unit-name: rework unit_name_replace_instance function()

https://bugzilla.redhat.com/show_bug.cgi?id=855863

TODO

@@ -49,6 +49,18 @@ Bugfixes:
 
 Features:
 
+* perfomance messages for selinux are gone from debug log?
+
+* http://lists.freedesktop.org/archives/systemd-devel/2012-September/006502.html
+
+* don't use writev() in tmpfiles for sake of compat with sysfs?
+
+* come up with a nice way to write queue/read_ahead_kb for a block device without interfering with readahead
+
+* journald: add kernel cmdline option to disable ratelimiting for debug purposes
+
+* Add a way to reference the machine/boot ID from ExecStart= and similar command lines
+
 * move PID 1 segfaults to /var/lib/systemd/coredump?
 
 * Document word splitting syntax for ExecStart= and friends

src/shared/unit-name.c

@@ -357,36 +357,29 @@ bool unit_name_is_instance(const char *n) {
 char *unit_name_replace_instance(const char *f, const char *i) {
         const char *p, *e;
         char *r, *k;
-        size_t a;
+        size_t a, b;
 
         assert(f);
 
         p = strchr(f, '@');
-        assert_se(e = strrchr(f, '.'));
+        if (!p)
+                return strdup(f);
+
+        e = strrchr(f, '.');
+        if (!e)
+                assert_se(e = strchr(f, 0));
 
         a = p - f;
+        b = strlen(i);
 
-        if (p) {
-                size_t b;
-
-                b = strlen(i);
-
-                r = new(char, a + 1 + b + strlen(e) + 1);
-                if (!r)
-                        return NULL;
-
-                k = mempcpy(r, f, a + 1);
-                k = mempcpy(k, i, b);
-        } else {
-
-                r = new(char, a + strlen(e) + 1);
-                if (!r)
-                        return NULL;
-
-                k = mempcpy(r, f, a);
-        }
+        r = new(char, a + 1 + b + strlen(e) + 1);
+        if (!r)
+                return NULL;
 
+        k = mempcpy(r, f, a + 1);
+        k = mempcpy(k, i, b);
         strcpy(k, e);
+
         return r;
 }
 

src/test/test-unit-name.c

@@ -29,6 +29,30 @@
 int main(int argc, char* argv[]) {
         char *t, *k;
 
+        t = unit_name_replace_instance("foo@.service", "waldo");
+        puts(t);
+        free(t);
+
+        t = unit_name_replace_instance("foo@xyz.service", "waldo");
+        puts(t);
+        free(t);
+
+        t = unit_name_replace_instance("xyz", "waldo");
+        puts(t);
+        free(t);
+
+        t = unit_name_replace_instance("", "waldo");
+        puts(t);
+        free(t);
+
+        t = unit_name_replace_instance("", "");
+        puts(t);
+        free(t);
+
+        t = unit_name_replace_instance("foo.service", "waldo");
+        puts(t);
+        free(t);
+
         t = unit_name_from_path("/waldo", ".mount");
         puts(t);
         k = unit_name_to_path(t);