ipc: negotiate preedit capability and caret messages

ipc.h

@@ -2,7 +2,7 @@
 #include <stdint.h>
 
 /*
- * Request: [flags, modifiers, key byte 0, ..., key byte 3].
+ * Legacy request: [flags, modifiers, key byte 0, ..., key byte 3].
  * Flags request preedit and distinguish lifecycle reset from physical Escape.
  * The server identifies the connection as the engine owner; that identity is
  * not sent on the wire.
@@ -11,12 +11,20 @@
  * followed, when requested, by
  * [preedit-length-low, preedit-length-high, preedit...].
  * Lengths are little-endian byte counts; fields are at most Ipcfieldmax bytes.
+ *
+ * Capability control is six bytes: [0x80|want, version, 0, 0, 0, 0].
+ * Caret control is sixteen bytes: [0x80, version, 1, valid, x, y, h],
+ * with the signed coordinates and height encoded as little-endian 32-bit words.
  */
 
 enum
 {
 	Ipcreqwant = 1<<0,
 	Ipcreqreset = 1<<1,
+	Ipcext = 1<<7,
+	Ipcversion = 1,
+	Ipcopcap = 0,
+	Ipcopcaret = 1,
 
 	Kspec = 0x110000,
 	Kback = Kspec|0x08,
@@ -35,12 +43,21 @@ enum
 	Mmask = Mshift|Mctrl|Malt|Msuper,
 
 	Ipcreqsz = 6,
+	Ipccaretsz = 16,
 	Ipclensz = 2,
 	Ipcresphdrsz = 1 + Ipclensz,
 	Ipcfieldmax = 256,
 	Ipcmaxresp = Ipcresphdrsz + Ipcfieldmax + Ipclensz + Ipcfieldmax,
 };
 
+enum
+{
+	Ipcunknown = -1,
+	Ipclegacy,
+	Ipccap,
+	Ipccaret,
+};
+
 typedef struct Ipcresp Ipcresp;
 struct Ipcresp
 {
@@ -51,7 +68,11 @@ struct Ipcresp
 
 void	ipcpackreq(unsigned char[Ipcreqsz], int, uint32_t, uint32_t);
 void	ipcpackreset(unsigned char[Ipcreqsz], int);
+void	ipcpackcap(unsigned char[Ipcreqsz], int);
+int	ipcpackcaret(unsigned char[Ipccaretsz], int, int32_t, int32_t, int32_t);
 void	ipcunpackreq(const unsigned char[Ipcreqsz], int*, uint32_t*, uint32_t*);
+int	ipcunpackcaret(const unsigned char[Ipccaretsz], int*, int32_t*, int32_t*, int32_t*);
+int	ipcreqtype(const unsigned char[Ipcreqsz]);
 int	ipcreqreset(const unsigned char[Ipcreqsz]);
 int	ipcpackresp(unsigned char*, size_t, int, const char*, size_t, const char*, size_t, int);
 int	ipcreadn(int, void*, size_t);