Implement XDG Base Directory Specification

$XDG_CONFIG_HOME/xephem can be used as an alternative to the
$HOME/.xephem directory. The old directory is checked first to
minimise disruption to existing installations.

GUI/xephem/help/xephem.html

@@ -559,6 +559,11 @@ resources then exit<br>
 <h3><a class="mozTocH3" name="mozTocId644691"></a> 1.3.1 <a
  name="SharedPrivateDirs"></a>Shared and Private Directories</h3>
 When XEphem is launched it looks for a file named <span
+ style="font-family: monospace;">xephemrc</span> in the user's <span
+ style="font-family: monospace;">$HOME/.config</span> directory (or
+the location specified by the <span
+ style="font-family: monospace;">$XDG_CONFIG_HOME</span>
+environment variable), or if that doesn't exist, <span
  style="font-family: monospace;">.xephemrc</span> in the user's <span
  style="font-family: monospace;">$HOME</span> directory. This file is
 optional. If it exists, it should contain a line with the following
@@ -576,10 +581,13 @@ A leading "." in the file name can be used to refer to the current
 working directory of the running program. The example above causes the
 Private directory to be <span style="font-family: monospace;">.xephem</span>
 in the users <span style="font-family: monospace;">$HOME</span>
-directory. If <span style="font-family: monospace;">.xephemrc</span>
-does not exist or does not contain this line the default Private
-directory is <span style="font-family: monospace;">~/.xephem</span>.
-The private directory will be created if it does not already exist.<br>
+directory. If <span style="font-family: monospace;">xephemrc</span>
+does not exist or does not contain this line XEphem will first search for
+the Private directory at <span style="font-family: monospace;">~/.xephem</span>,
+followed by <span style="font-family: monospace;">~/.config/xephem</span>.
+The private directory will be created in one of those locations if it doe
+not already exist, depending on whether the
+<span style="font-family: monospace;">~/.config</span> directory exists.<br>
 <br>
 XEphem then also searches for another directory for <i>Shared</i>
 files. This directory contains files presumed to be shared

GUI/xephem/homeio.c

@@ -31,6 +31,9 @@ expand_home (char *path)
 	char *p;
 	int l;
 
+	if (!path)
+	    return NULL;
+
 	/* get home, if we don't already know it */
 	if (!home) {
 	    home = getenv ("HOME");

GUI/xephem/saveres.c

@@ -172,6 +172,9 @@ static char mydirdef[] = "~/.xephem";
 static char mdovride[] = "~/.xephemrc";
 static char mdres[] = "XEphem.PrivateDir";
 #endif
+static char xdgprivdir[] = "xephem";
+static char xdgovride[] = "xephemrc";
+static char dotconfig[] = "~/.config";
 
 #define	RESWID	45		/* columns for resource name, if possible */
 #define	PGWID	75		/* overall number of default columns */
@@ -930,13 +933,49 @@ sr_getDirPM (Pixmap *pmopen, Pixmap *pmclose)
 	*pmclose = nomore_pm;
 }
 
+/* Returns a full path in the directory specified by $XDG_CONFIG_HOME, or
+ * $HOME/.config if not set. Passing NULL returns the root of the directory.
+ */
+static char *
+getXdgConfigPath (const char *subpath)
+{
+	static char *xdgconfig;
+	unsigned pathlen;
+	char *path;
+
+	if (!xdgconfig)
+	    xdgconfig = getenv("XDG_CONFIG_HOME");
+	if (!xdgconfig)
+	    xdgconfig = XtNewString(expand_home(dotconfig));
+
+	if (!subpath) {
+	    path = XtNewString(xdgconfig);
+	} else {
+	    pathlen = (unsigned)(strlen(xdgconfig) + strlen(subpath) + 2);
+	    path = XtMalloc(pathlen);
+	    snprintf(path, pathlen, "%s/%s", xdgconfig, subpath);
+	}
+
+	return path;
+}
+
 /* return full path of per-user working directory,
  * allowing for possible override.
+ * Directories are searched in this order:
+ * 1. Directory specified by $HOME/.xephemrc
+ * 2. Directory specified by $XDG_CONFIG_HOME/xephemrc or $home/.config/xephemrc
+ * 3. $HOME/.xephem
+ * 4. $XDG_CONFIG_HOME/xephem or $HOME/.config/xephem
+ * If none of these directories exists, a new one is created:
+ * 1. If $XDG_CONFIG_HOME or $HOME/.config exists, create xephem directory there
+ * 2. if not, create .xephem directory in $HOME
  */
 char *
 getPrivateDir (void)
 {
 	static char *mydir;
+	char *xdgdir;
+	char *ovride = mdovride;
 
 	if (!mydir) {
 	    /* try mdovride else use default */
@@ -944,6 +983,13 @@ getPrivateDir (void)
 	    char *vhome, *vp = NULL;
 	    char nam[MRNAM], val[MLL], buf[MLL];
 
+#if !defined(__APPLE__) || !defined(__VMS)
+	    if (!ofp) {
+		ovride = getXdgConfigPath(xdgovride);
+		ofp = fopenh (ovride, "r");
+	    }
+#endif
+
 	    if (ofp) {
 		while (fgets (buf, sizeof(buf), ofp)) {
 		    if (!crackNam (buf, nam) && !strcmp (nam, mdres) &&
@@ -954,13 +1000,24 @@ getPrivateDir (void)
 		}
 		fclose(ofp);
 		if (!vp)
-		    fprintf (stderr, "%s: %s not found. Using %s\n",
-						    mdovride, mdres, mydirdef);
+		    fprintf (stderr, "%s: %s not found. Trying default dirs\n",
+		             ovride, mdres);
 	    }
+
 	    if (!vp)
 		vp = mydirdef;
 	    vhome = expand_home(vp);
 	    mydir = XtNewString (vhome);	/* macro! */
+
+#if !defined(__APPLE__) || !defined(__VMS)
+	    xdgdir = getXdgConfigPath(NULL);
+	    if (access (mydir, X_OK) < 0 && access (xdgdir, X_OK) == 0) {
+		XtFree (mydir);
+		mydir = getXdgConfigPath(xdgprivdir);
+	    }
+	    XtFree (xdgdir);
+#endif
+
 	    if (access (mydir, X_OK) < 0 && mkdir (mydir, 0744) < 0) {
 		/* don't try and fake it */
 		printf ("%s: %s\n", mydir, syserrstr());

GUI/xephem/xephem.1

@@ -126,15 +126,22 @@ references; version number and the Copyright statement.
 .SH X Resources
 When first started, XEphem looks for a file named
 .B .xephemrc
-in your $HOME directory. It should contain one line of the form:
+in your $HOME directory, or if that doesn't exist,
+.B xephemrc
+in your $HOME/.config directory. It should contain one line of the form:
 
 XEphem.PrivateDir: ~/.xephem
 
 This defines the Private directory, where XEphem will store your personal
-settings. The example line shown here, which is also the assumption if the
-file is not present, means XEphem will create and use a directory named
+settings. The example line shown here means XEphem will create and use a
+directory named
 .B .xephem
-for this purpose in your home directory.
+for this purpose in your home directory. If the file is not present, the
+XEphem will look for the directory in
+.B $HOME/.xephem
+first, followed by
+.B $HOME/.config/xephem
+if that does not exist. If neither exists, a new directory will be created.
 
 Within this directory a text file named
 .B XEphem