Potential patch to filter mailboxes depending on annotation for non Kolab email clients

[Timotheus Pokorra via Cyrus-devel]

Hello,

we have this discussion in Kolab [0] about whether to have an
additional proxy (Guam) to process the data that comes from Cyrus
imapd, or to patch Cyrus imapd itself.

What do you think about the attached patch?
It checks if the email client identifies with Kolab in its name, and
if not, only mailbox folders with annotation containing "mail" are
published with the LIST command. If there are no folder annotations,
the folder is published as well.

Are there any flaws with that patch? My C knowledge is quite rusty...

Would this patch be suitable for merging upstream? Or is this
something we should keep in the Cyrus package packaged for Kolab?

Thank you, and have a nice weekend,
  Timotheus

[0]: https://lists.kolab.org/pipermail/devel/2016-November/015490.html

diff --git a/imap/imapd.c b/imap/imapd.c
index 017df58..1ba482d 100644
--- a/imap/imapd.c
+++ b/imap/imapd.c
@@ -177,6 +177,7 @@ static void *imapd_tls_comp = NULL; /* TLS compression method, if any */
 static int imapd_compress_done = 0; /* have we done a successful compress? */
 static const char *plaintextloginalert = NULL;
 static int ignorequota = 0;
+static int HideKolabFolders = 1;
 
 static struct id_data {
     struct attvaluelist *params;
@@ -2837,6 +2838,12 @@ static void cmd_id(char *tag)
 	}
 
 	syslog(LOG_INFO, "client id:%s", buf_cstring(&logbuf));
+
+        // must catch Roundcube/Kolab, Python/Kolab, PyKolab/Kolab
+        if (strstr(buf_cstring(&logbuf), "/Kolab")) {
+           HideKolabFolders = 0;
+        }
+
 	buf_free(&logbuf);
     }
 
@@ -11465,6 +11472,23 @@ static void list_response(const char *name, int attributes,
 	cmd = "LIST";
 	break;
     }
+
+    if (HideKolabFolders && mbentry) {
+        struct buf attrib = BUF_INITIALIZER;
+        if (!annotatemore_lookup(mbentry->name, "/vendor/kolab/folder-type", imapd_userid, &attrib) && attrib.len) {
+            imapd_sasl_log(NULL, SASL_LOG_DEBUG, mbentry->name);
+            imapd_sasl_log(NULL, SASL_LOG_DEBUG, attrib.s);
+            // folder annotation can be: mail.sentitems, mail.wastebasket, mail.inbox, mail.drafts, contact.default, etc
+            if (!strstr(attrib.s, "mail")) {
+                imapd_sasl_log(NULL, SASL_LOG_DEBUG, "do not publish");
+                imapd_sasl_log(NULL, SASL_LOG_DEBUG, mbentry->name);
+                buf_free(&attrib);
+                goto done;
+            }
+        }
+        buf_free(&attrib);
+    }
+
     prot_printf(imapd_out, "* %s (", cmd);
     for (sep = "", attr = mbox_name_attributes; attr->id; attr++) {
 	if (attributes & attr->flag) {