Invalid ETAG error with BreezeJS and IE9 - sharepoint

Question

I am using BreezeJS with the SharePoint Adapter and get a consistent invalid etag error on the second and following POST request from client-side. Strangely, this does not happen in IE11 or the latest Google Chrome browser.
Here are some details on what is happening:
An Agenda item (id 3) is pulled from the server and has the etag value W/"4"
An update of the Agenda item is posted to the server with etag value W/"4"
Another update of the same item is posted to the server with etag value W/"4"
I get the error message: The etag value '4' specified in one of the request headers is not valid. Please make sure only one etag value is specified and is valid
The error message makes at lot of sense as we must not use the same ETAG value in two different requests. Using Google Chrome the second (and consequetive) POST request have the correctly incremented etag value. So in this case it would send W/"5" and everything would be fine.
I have noticed that the first POST request returns the new ETAG (W/"5") but it is not being applied to the second POST request. I am using the following versions:
BreezeJS: 1.4.13
Rest adapter: 0.2.3
SharePoint adapter: 0.2.3
For reference I have included the requests and responses for the three operations from Fiddler.
Get agenda item
GET http://intranet/test/_vti_bin/listdata.svc/Agenda?$filter=Id%20eq%203 HTTP/1.1
DataServiceVersion: 2.0
Accept: application/json;odata=verbose
X-Requested-With: XMLHttpRequest
Referer: http://intranet/test/SitePages/test.aspx#inmeeting/2
Accept-Language: da
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E; InfoPath.3)
Host: intranet
Connection: Keep-Alive
HTTP/1.1 200 OK
Cache-Control: no-cache
Content-Type: application/json;charset=utf-8
Vary: Accept-Encoding
Server: Microsoft-IIS/7.5
SPRequestGuid: e4a8e96a-d476-41e8-8445-ecd50fe8f78e
X-SharePointHealthScore: 0
DataServiceVersion: 2.0;
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
MicrosoftSharePointTeamServices: 14.0.0.7015
X-MS-InvokeApp: 1; RequireReadOnly
Date: Fri, 15 Aug 2014 10:28:59 GMT
Content-Length: 1491
{
"d" : {
"results": [
{
"__metadata": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)", "etag": "W/\"4\"", "type": "Microsoft.SharePoint.DataService.AgendaItem"
}, "ContentTypeID": "0x0100EF440AFE5EDF49AD87D3B9A9484C2C0300ACA340FAC0DE1D49B8514C10085EC342", "Title": "Welcome", "Meeting": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/Meeting"
}
}, "MeetingId": 2, "Documents": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/Documents"
}
}, "Links": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/Links"
}
}, "Responsible": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/Responsible"
}
}, "ResponsibleId": 1, "StartTime": "\/Date(1408622400000)\/", "EndTime": "\/Date(1408623120000)\/", "DurationInMinutes": 12, "Done": true, "Comments": null, "Sort": 0, "Id": 3, "ContentType": "Meeting Agenda", "Modified": "\/Date(1408105622000)\/", "Created": "\/Date(1408010077000)\/", "CreatedBy": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/CreatedBy"
}
}, "CreatedById": 1, "ModifiedBy": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/ModifiedBy"
}
}, "ModifiedById": 1, "Owshiddenversion": 4, "Version": "4.0", "Attachments": {
"__deferred": {
"uri": "http://intranet/test/_vti_bin/listdata.svc/Agenda(3)/Attachments"
}
}, "Path": "/test/Lists/Agenda"
}
]
}
}
First update of agenda item
POST http://intranet/test/_vti_bin/listdata.svc/Agenda(3) HTTP/1.1
Accept: application/json;odata=verbose
Content-Type: application/json;odata=verbose
DataServiceVersion: 2.0
X-RequestDigest: 0x5B15EE86ACA321A71DA9A2939E8FE1E2A29D3F6A60A6424C4F497DFFCD4D509836B6FB85A127CBBC947547D8AB7AE0E91CE6C72E7C359D6CF83351C024858D84,15 Aug 2014 10:26:46 -0000
X-HTTP-Method: MERGE
If-Match: W/"4"
X-Requested-With: XMLHttpRequest
Referer: http://intranet/test/SitePages/test.aspx#inmeeting/2
Accept-Language: da
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E; InfoPath.3)
Host: intranet
Content-Length: 82
Connection: Keep-Alive
Pragma: no-cache
{"Done":false,"__metadata":{"type":"Microsoft.SharePoint.DataService.AgendaItem"}}
HTTP/1.1 204 No Content
Cache-Control: no-cache
ETag: W/"5"
Server: Microsoft-IIS/7.5
SPRequestGuid: dc4896d6-91b9-4894-a169-c70889ad0747
X-SharePointHealthScore: 0
DataServiceVersion: 1.0;
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
MicrosoftSharePointTeamServices: 14.0.0.7015
X-MS-InvokeApp: 1; RequireReadOnly
Date: Fri, 15 Aug 2014 10:29:02 GMT
Second update of Agenda item
POST http://intranet/test/_vti_bin/listdata.svc/Agenda(3) HTTP/1.1
Accept: application/json;odata=verbose
Content-Type: application/json;odata=verbose
DataServiceVersion: 2.0
X-RequestDigest: 0x5B15EE86ACA321A71DA9A2939E8FE1E2A29D3F6A60A6424C4F497DFFCD4D509836B6FB85A127CBBC947547D8AB7AE0E91CE6C72E7C359D6CF83351C024858D84,15 Aug 2014 10:26:46 -0000
X-HTTP-Method: MERGE
If-Match: W/"4"
X-Requested-With: XMLHttpRequest
Referer: http://intranet/test/SitePages/test.aspx#inmeeting/2
Accept-Language: da
Accept-Encoding: gzip, deflate
User-Agent: Mozilla/4.0 (compatible; MSIE 7.0; Windows NT 6.1; WOW64; Trident/5.0; SLCC2; .NET CLR 2.0.50727; .NET CLR 3.5.30729; .NET CLR 3.0.30729; .NET4.0C; .NET4.0E; InfoPath.3)
Host: intranet
Content-Length: 81
Connection: Keep-Alive
Pragma: no-cache
{"Done":true,"__metadata":{"type":"Microsoft.SharePoint.DataService.AgendaItem"}}
HTTP/1.1 412 Precondition Failed
Cache-Control: private
Content-Type: application/json
Server: Microsoft-IIS/7.5
SPRequestGuid: 965fbf16-8911-426b-9a90-8b21b4a78008
X-SharePointHealthScore: 0
DataServiceVersion: 1.0;
X-AspNet-Version: 2.0.50727
X-Powered-By: ASP.NET
MicrosoftSharePointTeamServices: 14.0.0.7015
X-MS-InvokeApp: 1; RequireReadOnly
Date: Fri, 15 Aug 2014 10:29:02 GMT
Content-Length: 214
{
"error": {
"code": "", "message": {
"lang": "en-US", "value": "The etag value '4' specified in one of the request headers is not valid. Please make sure only one etag value is specified and is valid."
}
}
}
UPDATE 1
I have done some debugging and started at the _processSavedEntity method of the SPAdapter. In Chrome it receives the new ETAG value from the response, in IE9 it gets null. Tracing this back I ended in breeze.debug.js (1.4.13) at line 15156 where the response gets into the system. Calling the getAllResponseHeaders() methods on the jqXHR returns an empty string in IE9, while Fiddler shows the headers present (same as above). So, that's a bit of a mystery. BTW. I'm using jQuery 1.9.1.

Answer 1

The problem is that IE9 and previous, when receiving a response code 204 No Content, throws away all the response headers.
It is discussed here jQuery.ajax with POST or PUT has no response headers for IE8 and IE9
If there are no concurrency problems, the driver could sniff IE9 and previous and issue a HEAD (I don't know if SharePoint supports it) or a GET for the same entity.
But both hacks give concurrency problems. Which one is worse depends on the context.
In any case, the whole purpose of having ETags for optimistic concurrency is defeated.
I am afraid that there is no way to fully support optimistic concurrency for OData in IE9 and previous.