ibus: name the address file as libibus does under Wayland

libibus looks for the file under WAYLAND_DISPLAY when a session has one,
DISPLAY only otherwise; strans always used DISPLAY, so in a Wayland
session it wrote <machine-id>-unix-0 while every IBus client looked for
<machine-id>-unix-wayland-0 and found nothing.  The machine id now comes
from D-Bus's copy first, as libibus reads it, and a host with neither
file gets libibus's own "machine-id" rather than a daemon that dies.

README.md

@@ -147,7 +147,8 @@ caller's standard error. A service supervisor should instead run
 `XDG_RUNTIME_DIR` and `DISPLAY`: the GTK module finds the daemon at
 `$XDG_RUNTIME_DIR/strans.sock` (else `/tmp/strans.UID`), and IBus clients
 through the address file libibus expects under `~/.config/ibus/bus/`,
-which strans writes as `ibus-daemon` would.
+which strans writes as `ibus-daemon` would, named after `WAYLAND_DISPLAY`
+when there is one and `DISPLAY` otherwise.
 
 The build does not copy or install the daemon or its data. `./strans DIR`
 opens `hira.map`, `kata.map`, `telex.map`, `kanji.dict`, `emoji.dict`, and

ibus.c

@@ -113,52 +113,63 @@ machineidfiles(char *buf, int sz, char **path, int npath)
 	buf[0] = '\0';
 }
 
+/* libibus reads the D-Bus file first and calls it "machine-id" if neither is there. */
 static void
 machineid(char *buf, int sz)
 {
 	char *path[] = {
-		"/etc/machine-id",
 		"/var/lib/dbus/machine-id",
+		"/etc/machine-id",
 	};
 
 	machineidfiles(buf, sz, path, nelem(path));
+	if(buf[0] == '\0')
+		snprintf(buf, sz, "machine-id");
 }
 
+static void
+copyfield(char *dst, int sz, char *src, int n)
+{
+	if(n >= sz)
+		n = sz - 1;
+	memcpy(dst, src, n);
+	dst[n] = '\0';
+}
+
+/*
+ * The display libibus names the file after: the whole WAYLAND_DISPLAY,
+ * else DISPLAY's host and number, else unix and 0.
+ */
 static void
 xdisplay(char *host, int hsz, char *num, int nsz)
 {
 	char *d, *colon, *dot, *p;
-	int n;
 
-	strncpy(host, "unix", hsz);
+	copyfield(host, hsz, "unix", 4);
-	host[hsz-1] = '\0';
+	copyfield(num, nsz, "0", 1);
-	strncpy(num, "0", nsz);
+	d = getenv("WAYLAND_DISPLAY");
-	num[nsz-1] = '\0';
+	if(d != nil && d[0] != '\0'){
+		copyfield(num, nsz, d, strlen(d));
+		return;
+	}
 	d = getenv("DISPLAY");
 	if(d == nil || d[0] == '\0')
 		return;
 	colon = strchr(d, ':');
 	if(colon == nil)
 		return;
-	if(colon > d){
+	if(colon > d)
-		n = colon - d;
+		copyfield(host, hsz, d, colon - d);
-		if(n >= hsz) n = hsz - 1;
-		memcpy(host, d, n);
-		host[n] = '\0';
-	}
 	p = colon + 1;
 	dot = strchr(p, '.');
-	n = dot ? dot - p : (int)strlen(p);
+	copyfield(num, nsz, p, dot ? dot - p : (int)strlen(p));
-	if(n >= nsz) n = nsz - 1;
-	memcpy(num, p, n);
-	num[n] = '\0';
 }
 
 /* The IBus address file lives where libibus looks: config/ibus/bus/. */
 static int
 buildaddrpath(char *buf, int sz)
 {
-	char mid[64], host[64], num[8], dir[512];
+	char mid[64], host[64], num[64], dir[512];
 	char *cfg, *home, *explicit, *p;
 	int n;
 
@@ -168,8 +179,6 @@ buildaddrpath(char *buf, int sz)
 		return explicit[0] == '\0' || n < 0 || n >= sz ? -1 : 0;
 	}
 	machineid(mid, sizeof(mid));
-	if(mid[0] == '\0')
-		return -1;
 	xdisplay(host, sizeof(host), num, sizeof(num));
 	cfg = getenv("XDG_CONFIG_HOME");
 	if(cfg != nil && cfg[0] != '\0')

tests/ibus_test.c

@@ -52,6 +52,9 @@ ibus_machine_id_fallback(struct ct *t)
 	path[1] = fallback;
 	machineidfiles(got, sizeof got, path, nelem(path));
 	CT_EQ_STR(t, "fallback-machine-id", got);
+	path[1] = primary;
+	machineidfiles(got, sizeof got, path, nelem(path));
+	CT_EQ_STR(t, "", got);
 
 	old = getenv("IBUS_ADDRESS_FILE");
 	saved = old == nil ? nil : strdup(old);