[PATCH v2] config: do not overwrite symlinks when saving config file

[Jani Nikula]

Use realpath to canonicalize the config path before writing.

Previously 'notmuch setup' and 'notmuch config set' overwrote the
config file even if it was a symbolic link.
---
 notmuch-config.c |   24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/notmuch-config.c b/notmuch-config.c
index b5c2066..89bc143 100644
--- a/notmuch-config.c
+++ b/notmuch-config.c
@@ -461,7 +461,7 @@ int
 notmuch_config_save (notmuch_config_t *config)
 {
     size_t length;
-    char *data;
+    char *data, *filename;
     GError *error = NULL;

     data = g_key_file_to_data (config->key_file, &length, NULL);
@@ -470,14 +470,30 @@ notmuch_config_save (notmuch_config_t *config)
        return 1;
     }

-    if (! g_file_set_contents (config->filename, data, length, &error)) {
-       fprintf (stderr, "Error saving configuration to %s: %s\n",
-                config->filename, error->message);
+    /* Try not to overwrite symlinks. */
+    filename = realpath (config->filename, NULL);
+    if (! filename) {
+       fprintf (stderr, "Error canonicalizing %s: %s\n", config->filename,
+                strerror (errno));
+       g_free (data);
+       return 1;
+    }
+
+    if (! g_file_set_contents (filename, data, length, &error)) {
+       if (strcmp (filename, config->filename)) {
+           fprintf (stderr, "Error saving configuration to %s (-> %s): %s\n",
+                    config->filename, filename, error->message);
+       } else {
+           fprintf (stderr, "Error saving configuration to %s: %s\n",
+                    filename, error->message);
+       }
        g_error_free (error);
+       free (filename);
        g_free (data);
        return 1;
     }

+    free (filename);
     g_free (data);
     return 0;
 }
-- 
1.7.10.4