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|
package xgb
import (
"errors"
)
type cookie struct {
Sequence uint16
replyChan chan []byte
errorChan chan error
pingChan chan bool
}
func (c *Conn) newCookie(checked, reply bool) cookie {
cookie := cookie{
Sequence: c.newSequenceId(),
replyChan: nil,
errorChan: nil,
pingChan: nil,
}
// There are four different kinds of cookies:
// Checked requests with replies get a reply channel and an error channel.
// Unchecked requests with replies get a reply channel and a ping channel.
// Checked requests w/o replies get a ping channel and an error channel.
// Unchecked requests w/o replies get no channels.
// The reply channel is used to send reply data.
// The error channel is used to send error data.
// The ping channel is used when one of the 'reply' or 'error' channels
// is missing but the other is present. The ping channel is way to force
// the blocking to stop and basically say "the error has been received
// in the main event loop" (when the ping channel is coupled with a reply
// channel) or "the request you made that has no reply was successful"
// (when the ping channel is coupled with an error channel).
if checked {
cookie.errorChan = make(chan error, 1)
if !reply {
cookie.pingChan = make(chan bool, 1)
}
}
if reply {
cookie.replyChan = make(chan []byte, 1)
if !checked {
cookie.pingChan = make(chan bool, 1)
}
}
return cookie
}
func (c cookie) reply() ([]byte, error) {
// checked
if c.errorChan != nil {
return c.replyChecked()
}
return c.replyUnchecked()
}
func (c cookie) replyChecked() ([]byte, error) {
if c.replyChan == nil {
return nil, errors.New("Cannot call 'replyChecked' on a cookie that " +
"is not expecting a *reply* or an error.")
}
if c.errorChan == nil {
return nil, errors.New("Cannot call 'replyChecked' on a cookie that " +
"is not expecting a reply or an *error*.")
}
select {
case reply := <-c.replyChan:
return reply, nil
case err := <-c.errorChan:
return nil, err
}
panic("unreachable")
}
func (c cookie) replyUnchecked() ([]byte, error) {
if c.replyChan == nil {
return nil, errors.New("Cannot call 'replyUnchecked' on a cookie " +
"that is not expecting a *reply*.")
}
select {
case reply := <-c.replyChan:
return reply, nil
case <-c.pingChan:
return nil, nil
}
panic("unreachable")
}
func (c cookie) Check() error {
if c.replyChan != nil {
return errors.New("Cannot call 'Check' on a cookie that is " +
"expecting a *reply*. Use 'Reply' instead.")
}
if c.errorChan == nil {
return errors.New("Cannot call 'Check' on a cookie that is " +
"not expecting a possible *error*.")
}
select {
case err := <-c.errorChan:
return err
case <-c.pingChan:
return nil
}
panic("unreachable")
}
|
