Add basic CONDSTORE support when fetching initial messages.

Store MODSEQ in the header cache, and use that to perform a "FETCH
CHANGEDSINCE" for header updates when initially downloading messages.

Further improvements could be made to add support when syncing.
Handling MODSEQ for FLAG updates while the mailbox is open would be
complicated by the fact that Mutt supports locally modified headers,
so we couldn't accept the new (or subsequent) MODSEQ.

However, this initial step may at least provide some benefit when
opening the mailbox, which is generally the most time and data
intensive.

1 files changed, 8 insertions, 0 deletions

diff --git a/init.h b/init.h
index c1724c13..30e1c766 100644
--- a/init.h
+++ b/init.h
@@ -1265,6 +1265,14 @@ struct option_t MuttVars[] = {
    ** it polls for new mail just as if you had issued individual ``$mailboxes''
    ** commands.
    */
+  { "imap_condstore",  DT_BOOL, R_NONE, OPTIMAPCONDSTORE, 0 },
+  /*
+   ** .pp
+   **
+   ** When \fIset\fP, mutt will use the CONDSTORE extension (RFC 7162)
+   ** if advertised by the server.  Mutt's current implementation is basic,
+   ** used only for initial message fetching and flag updates.
+   */
   { "imap_delim_chars",		DT_STR, R_NONE, UL &ImapDelimChars, UL "/." },
   /*
   ** .pp