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Zarafa SummerCamp 2012 - Exchange Web Services, technical information
- 1. Exchange Web Services (EWS) Steve Hardy
- 2. What is EWS - XML-based protocol (SOAP) - Introduced in Exchange 2007 - Successor to previous WebDAV approach - Used from introduction for OWA 2007 and later <?xml version="1.0" encoding="utf-8"?> <soap:Envelope> <soap:Body> <GetItem> <ItemShape> <t:BaseShape>Default</t:BaseShape> <t:IncludeMimeContent>true</t:IncludeMimeContent> </ItemShape> <ItemIds><t:ItemId Id="AAAlAF" ChangeKey="CQAAAB" /></ItemIds> </GetItem> </soap:Body> </soap:Envelope>
- 3. Who/what is using EWS at the moment? • Outlook 2010 – Free/Busy – Some minor features • Mac – Outlook 2011 – ‘Mail’ – ‘Addressbook’ – ‘Calendar’ • Other – Various opensource projects for accessing exchange server from opensource packages (eg. Evolution, Thunderbird, etc) – Various closed source projects (eg. Archivers, Indexers, etc)
- 4. EWS Authentication - Uses HTTP authentication - Digest - Kerberos - NTLM - Entire connection authenticated - All XML requests over a single HTTP connection are authenticated as the same user
- 5. EWS authentication: problems Authentication is done over multiple levels Zarafa-ewsd •Username / Password authentication always possible •Unable to use NTLM authentication build in zarafa-server Zarafa-server – Per-store authentication (not per connection) •Same goes for kerberos LDAP
- 6. EWS authentication: moving into zarafa-ewsd Zarafa-ewsd NTLM/Kerberos Trusted connection Zarafa-server LDAP
- 7. Protocol versions • Exchange 2007 – Original version • Exchange 2010 – Bulk transfer – Conversations – Exchange search – Inbox rules – Message tracking – Unified messaging – User configuration • Also differences in service packs – Message identifiers changes between RTM and SP1 of Exchange 2007
- 8. Synchronize vs Live • Synchronization calls – SyncFolderHierarchy – SyncFolderContents • Used in synchronization clients – Works a lot like IMAP – Gets incremental updates
- 9. Synchronization Old state Sync state A Changes SyncFolderContents()
- 10. Synchronization Old state Changes Sync state B
- 11. Live access • Used for – Search – Archiving – Anything that doesn’t require replication of data
- 12. Live access • GetFolder() • GetItem() • FindFolder() • FindItem() • MoveItem() Current store data • CopyItem() • DeleteItem()
- 13. MIME vs MAPI • Many current EWS clients started out as IMAP client • IMAP structure of clients is ‘synchronize’ pattern – SyncFolderHierarchy() / SyncFolderContents() • Actual email contents can be represented by – MIME content – MAPI content • MIME content – Same problem as for IMAP gateway, entire RFC822 message must be stored
- 14. MIME vs MAPI MIME MAPI From To Subject Headers RFC822 content Date Single blob of data Body Recipients Attachments
- 15. MIME vs MAPI • Mac ‘Mail’ – MIME • Outlook 2011 – MAPI • MAPI preferred due to – Overhead of converting to MIME (still needed in spite of RFC822 storage) – Modifications are always in MAPI model (you cannot modify the MIME data) – Why re-parse the email when the server has already done it – More efficient data access (possible to read separate attachments instead of entire email only)
- 16. Notifications • EWS supports various notification models • Client can subscribe for events • Three modes – Polling – Push – Pull
- 17. Polling events 1. Subscribe (any change in inbox) -> Subscription ID 2. GetEvents(subscription id) -> 0 or more events 3. Sleep(60) 4. Goto 2 Pro: easy Con: requires request every N seconds Con: latency N seconds
- 18. Pull 1. Subscribe (any change in inbox) -> Subscription ID 2. GetEvents(subscription id, timeout 60s) -> 0 or more events 3. Goto 2 Pro: Only one call per, say, 10 minutes Pro: Latency in the millisecond range Con: Requires TCP open connection at all times
- 19. Push 1. Subscribe (any change in inbox, call me back at http://server:port/url) -> Subscription ID 2. Wait for server to connect Pro: No calls open to server Con: server must be able to contact client (only useful in server-to-server applications)
- 20. The socket problem • With ‘pull’ notifications – Each client has open socket – Zarafa-ewsd is ‘forked’ – Normally this would mean 1 process per client – 10000 users = 10000 process – Bad for memory consumption and scalability
- 21. The socket solution request Main Forked server worker
- 22. The socket solution reply Main Forked server worker
- 23. The socket solution Main Forked server worker Waiting for notification event
- 24. The socket solution Main Forked server worker Socket passed back to Main server, which handles notifications
- 25. The socket solution Main server Main process Replies after Some time
- 26. The wsdl file • Wsdl file(s) define the SOAP structure • We must present a wsdl that is compatible with exchange EWS • We cannot ship the file from exchange directly due to copyright • Generating our own may introduce subtle differences • Unknown if clients actually read the file in practice