harden ipc and frontend recovery

ipc.h

@@ -1,9 +1,21 @@
-// req: 4 bytes [type, mod, key lo, key hi]
-// resp: 2+n bytes [type, n, ...]
+#ifndef STRANS_IPC_H
+#define STRANS_IPC_H
+
+#include <stddef.h>
+
+#define IPCPATH "/tmp/strans.2.%d"
+
+/*
+ * Request: [want-preedit, modifiers, key byte 0, ..., key byte 3].
+ * Response: [eaten, commit-length-low, commit-length-high, commit...],
+ * followed, when requested, by
+ * [preedit-length-low, preedit-length-high, preedit...].
+ * Lengths are little-endian byte counts; fields are at most Ipcfieldmax bytes.
+ */
 
 enum
 {
-	Kspec = 0xf000,
+	Kspec = 0x110000,
 	Kback = Kspec|0x08,
 	Ktab = Kspec|0x09,
 	Kret = Kspec|0x0d,
@@ -17,4 +29,27 @@ enum
 	Mctrl = 1<<2,
 	Malt = 1<<3,
 	Msuper = 1<<6,
+
+	Ipcreqsz = 6,
+	Ipclensz = 2,
+	Ipcresphdrsz = 1 + Ipclensz,
+	Ipcfieldmax = 256,
+	Ipcmaxresp = Ipcresphdrsz + Ipcfieldmax + Ipclensz + Ipcfieldmax,
 };
+
+typedef struct Ipcresp Ipcresp;
+struct Ipcresp
+{
+	int	eaten;
+	size_t	ncommit;
+	size_t	npreedit;
+};
+
+void	ipcpackreq(unsigned char[Ipcreqsz], int, unsigned int, unsigned int);
+void	ipcunpackreq(const unsigned char[Ipcreqsz], int*, unsigned int*, unsigned int*);
+int	ipcpackresp(unsigned char*, size_t, int, const char*, size_t, const char*, size_t, int);
+int	ipcreadn(int, void*, size_t);
+int	ipcsend(int, const void*, size_t);
+int	ipcreadresp(int, int, char*, size_t, char*, size_t, Ipcresp*);
+
+#endif