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