func WithAppendUserAgent(s string) Option {
	return func(r *Request) {
		r.Handlers.Build.PushBack(func(r2 *Request) {
			AddToUserAgent(r, s)
		})
	}
}
WithAppendUserAgent will add a string to the user agent prefixed with a
single white space.
package request
import (
	"fmt"
	"strings"
)
type Handlers struct {
	Validate         HandlerList
	Build            HandlerList
	BuildStream      HandlerList
	Sign             HandlerList
	Send             HandlerList
	ValidateResponse HandlerList
	Unmarshal        HandlerList
	UnmarshalStream  HandlerList
	UnmarshalMeta    HandlerList
	UnmarshalError   HandlerList
	Retry            HandlerList
	AfterRetry       HandlerList
	CompleteAttempt  HandlerList
	Complete         HandlerList
}
func (h *Handlers) Copy() Handlers {
	return Handlers{
		Validate:         h.Validate.copy(),
		Build:            h.Build.copy(),
		BuildStream:      h.BuildStream.copy(),
		Sign:             h.Sign.copy(),
		Send:             h.Send.copy(),
		ValidateResponse: h.ValidateResponse.copy(),
		Unmarshal:        h.Unmarshal.copy(),
		UnmarshalStream:  h.UnmarshalStream.copy(),
		UnmarshalError:   h.UnmarshalError.copy(),
		UnmarshalMeta:    h.UnmarshalMeta.copy(),
		Retry:            h.Retry.copy(),
		AfterRetry:       h.AfterRetry.copy(),
		CompleteAttempt:  h.CompleteAttempt.copy(),
		Complete:         h.Complete.copy(),
	}
}
func (h *Handlers) Clear() {
	h.Validate.Clear()
	h.Build.Clear()
	h.BuildStream.Clear()
	h.Send.Clear()
	h.Sign.Clear()
	h.Unmarshal.Clear()
	h.UnmarshalStream.Clear()
	h.UnmarshalMeta.Clear()
	h.UnmarshalError.Clear()
	h.ValidateResponse.Clear()
	h.Retry.Clear()
	h.AfterRetry.Clear()
	h.CompleteAttempt.Clear()
	h.Complete.Clear()
}
func (h *Handlers) IsEmpty() bool {
	if h.Validate.Len() != 0 {
		return false
	}
	if h.Build.Len() != 0 {
		return false
	}
	if h.BuildStream.Len() != 0 {
		return false
	}
	if h.Send.Len() != 0 {
		return false
	}
	if h.Sign.Len() != 0 {
		return false
	}
	if h.Unmarshal.Len() != 0 {
		return false
	}
	if h.UnmarshalStream.Len() != 0 {
		return false
	}
	if h.UnmarshalMeta.Len() != 0 {
		return false
	}
	if h.UnmarshalError.Len() != 0 {
		return false
	}
	if h.ValidateResponse.Len() != 0 {
		return false
	}
	if h.Retry.Len() != 0 {
		return false
	}
	if h.AfterRetry.Len() != 0 {
		return false
	}
	if h.CompleteAttempt.Len() != 0 {
		return false
	}
	if h.Complete.Len() != 0 {
		return false
	}
	return true
}
type HandlerListRunItem struct {
	Index   int
	Handler NamedHandler
	Request *Request
}
type HandlerList struct {
	list []NamedHandler
	AfterEachFn func(item HandlerListRunItem) bool
}
type NamedHandler struct {
	Name string
	Fn   func(*Request)
}
func (l *HandlerList) copy() HandlerList {
	n := HandlerList{
		AfterEachFn: l.AfterEachFn,
	}
	if len(l.list) == 0 {
		return n
	}
	n.list = append(make([]NamedHandler, 0, len(l.list)), l.list...)
	return n
}
func (l *HandlerList) Clear() {
	l.list = l.list[0:0]
}
func (l *HandlerList) Len() int {
	return len(l.list)
}
func (l *HandlerList) PushBack(f func(*Request)) {
	l.PushBackNamed(NamedHandler{"__anonymous", f})
}
func (l *HandlerList) PushBackNamed(n NamedHandler) {
	if cap(l.list) == 0 {
		l.list = make([]NamedHandler, 0, 5)
	}
	l.list = append(l.list, n)
}
func (l *HandlerList) PushFront(f func(*Request)) {
	l.PushFrontNamed(NamedHandler{"__anonymous", f})
}
func (l *HandlerList) PushFrontNamed(n NamedHandler) {
	if cap(l.list) == len(l.list) {
		l.list = append([]NamedHandler{n}, l.list...)
	} else {
		l.list = append(l.list, NamedHandler{})
		copy(l.list[1:], l.list)
		l.list[0] = n
	}
}
func (l *HandlerList) Remove(n NamedHandler) {
	l.RemoveByName(n.Name)
}
func (l *HandlerList) RemoveByName(name string) {
	for i := 0; i < len(l.list); i++ {
		m := l.list[i]
		if m.Name == name {
			copy(l.list[i:], l.list[i+1:])
			l.list[len(l.list)-1] = NamedHandler{}
			l.list = l.list[:len(l.list)-1]
			i--
		}
	}
}
func (l *HandlerList) SwapNamed(n NamedHandler) (swapped bool) {
	for i := 0; i < len(l.list); i++ {
		if l.list[i].Name == n.Name {
			l.list[i].Fn = n.Fn
			swapped = true
		}
	}
	return swapped
}
func (l *HandlerList) Swap(name string, replace NamedHandler) bool {
	var swapped bool
	for i := 0; i < len(l.list); i++ {
		if l.list[i].Name == name {
			l.list[i] = replace
			swapped = true
		}
	}
	return swapped
}
func (l *HandlerList) SetBackNamed(n NamedHandler) {
	if !l.SwapNamed(n) {
		l.PushBackNamed(n)
	}
}
func (l *HandlerList) SetFrontNamed(n NamedHandler) {
	if !l.SwapNamed(n) {
		l.PushFrontNamed(n)
	}
}
func (l *HandlerList) Run(r *Request) {
	for i, h := range l.list {
		h.Fn(r)
		item := HandlerListRunItem{
			Index: i, Handler: h, Request: r,
		}
		if l.AfterEachFn != nil && !l.AfterEachFn(item) {
			return
		}
	}
}
func HandlerListLogItem(item HandlerListRunItem) bool {
	if item.Request.Config.Logger == nil {
		return true
	}
	item.Request.Config.Logger.Log("DEBUG: RequestHandler",
		item.Index, item.Handler.Name, item.Request.Error)
	return true
}
func HandlerListStopOnError(item HandlerListRunItem) bool {
	return item.Request.Error == nil
}