refactor both i3-nagbar starts into src/util.c

With this change, libev >= 4 is a hard dependency. It should be present
in all major linux distributions (even the latest ubuntu LTS).

libi3/get_process_filename.c

@@ -0,0 +1,58 @@
+/*
+ * vim:ts=4:sw=4:expandtab
+ *
+ * i3 - an improved dynamic tiling window manager
+ * © 2009-2012 Michael Stapelberg and contributors (see also: LICENSE)
+ *
+ */
+#include <assert.h>
+#include <stdint.h>
+#include <stdlib.h>
+#include <string.h>
+#include <stdbool.h>
+#include <err.h>
+#include <sys/stat.h>
+#include <sys/types.h>
+#include <pwd.h>
+#include <unistd.h>
+
+#include "libi3.h"
+
+/*
+ * Returns the name of a temporary file with the specified prefix.
+ *
+ */
+char *get_process_filename(const char *prefix) {
+    /* dir stores the directory path for this and all subsequent calls so that
+     * we only create a temporary directory once per i3 instance. */
+    static char *dir = NULL;
+    if (dir == NULL) {
+        /* Check if XDG_RUNTIME_DIR is set. If so, we use XDG_RUNTIME_DIR/i3 */
+        if ((dir = getenv("XDG_RUNTIME_DIR"))) {
+            char *tmp;
+            sasprintf(&tmp, "%s/i3", dir);
+            dir = tmp;
+			struct stat buf;
+			if (stat(dir, &buf) != 0) {
+                if (mkdir(dir, 0700) == -1) {
+                    perror("mkdir()");
+                    return NULL;
+                }
+            }
+        } else {
+            /* If not, we create a (secure) temp directory using the template
+             * /tmp/i3-<user>.XXXXXX */
+            struct passwd *pw = getpwuid(getuid());
+            const char *username = pw ? pw->pw_name : "unknown";
+            sasprintf(&dir, "/tmp/i3-%s.XXXXXX", username);
+            /* mkdtemp modifies dir */
+            if (mkdtemp(dir) == NULL) {
+                perror("mkdtemp()");
+                return NULL;
+            }
+        }
+    }
+    char *filename;
+    sasprintf(&filename, "%s/%s.%d", dir, prefix, getpid());
+    return filename;
+}