From 8c0f59f3f3add18a9ee8be767f54f43996ddbd78 Mon Sep 17 00:00:00 2001
From: Guilhem Moulin <guilhem@fripost.org>
Date: Sun, 20 Jan 2019 20:16:53 +0100
Subject: Note on migrations.

---
 README       | 2 +-
 interimap    | 4 ++++
 interimap.md | 4 +++-
 pullimap     | 5 +++++
 4 files changed, 13 insertions(+), 2 deletions(-)

diff --git a/README b/README
index 70bf1df..cb34ef1 100644
--- a/README
+++ b/README
@@ -1,6 +1,6 @@
 InterIMAP is a fast bidirectional synchronization program for QRESYNC-capable
 IMAP4rev1 servers.  PullIMAP retrieves messages a remote IMAP mailbox and
-deliver them to a SMTP session.  Consult the manuals for more information.
+deliver them to an SMTP session.  Consult the manuals for more information.
 
     https://guilhem.org/man/interimap.1.html
     https://guilhem.org/man/pullimap.1.html
diff --git a/interimap b/interimap
index 41a0cb9..0fb6c1c 100755
--- a/interimap
+++ b/interimap
@@ -162,6 +162,10 @@ $DBH->do('PRAGMA foreign_keys = ON');
             # also, lUID  < local.UIDNEXT and rUID < remote.UIDNEXT (except for interrupted syncs)
             # mapping.idx must be found among local.idx (and remote.idx)
         ],
+
+        # We have no version number in the schema, but if we ever need a
+        # migration, we'll add a new table, and assume version 1.0 if
+        # the table is missing.
     );
 
     # Invariants:
diff --git a/interimap.md b/interimap.md
index ca83dba..1831d39 100644
--- a/interimap.md
+++ b/interimap.md
@@ -398,7 +398,9 @@ Known bugs and limitations
 
  * Using `interimap` on two identical servers with a non-existent or
    empty *database* will duplicate each message due to the absence of
-   local ↔ remote UID association.
+   local ↔ remote UID association.  Hence one needs to manually empty
+   the mail store on one end when migrating to `interimap` from another
+   synchronisation solution.
 
  * `interimap` is single threaded and doesn't use IMAP command
    pipelining.  Synchronization could be boosted up by sending
diff --git a/pullimap b/pullimap
index e044df5..bd9b1cf 100755
--- a/pullimap
+++ b/pullimap
@@ -88,6 +88,11 @@ do {
     fcntl($STATE, F_SETLK, $struct_flock) or die "Can't lock $statefile: $!";
     my $flags = fcntl($STATE, F_GETFD, 0)       or die "fcntl F_GETFD: $!";
     fcntl($STATE, F_SETFD, $flags | FD_CLOEXEC) or die "fcntl F_SETFD: $!";
+
+    # We have no version number in the statefile, but if we ever need a
+    # migration, we'll add a 1-byte header for the version number, and
+    # assume version 1.0 if the size of the file is a multiple of 4
+    # bytes. (We can also use the fact that bytes 5 to 8 are never all 0.)
 };
 
 
-- 
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