gdm-common: Add gdm_shell_expand() and tests

This allows shell-like expansion of strings. It will be later
used to allow configuring the environment via config files.

https://bugzilla.gnome.org/show_bug.cgi?id=751158

2 files changed, 96 insertions, 0 deletions

diff --git a/common/gdm-common.c b/common/gdm-common.c
index 5beeebf9..a96b30f2 100644
--- a/common/gdm-common.c
+++ b/common/gdm-common.c
@@ -710,3 +710,90 @@ gdm_run_script (const char *dir,
 
         return ret;
 }
+
+gboolean
+gdm_shell_var_is_valid_char (gchar c, gboolean first)
+{
+        return (!first && g_ascii_isdigit (c)) ||
+                c == '_' ||
+                g_ascii_isalpha (c);
+}
+
+/* This expands a string somewhat similar to how a shell would do it
+   if it was enclosed inside double quotes.  It handles variable
+   expansion like $FOO and ${FOO}, single-char escapes using \, and
+   non-escaped # at the begining of a word is taken as a comment and ignored */
+char *
+gdm_shell_expand (const char *str,
+                  GdmExpandVarFunc expand_var_func,
+                  gpointer user_data)
+{
+        GString *s = g_string_new("");
+        const gchar *p, *start;
+        gchar c;
+        gboolean at_new_word;
+
+        p = str;
+        at_new_word = TRUE;
+        while (*p) {
+                c = *p;
+                if (c == '\\') {
+                        p++;
+                        c = *p;
+                        if (c != '\0') {
+                                p++;
+                                switch (c) {
+                                case '\\':
+                                        g_string_append_c (s, '\\');
+                                        break;
+                                case '$':
+                                        g_string_append_c (s, '$');
+                                        break;
+                                case '#':
+                                        g_string_append_c (s, '#');
+                                        break;
+                                default:
+                                        g_string_append_c (s, '\\');
+                                        g_string_append_c (s, c);
+                                        break;
+                                }
+                        }
+                } else if (c == '#' && at_new_word) {
+                        break;
+                } else if (c == '$') {
+                        gboolean brackets = FALSE;
+                        p++;
+                        if (*p == '{') {
+                                brackets = TRUE;
+                                p++;
+                        }
+                        start = p;
+                        while (*p != '\0' &&
+                               gdm_shell_var_is_valid_char (*p, p == start))
+                                p++;
+                        if (p == start || (brackets && *p != '}')) {
+                                /* Invalid variable, use as-is */
+                                g_string_append_c (s, '$');
+                                if (brackets)
+                                        g_string_append_c (s, '{');
+                                g_string_append_len (s, start, p - start);
+                        } else {
+                                gchar *expanded;
+                                gchar *var = g_strndup (start, p - start);
+                                if (brackets && *p == '}')
+                                        p++;
+
+                                expanded = expand_var_func (var, user_data);
+                                if (expanded)
+                                        g_string_append (s, expanded);
+                                g_free (var);
+                                g_free (expanded);
+                        }
+                } else {
+                        p++;
+                        g_string_append_c (s, c);
+                        at_new_word = g_ascii_isspace (c);
+                }
+        }
+        return g_string_free (s, FALSE);
+}
diff --git a/common/gdm-common.h b/common/gdm-common.h
index 3302afec..d0812ed3 100644
--- a/common/gdm-common.h
+++ b/common/gdm-common.h
@@ -36,6 +36,9 @@
 GQuark gdm_common_error_quark (void);
 #define GDM_COMMON_ERROR gdm_common_error_quark()
 
+typedef char * (*GdmExpandVarFunc) (const char *var,
+                                    gpointer user_data);
+
 G_BEGIN_DECLS
 
 int            gdm_wait_on_pid           (int pid);
@@ -64,6 +67,12 @@ gboolean       gdm_run_script             (const char *dir,
                                            const char *display_hostname,
                                            const char *display_x11_authority_file);
 
+gboolean      gdm_shell_var_is_valid_char (char c,
+                                           gboolean first);
+char *        gdm_shell_expand            (const char *str,
+                                           GdmExpandVarFunc expand_func,
+                                           gpointer user_data);
+
 G_END_DECLS
 
 #endif /* _GDM_COMMON_H */