hpcu: add a selection unifier

So far not supporting large selections.

README

@@ -173,6 +173,22 @@ The result of testing hid with telnet, OpenSSL s_client, OpenBSD nc, GNU nc and
 Ncat is that neither of them can properly shutdown the connection.  We need
 a good implementation with TLS support.
 
+hpcu -- PRIMARY-CLIPBOARD unifier
+~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
+An improved replacement for autocutsel in selection synchronization "mode":
+
+ - using only one OS process;
+ - not polling selections twice a second unnecessarily;
+ - calling SetSelectionOwner on change even when it already owns the selection,
+   so that XFIXES SelectionNotify events are delivered;
+ - not using cut buffers for anything.
+
+Only UTF8_STRING-convertible selections are synchronized.
+
+ht -- terminal emulator
+~~~~~~~~~~~~~~~~~~~~~~~
+Similar scope to st(1).  Clever display of internal padding for better looks.
+
 hib and hic -- IRC bouncer and client
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
 An IRC client is a good starting application for building a GUI toolkit, as the
@@ -241,6 +257,7 @@ most basic features includes a VFS for archives.  The editing widget in read-
 -only mode could be used for F3.  The shell is going to work very simply,
 creating a PTY device and running things under TERM=dumb while decoding SGR,
 or one could decide to run a new terminal emulator with a different shortcut.
+ht could probably also be integrated.
 
 Eventually the number of panels should be arbitrary with proper shortcuts for
 working with them.  We might also integrate a special view for picture previews,
@@ -255,10 +272,6 @@ Indexing and search may be based on a common database, no need to get all fancy:
 http://rachbelaid.com/postgres-full-text-search-is-good-enough/
 https://www.sqlite.org/fts3.html#full_text_index_queries (FTS4 seems better)
 
-ht -- terminal emulator
-~~~~~~~~~~~~~~~~~~~~~~~
-Similar scope to st(1).  Clever display of internal padding for better looks.
-
 The rest
 ~~~~~~~~
 Currently there are no significant, specific plans about the other applications.

hpcu/main.go

@@ -0,0 +1,351 @@
+// hpcu unifies the PRIMARY and CLIPBOARD X11 selections for text contents.
+package main
+
+import (
+	"errors"
+	"janouch.name/haven/nexgb"
+	"janouch.name/haven/nexgb/xfixes"
+	"janouch.name/haven/nexgb/xproto"
+	"log"
+)
+
+type selectionState struct {
+	name       string           // name of the selection
+	inProgress xproto.Timestamp // timestamp of retrieved selection
+	buffer     []byte           // UTF-8 text buffer
+	incr       bool             // INCR running
+	incrFailed bool             // INCR failure indicator
+	owning     xproto.Timestamp // since when we own the selection
+}
+
+var (
+	X      *nexgb.Conn
+	setup  *xproto.SetupInfo
+	screen *xproto.ScreenInfo
+
+	atomCLIPBOARD  xproto.Atom // X11 atom for CLIPBOARD
+	atomUTF8String xproto.Atom // X11 atom for UTF8_STRING
+	atomINCR       xproto.Atom // X11 atom for INCR
+	atomTARGETS    xproto.Atom // X11 atom for TARGETS
+	atomTIMESTAMP  xproto.Atom // X11 atom for TIMESTAMP
+
+	wid        xproto.Window // auxiliary window
+	selections map[xproto.Atom]*selectionState
+	contents   string // current shared selection contents
+)
+
+// resolveAtoms resolves a few required atoms that are not in the core protocol.
+func resolveAtoms() error {
+	for _, i := range []struct {
+		placement *xproto.Atom
+		name      string
+	}{
+		{&atomCLIPBOARD, "CLIPBOARD"},
+		{&atomUTF8String, "UTF8_STRING"},
+		{&atomINCR, "INCR"},
+		{&atomTARGETS, "TARGETS"},
+		{&atomTIMESTAMP, "TIMESTAMP"},
+	} {
+		if reply, err := xproto.InternAtom(X,
+			false, uint16(len(i.name)), i.name).Reply(); err != nil {
+			return err
+		} else {
+			*i.placement = reply.Atom
+		}
+	}
+	return nil
+}
+
+// setupAuxiliaryWindow creates a window that receives notifications about
+// changed selection contents, and serves
+func setupAuxiliaryWindow() error {
+	var err error
+	if wid, err = xproto.NewWindowId(X); err != nil {
+		return err
+	}
+
+	_ = xproto.CreateWindow(X, screen.RootDepth, wid, screen.Root, 0, 0, 1, 1,
+		0, xproto.WindowClassInputOutput, screen.RootVisual, xproto.CwEventMask,
+		[]uint32{xproto.EventMaskPropertyChange})
+
+	for _, selection := range []xproto.Atom{xproto.AtomPrimary, atomCLIPBOARD} {
+		_ = xfixes.SelectSelectionInput(X, wid, selection,
+			xfixes.SelectionEventMaskSetSelectionOwner|
+				xfixes.SelectionEventMaskSelectionWindowDestroy|
+				xfixes.SelectionEventMaskSelectionClientClose)
+	}
+	return nil
+}
+
+// getProperty reads a window property in a memory-efficient manner.
+func getProperty(window xproto.Window, property xproto.Atom) (
+	*xproto.GetPropertyReply, error) {
+	// xorg-xserver doesn't seem to limit the length of replies or even
+	// the length of properties in the first place. It only has a huge
+	// (0xffffffff - sizeof(xChangePropertyReq))/4 limit for ChangeProperty
+	// requests, even though I can't XChangeProperty more than 0xffffe0
+	// bytes at a time.
+	//
+	// Since the XGB API doesn't let us provide our own buffer for
+	// value data, let us avoid multiplying the amount of consumed memory in
+	// pathological cases where properties are several gigabytes in size by
+	// chunking the requests. This has a cost of losing atomicity, although
+	// it shouldn't pose a problem except for timeout-caused INCR races.
+	var result xproto.GetPropertyReply
+	for result.Length == 0 || result.BytesAfter > 0 {
+		reply, err := xproto.GetProperty(X, false, /* delete */
+			window, property, xproto.GetPropertyTypeAny,
+			uint32(len(result.Value))/4,
+			uint32(setup.MaximumRequestLength)).Reply()
+		if err != nil {
+			return nil, err
+		}
+		if result.Length != 0 &&
+			(reply.Format != result.Format || reply.Type != result.Type) {
+			return nil, errors.New("property type changed during read")
+		}
+
+		reply.Value = append(result.Value, reply.Value...)
+		reply.ValueLen += result.ValueLen
+		result = *reply
+	}
+	return &result, nil
+}
+
+// appendText tries to append UTF-8 text to the selection state buffer.
+func appendText(state *selectionState, prop *xproto.GetPropertyReply) bool {
+	if prop.Type == atomUTF8String && prop.Format == 8 {
+		state.buffer = append(state.buffer, prop.Value...)
+		return true
+	}
+	return false
+}
+
+func requestOwnership(origin *selectionState, time xproto.Timestamp) {
+	contents = string(origin.buffer)
+	for selection, state := range selections {
+		// We might want to replace the originator as well but it might have
+		// undesirable effects, mainly with PRIMARY.
+		if state != origin {
+			// No need to GetSelectionOwner, XFIXES is more reliable.
+			_ = xproto.SetSelectionOwner(X, wid, selection, time)
+		}
+	}
+}
+
+func handleEvent(ev nexgb.Event) {
+	switch e := ev.(type) {
+	case xfixes.SelectionNotifyEvent:
+		state, ok := selections[e.Selection]
+		if !ok {
+			break
+		}
+
+		// Ownership request has been granted, don't ask ourselves for data.
+		if e.Owner == wid {
+			state.owning = e.SelectionTimestamp
+			break
+		}
+
+		// This should always be true.
+		if state.owning < e.SelectionTimestamp {
+			state.owning = 0
+		}
+
+		// Not checking whether we should give up when our current retrieval
+		// attempt is interrupted--the timeout mostly solves this.
+		if e.Owner == xproto.WindowNone {
+			break
+		}
+
+		// Don't try to process two things at once. Each request gets a few
+		// seconds to finish, then we move on, hoping that a property race
+		// doesn't commence. Ideally we'd set up a separate queue for these
+		// skipped requests and process them later.
+		if state.inProgress != 0 && e.Timestamp-state.inProgress < 5000 {
+			break
+		}
+
+		// ICCCM says we should ensure the named property doesn't exist.
+		_ = xproto.DeleteProperty(X, e.Window, e.Selection)
+
+		_ = xproto.ConvertSelection(X, e.Window, e.Selection,
+			atomUTF8String, e.Selection, e.Timestamp)
+
+		state.inProgress = e.Timestamp
+		state.incr = false
+
+	case xproto.SelectionNotifyEvent:
+		state, ok := selections[e.Selection]
+		if e.Requestor != wid || !ok || e.Time != state.inProgress {
+			break
+		}
+
+		state.inProgress = 0
+		if e.Property == xproto.AtomNone {
+			break
+		}
+
+		state.buffer = nil
+		reply, err := getProperty(e.Requestor, e.Property)
+		if err != nil {
+			break
+		}
+
+		// When you select a lot of text in VIM, it starts the ICCCM
+		// INCR mechanism, from which there is no opt-out.
+		if reply.Type == atomINCR {
+			state.inProgress = e.Time
+			state.incr = true
+			state.incrFailed = false
+		} else if appendText(state, reply) {
+			requestOwnership(state, e.Time)
+		}
+
+		_ = xproto.DeleteProperty(X, e.Requestor, e.Property)
+
+	case xproto.PropertyNotifyEvent:
+		state, ok := selections[e.Atom]
+		if e.Window != wid || e.State != xproto.PropertyNewValue ||
+			!ok || !state.incr {
+			break
+		}
+
+		reply, err := getProperty(e.Window, e.Atom)
+		if err != nil {
+			state.incrFailed = true
+			break
+		}
+
+		if !appendText(state, reply) {
+			// We need to keep deleting the property.
+			state.incrFailed = true
+		}
+
+		if reply.ValueLen == 0 {
+			if !state.incrFailed {
+				requestOwnership(state, e.Time)
+			}
+			state.inProgress = 0
+			state.incr = false
+		}
+
+		_ = xproto.DeleteProperty(X, e.Window, e.Atom)
+
+	case xproto.SelectionRequestEvent:
+		property := e.Property
+		if property == xproto.AtomNone {
+			property = e.Target
+		}
+
+		state, ok := selections[e.Selection]
+		if e.Owner != wid || !ok {
+			break
+		}
+
+		var (
+			typ    xproto.Atom
+			format byte
+			data   []byte
+		)
+
+		// XXX: We should also support the MULTIPLE target but it seems to be
+		// unimportant and largely abandoned today.
+		targets := []xproto.Atom{atomTARGETS, atomTIMESTAMP, atomUTF8String}
+
+		switch e.Target {
+		case atomTARGETS:
+			typ = xproto.AtomAtom
+			format = 32
+
+			data = make([]byte, len(targets)*4)
+			for i, atom := range targets {
+				nexgb.Put32(data[i*4:], uint32(atom))
+			}
+
+		case atomTIMESTAMP:
+			typ = xproto.AtomInteger
+			format = 32
+
+			data = make([]byte, 4)
+			nexgb.Put32(data, uint32(state.owning))
+
+		case atomUTF8String:
+			typ = atomUTF8String
+			format = 8
+
+			data = []byte(contents)
+		}
+
+		response := xproto.SelectionNotifyEvent{
+			Time:      e.Time,
+			Requestor: e.Requestor,
+			Selection: e.Selection,
+			Target:    e.Target,
+			Property:  xproto.AtomNone,
+		}
+
+		if typ == 0 || len(data) > int(setup.MaximumRequestLength)*4-64 ||
+			state.owning == 0 || e.Time < state.owning {
+			// TODO: Use the INCR mechanism for large data transfers instead
+			// of refusing the request, or at least use PropModeAppend.
+			//
+			// According to the ICCCM we need to set up a queue for concurrent
+			// (requestor, selection, target, timestamp) requests that differ
+			// only in the target property, and process them in order. The ICCCM
+			// has a nice rationale. It seems to only concern INCR. The queue
+			// might be a map[(who, what, how, when)][](where, data, offset).
+			//
+			// NOTE: Even with BigRequests support, it may technically be
+			// missing on the particular X server, and XGB copies buffers to yet
+			// another buffer, making very large transfers a very bad idea.
+		} else if xproto.ChangePropertyChecked(X, xproto.PropModeReplace,
+			e.Requestor, property, typ, format,
+			uint32(len(data)/int(format/8)), data).Check() == nil {
+			response.Property = property
+		}
+
+		_ = xproto.SendEvent(X, false /* propagate */, e.Requestor,
+			0 /* event mask */, string(response.Bytes()))
+	}
+}
+
+func main() {
+	var err error
+	if X, err = nexgb.NewConn(); err != nil {
+		log.Fatalln(err)
+	}
+	if err = xfixes.Init(X); err != nil {
+		log.Fatalln(err)
+	}
+
+	// Enable the extension.
+	_ = xfixes.QueryVersion(X, xfixes.MajorVersion, xfixes.MinorVersion)
+
+	setup = xproto.Setup(X)
+	screen = setup.DefaultScreen(X)
+
+	if err = resolveAtoms(); err != nil {
+		log.Fatalln(err)
+	}
+	if err = setupAuxiliaryWindow(); err != nil {
+		log.Fatalln(err)
+	}
+
+	// Now that we have our atoms, we can initialize state.
+	selections = map[xproto.Atom]*selectionState{
+		xproto.AtomPrimary: {name: "PRIMARY"},
+		atomCLIPBOARD:      {name: "CLIPBOARD"},
+	}
+
+	for {
+		ev, xerr := X.WaitForEvent()
+		if xerr != nil {
+			log.Printf("Error: %s\n", xerr)
+			return
+		}
+		if ev != nil {
+			handleEvent(ev)
+		}
+	}
+}