haven/nexgb/xgb.go

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// Copyright 2009 The XGB Authors. All rights reserved.
// Use of this source code is governed by a BSD-style
// license that can be found in the LICENSE file.
// The XGB package implements the X11 core protocol.
// It is based on XCB: http://xcb.freedesktop.org/
package xgb
import (
"errors"
"fmt"
"io"
"net"
"os"
"strings"
"sync"
)
const (
readBuffer = 100
writeBuffer = 100
)
// A Conn represents a connection to an X server.
type Conn struct {
host string
conn net.Conn
err error
display string
defaultScreen int
Setup SetupInfo
extensions map[string]byte
eventChan chan eventOrError
cookieChan chan cookie
xidChan chan xid
seqChan chan uint16
reqChan chan *request
extLock sync.Mutex
}
// NewConn creates a new connection instance. It initializes locks, data
// structures, and performs the initial handshake. (The code for the handshake
// has been relegated to conn.go.)
func NewConn() (*Conn, error) {
return NewConnDisplay("")
}
// NewConnDisplay is just like NewConn, but allows a specific DISPLAY
// string to be used.
// If 'display' is empty it will be taken from os.Getenv("DISPLAY").
//
// Examples:
// NewConn(":1") -> net.Dial("unix", "", "/tmp/.X11-unix/X1")
// NewConn("/tmp/launch-123/:0") -> net.Dial("unix", "", "/tmp/launch-123/:0")
// NewConn("hostname:2.1") -> net.Dial("tcp", "", "hostname:6002")
// NewConn("tcp/hostname:1.0") -> net.Dial("tcp", "", "hostname:6001")
func NewConnDisplay(display string) (*Conn, error) {
conn := &Conn{}
// First connect. This reads authority, checks DISPLAY environment
// variable, and loads the initial Setup info.
err := conn.connect(display)
if err != nil {
return nil, err
}
conn.extensions = make(map[string]byte)
conn.cookieChan = make(chan cookie, 100)
conn.xidChan = make(chan xid, 5)
conn.seqChan = make(chan uint16, 20)
conn.reqChan = make(chan *request, 100)
conn.eventChan = make(chan eventOrError, 100)
go conn.generateXIds()
go conn.generateSeqIds()
go conn.sendRequests()
go conn.readResponses()
return conn, nil
}
// Close closes the connection to the X server.
func (c *Conn) Close() {
c.conn.Close()
}
// Id is used for all X identifiers, such as windows, pixmaps, and GCs.
type Id uint32
// Event is an interface that can contain any of the events returned by the
// server. Use a type assertion switch to extract the Event structs.
type Event interface {
ImplementsEvent()
Bytes() []byte
}
// newEventFuncs is a map from event numbers to functions that create
// the corresponding event.
var newEventFuncs = map[int]func(buf []byte) Event{}
// Error is an interface that can contain any of the errors returned by
// the server. Use a type assertion switch to extract the Error structs.
type Error interface {
ImplementsError()
SequenceId() uint16
BadId() Id
Error() string
}
// newErrorFuncs is a map from error numbers to functions that create
// the corresponding error.
var newErrorFuncs = map[int]func(buf []byte) Error{}
// eventOrError corresponds to values that can be either an event or an
// error.
type eventOrError interface{}
// NewID generates a new unused ID for use with requests like CreateWindow.
// If no new ids can be generated, the id returned is 0 and error is non-nil.
func (c *Conn) NewId() (Id, error) {
xid := <-c.xidChan
if xid.err != nil {
return 0, xid.err
}
return xid.id, nil
}
// xid encapsulates a resource identifier being sent over the Conn.xidChan
// channel. If no new resource id can be generated, id is set to 0 and a
// non-nil error is set in xid.err.
type xid struct {
id Id
err error
}
// generateXids sends new Ids down the channel for NewId to use.
// This needs to be updated to use the XC Misc extension once we run out of
// new ids.
// Thanks to libxcb/src/xcb_xid.c. This code is greatly inspired by it.
func (conn *Conn) generateXIds() {
// This requires some explanation. From the horse's mouth:
// "The resource-id-mask contains a single contiguous set of bits (at least
// 18). The client allocates resource IDs for types WINDOW, PIXMAP,
// CURSOR, FONT, GCONTEXT, and COLORMAP by choosing a value with only some
// subset of these bits set and ORing it with resource-id-base. Only values
// constructed in this way can be used to name newly created resources over
// this connection."
// So for example (using 8 bit integers), the mask might look like:
// 00111000
// So that valid values would be 00101000, 00110000, 00001000, and so on.
// Thus, the idea is to increment it by the place of the last least
// significant '1'. In this case, that value would be 00001000. To get
// that value, we can AND the original mask with its two's complement:
// 00111000 & 11001000 = 00001000.
// And we use that value to increment the last resource id to get a new one.
// (And then, of course, we OR it with resource-id-base.)
inc := conn.Setup.ResourceIdMask & -conn.Setup.ResourceIdMask
max := conn.Setup.ResourceIdMask
last := uint32(0)
for {
// TODO: Use the XC Misc extension to look for released ids.
if last > 0 && last >= max - inc + 1 {
conn.xidChan <- xid{
id: Id(0),
err: errors.New("There are no more available resource" +
"identifiers."),
}
}
last += inc
conn.xidChan <- xid{
id: Id(last | conn.Setup.ResourceIdBase),
err: nil,
}
}
}
// newSeqId fetches the next sequence id from the Conn.seqChan channel.
func (c *Conn) newSequenceId() uint16 {
return <-c.seqChan
}
// generateSeqIds returns new sequence ids.
// A sequence id is generated for *every* request. It's the identifier used
// to match up replies with requests.
// Since sequence ids can only be 16 bit integers we start over at zero when it
// comes time to wrap.
// FIXME: 65,536 requests without replies cannot be made in a single sequence.
func (c *Conn) generateSeqIds() {
seqid := uint16(1)
for {
c.seqChan <- seqid
if seqid == uint16((1 << 16) - 1) {
seqid = 0
} else {
seqid++
}
}
}
// request encapsulates a buffer of raw bytes (containing the request data)
// and a cookie, which when combined represents a single request.
// The cookie is used to match up the reply/error.
type request struct {
buf []byte
cookie cookie
}
// newRequest takes the bytes an a cookie, constructs a request type,
// and sends it over the Conn.reqChan channel. It then returns the cookie
// (for convenience).
func (c *Conn) newRequest(buf []byte, cookie cookie) {
c.reqChan <- &request{buf: buf, cookie: cookie}
}
// sendRequests is run as a single goroutine that takes requests and writes
// the bytes to the wire and adds the cookie to the cookie queue.
func (c *Conn) sendRequests() {
for req := range c.reqChan {
c.cookieChan <- req.cookie
if _, err := c.conn.Write(req.buf); err != nil {
fmt.Fprintf(os.Stderr, "x protocol write error: %s\n", err)
close(c.reqChan)
return
}
}
}
// readResponses is a goroutine that reads events, errors and
// replies off the wire.
// When an event is read, it is always added to the event channel.
// When an error is read, if it corresponds to an existing checked cookie,
// it is sent to that cookie's error channel. Otherwise it is added to the
// event channel.
// When a reply is read, it is added to the corresponding cookie's reply
// channel. (It is an error if no such cookie exists in this case.)
// Finally, cookies that came "before" this reply are always cleaned up.
func (c *Conn) readResponses() {
var (
err Error
event Event
seq uint16
replyBytes []byte
)
buf := make([]byte, 32)
for {
err, event, seq = nil, nil, 0
if _, err := io.ReadFull(c.conn, buf); err != nil {
fmt.Fprintf(os.Stderr, "x protocol read error: %s\n", err)
close(c.eventChan)
break
}
switch buf[0] {
case 0: // This is an error
// Use the constructor function for this error (that is auto
// generated) by looking it up by the error number.
err = newErrorFuncs[int(buf[1])](buf)
seq = err.SequenceId()
// This error is either sent to the event channel or a specific
// cookie's error channel below.
case 1: // This is a reply
seq = Get16(buf[2:])
// check to see if this reply has more bytes to be read
size := Get32(buf[4:])
if size > 0 {
byteCount := 32 + size * 4
biggerBuf := make([]byte, byteCount)
copy(biggerBuf[:32], buf)
if _, err := io.ReadFull(c.conn, biggerBuf[32:]); err != nil {
fmt.Fprintf(os.Stderr, "x protocol read error: %s\n", err)
close(c.eventChan)
break
}
replyBytes = biggerBuf
} else {
replyBytes = buf
}
// This reply is sent to its corresponding cookie below.
default: // This is an event
// Use the constructor function for this event (like for errors,
// and is also auto generated) by looking it up by the event number.
// Note that we AND the event number with 127 so that we ignore
// the most significant bit (which is set when it was sent from
// a SendEvent request).
event = newEventFuncs[int(buf[0] & 127)](buf)
// seq = event.SequenceId() // 0 for KeymapNotify
// Put the event into the queue.
c.eventChan <- event
// No more processing for events.
continue
// If this was a KeymapNotify event, then we don't do any more
// processing since we don't have any sequence id.
// if event != nil {
// if _, ok := event.(KeymapNotifyEvent); ok {
// continue
// }
// }
}
// At this point, we have a sequence number and we're either
// processing an error or a reply, which are both responses to
// requests. So all we have to do is find the cookie corresponding
// to this error/reply, and send the appropriate data to it.
// In doing so, we make sure that any cookies that came before it
// are marked as successful if they are void and checked.
// If there's a cookie that requires a reply that is before this
// reply, then something is wrong.
for cookie := range c.cookieChan {
// This is the cookie we're looking for. Process and break.
if cookie.Sequence == seq {
if err != nil { // this is an error to a request
// synchronous processing
if cookie.errorChan != nil {
cookie.errorChan <- err
} else { // asynchronous processing
c.eventChan <- err
}
} else { // this is a reply
if cookie.replyChan == nil {
fmt.Fprintf(os.Stderr,
"Reply with sequence id %d does not have a " +
"cookie with a valid reply channel.\n", seq)
} else {
cookie.replyChan <- replyBytes
}
}
break
}
switch {
// Checked requests with replies
case cookie.replyChan != nil && cookie.errorChan != nil:
fmt.Fprintf(os.Stderr,
"Found cookie with sequence id %d that is expecting a " +
"reply but will never get it.\n", cookie.Sequence)
// Unchecked requests with replies
case cookie.replyChan != nil && cookie.pingChan != nil:
cookie.pingChan <- true
// Checked requests without replies
case cookie.pingChan != nil && cookie.errorChan != nil:
cookie.pingChan <- true
// Unchecked requests without replies don't have any channels,
// so we can't do anything with them except let them pass by.
}
}
}
}
// processEventOrError takes an eventOrError, type switches on it,
// and returns it in Go idiomatic style.
func processEventOrError(everr eventOrError) (Event, Error) {
switch ee := everr.(type) {
case Event:
return ee, nil
case Error:
return nil, ee
default:
fmt.Fprintf(os.Stderr, "Invalid event/error type: %T\n", everr)
}
panic("unreachable")
}
// WaitForEvent returns the next event from the server.
// It will block until an event is available.
func (c *Conn) WaitForEvent() (Event, Error) {
return processEventOrError(<-c.eventChan)
}
// PollForEvent returns the next event from the server if one is available in
// the internal queue.
// It will not block.
func (c *Conn) PollForEvent() (Event, Error) {
select {
case everr := <-c.eventChan:
return processEventOrError(everr)
default:
return nil, nil
}
panic("unreachable")
}
// RegisterExtension adds the respective extension's major op code to
// the extensions map.
func (c *Conn) RegisterExtension(name string) error {
nameUpper := strings.ToUpper(name)
reply, err := c.QueryExtension(uint16(len(nameUpper)), nameUpper).Reply()
switch {
case err != nil:
return err
case !reply.Present:
return errors.New(fmt.Sprintf("No extension named '%s' is present.",
nameUpper))
}
c.extLock.Lock()
c.extensions[nameUpper] = reply.MajorOpcode
c.extLock.Unlock()
return nil
}