wip modernize code base

vendor/github.com/kelseyhightower/envconfig/.travis.yml

@@ -0,0 +1,13 @@
+language: go
+
+go:
+  - 1.4.x
+  - 1.5.x
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - 1.9.x
+  - 1.10.x
+  - 1.11.x
+  - 1.12.x
+  - tip

vendor/github.com/kelseyhightower/envconfig/LICENSE

@@ -0,0 +1,19 @@
+Copyright (c) 2013 Kelsey Hightower
+
+Permission is hereby granted, free of charge, to any person obtaining a copy of
+this software and associated documentation files (the "Software"), to deal in
+the Software without restriction, including without limitation the rights to
+use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies
+of the Software, and to permit persons to whom the Software is furnished to do
+so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.

vendor/github.com/kelseyhightower/envconfig/MAINTAINERS

@@ -0,0 +1,2 @@
+Kelsey Hightower kelsey.hightower@gmail.com github.com/kelseyhightower
+Travis Parker    travis.parker@gmail.com    github.com/teepark

vendor/github.com/kelseyhightower/envconfig/README.md

@@ -0,0 +1,192 @@
+# envconfig
+
+[![Build Status](https://travis-ci.org/kelseyhightower/envconfig.svg)](https://travis-ci.org/kelseyhightower/envconfig)
+
+```Go
+import "github.com/kelseyhightower/envconfig"
+```
+
+## Documentation
+
+See [godoc](http://godoc.org/github.com/kelseyhightower/envconfig)
+
+## Usage
+
+Set some environment variables:
+
+```Bash
+export MYAPP_DEBUG=false
+export MYAPP_PORT=8080
+export MYAPP_USER=Kelsey
+export MYAPP_RATE="0.5"
+export MYAPP_TIMEOUT="3m"
+export MYAPP_USERS="rob,ken,robert"
+export MYAPP_COLORCODES="red:1,green:2,blue:3"
+```
+
+Write some code:
+
+```Go
+package main
+
+import (
+    "fmt"
+    "log"
+    "time"
+
+    "github.com/kelseyhightower/envconfig"
+)
+
+type Specification struct {
+    Debug       bool
+    Port        int
+    User        string
+    Users       []string
+    Rate        float32
+    Timeout     time.Duration
+    ColorCodes  map[string]int
+}
+
+func main() {
+    var s Specification
+    err := envconfig.Process("myapp", &s)
+    if err != nil {
+        log.Fatal(err.Error())
+    }
+    format := "Debug: %v\nPort: %d\nUser: %s\nRate: %f\nTimeout: %s\n"
+    _, err = fmt.Printf(format, s.Debug, s.Port, s.User, s.Rate, s.Timeout)
+    if err != nil {
+        log.Fatal(err.Error())
+    }
+
+    fmt.Println("Users:")
+    for _, u := range s.Users {
+        fmt.Printf("  %s\n", u)
+    }
+
+    fmt.Println("Color codes:")
+    for k, v := range s.ColorCodes {
+        fmt.Printf("  %s: %d\n", k, v)
+    }
+}
+```
+
+Results:
+
+```Bash
+Debug: false
+Port: 8080
+User: Kelsey
+Rate: 0.500000
+Timeout: 3m0s
+Users:
+  rob
+  ken
+  robert
+Color codes:
+  red: 1
+  green: 2
+  blue: 3
+```
+
+## Struct Tag Support
+
+Envconfig supports the use of struct tags to specify alternate, default, and required
+environment variables.
+
+For example, consider the following struct:
+
+```Go
+type Specification struct {
+    ManualOverride1 string `envconfig:"manual_override_1"`
+    DefaultVar      string `default:"foobar"`
+    RequiredVar     string `required:"true"`
+    IgnoredVar      string `ignored:"true"`
+    AutoSplitVar    string `split_words:"true"`
+    RequiredAndAutoSplitVar    string `required:"true" split_words:"true"`
+}
+```
+
+Envconfig has automatic support for CamelCased struct elements when the
+`split_words:"true"` tag is supplied. Without this tag, `AutoSplitVar` above
+would look for an environment variable called `MYAPP_AUTOSPLITVAR`. With the
+setting applied it will look for `MYAPP_AUTO_SPLIT_VAR`. Note that numbers
+will get globbed into the previous word. If the setting does not do the
+right thing, you may use a manual override.
+
+Envconfig will process value for `ManualOverride1` by populating it with the
+value for `MYAPP_MANUAL_OVERRIDE_1`. Without this struct tag, it would have
+instead looked up `MYAPP_MANUALOVERRIDE1`. With the `split_words:"true"` tag
+it would have looked up `MYAPP_MANUAL_OVERRIDE1`.
+
+```Bash
+export MYAPP_MANUAL_OVERRIDE_1="this will be the value"
+
+# export MYAPP_MANUALOVERRIDE1="and this will not"
+```
+
+If envconfig can't find an environment variable value for `MYAPP_DEFAULTVAR`,
+it will populate it with "foobar" as a default value.
+
+If envconfig can't find an environment variable value for `MYAPP_REQUIREDVAR`,
+it will return an error when asked to process the struct.  If
+`MYAPP_REQUIREDVAR` is present but empty, envconfig will not return an error.
+
+If envconfig can't find an environment variable in the form `PREFIX_MYVAR`, and there
+is a struct tag defined, it will try to populate your variable with an environment
+variable that directly matches the envconfig tag in your struct definition:
+
+```shell
+export SERVICE_HOST=127.0.0.1
+export MYAPP_DEBUG=true
+```
+```Go
+type Specification struct {
+    ServiceHost string `envconfig:"SERVICE_HOST"`
+    Debug       bool
+}
+```
+
+Envconfig won't process a field with the "ignored" tag set to "true", even if a corresponding
+environment variable is set.
+
+## Supported Struct Field Types
+
+envconfig supports these struct field types:
+
+  * string
+  * int8, int16, int32, int64
+  * bool
+  * float32, float64
+  * slices of any supported type
+  * maps (keys and values of any supported type)
+  * [encoding.TextUnmarshaler](https://golang.org/pkg/encoding/#TextUnmarshaler)
+  * [encoding.BinaryUnmarshaler](https://golang.org/pkg/encoding/#BinaryUnmarshaler)
+  * [time.Duration](https://golang.org/pkg/time/#Duration)
+
+Embedded structs using these fields are also supported.
+
+## Custom Decoders
+
+Any field whose type (or pointer-to-type) implements `envconfig.Decoder` can
+control its own deserialization:
+
+```Bash
+export DNS_SERVER=8.8.8.8
+```
+
+```Go
+type IPDecoder net.IP
+
+func (ipd *IPDecoder) Decode(value string) error {
+    *ipd = IPDecoder(net.ParseIP(value))
+    return nil
+}
+
+type DNSConfig struct {
+    Address IPDecoder `envconfig:"DNS_SERVER"`
+}
+```
+
+Also, envconfig will use a `Set(string) error` method like from the
+[flag.Value](https://godoc.org/flag#Value) interface if implemented.

vendor/github.com/kelseyhightower/envconfig/doc.go

@@ -0,0 +1,8 @@
+// Copyright (c) 2013 Kelsey Hightower. All rights reserved.
+// Use of this source code is governed by the MIT License that can be found in
+// the LICENSE file.
+
+// Package envconfig implements decoding of environment variables based on a user
+// defined specification. A typical use is using environment variables for
+// configuration settings.
+package envconfig

vendor/github.com/kelseyhightower/envconfig/env_os.go

@@ -0,0 +1,7 @@
+// +build appengine go1.5
+
+package envconfig
+
+import "os"
+
+var lookupEnv = os.LookupEnv

vendor/github.com/kelseyhightower/envconfig/env_syscall.go

@@ -0,0 +1,7 @@
+// +build !appengine,!go1.5
+
+package envconfig
+
+import "syscall"
+
+var lookupEnv = syscall.Getenv

vendor/github.com/kelseyhightower/envconfig/envconfig.go

@@ -0,0 +1,382 @@
+// Copyright (c) 2013 Kelsey Hightower. All rights reserved.
+// Use of this source code is governed by the MIT License that can be found in
+// the LICENSE file.
+
+package envconfig
+
+import (
+	"encoding"
+	"errors"
+	"fmt"
+	"os"
+	"reflect"
+	"regexp"
+	"strconv"
+	"strings"
+	"time"
+)
+
+// ErrInvalidSpecification indicates that a specification is of the wrong type.
+var ErrInvalidSpecification = errors.New("specification must be a struct pointer")
+
+var gatherRegexp = regexp.MustCompile("([^A-Z]+|[A-Z]+[^A-Z]+|[A-Z]+)")
+var acronymRegexp = regexp.MustCompile("([A-Z]+)([A-Z][^A-Z]+)")
+
+// A ParseError occurs when an environment variable cannot be converted to
+// the type required by a struct field during assignment.
+type ParseError struct {
+	KeyName   string
+	FieldName string
+	TypeName  string
+	Value     string
+	Err       error
+}
+
+// Decoder has the same semantics as Setter, but takes higher precedence.
+// It is provided for historical compatibility.
+type Decoder interface {
+	Decode(value string) error
+}
+
+// Setter is implemented by types can self-deserialize values.
+// Any type that implements flag.Value also implements Setter.
+type Setter interface {
+	Set(value string) error
+}
+
+func (e *ParseError) Error() string {
+	return fmt.Sprintf("envconfig.Process: assigning %[1]s to %[2]s: converting '%[3]s' to type %[4]s. details: %[5]s", e.KeyName, e.FieldName, e.Value, e.TypeName, e.Err)
+}
+
+// varInfo maintains information about the configuration variable
+type varInfo struct {
+	Name  string
+	Alt   string
+	Key   string
+	Field reflect.Value
+	Tags  reflect.StructTag
+}
+
+// GatherInfo gathers information about the specified struct
+func gatherInfo(prefix string, spec interface{}) ([]varInfo, error) {
+	s := reflect.ValueOf(spec)
+
+	if s.Kind() != reflect.Ptr {
+		return nil, ErrInvalidSpecification
+	}
+	s = s.Elem()
+	if s.Kind() != reflect.Struct {
+		return nil, ErrInvalidSpecification
+	}
+	typeOfSpec := s.Type()
+
+	// over allocate an info array, we will extend if needed later
+	infos := make([]varInfo, 0, s.NumField())
+	for i := 0; i < s.NumField(); i++ {
+		f := s.Field(i)
+		ftype := typeOfSpec.Field(i)
+		if !f.CanSet() || isTrue(ftype.Tag.Get("ignored")) {
+			continue
+		}
+
+		for f.Kind() == reflect.Ptr {
+			if f.IsNil() {
+				if f.Type().Elem().Kind() != reflect.Struct {
+					// nil pointer to a non-struct: leave it alone
+					break
+				}
+				// nil pointer to struct: create a zero instance
+				f.Set(reflect.New(f.Type().Elem()))
+			}
+			f = f.Elem()
+		}
+
+		// Capture information about the config variable
+		info := varInfo{
+			Name:  ftype.Name,
+			Field: f,
+			Tags:  ftype.Tag,
+			Alt:   strings.ToUpper(ftype.Tag.Get("envconfig")),
+		}
+
+		// Default to the field name as the env var name (will be upcased)
+		info.Key = info.Name
+
+		// Best effort to un-pick camel casing as separate words
+		if isTrue(ftype.Tag.Get("split_words")) {
+			words := gatherRegexp.FindAllStringSubmatch(ftype.Name, -1)
+			if len(words) > 0 {
+				var name []string
+				for _, words := range words {
+					if m := acronymRegexp.FindStringSubmatch(words[0]); len(m) == 3 {
+						name = append(name, m[1], m[2])
+					} else {
+						name = append(name, words[0])
+					}
+				}
+
+				info.Key = strings.Join(name, "_")
+			}
+		}
+		if info.Alt != "" {
+			info.Key = info.Alt
+		}
+		if prefix != "" {
+			info.Key = fmt.Sprintf("%s_%s", prefix, info.Key)
+		}
+		info.Key = strings.ToUpper(info.Key)
+		infos = append(infos, info)
+
+		if f.Kind() == reflect.Struct {
+			// honor Decode if present
+			if decoderFrom(f) == nil && setterFrom(f) == nil && textUnmarshaler(f) == nil && binaryUnmarshaler(f) == nil {
+				innerPrefix := prefix
+				if !ftype.Anonymous {
+					innerPrefix = info.Key
+				}
+
+				embeddedPtr := f.Addr().Interface()
+				embeddedInfos, err := gatherInfo(innerPrefix, embeddedPtr)
+				if err != nil {
+					return nil, err
+				}
+				infos = append(infos[:len(infos)-1], embeddedInfos...)
+
+				continue
+			}
+		}
+	}
+	return infos, nil
+}
+
+// CheckDisallowed checks that no environment variables with the prefix are set
+// that we don't know how or want to parse. This is likely only meaningful with
+// a non-empty prefix.
+func CheckDisallowed(prefix string, spec interface{}) error {
+	infos, err := gatherInfo(prefix, spec)
+	if err != nil {
+		return err
+	}
+
+	vars := make(map[string]struct{})
+	for _, info := range infos {
+		vars[info.Key] = struct{}{}
+	}
+
+	if prefix != "" {
+		prefix = strings.ToUpper(prefix) + "_"
+	}
+
+	for _, env := range os.Environ() {
+		if !strings.HasPrefix(env, prefix) {
+			continue
+		}
+		v := strings.SplitN(env, "=", 2)[0]
+		if _, found := vars[v]; !found {
+			return fmt.Errorf("unknown environment variable %s", v)
+		}
+	}
+
+	return nil
+}
+
+// Process populates the specified struct based on environment variables
+func Process(prefix string, spec interface{}) error {
+	infos, err := gatherInfo(prefix, spec)
+
+	for _, info := range infos {
+
+		// `os.Getenv` cannot differentiate between an explicitly set empty value
+		// and an unset value. `os.LookupEnv` is preferred to `syscall.Getenv`,
+		// but it is only available in go1.5 or newer. We're using Go build tags
+		// here to use os.LookupEnv for >=go1.5
+		value, ok := lookupEnv(info.Key)
+		if !ok && info.Alt != "" {
+			value, ok = lookupEnv(info.Alt)
+		}
+
+		def := info.Tags.Get("default")
+		if def != "" && !ok {
+			value = def
+		}
+
+		req := info.Tags.Get("required")
+		if !ok && def == "" {
+			if isTrue(req) {
+				key := info.Key
+				if info.Alt != "" {
+					key = info.Alt
+				}
+				return fmt.Errorf("required key %s missing value", key)
+			}
+			continue
+		}
+
+		err = processField(value, info.Field)
+		if err != nil {
+			return &ParseError{
+				KeyName:   info.Key,
+				FieldName: info.Name,
+				TypeName:  info.Field.Type().String(),
+				Value:     value,
+				Err:       err,
+			}
+		}
+	}
+
+	return err
+}
+
+// MustProcess is the same as Process but panics if an error occurs
+func MustProcess(prefix string, spec interface{}) {
+	if err := Process(prefix, spec); err != nil {
+		panic(err)
+	}
+}
+
+func processField(value string, field reflect.Value) error {
+	typ := field.Type()
+
+	decoder := decoderFrom(field)
+	if decoder != nil {
+		return decoder.Decode(value)
+	}
+	// look for Set method if Decode not defined
+	setter := setterFrom(field)
+	if setter != nil {
+		return setter.Set(value)
+	}
+
+	if t := textUnmarshaler(field); t != nil {
+		return t.UnmarshalText([]byte(value))
+	}
+
+	if b := binaryUnmarshaler(field); b != nil {
+		return b.UnmarshalBinary([]byte(value))
+	}
+
+	if typ.Kind() == reflect.Ptr {
+		typ = typ.Elem()
+		if field.IsNil() {
+			field.Set(reflect.New(typ))
+		}
+		field = field.Elem()
+	}
+
+	switch typ.Kind() {
+	case reflect.String:
+		field.SetString(value)
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		var (
+			val int64
+			err error
+		)
+		if field.Kind() == reflect.Int64 && typ.PkgPath() == "time" && typ.Name() == "Duration" {
+			var d time.Duration
+			d, err = time.ParseDuration(value)
+			val = int64(d)
+		} else {
+			val, err = strconv.ParseInt(value, 0, typ.Bits())
+		}
+		if err != nil {
+			return err
+		}
+
+		field.SetInt(val)
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		val, err := strconv.ParseUint(value, 0, typ.Bits())
+		if err != nil {
+			return err
+		}
+		field.SetUint(val)
+	case reflect.Bool:
+		val, err := strconv.ParseBool(value)
+		if err != nil {
+			return err
+		}
+		field.SetBool(val)
+	case reflect.Float32, reflect.Float64:
+		val, err := strconv.ParseFloat(value, typ.Bits())
+		if err != nil {
+			return err
+		}
+		field.SetFloat(val)
+	case reflect.Slice:
+		sl := reflect.MakeSlice(typ, 0, 0)
+		if typ.Elem().Kind() == reflect.Uint8 {
+			sl = reflect.ValueOf([]byte(value))
+		} else if len(strings.TrimSpace(value)) != 0 {
+			vals := strings.Split(value, ",")
+			sl = reflect.MakeSlice(typ, len(vals), len(vals))
+			for i, val := range vals {
+				err := processField(val, sl.Index(i))
+				if err != nil {
+					return err
+				}
+			}
+		}
+		field.Set(sl)
+	case reflect.Map:
+		mp := reflect.MakeMap(typ)
+		if len(strings.TrimSpace(value)) != 0 {
+			pairs := strings.Split(value, ",")
+			for _, pair := range pairs {
+				kvpair := strings.Split(pair, ":")
+				if len(kvpair) != 2 {
+					return fmt.Errorf("invalid map item: %q", pair)
+				}
+				k := reflect.New(typ.Key()).Elem()
+				err := processField(kvpair[0], k)
+				if err != nil {
+					return err
+				}
+				v := reflect.New(typ.Elem()).Elem()
+				err = processField(kvpair[1], v)
+				if err != nil {
+					return err
+				}
+				mp.SetMapIndex(k, v)
+			}
+		}
+		field.Set(mp)
+	}
+
+	return nil
+}
+
+func interfaceFrom(field reflect.Value, fn func(interface{}, *bool)) {
+	// it may be impossible for a struct field to fail this check
+	if !field.CanInterface() {
+		return
+	}
+	var ok bool
+	fn(field.Interface(), &ok)
+	if !ok && field.CanAddr() {
+		fn(field.Addr().Interface(), &ok)
+	}
+}
+
+func decoderFrom(field reflect.Value) (d Decoder) {
+	interfaceFrom(field, func(v interface{}, ok *bool) { d, *ok = v.(Decoder) })
+	return d
+}
+
+func setterFrom(field reflect.Value) (s Setter) {
+	interfaceFrom(field, func(v interface{}, ok *bool) { s, *ok = v.(Setter) })
+	return s
+}
+
+func textUnmarshaler(field reflect.Value) (t encoding.TextUnmarshaler) {
+	interfaceFrom(field, func(v interface{}, ok *bool) { t, *ok = v.(encoding.TextUnmarshaler) })
+	return t
+}
+
+func binaryUnmarshaler(field reflect.Value) (b encoding.BinaryUnmarshaler) {
+	interfaceFrom(field, func(v interface{}, ok *bool) { b, *ok = v.(encoding.BinaryUnmarshaler) })
+	return b
+}
+
+func isTrue(s string) bool {
+	b, _ := strconv.ParseBool(s)
+	return b
+}

vendor/github.com/kelseyhightower/envconfig/go.mod

@@ -0,0 +1 @@
+module github.com/kelseyhightower/envconfig

vendor/github.com/kelseyhightower/envconfig/usage.go

@@ -0,0 +1,164 @@
+// Copyright (c) 2016 Kelsey Hightower and others. All rights reserved.
+// Use of this source code is governed by the MIT License that can be found in
+// the LICENSE file.
+
+package envconfig
+
+import (
+	"encoding"
+	"fmt"
+	"io"
+	"os"
+	"reflect"
+	"strconv"
+	"strings"
+	"text/tabwriter"
+	"text/template"
+)
+
+const (
+	// DefaultListFormat constant to use to display usage in a list format
+	DefaultListFormat = `This application is configured via the environment. The following environment
+variables can be used:
+{{range .}}
+{{usage_key .}}
+  [description] {{usage_description .}}
+  [type]        {{usage_type .}}
+  [default]     {{usage_default .}}
+  [required]    {{usage_required .}}{{end}}
+`
+	// DefaultTableFormat constant to use to display usage in a tabular format
+	DefaultTableFormat = `This application is configured via the environment. The following environment
+variables can be used:
+
+KEY	TYPE	DEFAULT	REQUIRED	DESCRIPTION
+{{range .}}{{usage_key .}}	{{usage_type .}}	{{usage_default .}}	{{usage_required .}}	{{usage_description .}}
+{{end}}`
+)
+
+var (
+	decoderType           = reflect.TypeOf((*Decoder)(nil)).Elem()
+	setterType            = reflect.TypeOf((*Setter)(nil)).Elem()
+	textUnmarshalerType   = reflect.TypeOf((*encoding.TextUnmarshaler)(nil)).Elem()
+	binaryUnmarshalerType = reflect.TypeOf((*encoding.BinaryUnmarshaler)(nil)).Elem()
+)
+
+func implementsInterface(t reflect.Type) bool {
+	return t.Implements(decoderType) ||
+		reflect.PtrTo(t).Implements(decoderType) ||
+		t.Implements(setterType) ||
+		reflect.PtrTo(t).Implements(setterType) ||
+		t.Implements(textUnmarshalerType) ||
+		reflect.PtrTo(t).Implements(textUnmarshalerType) ||
+		t.Implements(binaryUnmarshalerType) ||
+		reflect.PtrTo(t).Implements(binaryUnmarshalerType)
+}
+
+// toTypeDescription converts Go types into a human readable description
+func toTypeDescription(t reflect.Type) string {
+	switch t.Kind() {
+	case reflect.Array, reflect.Slice:
+		if t.Elem().Kind() == reflect.Uint8 {
+			return "String"
+		}
+		return fmt.Sprintf("Comma-separated list of %s", toTypeDescription(t.Elem()))
+	case reflect.Map:
+		return fmt.Sprintf(
+			"Comma-separated list of %s:%s pairs",
+			toTypeDescription(t.Key()),
+			toTypeDescription(t.Elem()),
+		)
+	case reflect.Ptr:
+		return toTypeDescription(t.Elem())
+	case reflect.Struct:
+		if implementsInterface(t) && t.Name() != "" {
+			return t.Name()
+		}
+		return ""
+	case reflect.String:
+		name := t.Name()
+		if name != "" && name != "string" {
+			return name
+		}
+		return "String"
+	case reflect.Bool:
+		name := t.Name()
+		if name != "" && name != "bool" {
+			return name
+		}
+		return "True or False"
+	case reflect.Int, reflect.Int8, reflect.Int16, reflect.Int32, reflect.Int64:
+		name := t.Name()
+		if name != "" && !strings.HasPrefix(name, "int") {
+			return name
+		}
+		return "Integer"
+	case reflect.Uint, reflect.Uint8, reflect.Uint16, reflect.Uint32, reflect.Uint64:
+		name := t.Name()
+		if name != "" && !strings.HasPrefix(name, "uint") {
+			return name
+		}
+		return "Unsigned Integer"
+	case reflect.Float32, reflect.Float64:
+		name := t.Name()
+		if name != "" && !strings.HasPrefix(name, "float") {
+			return name
+		}
+		return "Float"
+	}
+	return fmt.Sprintf("%+v", t)
+}
+
+// Usage writes usage information to stdout using the default header and table format
+func Usage(prefix string, spec interface{}) error {
+	// The default is to output the usage information as a table
+	// Create tabwriter instance to support table output
+	tabs := tabwriter.NewWriter(os.Stdout, 1, 0, 4, ' ', 0)
+
+	err := Usagef(prefix, spec, tabs, DefaultTableFormat)
+	tabs.Flush()
+	return err
+}
+
+// Usagef writes usage information to the specified io.Writer using the specifed template specification
+func Usagef(prefix string, spec interface{}, out io.Writer, format string) error {
+
+	// Specify the default usage template functions
+	functions := template.FuncMap{
+		"usage_key":         func(v varInfo) string { return v.Key },
+		"usage_description": func(v varInfo) string { return v.Tags.Get("desc") },
+		"usage_type":        func(v varInfo) string { return toTypeDescription(v.Field.Type()) },
+		"usage_default":     func(v varInfo) string { return v.Tags.Get("default") },
+		"usage_required": func(v varInfo) (string, error) {
+			req := v.Tags.Get("required")
+			if req != "" {
+				reqB, err := strconv.ParseBool(req)
+				if err != nil {
+					return "", err
+				}
+				if reqB {
+					req = "true"
+				}
+			}
+			return req, nil
+		},
+	}
+
+	tmpl, err := template.New("envconfig").Funcs(functions).Parse(format)
+	if err != nil {
+		return err
+	}
+
+	return Usaget(prefix, spec, out, tmpl)
+}
+
+// Usaget writes usage information to the specified io.Writer using the specified template
+func Usaget(prefix string, spec interface{}, out io.Writer, tmpl *template.Template) error {
+	// gather first
+	infos, err := gatherInfo(prefix, spec)
+	if err != nil {
+		return err
+	}
+
+	return tmpl.Execute(out, infos)
+}