wsutil: Add config_file_exists_with_entries()

The purpose of this function is to check if a configuration file exists
and has at least one entry which is not a comment.

Use this when building the list of profiles where the user can copy
configuration from, to avoid listing profiles with empty files or files
with only comments.

Change-Id: If45f52025959818fb1213ffac488cd59441e9fce
Reviewed-on: https://code.wireshark.org/review/30113
Petri-Dish: Stig Bjørlykke <stig@bjorlykke.org>
Tested-by: Petri Dish Buildbot
Reviewed-by: Peter Wu <peter@lekensteyn.nl>

debian/libwsutil0.symbols

@@ -10,6 +10,7 @@ libwsutil.so.0 libwsutil0 #MINVER#
  cmdarg_err@Base 1.99.0
  cmdarg_err_cont@Base 1.99.0
  cmdarg_err_init@Base 1.99.0
+ config_file_exists_with_entries@Base 2.9.0
  copy_file_binary_mode@Base 1.12.0~rc1
  copy_persconffile_profile@Base 1.12.0~rc1
  crc11_307_noreflect_noxor@Base 1.10.0

ui/qt/widgets/copy_from_profile_menu.cpp

@@ -25,7 +25,7 @@ CopyFromProfileMenu::CopyFromProfileMenu(QString filename) :
         profile_def *profile = (profile_def *) fl_entry->data;
         char *profile_dir = get_profile_dir(profile->name, profile->is_global);
         char *file_name = g_build_filename(profile_dir, filename_.toUtf8().constData(), NULL);
-        if (file_exists(file_name) && strcmp(profile_name, profile->name) != 0) {
+        if ((strcmp(profile_name, profile->name) != 0) && config_file_exists_with_entries(file_name, '#')) {
             if (profile->is_global && !globals_started) {
                 if (have_profiles_) {
                     addSeparator();

wsutil/filesystem.c

@@ -2024,6 +2024,36 @@ file_exists(const char *fname)
     }
 }
 
+gboolean config_file_exists_with_entries(const char *fname, char comment_char)
+{
+    gboolean start_of_line = TRUE;
+    gboolean has_entries = FALSE;
+    FILE *file;
+    int c;
+
+    if (!fname) {
+        return FALSE;
+    }
+
+    if ((file = ws_fopen(fname, "r")) == NULL) {
+        return FALSE;
+    }
+
+    do {
+        c = ws_getc_unlocked(file);
+        if (start_of_line && c != comment_char && !g_ascii_isspace(c) && g_ascii_isprint(c)) {
+            has_entries = TRUE;
+            break;
+        }
+        if (c == '\n' || !g_ascii_isspace(c)) {
+            start_of_line = (c == '\n');
+        }
+    } while (c != EOF);
+
+    fclose(file);
+    return has_entries;
+}
+
 /*
  * Check that the from file is not the same as to file
  * We do it here so we catch all cases ...

wsutil/filesystem.h

@@ -286,6 +286,12 @@ WS_DLL_PUBLIC int test_for_fifo(const char *);
  */
 WS_DLL_PUBLIC gboolean file_exists(const char *fname);
 
+/*
+ * Check if file is existing and has text entries which does not start
+ * with the comment character.
+ */
+WS_DLL_PUBLIC gboolean config_file_exists_with_entries(const char *fname, char comment_char);
+
 /*
  * Check if two filenames are identical (with absolute and relative paths).
  */