envconf/envconf.go

package envconf

import (
	"errors"
	"fmt"
	"os"
	"strings"
	"time"
	"unicode"
)

type cEntry struct {
	value  string
	parsed cValue
	dtype  DataType
	unset  bool
	empty  bool
}
type Config struct {
	parsed bool
	env    map[string]cEntry
}

// NewConfig returns an envconf.Config that is used to read configuration from environment variables.
// The environment variables are stored in envconf.Config, so changes to the environment after NewConfig has been called
// will not be taken into account.
func NewConfig() *Config {
	config := new(Config)
	config.parsed = false
	config.env = make(map[string]cEntry)
	for _, v := range os.Environ() {
		splitted := strings.SplitN(v, "=", 2)
		if len(splitted) == 2 {
			key := strings.TrimSpace(strings.ToUpper(splitted[0]))
			if unicode.IsLetter(getFirstRune(key)) {
				var entry cEntry
				entry.value = splitted[1]
				entry.dtype = TypeNone
				entry.unset = false
				entry.empty = false
				config.env[key] = entry
			}
		}
	}
	return config
}

// Define defines the type of an environment variable.
// Variables without a defined type will be ignored by Parse.
func (c *Config) Define(key string, dtype DataType) {
	upper := strings.ToUpper(key)
	entry, ok := c.env[upper]
	if ok {
		entry.dtype = dtype
		c.env[upper] = entry
	} else {
		var entry cEntry
		entry.dtype = dtype
		entry.unset = true
		entry.empty = true
		c.env[upper] = entry
	}
}

// DefineDefault defines the type and default value of an environment variable.
// Variables without a defined type will be ignored by Parse.
func (c *Config) DefineDefault(key string, val string, dtype DataType) {
	upper := strings.ToUpper(key)
	entry, ok := c.env[upper]
	if ok {
		if entry.unset {
			entry.value = val
		}
		entry.dtype = dtype
		entry.empty = false
		c.env[upper] = entry
	} else {
		var entry cEntry
		entry.dtype = dtype
		entry.unset = true
		entry.empty = false
		entry.value = val
		c.env[upper] = entry
	}
}

// Parse parses the environment variables previously defined by Define and DefineDefault.
// Parse should only be called once for a given envconf.Config.
func (c *Config) Parse() {
	if c.parsed {
		return
	}
	c.parsed = true
	failed := false
	for k, v := range c.env {
		if v.empty {
			if v.unset {
				failed = true
			}
		} else {
			v.parsed = v.dtype.parse(k, v.value)
			c.env[k] = v
		}
	}
	for k, v := range c.env {
		if failed && (v.parsed.err == nil) {
			if v.empty {
				if v.unset {
					v.parsed.err = errors.New(fmt.Sprintf(`Environment variable "%s" not found. It should have been of type %s.`, k, v.dtype))
					c.env[k] = v
				} else {
					v.parsed.err = errors.New(fmt.Sprintf(`Environment variable "%s" not found. Default value of "%s"(%s) used.`, k, v.value, v.dtype))
					c.env[k] = v
				}
			}
		}
	}
}

// Status prints out failures that occured while parsing the environment to os.Stderr.
// Variables that have been defined without a default value and are
// missing from the environment will be considered a failure.
// If parsing of any of the variables has failed Status will return false.
func (c *Config) Status() (ok bool) {
	ok = c.parsed
	if ok {
		for _, v := range c.env {
			err := v.parsed.err
			if err != nil {
				ok = false
				fmt.Fprintln(os.Stderr, err)
			}
		}
	}
	return
}

func (c *Config) getRaw(key string, dtype DataType) (val cValue) {
	val.dtype = TypeNone
	if c.parsed {
		upper := strings.ToUpper(key)
		entry, ok := c.env[upper]
		if ok && (entry.dtype == dtype) {
			return entry.parsed
		}
	}
	return
}

// GetInt returns the value of an environment variable.
// If the variable is not defined as envconf.TypeInt the function will return 0.
func (c *Config) GetInt(key string) int64 {
	val := c.getRaw(key, TypeInt)
	return val.intval
}

// GetMetric returns the value of an environment variable.
// If the variable is not defined as envconf.TypeMetric the function will return 0.
func (c *Config) GetMetric(key string) int64 {
	val := c.getRaw(key, TypeMetric)
	return val.intval
}

// GetDirectory returns the value of an environment variable.
// If the variable is not defined as envconf.TypeDirectory the
// function will return the empty string.
func (c *Config) GetDirectory(key string) string {
	val := c.getRaw(key, TypeDirectory)
	return val.strval
}

// GetString returns the value of an environment variable.
// If the variable is not defined as envconf.TypeString the
// function will return the empty string.
func (c *Config) GetString(key string) string {
	val := c.getRaw(key, TypeString)
	return val.strval
}

// GetDuration returns the value of an environment variable.
// If the variable is not defined as envconf.TypeDuration the
// function will return time.Duration(0).
func (c *Config) GetDuration(key string) time.Duration {
	val := c.getRaw(key, TypeDuration)
	return val.durval
}

// GetBool returns the value of an environment variable.
// If the variable is not defined as envconf.TypeBool the
// function will return false.
func (c *Config) GetBool(key string) bool {
	val := c.getRaw(key, TypeBool)
	return val.boolval
}

func getFirstRune(str string) rune {
	for _, v := range str {
		return v
	}
	return rune(0)
}