Code 101

Here we hope to put a few tests for you to see if you are fit in C to fiddle around with the gtk-gnutella code. They are taken from our experiences with the pitfalls of coding on the project.

Test 1

Author: Richard Eckart
Difficulty: moderate

Question

The code below extracts the user agent from the headers of an upload. The gui displays the useragent string or "..." if u->user_agent is NULL. Unfortunately there is a bug in that piece of code that caused the GUI of our test user to always display "...". Can you locate it?

 1: /*
 2:  * Extract User-Agent.
 3:  *
 4:  * X-Token: GTKG token
 5:  * User-Agent: whatever
 6:  * Server: whatever (in case no User-Agent)
 7:  */
 8:
 9: token = header_get(header, "X-Token");
10: user_agent = header_get(header, "User-Agent");
11:
12: /* Maybe they sent a Server: line, thinking they're a server? */
13: if (user_agent != NULL)
14:     user_agent = header_get(header, "Server");
15:
16: if (user_agent != NULL)
17:     faked = !version_check(user_agent, token, u->ip);
18:
19: if (u->user_agent == NULL && user_agent != NULL) {
20:     if (faked) {
21:         gchar *name = g_strdup_printf("!%s", user_agent);
22:
23:         u->user_agent = atom_str_get(name);
24:         g_free(name);
25:     } else
26:         u->user_agent = atom_str_get(user_agent);
27: }

Test 2

Author: Richard Eckart
Difficulty: moderate

Question

While running gtkg compiled with Gtk1 support we found that the code below contains a memory leak. There are two places in the code where new memory is allocated. Those are on the lines 18 and 19. Can you find out where the leak is?

 1: /*
 2: * on_popup_downloads_push_activate
 3: *
 4: * All selected downloads fallback to push
 5: */
 6: void on_popup_downloads_push_activate(
 7:    GtkMenuItem * menuitem, gpointer user_data)
 8: {
 9:     struct download *d;
10:     GList *node_list, *data_list = NULL;
11:     GtkCTree *ctree_downloads = GTK_CTREE
12:         (lookup_widget(main_window, "ctree_downloads"));
13:     GtkCTree *ctree_downloads_queue = GTK_CTREE
14:         (lookup_widget(main_window, "ctree_downloads_queue"));
15:
16:     gtk_clist_freeze(GTK_CLIST(ctree_downloads_queue));
17:     gtk_clist_freeze(GTK_CLIST(ctree_downloads));
18:     node_list = g_list_copy(GTK_CLIST(ctree_downloads)->selection);
19:     data_list = downloads_gui_collect_ctree_data(ctree_downloads,
20:         node_list, TRUE, TRUE);
21:
23:     for (; NULL != data_list; data_list = g_list_next(data_list)) {
24:         d = (struct download *) data_list->data;
25:
26:         if (!d) {
27:             g_warning(
28:                 "on_popup_downloads_push_activate(): row has NULL data\n");
29:             continue;
30:         }
31:         download_fallback_to_push(d, FALSE, TRUE);
32:     }
33:
34:     gtk_clist_thaw(GTK_CLIST(ctree_downloads_queue));
35:     gtk_clist_thaw(GTK_CLIST(ctree_downloads));
36:     g_list_free(data_list);
37:     g_list_free(node_list);
38: }

Answers

The answers are here on a separate page. Don't cheat yourself by reading a answer before trying the test.