1 files changed, 165 insertions, 0 deletions
diff --git a/nexgb/cookie.go b/nexgb/cookie.go
new file mode 100644
index 0000000..d5cdb29
--- /dev/null
+++ b/nexgb/cookie.go
@@ -0,0 +1,165 @@
+package xgb
+
+import (
+	"errors"
+)
+
+// Cookie is the internal representation of a cookie, where one is generated
+// for *every* request sent by XGB.
+// 'cookie' is most frequently used by embedding it into a more specific
+// kind of cookie, i.e., 'GetInputFocusCookie'.
+type Cookie struct {
+	conn      *Conn
+	Sequence  uint16
+	replyChan chan []byte
+	errorChan chan error
+	pingChan  chan bool
+}
+
+// NewCookie creates a new cookie with the correct channels initialized
+// depending upon the values of 'checked' and 'reply'. Together, there are
+// four different kinds of cookies. (See more detailed comments in the
+// function for more info on those.)
+// Note that a sequence number is not set until just before the request
+// corresponding to this cookie is sent over the wire.
+//
+// Unless you're building requests from bytes by hand, this method should
+// not be used.
+func (c *Conn) NewCookie(checked, reply bool) *Cookie {
+	cookie := &Cookie{
+		conn:      c,
+		Sequence:  0, // we add the sequence id just before sending a request
+		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
+}
+
+// Reply detects whether this is a checked or unchecked cookie, and calls
+// 'replyChecked' or 'replyUnchecked' appropriately.
+//
+// Unless you're building requests from bytes by hand, this method should
+// not be used.
+func (c Cookie) Reply() ([]byte, error) {
+	// checked
+	if c.errorChan != nil {
+		return c.replyChecked()
+	}
+	return c.replyUnchecked()
+}
+
+// replyChecked waits for a response on either the replyChan or errorChan
+// channels. If the former arrives, the bytes are returned with a nil error.
+// If the latter arrives, no bytes are returned (nil) and the error received
+// is returned.
+//
+// Unless you're building requests from bytes by hand, this method should
+// not be used.
+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
+	}
+}
+
+// replyUnchecked waits for a response on either the replyChan or pingChan
+// channels. If the former arrives, the bytes are returned with a nil error.
+// If the latter arrives, no bytes are returned (nil) and a nil error
+// is returned. (In the latter case, the corresponding error can be retrieved
+// from (Wait|Poll)ForEvent asynchronously.)
+// In all honesty, you *probably* don't want to use this method.
+//
+// Unless you're building requests from bytes by hand, this method should
+// not be used.
+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
+	}
+}
+
+// Check is used for checked requests that have no replies. It is a mechanism
+// by which to report "success" or "error" in a synchronous fashion. (Therefore,
+// unchecked requests without replies cannot use this method.)
+// If the request causes an error, it is sent to this cookie's errorChan.
+// If the request was successful, there is no response from the server.
+// Thus, pingChan is sent a value when the *next* reply is read.
+// If no more replies are being processed, we force a round trip request with
+// GetInputFocus.
+//
+// Unless you're building requests from bytes by hand, this method should
+// not be used.
+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*.")
+	}
+
+	// First do a quick non-blocking check to see if we've been pinged.
+	select {
+	case err := <-c.errorChan:
+		return err
+	case <-c.pingChan:
+		return nil
+	default:
+	}
+
+	// Now force a round trip and try again, but block this time.
+	c.conn.Sync()
+	select {
+	case err := <-c.errorChan:
+		return err
+	case <-c.pingChan:
+		return nil
+	}
+}