internal/pipewire: specify opcode and file count with message

This adds checking of FileCount while writing a message. Message encoding is relocated to an exported method to be used externally, probably for test stubbing.

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

internal/pipewire/client.go

@@ -46,6 +46,12 @@ type ClientInfo struct {
 	Properties *SPADict `json:"props"`
 }
 
+// Opcode satisfies [Message] with a constant value.
+func (c *ClientInfo) Opcode() byte { return PW_CLIENT_EVENT_INFO }
+
+// FileCount satisfies [Message] with a constant value.
+func (c *ClientInfo) FileCount() Int { return 0 }
+
 // Size satisfies [KnownSize] with a value computed at runtime.
 func (c *ClientInfo) Size() Word {
 	return SizePrefix +
@@ -66,6 +72,12 @@ type ClientUpdateProperties struct {
 	Properties *SPADict `json:"props"`
 }
 
+// Opcode satisfies [Message] with a constant value.
+func (c *ClientUpdateProperties) Opcode() byte { return PW_CLIENT_METHOD_UPDATE_PROPERTIES }
+
+// FileCount satisfies [Message] with a constant value.
+func (c *ClientUpdateProperties) FileCount() Int { return 0 }
+
 // Size satisfies [KnownSize] with a value computed at runtime.
 func (c *ClientUpdateProperties) Size() Word { return SizePrefix + c.Properties.Size() }
 
@@ -80,7 +92,6 @@ func (c *ClientUpdateProperties) UnmarshalBinary(data []byte) error { return Unm
 func (ctx *Context) clientUpdateProperties(props SPADict) error {
 	return ctx.writeMessage(
 		PW_ID_CLIENT,
-		PW_CLIENT_METHOD_UPDATE_PROPERTIES,
 		&ClientUpdateProperties{&props},
 	)
 }