From 8436b07153c9c394a7a2ec72db265a79c8494da0 Mon Sep 17 00:00:00 2001
From: cketti <cketti@thunderbird.net>
Date: Thu, 28 Mar 2024 15:10:16 +0100
Subject: [PATCH] IMAP: Add support for the \NonExistent LIST response
 attribute

---
 .../fsck/k9/mail/store/imap/RealImapStore.kt  |  5 +++
 .../k9/mail/store/imap/RealImapStoreTest.kt   | 43 ++++++++++++++++++-
 2 files changed, 46 insertions(+), 2 deletions(-)

diff --git a/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.kt b/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.kt
index 7f3e07ab2..5f349fd05 100644
--- a/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.kt
+++ b/mail/protocols/imap/src/main/java/com/fsck/k9/mail/store/imap/RealImapStore.kt
@@ -143,8 +143,13 @@ internal open class RealImapStore(
             }
 
             if (RealImapFolder.INBOX.equals(serverId, ignoreCase = true)) {
+                // We always add our own inbox entry to the returned list.
                 continue
             } else if (listResponse.hasAttribute("\\NoSelect")) {
+                // RFC 3501, section 7.2.2: It is not possible to use this name as a selectable mailbox.
+                continue
+            } else if (listResponse.hasAttribute("\\NonExistent")) {
+                // RFC 5258, section 3: The "\NonExistent" attribute implies "\NoSelect".
                 continue
             }
 
diff --git a/mail/protocols/imap/src/test/java/com/fsck/k9/mail/store/imap/RealImapStoreTest.kt b/mail/protocols/imap/src/test/java/com/fsck/k9/mail/store/imap/RealImapStoreTest.kt
index 42485bc9a..3ea6cf138 100644
--- a/mail/protocols/imap/src/test/java/com/fsck/k9/mail/store/imap/RealImapStoreTest.kt
+++ b/mail/protocols/imap/src/test/java/com/fsck/k9/mail/store/imap/RealImapStoreTest.kt
@@ -117,12 +117,33 @@ class RealImapStoreTest {
     }
 
     @Test
-    fun `getFolders() with subscribedFoldersOnly = false`() {
+    fun `getFolders() should ignore NoSelect entries`() {
         val imapStore = createTestImapStore(isSubscribedFoldersOnly = false)
         val imapConnection = createMockConnection().stub {
             on { executeSimpleCommand("""LIST "" "*"""") } doReturn listOf(
+                createImapResponse("""* LIST () "." "INBOX""""),
+                createImapResponse("""* LIST (\Noselect) "." "Folder""""),
+                createImapResponse("""* LIST () "." "Folder.SubFolder""""),
+                createImapResponse("6 OK Success"),
+            )
+        }
+        imapStore.enqueueImapConnection(imapConnection)
+
+        val folders = imapStore.getFolders()
+
+        assertThat(folders).isNotNull()
+        assertThat(folders.map { it.serverId }).containsExactly("INBOX", "Folder.SubFolder")
+    }
+
+    @Test
+    fun `getFolders() should ignore NonExistent entries`() {
+        val imapStore = createTestImapStore(isSubscribedFoldersOnly = false)
+        val imapConnection = createMockConnection().stub {
+            on { hasCapability(Capabilities.LIST_EXTENDED) } doReturn true
+            on { hasCapability(Capabilities.SPECIAL_USE) } doReturn true
+            on { executeSimpleCommand("""LIST "" "*" RETURN (SPECIAL-USE)""") } doReturn listOf(
                 createImapResponse("""* LIST (\HasNoChildren) "." "INBOX""""),
-                createImapResponse("""* LIST (\Noselect \HasChildren) "." "Folder""""),
+                createImapResponse("""* LIST (\NonExistent \HasChildren) "." "Folder""""),
                 createImapResponse("""* LIST (\HasNoChildren) "." "Folder.SubFolder""""),
                 createImapResponse("6 OK Success"),
             )
@@ -135,6 +156,24 @@ class RealImapStoreTest {
         assertThat(folders.map { it.serverId }).containsExactly("INBOX", "Folder.SubFolder")
     }
 
+    @Test
+    fun `getFolders() with subscribedFoldersOnly = false`() {
+        val imapStore = createTestImapStore(isSubscribedFoldersOnly = false)
+        val imapConnection = createMockConnection().stub {
+            on { executeSimpleCommand("""LIST "" "*"""") } doReturn listOf(
+                createImapResponse("""* LIST (\HasNoChildren) "." "INBOX""""),
+                createImapResponse("""* LIST (\HasNoChildren) "." "Folder""""),
+                createImapResponse("6 OK Success"),
+            )
+        }
+        imapStore.enqueueImapConnection(imapConnection)
+
+        val folders = imapStore.getFolders()
+
+        assertThat(folders).isNotNull()
+        assertThat(folders.map { it.serverId }).containsExactly("INBOX", "Folder")
+    }
+
     @Test
     fun `getFolders() with subscribedFoldersOnly = true should only return existing subscribed folders`() {
         val imapStore = createTestImapStore(isSubscribedFoldersOnly = true)