1 files changed, 111 insertions, 0 deletions
diff --git a/nexgb/cookie.go b/nexgb/cookie.go
new file mode 100644
index 0000000..502ccbf
--- /dev/null
+++ b/nexgb/cookie.go
@@ -0,0 +1,111 @@
+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")
+}
+