Exchange Web Services (EWS)Steve Hardy

- XML-based protocol (SOAP)- Introduced in Exchange 2007- Successor to previous WebDAV approach- Used from introduction for OWA 2007 and later

What is EWS

<?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>

• 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)

Who/what is using EWS at the moment?

- Uses HTTP authentication- Digest

- Kerberos

- NTLM

- Entire connection authenticated- All XML requests over a single HTTP connection are authenticated

as the same user

EWS Authentication

Authentication is done over multiple levels

•Username / Password authentication always possible•Unable to use NTLM authentication build in zarafa-server

– Per-store authentication (not per connection)

•Same goes for kerberos

EWS authentication: problems

Zarafa-ewsd

Zarafa-server

LDAP

EWS authentication: moving into zarafa-ewsd

Zarafa-ewsd

Zarafa-server

LDAP

NTLM/Kerberos

Trusted connection

• 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

Protocol versions

• Synchronization calls– SyncFolderHierarchy

– SyncFolderContents

• Used in synchronization clients– Works a lot like IMAP

– Gets incremental updates

Synchronize vs Live

Synchronization

Old state

ChangesSync state A

SyncFolderContents()

Synchronization

Old state

ChangesSync state B

• Used for– Search

– Archiving

– Anything that doesn’t require replication of data

Live access

• GetFolder()• GetItem()• FindFolder()• FindItem()

• MoveItem()• CopyItem()• DeleteItem()

Live access

Current store data

• 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

MIME vs MAPI

MIME vs MAPI

MIME MAPI

RFC822 contentSingle blob of data

FromTo

SubjectHeaders

DateBody

RecipientsAttachments

• 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)

MIME vs MAPI

• EWS supports various notification models• Client can subscribe for events• Three modes

– Polling

– Push

– Pull

Notifications

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

Polling events

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

Pull

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)

Push

• 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

The socket problem

The socket solution

Main server

Forkedworker

request

The socket solution

Main server

Forkedworker

reply

The socket solution

Main server

Forkedworker

Waiting for notificationevent

The socket solution

Main server

Forkedworker

Socket passed back toMain server, which handlesnotifications

The socket solution

Main server

Main processReplies afterSome time

• 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

The wsdl file