DRAFT: Implement IntRangeSet class to be used for IMAP ActiveSync

[amulet1]

I would like to rework some internals related to how Horde handles IMAP sync.

As this point it is just to introduce a class that could be used to work with UIDs effectively by storing them as sorted array of non-overlaping pairs like these: [start1, end1, start2, end2, ... ].

Based on my preliminary tests it would significantly outperform most array-based operations that are currently used, both memory- and speed-wise. The class is based on my work for an unrelated project.

The class is obviously will be further enhanced/reworked, and moved to the right place. So for how this is just a draft.

The class could be used for servers without MODSEQ too. For that we would have to keep flags differently - instead of keeping flags by UID/type like $flags[$uid]['read'], we would keep separate flags as instance of the IntRangeSet class with UIDs for which the flag is set, e.g.

// just a rough idea
$uids = new IntSetRange();
$read = new IntSetRange();
$flagged = new IntSetRange();
...
$read->add($uid);        // set flag
$read->remove($uid); // remove flag

// check if 'read' flag is set for UID
if ($read->contains($uid)) {
...

}

The class implements several optimized methods that should be helpful for syncing IMAP folders via Activesync:

• contains - uses binary search to locate specific UID
• union - add elements of another set to the current set
• intersect - keep elements that belong to current and another set
• subtract - remove elements from set that exist in another set.
• diff (static, optimized) - compares set A with B and returns 3 sets in a single pass: added, unchanged, removed
• __toString - returns IMAP message sequence string
• fromString - parses IMAP message sequence string

As the first step, the Horde_ActiveSync_Folder_Imap should be updated to use the new class.

Other potential uses: replace/improve Horde_Imap_Client_Ids class.

[ralflang]

This looks promising. Let's sync with Torben when it's in "ready for review" state.

[ralflang]

@amulet1 This looks pretty good already - do you feel it is ready?

[amulet1]

It still cannot be incorporated directly into any existing code without some serious changes in IMAP client, Activesync and possible in the Core. I am slowly (not enough time) studying the existing code to see how to fit it better. Plugging it here and there without overall redesign, just to have it, makes little sense.

[TDannhauer]

@amulet1 what is your proposal to continue with?