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config.go
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config.go
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package configs
import (
"encoding/json"
"fmt"
"io/ioutil"
"strconv"
"strings"
)
// Config represents a configuration with convenient access methods.
type Config struct {
Root interface{}
}
// Get returns a nested config according to a dotted path.
func (c *Config) Get(path string) (*Config, error) {
n, err := Get(c.Root, path)
if err != nil {
return nil, err
}
return &Config{Root: n}, nil
}
// String returns a string according to a dotted path.
func (c *Config) String(path string) (string, error) {
n, err := Get(c.Root, path)
if err != nil {
return "", err
}
switch n := n.(type) {
case bool, float64, int:
return fmt.Sprint(n), nil
case string:
return n, nil
}
return "", fmt.Errorf("Type mismatch: expected string; got %T", n)
}
// UString returns a string according to a dotted path or default or "".
func (c *Config) UString(path string, defaults ...string) string {
value, err := c.String(path)
if err == nil {
return value
}
for _, def := range defaults {
return def
}
return ""
}
// Bool returns a bool according to a dotted path.
func (c *Config) Bool(path string) (bool, error) {
n, err := Get(c.Root, path)
if err != nil {
return false, err
}
switch n := n.(type) {
case bool:
return n, nil
case string:
return strconv.ParseBool(n)
}
return false, fmt.Errorf("Type mismatch: expected bool; got %T", n)
}
// UBool retirns a bool according to a dotted path or default value or false.
func (c *Config) UBool(path string, defaults ...bool) bool {
value, err := c.Bool(path)
if err == nil {
return value
}
for _, def := range defaults {
return def
}
return false
}
// Float64 returns a float64 according to a dotted path.
func (c *Config) Float64(path string) (float64, error) {
n, err := Get(c.Root, path)
if err != nil {
return 0, err
}
switch n := n.(type) {
case float64:
return n, nil
case int:
return float64(n), nil
case string:
return strconv.ParseFloat(n, 64)
}
return 0, fmt.Errorf("Type mismatch: expected float64; got %T", n)
}
// UFloat64 returns a float64 according to a dotted path or default value or 0.
func (c *Config) UFloat64(path string, defaults ...float64) float64 {
value, err := c.Float64(path)
if err == nil {
return value
}
for _, def := range defaults {
return def
}
return float64(0)
}
// Int returns an int according to a dotted path.
func (c *Config) Int(path string) (int, error) {
n, err := Get(c.Root, path)
if err != nil {
return 0, err
}
switch n := n.(type) {
case float64:
// encoding/json unmarshals numbers into floats, so we compare
// the string representation to see if we can return an int.
if i := int(n); fmt.Sprint(i) == fmt.Sprint(n) {
return i, nil
}
return 0, fmt.Errorf("Value can't be converted to int: %v", n)
case int:
return n, nil
case string:
if v, err := strconv.ParseInt(n, 10, 0); err == nil {
return int(v), nil
}
return 0, err
}
return 0, fmt.Errorf("Type mismatch: expected int; got %T", n)
}
// UInt returns an int according to a dotted path or default value or 0.
func (c *Config) UInt(path string, defaults ...int) int {
value, err := c.Int(path)
if err == nil {
return value
}
for _, def := range defaults {
return def
}
return 0
}
// List returns a []interface{} according to a dotted path.
func (c *Config) List(path string) ([]interface{}, error) {
n, err := Get(c.Root, path)
if err != nil {
return nil, err
}
if value, ok := n.([]interface{}); ok {
return value, nil
}
return nil, fmt.Errorf("Type mismatch: expected []interface{}; got %T", n)
}
// UList returns a []interface{} according to a dotted path or defaults or []interface{}.
func (c *Config) UList(path string, defaults ...[]interface{}) []interface{} {
value, err := c.List(path)
if err == nil {
return value
}
for _, def := range defaults {
return def
}
return make([]interface{}, 0)
}
// Map returns a map[string]interface{} according to a dotted path.
func (c *Config) Map(path string) (map[string]interface{}, error) {
n, err := Get(c.Root, path)
if err != nil {
return nil, err
}
if value, ok := n.(map[string]interface{}); ok {
return value, nil
}
return nil, fmt.Errorf("Type mismatch: expected map[string]interface{}; got %T", n)
}
// UMap returns a map[string]interface{} according to a dotted path or default or map[string]interface{}.
func (c *Config) UMap(path string, defaults ...map[string]interface{}) map[string]interface{} {
value, err := c.Map(path)
if err == nil {
return value
}
for _, def := range defaults {
return def
}
return map[string]interface{}{}
}
// Get returns a child of the given value according to a dotted path.
func Get(cfg interface{}, path string) (interface{}, error) {
parts := strings.Split(path, ".")
// Normalize path.
for k, v := range parts {
if v == "" {
if k == 0 {
parts = parts[1:]
} else {
return nil, fmt.Errorf("Invalid path %q", path)
}
}
}
// Get the value.
for pos, part := range parts {
switch c := cfg.(type) {
case []interface{}:
if i, error := strconv.ParseInt(part, 10, 0); error == nil {
if int(i) < len(c) {
cfg = c[i]
} else {
return nil, fmt.Errorf(
"Index out of range at %q: list has only %v items",
strings.Join(parts[:pos+1], "."), len(c))
}
} else {
return nil, fmt.Errorf("Invalid list index at %q",
strings.Join(parts[:pos+1], "."))
}
case map[string]interface{}:
if value, ok := c[part]; ok {
cfg = value
} else {
return nil, fmt.Errorf("Nonexistent map key at %q",
strings.Join(parts[:pos+1], "."))
}
default:
return nil, fmt.Errorf(
"Invalid type at %q: expected []interface{} or map[string]interface{}; got %T",
strings.Join(parts[:pos+1], "."), cfg)
}
}
return cfg, nil
}
// Load reads a JSON configuration from given filename
func Load(filename string) (*Config, error) {
cfg, err := ioutil.ReadFile(filename)
if err != nil {
return nil, err
}
return parse(cfg)
}
// parse perform JSON parsing
func parse(cfg []byte) (*Config, error) {
var out interface{}
var err error
if err = json.Unmarshal(cfg, &out); err != nil {
return nil, err
}
if out, err = normalize(out); err != nil {
return nil, err
}
return &Config{Root: out}, nil
}
// normalizes a unmarshalled value. This is needed because
// encoding/json doesn't support marshalling map[interface{}]interface{}.
func normalize(value interface{}) (interface{}, error) {
switch value := value.(type) {
case map[interface{}]interface{}:
node := make(map[string]interface{}, len(value))
for k, v := range value {
key, ok := k.(string)
if !ok {
return nil, fmt.Errorf("Unsupported map key: %#v", k)
}
item, err := normalize(v)
if err != nil {
return nil, fmt.Errorf("Unsupported map value: %#v", v)
}
node[key] = item
}
return node, nil
case map[string]interface{}:
node := make(map[string]interface{}, len(value))
for key, v := range value {
item, err := normalize(v)
if err != nil {
return nil, fmt.Errorf("Unsupported map value: %#v", v)
}
node[key] = item
}
return node, nil
case []interface{}:
node := make([]interface{}, len(value))
for key, v := range value {
item, err := normalize(v)
if err != nil {
return nil, fmt.Errorf("Unsupported list item: %#v", v)
}
node[key] = item
}
return node, nil
case bool, float64, int, string:
return value, nil
}
return nil, fmt.Errorf("Unsupported type: %T", value)
}