locations: []string{"."},
BaseName: "config",
Separator: defaultFileSeparator,
Disabled: false,
},
Env: EnvConfig{
Prefix: "",
Separator: defaultEnvSeparator,
Disabled: false,
},
Flags: FlagsConfig{
Separator: defaultFlagSeparator,
Disabled: false,
},
}
// Get is a wrapper around DefaultCollector.Get.
// All configuration sources are enabled.
// For environment variables it uses no prefix and "_" as the separator.
// For flags it use "-" as the separator.
// For config files it uses "config" as the basename and searches in the current directory.
// It uses "." as the separator.
func Get(v interface{}) error {
return DefaultCollector.Get(v)
}
// Collector is the root struct that implements the main package api.
// The only method that can be called is Collector.Get to unmarshal the found configuration
// values from the configured sources into the provided struct.
// If the default configuration suffices your needs you can just use the package level Get function instead
// without initializing a new Collector struct.
//
// The order in which the different configuration sources overwrite each other is the following:
// defaults -> config files -> environment variables -> command line flags
// (each source is overwritten by the following source)
//
// To define defaults for the config variables it can just be predefined in the struct that the
// configuration is supposed to be unmarshalled into. Properties that are not set in any of
// the configuration sources will keep the preset value.
//
// Since environment variables and flags are purely text based it also supports types that implement
// the encoding.TextUnmarshaler interface like for example zapcore.Level and logrus.Level.
// On top of that custom implementations are already baked into the package to support
// duration strings using time.ParseDuration() as well as string slices ([]string) in the format val1,val2,val3
// and string maps (map[string]string) in the format key1=val1,key2=val2.
type Collector struct {
Files FilesConfig
Env EnvConfig
Flags FlagsConfig
}
// New returns a new Collector.
// Various options can be used to customize the result.
// If no options are present the resulting Collector won't have any configuration sources and return
// the input struct without any changes in the Collector.Get method.
// Available options are:
// - FromFiles to configure configuration files as input source
// - FromEnvVars to configure environment variables as input source
// - FromCLIFlags to configure command line flags as input source
// Each of these options has an option itself to provide a custom separator.
// They are named WithFileSeparator, WithEnvSeparator and WithFlagSeparator.
func New(opts ...CollectorOption) *Collector {
c := &Collector{
Files: FilesConfig{
Disabled: true,
},
Env: EnvConfig{
Disabled: true,
},
Flags: FlagsConfig{
Disabled: true,
},
}
for _, opt := range opts {
opt(c)
}
return c
}
// CollectorOption takes a Collector as input and modifies it.
type CollectorOption func(*Collector)
// FromFiles is a option for New to enable configuration files as configuration source.
// It takes the locations/ dirs where to look for files and the basename (without file extension) as input parameters.
// FromFiles itself takes more options to customize the used separator (WithFileSeparator).
func FromFiles(locations []string, baseName string, opts ...FileOption) CollectorOption {
return func(collector *Collector) {
collector.Files = FilesConfig{
Locations: locations,
BaseName: baseName,
Separator: defaultFileSeparator,
Disabled: false,
}
for _, opt := range opts {
opt(&collector.Files)
}
}
}
// FileOption takes a FilesConfig as input and modifies it.
type FileOption func(*FilesConfig)
// WithFileSeparator adds a custom separator to a FilesConfig struct.
func WithFileSeparator(separator string) FileOption {
return func(config *FilesConfig) {
config.Separator = separator
}
}
// FromEnvVars is a option for New to enable environment variables as configuration source.
// It takes the prefix for the used environment variables as input parameter.
// FromEnvVars itself takes more options to customize the used separator (WithEnvSeparator).
func FromEnvVars(prefix string, opts ...EnvOption) CollectorOption {
return func(collector *Collector) {
collector.Env = EnvConfig{
Prefix: prefix,
Separator: defaultEnvSeparator,
Disabled: false,
}
for _, opt := range opts {
opt(&collector.Env)
}
}
}
// EnvOption takes an EnvConfig as input and modifies it.
type EnvOption func(*EnvConfig)
// WithEnvSeparator adds a custom separator to an EnvConfig struct.
func WithEnvSeparator(separator string) EnvOption {
return func(config *EnvConfig) {
config.Separator = separator
}
}
// FromCLIFlags is a option for New to enable command line flags as configuration source.
// FromCLIFlags itself takes more options to customize the used separator (WithFlagSeparator).
func FromCLIFlags(opts ...FlagOption) CollectorOption {
return func(collector *Collector) {
collector.Flags = FlagsConfig{
Separator: defaultFlagSeparator,
Disabled: false,
}
for _, opt := range opts {
opt(&collector.Flags)
}
}
}
// FlagOption takes a FlagsConfig as input and modifies it.
type FlagOption func(*FlagsConfig)
// WithFlagSeparator adds a custom separator to a FlagsConfig struct.
func WithFlagSeparator(separator string) FlagOption {
return func(config *FlagsConfig) {
config.Separator = separator
}
}
// FilesConfig is used to configure the configuration from files.
// Locations can be used to define where to look for files with the defined BaseName.
// Currently only json and yaml files are supported.
// The Separator is used for nested structs.
// If Disabled is true the configuration from files is skipped.
type FilesConfig struct {
Locations []string
BaseName string
Separator string
Disabled bool
}
// EnvConfig is used to configure the configuration from environment variables.
// Prefix can be defined the Collector should look for environment variables with a certain prefix.
// Separator is used for nested structs and also for the Prefix.
// As an example:
// If Prefix is set to "example", the Separator is set to "_" and the config struct's field is named Port,
// the Collector will by default look for the environment variable "EXAMPLE_PORT"
// If Disabled is true the configuration from environment variables is skipped.
type EnvConfig struct {
Prefix string
Separator string
Disabled bool
}
// FlagsConfig is used to configure the configuration from command line flags.
// Separator is used for nested structs to construct flag names from parent and child properties recursively.
// If Disabled is true the configuration from flags is skipped.
type FlagsConfig struct {
Separator string
Disabled bool
}
type field struct {
Base []string
Name string
Value reflect.Value
Config parameterConfig
}
func (f *field) FullName(separator string) string {
return strings.Join(append(f.Base, f.Name), separator)
}
type parameterConfig struct {
DefaultFileField string
DefaultEnvName string
Flag flag
}
type flag struct {
DefaultName string
ShortName string
}
// Get is the main package function and can be used by its wrapper Get or on a defined Collector struct.
// It expects a pointer to the config struct to write the config variables from the configured source to.
// If the input param is not a pointer, Get will return an error.
//
// Get looks for config variables all sources that are not disabled.
// Further usage details can be found in the examples or the Collector struct's documentation.
func (c *Collector) Get(v interface{}) error {
value := reflect.ValueOf(v)
if value.Kind() != reflect.Ptr {
return ErrPointerExpected
}
t := reflect.Indirect(value)
// collect info about fields with tags, value...
fields, err := getFieldsConfigsFromValue(t)
if err != nil {
return err
}
// read files
if !c.Files.Disabled {
if err := readFiles(fields, c.Files); err != nil {
if !errors.Is(err, ErrNoFileFound) {
fmt.Printf("could not find any files, proceeding with env and flags")
return err
}
}
}
// read env
if !c.Env.Disabled {
if err := readEnv(fields, c.Env, getEnvAsMap()); err != nil {
return err
}
}
// read flags
if !c.Flags.Disabled {
if err := readPFlags(fields, c.Flags, os.Args[1:]); err != nil {
return err
}
}
return nil
}
func getFieldsConfigsFromValue(value reflect.Value, base ...string) ([]*field, error) {
var fields []*field
for i := 0; i < value.NumField(); i++ {
fieldType := value.Type().Field(i)
fieldValue := reflect.Indirect(value.Field(i))
fieldConfig, err := readParameterConfig(fieldType.Tag.Get(tag))
if err != nil {
return nil, err
}
fields = append(fields, &field{
Base: base,
Name: fieldType.Name,
Value: fieldValue,
Config: fieldConfig,
})
if fieldValue.Kind() == reflect.Struct {
newBase := append(base, fieldType.Name)
subFields, err := getFieldsConfigsFromValue(fieldValue, newBase...)
if err != nil {
return nil, err
}
fields = append(fields, subFields...)
}
}
return fields, nil
}
func readParameterConfig(configStr string) (parameterConfig, error) {
fieldConfig := parameterConfig{}
if configStr == "" {
return parameterConfig{}, nil
}
for _, paramStr := range strings.Split(configStr, ",") {
keyVal := strings.SplitN(paramStr, "=", 2)
if len(keyVal) != 2 {
panic("invalid config struct tag format")
}
for _, v := range keyVal {
if v == "" {
panic(`config struct tag needs to have the format: config:"file=val,env=val,flag=l long"`)
}
}
key := keyVal[0]
val := keyVal[1]
switch key {
case envKey:
fieldConfig.DefaultEnvName = val
case fileKey:
fieldConfig.DefaultFileField = val
case flagKey:
flagConf, err := readFlagConfig(val)
if err != nil {
return parameterConfig{}, err
}
fieldConfig.Flag = flagConf
default:
panic(
fmt.Sprintf("only %s, %s, and %s are allowed as config tag keys", envKey, fileKey, flagKey),
)
}
}
return fieldConfig, nil
}
func readFiles(fields []*field, config FilesConfig) error {
fileFound := false
for _, fileLocation := range config.Locations {
fileInfos, err := ioutil.ReadDir(fileLocation)
if err != nil {
continue
}
for _, fileInfo := range fileInfos {
name := fileInfo.Name()
if strings.TrimSuffix(name, path.Ext(name)) != config.BaseName {
continue
}
fileFound = true
fileBytes, err := ioutil.ReadFile(path.Join(fileLocation, name))
if err != nil {
return err
}
m, err := unmarshal(config.Separator, fileBytes)
if err != nil {
return err
}
if err := readFileMap(fields, config.Separator, m); err != nil {
return err
}
}
}
if !fileFound {
return ErrNoFileFound
}
return nil
}
func readFileMap(fields []*field, separator string, m *ciMap) error {
for _, f := range fields {
fieldNames := []string{
f.Config.DefaultFileField,
f.FullName(separator),
}
for _, fieldName := range fieldNames {
valueForField, ok := m.Get(fieldName)
if !ok {
continue
}
fieldTypeZero := reflect.Zero(f.Value.Type())
v := fieldTypeZero.Interface()
if err := mapstructure.Decode(valueForField, &v); err != nil {
// if theres a type mismatch check if value is a string and try to use setFromString (e.g. for duration strings)
if valueString, ok := valueForField.(string); ok {
if err := setFromString(f.Value, valueString); err != nil {
return err
}
continue
}
// if the target is a struct there are also fields for the child properties and it should be tried
// to set these before returning an error
if f.Value.Kind() == reflect.Struct {
continue
}
return err
}
f.Value.Set(reflect.ValueOf(v))
}
}
return nil
}
func getEnvAsMap() map[string]string {
envMap := map[string]string{}
envKeyVal := os.Environ()
for _, keyVal := range envKeyVal {
split := strings.SplitN(keyVal, "=", 2)
envMap[split[0]] = split[1]
}
return envMap
}
func readEnv(fields []*field, config EnvConfig, vars map[string]string) error {
for _, f := range fields {
distinctEnvName := f.FullName(config.Separator)
if config.Prefix != "" {
distinctEnvName = config.Prefix + config.Separator + distinctEnvName
}
envNames := []string{
f.Config.DefaultEnvName,
distinctEnvName,
}
for _, envName := range envNames {
envVal, ok := vars[strings.ToUpper(envName)]
if !ok {
continue
}
if err := setFromString(f.Value, envVal); err != nil {
return err
}
}
}
return nil
}
type flagInfo struct {
valueStr *string
flag *pflag.Flag
}
func readPFlags(fields []*field, config FlagsConfig, args []string) error {
flagSet := pflag.NewFlagSet("config", pflag.ContinueOnError)
flagSet.ParseErrorsWhitelist = pflag.ParseErrorsWhitelist{UnknownFlags: true}
fieldToFlagInfo := make(map[*field][]*flagInfo)
fieldCache := map[string]*flagInfo{}
for _, f := range fields {
longName := strings.ToLower(f.FullName(config.Separator))
defaultName := f.Config.Flag.DefaultName
defaultFlag, ok := fieldCache[defaultName]
if !ok {
defaultFlag = &flagInfo{
valueStr: flagSet.StringP(defaultName, "", "", "default"),
flag: flagSet.Lookup(defaultName),
}
fieldCache[defaultName] = defaultFlag
}
fieldToFlagInfo[f] = []*flagInfo{
defaultFlag,
{
valueStr: flagSet.StringP(longName, f.Config.Flag.ShortName, "", "specific"),
flag: flagSet.Lookup(longName),
},
}
}
if err := flagSet.Parse(args); err != nil {
return err
}
for f, flagInfoSlice := range fieldToFlagInfo {
for _, flagInfo := range flagInfoSlice {
// differentiate a flag that is not set from a flag that is set to ""
if !flagInfo.flag.Changed {
continue
}
if err := setFromString(f.Value, *flagInfo.valueStr); err != nil {
return err
}
}
}
return nil
}
func setFromString(target reflect.Value, value string) (err error) { // nolint: funlen,gocyclo // just huge switch case
defer func() {
if e := recover(); e != nil {
err = ErrUnsupportedType
}
}()
if !target.CanSet() {
return ErrCantSet
}
if value == "" {
zeroValue := reflect.Zero(target.Type())
target.Set(zeroValue)
return nil
}
var valToSet interface{}
switch target.Interface().(type) {
case int, int8, int16, int32, int64:
intVal, err := strconv.ParseInt(value, 10, 0)
if err != nil {
return err
}
target.SetInt(intVal)
return nil
case complex64, complex128:
complexVal, err := strconv.ParseComplex(value, 0)
if err != nil {
return err
}
target.SetComplex(complexVal)
return nil
case uint, uint8, uint16, uint32, uint64:
uintVal, err := strconv.ParseUint(value, 10, 0)
if err != nil {
return err
}
target.SetUint(uintVal)
return nil
case float32, float64:
floatVal, err := strconv.ParseFloat(value, 0)
if err != nil {
return err
}
target.SetFloat(floatVal)
return nil
case time.Duration:
valToSet, err = time.ParseDuration(value)
case time.Time:
valToSet, err = time.Parse(time.RFC3339, value)
case bool:
valToSet, err = strconv.ParseBool(value)
case string:
valToSet = value
case []string:
strSlice := stringSlice{}
_ = strSlice.UnmarshalText([]byte(value))
valToSet = []string(strSlice)
case map[string]string:
strMap := stringMap{}
_ = strMap.UnmarshalText([]byte(value))
valToSet = map[string]string(strMap)
case encoding.TextUnmarshaler:
return target.Interface().(encoding.TextUnmarshaler).UnmarshalText([]byte(value))
default:
// check if Addr implements TextUnmarshaler interface
if t, ok := target.Addr().Interface().(encoding.TextUnmarshaler); ok {
return t.UnmarshalText([]byte(value))
}
valToSet = value
}
if err != nil {
return err
}
target.Set(reflect.ValueOf(valToSet))
return nil
}
func unmarshal(fileSeparator string, bytes []byte) (*ciMap, error) {
m := newCiMap(withSeparator(fileSeparator))
if err := yaml.Unmarshal(bytes, m); err == nil {
return m, nil
}
if err := json.Unmarshal(bytes, m); err == nil {
return m, nil
}
return nil, ErrFileTypeNotSupported
}
func readFlagConfig(flagStr string) (flag, error) {
flagConf := flag{}
flags := strings.Split(flagStr, flagConfigSeparator)
if len(flags) > 2 {
return flag{}, ErrMalformedFlagConfig
}
for _, f := range flags {
if len([]rune(f)) == 1 {
if flagConf.ShortName != "" {
return flag{}, ErrMalformedFlagConfig
}
flagConf.ShortName = f
} else {
if flagConf.DefaultName != "" {
return flag{}, ErrMalformedFlagConfig
}
flagConf.DefaultName = f
}
}
return flagConf, nil
}
type stringMap map[string]string
func (m stringMap) UnmarshalText(text []byte) error {
keyVals := stringSlice{}
_ = keyVals.UnmarshalText(text)
for _, keyVal := range keyVals {
split := strings.SplitN(keyVal, "=", 2)
for i := range split {
split[i] = strings.TrimSpace(split[i])
}
m[split[0]] = split[1]
}
return nil
}
func (m stringMap) MarshalText() ([]byte, error) {
keyVals := make([]string, 0, len(m))
for k, v := range m {
keyVals = append(keyVals, strings.Join([]string{k, v}, "="))
}
return stringSlice(keyVals).MarshalText()
}
type stringSlice []string
func (s *stringSlice) UnmarshalText(text []byte) error {
tmpSlice := strings.Split(string(text), ",")
for i := range tmpSlice {
tmpSlice[i] = strings.TrimSpace(tmpSlice[i])
}
*s = tmpSlice
return nil
}
func (s stringSlice) MarshalText() ([]byte, error) {
return []byte(strings.Join(s, ",")), nil
}