internal/pipewire: respond to Core::Ping

There is currently no known message that will get the PipeWire server to emit this event. It should be handled regardless.

Signed-off-by: Ophestra <cat@gensokyo.uk>

internal/pipewire/core.go

@@ -6,6 +6,7 @@ import (
 	"maps"
 	"slices"
 	"strconv"
+	"syscall"
 	"time"
 )
 
@@ -615,6 +616,14 @@ func (e *UnknownBoundIdError[E]) Error() string {
 	return "unknown bound proxy id " + strconv.Itoa(int(e.Id))
 }
 
+// An InvalidPingError is a [CorePing] event targeting a proxy id that was never allocated.
+type InvalidPingError CorePing
+
+func (e *InvalidPingError) Error() string {
+	return "received Core::Ping seq " + strconv.Itoa(int(e.Sequence)) +
+		" targeting unknown proxy id " + strconv.Itoa(int(e.ID))
+}
+
 func (core *Core) consume(opcode byte, files []int, unmarshal func(v any)) error {
 	closeReceivedFiles(files...)
 	switch opcode {
@@ -637,6 +646,23 @@ func (core *Core) consume(opcode byte, files []int, unmarshal func(v any)) error
 		// anything, and this behaviour is never mentioned in documentation
 		return nil
 
+	case PW_CORE_EVENT_PING:
+		var ping CorePing
+		unmarshal(&ping)
+		if _, ok := core.ctx.proxy[ping.ID]; ok {
+			core.ctx.mustWriteMessage(PW_ID_CORE, (*CorePong)(&ping))
+			return nil
+		} else {
+			invalidPingError := InvalidPingError(ping)
+			core.ctx.mustWriteMessage(PW_ID_CORE, &CoreErrorMethod{CoreError{
+				ID:       PW_ID_CORE,
+				Sequence: core.ctx.currentRemoteSeq(),
+				Result:   -Int(syscall.EINVAL),
+				Message:  invalidPingError.Error(),
+			}})
+			return &invalidPingError
+		}
+
 	case PW_CORE_EVENT_ERROR:
 		var coreError CoreError
 		unmarshal(&coreError)

internal/pipewire/pipewire.go

@@ -218,6 +218,14 @@ func (ctx *Context) writeMessage(Id Int, v Message) (err error) {
 	return
 }
 
+// mustWriteMessage calls writeMessage and panics if a non-nil error is returned.
+// This must only be called from eventProxy.consume.
+func (ctx *Context) mustWriteMessage(Id Int, v Message) {
+	if err := ctx.writeMessage(Id, v); err != nil {
+		panic(err)
+	}
+}
+
 // newProxyId returns a newly allocated proxy Id for the specified type.
 func (ctx *Context) newProxyId(proxy eventProxy, ack bool) Int {
 	newId := ctx.nextId
@@ -620,6 +628,10 @@ func (ctx *Context) roundtrip() (err error) {
 	}
 }
 
+// currentRemoteSeq returns the current remote sequence number.
+// This must only be called from eventProxy.consume.
+func (ctx *Context) currentRemoteSeq() Int { return ctx.remoteSequence - 1 }
+
 // consume receives messages from the server and processes events.
 func (ctx *Context) consume(receiveRemaining []byte) (remaining []byte, err error) {
 	defer func() {

internal/pipewire/pipewire_test.go

@@ -845,6 +845,7 @@ func TestContextErrors(t *testing.T) {
 		{"RoundtripUnexpectedEOFError ErrRoundtripEOFFooter", pipewire.ErrRoundtripEOFFooter, "unexpected EOF establishing message footer bounds"},
 		{"RoundtripUnexpectedEOFError ErrRoundtripEOFFooterOpcode", pipewire.ErrRoundtripEOFFooterOpcode, "unexpected EOF decoding message footer opcode"},
 		{"RoundtripUnexpectedEOFError invalid", pipewire.RoundtripUnexpectedEOFError(0xbad), "unexpected EOF"},
+		{"InconsistentFilesError", &pipewire.InconsistentFilesError{0, 2}, "queued 0 files instead of the expected 2"},
 
 		{"UnsupportedOpcodeError", &pipewire.UnsupportedOpcodeError{
 			Opcode:    0xff,
@@ -855,6 +856,11 @@ func TestContextErrors(t *testing.T) {
 			Id:   -1,
 			Data: "\x00",
 		}, "unknown proxy id -1"},
+
+		{"InvalidPingError", &pipewire.InvalidPingError{
+			ID:       0xbad,
+			Sequence: 0xcafe,
+		}, "received Core::Ping seq 51966 targeting unknown proxy id 2989"},
 	}
 	for _, tc := range testCases {
 		t.Run(tc.name, func(t *testing.T) {