zorldo

xgb.go (20209B)

---

 package xgb
 
 import (
 	"errors"
 	"io"
 	"log"
 	"net"
 	"os"
 	"sync"
 )
 
 var (
 	// Where to log error-messages. Defaults to stderr.
 	// To disable logging, just set this to log.New(ioutil.Discard, "", 0)
 	Logger = log.New(os.Stderr, "XGB: ", log.Lshortfile)
 )
 
 const (
 	// cookieBuffer represents the queue size of cookies existing at any
 	// point in time. The size of the buffer is really only important when
 	// there are many requests without replies made in sequence. Once the
 	// buffer fills, a round trip request is made to clear the buffer.
 	cookieBuffer = 1000
 
 	// xidBuffer represents the queue size of the xid channel.
 	// I don't think this value matters much, since xid generation is not
 	// that expensive.
 	xidBuffer = 5
 
 	// seqBuffer represents the queue size of the sequence number channel.
 	// I don't think this value matters much, since sequence number generation
 	// is not that expensive.
 	seqBuffer = 5
 
 	// reqBuffer represents the queue size of the number of requests that
 	// can be made until new ones block. This value seems OK.
 	reqBuffer = 100
 
 	// eventBuffer represents the queue size of the number of events or errors
 	// that can be loaded off the wire and not grabbed with WaitForEvent
 	// until reading an event blocks. This value should be big enough to handle
 	// bursts of events.
 	eventBuffer = 5000
 )
 
 // A Conn represents a connection to an X server.
 type Conn struct {
 	host          string
 	conn          net.Conn
 	display       string
 	DisplayNumber int
 	DefaultScreen int
 	SetupBytes    []byte
 
 	setupResourceIdBase uint32
 	setupResourceIdMask uint32
 
 	eventChan  chan eventOrError
 	cookieChan chan *Cookie
 	xidChan    chan xid
 	seqChan    chan uint16
 	reqChan    chan *request
 	doneSend   chan struct{}
 	doneRead   chan struct{}
 
 	// ExtLock is a lock used whenever new extensions are initialized.
 	// It should not be used. It is exported for use in the extension
 	// sub-packages.
 	ExtLock sync.RWMutex
 
 	// Extensions is a map from extension name to major opcode. It should
 	// not be used. It is exported for use in the extension sub-packages.
 	Extensions map[string]byte
 }
 
 // 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.)
 // It is up to user to close connection with Close() method to finish all unfinished requests and clean up spawned goroutines.
 // If the connection unexpectedly closes itself and WaitForEvent() returns "nil, nil", everything is cleaned by that moment, but nothing bad happens if you call Close() after.
 func NewConn() (*Conn, error) {
 	return NewConnDisplay("")
 }
 
 // NewConnDisplay is just like NewConn (see closing instructions), 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-12/:0") -> net.Dial("unix", "", "/tmp/launch-12/: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) {
 	c := &Conn{}
 
 	// First connect. This reads authority, checks DISPLAY environment
 	// variable, and loads the initial Setup info.
 	err := c.connect(display)
 	if err != nil {
 		return nil, err
 	}
 
 	return postNewConn(c)
 }
 
 // NewConnNet is just like NewConn (see closing instructions), but allows a specific net.Conn
 // to be used.
 func NewConnNet(netConn net.Conn) (*Conn, error) {
 	c := &Conn{}
 
 	// First connect. This reads authority, checks DISPLAY environment
 	// variable, and loads the initial Setup info.
 	err := c.connectNet(netConn)
 
 	if err != nil {
 		return nil, err
 	}
 
 	return postNewConn(c)
 }
 
 func postNewConn(c *Conn) (*Conn, error) {
 	c.Extensions = make(map[string]byte)
 
 	c.cookieChan = make(chan *Cookie, cookieBuffer)
 	c.xidChan = make(chan xid, xidBuffer)
 	c.seqChan = make(chan uint16, seqBuffer)
 	c.reqChan = make(chan *request, reqBuffer)
 	c.eventChan = make(chan eventOrError, eventBuffer)
 	c.doneSend = make(chan struct{})
 	c.doneRead = make(chan struct{})
 
 	go c.generateXIds()
 	go c.generateSeqIds()
 	go c.sendRequests()
 	go c.readResponses()
 
 	return c, nil
 }
 
 // Close gracefully closes the connection to the X server.
 // When everything is cleaned up, the WaitForEvent method will return (nil, nil)
 func (c *Conn) Close() {
 	select {
 	case c.reqChan <- nil:
 	case <-c.doneSend:
 	}
 }
 
 // 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 {
 	Bytes() []byte
 	String() string
 }
 
 // NewEventFun is the type of function use to construct events from raw bytes.
 // It should not be used. It is exported for use in the extension sub-packages.
 type NewEventFun func(buf []byte) Event
 
 // NewEventFuncs is a map from event numbers to functions that create
 // the corresponding event. It should not be used. It is exported for use
 // in the extension sub-packages.
 var NewEventFuncs = make(map[int]NewEventFun)
 
 // NewExtEventFuncs is a temporary map that stores event constructor functions
 // for each extension. When an extension is initialized, each event for that
 // extension is added to the 'NewEventFuncs' map. It should not be used. It is
 // exported for use in the extension sub-packages.
 var NewExtEventFuncs = make(map[string]map[int]NewEventFun)
 
 // 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 {
 	SequenceId() uint16
 	BadId() uint32
 	Error() string
 }
 
 // NewErrorFun is the type of function use to construct errors from raw bytes.
 // It should not be used. It is exported for use in the extension sub-packages.
 type NewErrorFun func(buf []byte) Error
 
 // NewErrorFuncs is a map from error numbers to functions that create
 // the corresponding error. It should not be used. It is exported for use in
 // the extension sub-packages.
 var NewErrorFuncs = make(map[int]NewErrorFun)
 
 // NewExtErrorFuncs is a temporary map that stores error constructor functions
 // for each extension. When an extension is initialized, each error for that
 // extension is added to the 'NewErrorFuncs' map. It should not be used. It is
 // exported for use in the extension sub-packages.
 var NewExtErrorFuncs = make(map[string]map[int]NewErrorFun)
 
 // 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.
 // This shouldn't be used directly, and is exported for use in the extension
 // sub-packages.
 // If you need identifiers, use the appropriate constructor.
 // e.g., For a window id, use xproto.NewWindowId. For
 // a new pixmap id, use xproto.NewPixmapId. And so on.
 // Returns (0, io.EOF) when the connection is closed.
 func (c *Conn) NewId() (uint32, error) {
 	xid, ok := <-c.xidChan
 	if !ok {
 		return 0, io.EOF
 	}
 	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  uint32
 	err error
 }
 
 // generateXids sends new Ids down the channel for NewId to use.
 // generateXids should be run in its own goroutine.
 // 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 (c *Conn) generateXIds() {
 	defer close(c.xidChan)
 
 	// 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 := c.setupResourceIdMask & -c.setupResourceIdMask
 	max := c.setupResourceIdMask
 	last := uint32(0)
 	for {
 		id := xid{}
 		if last > 0 && last >= max-inc+1 {
 			// TODO: Use the XC Misc extension to look for released ids.
 			id = xid{
 				id:  0,
 				err: errors.New("There are no more available resource identifiers."),
 			}
 		} else {
 			last += inc
 			id = xid{
 				id:  last | c.setupResourceIdBase,
 				err: nil,
 			}
 		}
 
 		select {
 		case c.xidChan <- id:
 		case <-c.doneSend:
 			// c.sendRequests is down and since this id is used by requests, we don't need this goroutine running anymore.
 			return
 		}
 	}
 }
 
 // newSeqId fetches the next sequence id from the Conn.seqChan channel.
 func (c *Conn) newSequenceId() uint16 {
 	return <-c.seqChan
 }
 
 // generateSeqIds returns new sequence ids. It is meant to be run in its
 // own goroutine.
 // 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.
 // N.B. As long as the cookie buffer is less than 2^16, there are no limitations
 // on the number (or kind) of requests made in sequence.
 func (c *Conn) generateSeqIds() {
 	defer close(c.seqChan)
 
 	seqid := uint16(1)
 	for {
 		select {
 		case c.seqChan <- seqid:
 			if seqid == uint16((1<<16)-1) {
 				seqid = 0
 			} else {
 				seqid++
 			}
 		case <-c.doneSend:
 			// c.sendRequests is down and since only that function uses sequence ids (via newSequenceId method), we don't need this goroutine running anymore.
 			return
 		}
 	}
 }
 
 // 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
 
 	// seq is closed when the request (cookie) has been sequenced by the Conn.
 	seq chan struct{}
 }
 
 // NewRequest takes the bytes and a cookie of a particular request, constructs
 // a request type, and sends it over the Conn.reqChan channel.
 // Note that the sequence number is added to the cookie after it is sent
 // over the request channel, but before it is sent to X.
 //
 // Note that you may safely use NewRequest to send arbitrary byte requests
 // to X. The resulting cookie can be used just like any normal cookie and
 // abides by the same rules, except that for replies, you'll get back the
 // raw byte data. This may be useful for performance critical sections where
 // every allocation counts, since all X requests in XGB allocate a new byte
 // slice. In contrast, NewRequest allocates one small request struct and
 // nothing else. (Except when the cookie buffer is full and has to be flushed.)
 //
 // If you're using NewRequest manually, you'll need to use NewCookie to create
 // a new cookie.
 //
 // In all likelihood, you should be able to copy and paste with some minor
 // edits the generated code for the request you want to issue.
 func (c *Conn) NewRequest(buf []byte, cookie *Cookie) {
 	seq := make(chan struct{})
 	select {
 	case c.reqChan <- &request{buf: buf, cookie: cookie, seq: seq}:
 		// request is in buffer
 		// wait until request is processed or connection is closed
 		select {
 		case <-seq:
 			// request was successfully sent to X server
 		case <-c.doneSend:
 			// c.sendRequests is down, your request was not handled
 		}
 	case <-c.doneSend:
 		// c.sendRequests is down, nobody is listening to your requests
 	}
 }
 
 // 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.
 // It is meant to be run as its own goroutine.
 func (c *Conn) sendRequests() {
 	defer close(c.cookieChan)
 	defer c.conn.Close()
 	defer close(c.doneSend)
 
 	for {
 		select {
 		case req := <-c.reqChan:
 			if req == nil {
 				// a request by c.Close() to gracefully exit
 				// Flush the response reading goroutine.
 				if err := c.noop(); err != nil {
 					c.conn.Close()
 					<-c.doneRead
 				}
 				return
 			}
 			// ho there! if the cookie channel is nearly full, force a round
 			// trip to clear out the cookie buffer.
 			// Note that we circumvent the request channel, because we're *in*
 			// the request channel.
 			if len(c.cookieChan) == cookieBuffer-1 {
 				if err := c.noop(); err != nil {
 					// Shut everything down.
 					c.conn.Close()
 					<-c.doneRead
 					return
 				}
 			}
 			req.cookie.Sequence = c.newSequenceId()
 			c.cookieChan <- req.cookie
 			if err := c.writeBuffer(req.buf); err != nil {
 				c.conn.Close()
 				<-c.doneRead
 				return
 			}
 			close(req.seq)
 		case <-c.doneRead:
 			return
 		}
 	}
 }
 
 // noop circumvents the usual request sending goroutines and forces a round
 // trip request manually.
 func (c *Conn) noop() error {
 	cookie := c.NewCookie(true, true)
 	cookie.Sequence = c.newSequenceId()
 	c.cookieChan <- cookie
 	if err := c.writeBuffer(c.getInputFocusRequest()); err != nil {
 		return err
 	}
 	cookie.Reply() // wait for the buffer to clear
 	return nil
 }
 
 // writeBuffer is a convenience function for writing a byte slice to the wire.
 func (c *Conn) writeBuffer(buf []byte) error {
 	if _, err := c.conn.Write(buf); err != nil {
 		Logger.Printf("A write error is unrecoverable: %s", err)
 		return err
 	}
 	return nil
 }
 
 // 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() {
 	defer close(c.eventChan)
 	defer c.conn.Close()
 	defer close(c.doneRead)
 
 	var (
 		err        Error
 		seq        uint16
 		replyBytes []byte
 	)
 
 	for {
 		buf := make([]byte, 32)
 		err, seq = nil, 0
 		if _, err := io.ReadFull(c.conn, buf); err != nil {
 			select {
 			case <-c.doneSend:
 				// gracefully closing
 				return
 			default:
 			}
 			Logger.Printf("A read error is unrecoverable: %s", err)
 			c.eventChan <- err
 			return
 		}
 		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.
 			newErrFun, ok := NewErrorFuncs[int(buf[1])]
 			if !ok {
 				Logger.Printf("BUG: Could not find error constructor function "+
 					"for error with number %d.", buf[1])
 				continue
 			}
 			err = newErrFun(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 {
 					Logger.Printf("A read error is unrecoverable: %s", err)
 					c.eventChan <- err
 					return
 				}
 				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).
 			evNum := int(buf[0] & 127)
 			newEventFun, ok := NewEventFuncs[evNum]
 			if !ok {
 				Logger.Printf("BUG: Could not find event construct function "+
 					"for event with number %d.", evNum)
 				continue
 			}
 			c.eventChan <- newEventFun(buf)
 			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
 						// if this is an unchecked reply, ping the cookie too
 						if cookie.pingChan != nil {
 							cookie.pingChan <- true
 						}
 					}
 				} else { // this is a reply
 					if cookie.replyChan == nil {
 						Logger.Printf("Reply with sequence id %d does not "+
 							"have a cookie with a valid reply channel.", seq)
 						continue
 					} else {
 						cookie.replyChan <- replyBytes
 					}
 				}
 				break
 			}
 
 			switch {
 			// Checked requests with replies
 			case cookie.replyChan != nil && cookie.errorChan != nil:
 				Logger.Printf("Found cookie with sequence id %d that is "+
 					"expecting a reply but will never get it. Currently "+
 					"on sequence number %d", cookie.Sequence, seq)
 			// Unchecked requests with replies
 			case cookie.replyChan != nil && cookie.pingChan != nil:
 				Logger.Printf("Found cookie with sequence id %d that is "+
 					"expecting a reply (and not an error) but will never "+
 					"get it. Currently on sequence number %d",
 					cookie.Sequence, seq)
 			// 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
 	case error:
 		// c.conn read error
 	case nil:
 		// c.eventChan is closed
 	default:
 		Logger.Printf("Invalid event/error type: %T", everr)
 	}
 	return nil, nil
 }
 
 // WaitForEvent returns the next event from the server.
 // It will block until an event is available.
 // WaitForEvent returns either an Event or an Error. (Returning both
 // is a bug.) Note than an Error here is an X error and not an XGB error. That
 // is, X errors are sometimes completely expected (and you may want to ignore
 // them in some cases).
 //
 // If both the event and error are nil, then the connection has been closed.
 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 without blocking. Note that unlike WaitForEvent, both
 // Event and Error could be nil. Indeed, they are both nil when the event queue
 // is empty.
 func (c *Conn) PollForEvent() (Event, Error) {
 	select {
 	case everr := <-c.eventChan:
 		return processEventOrError(everr)
 	default:
 		return nil, nil
 	}
 }