Use the XDG Base Directory Specification for storing game files

NEWS

@@ -25,6 +25,14 @@ __ https://www.zap.org.au/
 Version 7.15 (not yet released)
 -------------------------------
 
+Changed the default location where game files are saved from `~/.trader`
+to `~/.local/share/trader`, so as to follow the `XDG Base Directory
+Specification`__.  If set, the ``XDG_DATA_HOME`` environment variable
+will override this location.  If the `~/.trader` directory is already
+present, it will continue to be used.  Updated the manual page to suit.
+
+__ https://specifications.freedesktop.org/basedir-spec/basedir-spec-latest.html
+
 Updated to GNU Gettext 0.20 or later.  Updated to the latest snapshot of
 the Gnulib GNU Portability Library.  Also updated the `INSTALL` file to
 list the latest tested versions of operating systems, including a new

doc/trader.6

@@ -154,6 +154,15 @@ Or, if you prefer the old amber screens of yesteryear:
 .\" *********************************************************************
 .SH ENVIRONMENT
 .TP
+.BR XDG_DATA_HOME ", " HOME
+If \fBXDG_DATA_HOME\fR is set to an absolute pathname (that is, a path
+that starts with \*(lq\fI/\fR\*(rq), Star Traders will use that
+directory, with a subdirectory \fItrader\fR, to store game files.  If
+this environment variable is not set or does not start with
+\*(lq\fI/\fR\*(rq, \fI\(ti/.local/share/trader\fR will be used instead,
+where \*(lq\fI\(ti\fR\*(rq represents your home directory, as contained
+in the \fBHOME\fR environment variable.
+.TP
 .BR LINES ", " COLUMNS
 Star Traders uses the Curses library for displaying text on the screen.
 As such, it will access these two environment variables if the underlying
@@ -177,11 +186,17 @@ manual pages for more details on locale settings.
 .\" *********************************************************************
 .SH FILES
 .TP
+.IB \(ti/.local/share/trader/game N
+Star Traders stores saved game files in the \fI.local/share/trader\fR
+subdirectory in your home directory (unless overriden by the
+\fBXDG_DATA_HOME\fR environment variable).  \fIN\fR is a number between
+\fB1\fR and \fB9\fR inclusive.  The game file is scrambled to prevent you
+or others from casually cheating!
+.TP
 .IB \(ti/.trader/game N
-Star Traders stores saved game files in the \fI.trader\fR subdirectory in
-your home directory.  \fIN\fR is a number between \fB1\fR and \fB9\fR
-inclusive.  The game file is scrambled to prevent you or others from
-casually cheating!
+If the \fI\(ti/.trader\fR directory exists, game files will be read from
+and saved to this location instead.  This is for compatibility with
+versions of Star Traders prior to version 7.15.
 .\" *********************************************************************
 .SH BUGS
 None yet known...

src/utils.c

@@ -53,6 +53,10 @@ wchar_t *mon_thousands_sep;		// Locale's monetary thousands separator
 *                 Module-specific constants and macros                  *
 ************************************************************************/
 
+#define DIRSEP			"/"		// Directory separator
+#define HIDDEN_PATH		"."		// Hidden file start char
+#define XDG_DATA_DEFAULT	".local" DIRSEP "share"
+
 #define GAME_FILENAME_PROTO	"game%d"
 #define GAME_FILENAME_BUFSIZE	16
 
@@ -306,10 +310,15 @@ void init_program_name (const char *argv0)
     /* This implementation assumes a POSIX environment with an ASCII-safe
        character encoding (such as ASCII or UTF-8). */
 
+    const char *dirsep = DIRSEP;
+
+
+    assert(strlen(dirsep) == 1);
+
     if (argv0 == NULL || *argv0 == '\0') {
 	program_name = PACKAGE;
     } else {
-	char *p = strrchr(argv0, '/');
+	char *p = strrchr(argv0, dirsep[0]);
 
 	if (p != NULL && *++p != '\0') {
 	    program_name = xstrdup(p);
@@ -343,21 +352,74 @@ const char *home_directory (void)
 
 const char *data_directory (void)
 {
-    /* This implementation assumes a POSIX environment by using "/" as
+    /* This implementation assumes a POSIX environment by using DIRSEP as
        the directory separator.  It also assumes a dot-starting directory
        name is permissible (again, true on POSIX systems) and that the
        character encoding is ASCII-safe. */
 
+    const char *dirsep            = DIRSEP;
+    const char *dirsep_hiddenpath = DIRSEP HIDDEN_PATH;
+    const char *datahome_part     = DIRSEP XDG_DATA_DEFAULT DIRSEP;
+
+    struct stat statbuf;
+
+
+    assert(strlen(dirsep) == 1);
+
     if (data_directory_str == NULL) {
 	const char *home = home_directory();
+	const char *xdg_data_home = getenv("XDG_DATA_HOME");
 
-	if (program_name != NULL && home != NULL) {
-	    char *p = xmalloc(strlen(home) + strlen(program_name) + 3);
+	if (program_name != NULL) {
+	    int len_program_name = strlen(program_name);
+
+	    if (home != NULL) {
+		char *p = xmalloc(strlen(home) + strlen(dirsep_hiddenpath)
+				  + len_program_name + 1);
 
 		strcpy(p, home);
-	    strcat(p, "/.");
+		strcat(p, dirsep_hiddenpath);
 		strcat(p, program_name);
+
+		if (stat(p, &statbuf) == 0 && S_ISDIR(statbuf.st_mode)) {
+		    // Directory "$HOME/.trader" exists: use that
 		    data_directory_str = p;
+		} else {
+		    free(p);
+		}
+	    }
+
+	    if (data_directory_str == NULL && xdg_data_home != NULL
+		&& *xdg_data_home != '\0' && *xdg_data_home == dirsep[0]) {
+		// Use directory "$XDG_DATA_HOME/trader"
+
+		/* Note that the XDG Base Directory Specification v0.7
+		   requires XDG_DATA_HOME to contain an absolute path:
+		   the variable must be ignored if it does not start with
+		   the directory separator DIRSEP ("/") */
+
+		char *p = xmalloc(strlen(xdg_data_home) + strlen(DIRSEP)
+				  + len_program_name + 1);
+
+		strcpy(p, xdg_data_home);
+		strcat(p, dirsep);
+		strcat(p, program_name);
+
+		data_directory_str = p;
+	    }
+
+	    if (data_directory_str == NULL && home != NULL) {
+		// Use directory "$HOME/.local/share/trader"
+
+		char *p = xmalloc(strlen(home) + strlen(datahome_part)
+				  + len_program_name + 1);
+
+		strcpy(p, home);
+		strcat(p, datahome_part);
+		strcat(p, program_name);
+
+		data_directory_str = p;
+	    }
 	}
     }
 
@@ -373,6 +435,8 @@ char *game_filename (int gamenum)
     /* This implementation assumes a POSIX environment and an ASCII-safe
        character encoding. */
 
+    const char *dirsep = DIRSEP;
+
     char buf[GAME_FILENAME_BUFSIZE];	// Buffer for part of filename
     const char *dd;			// Data directory
 
@@ -387,10 +451,10 @@ char *game_filename (int gamenum)
     if (dd == NULL) {
 	return xstrdup(buf);
     } else {
-	char *p = xmalloc(strlen(dd) + strlen(buf) + 2);
+	char *p = xmalloc(strlen(dd) + strlen(dirsep) + strlen(buf) + 1);
 
 	strcpy(p, dd);
-	strcat(p, "/");
+	strcat(p, dirsep);
 	strcat(p, buf);
 	return p;
     }

src/utils.h

@@ -99,12 +99,18 @@ extern const char *home_directory (void);
   Parameters: (none)
   Returns:    const char *   - Pointer to data directory
 
-  This function returns the full pathname to a potentially-writable
-  subdirectory within the user's home directory.  Essentially, this
-  function returns home_directory() + "/."  + program_name.  Note that
-  this path is NOT created by this function, nor is the ability to write
-  to this path checked.  NULL is returned if this path cannot be
-  determined.
+  This function returns the full pathname to a potentially-writable data
+  directory, usually within the user's home directory.
+
+  Assuming program_name is set to "trader", if "$HOME/.trader" exists,
+  that directory is returned as the data directory.  Otherwise, if the
+  environment variable XDG_DATA_HOME is set and contains an absolute
+  pathname, "$XDG_DATA_HOME/trader" is returned.  Otherwise,
+  "$HOME/.local/share/trader" is returned.
+
+  Note that the returned path is NOT created by this function, nor is the
+  ability to read from or write to this path checked.  NULL is returned
+  if the path cannot be determined.
 */
 extern const char *data_directory (void);