What exactly is the webPermMasks property?

Question

I'm trying to understand what exactly is the "webPermMasks" property inside the "_spPageContextInfo" object, I tried to look in many websites on the web and also in the MSDN.

In the MSDN I wasn't able to find anything... and on another website the only thing I found is a very basic (and not very useful) answer that is: "Object with properties High & Low" which in my opinion doesn't really explain anything.

Can anyone please try to give me a better explaination?

Cheers and thanks in advance!

Answer 1

webPermMasks are TWO 32-bit integers indicating which permissions a user has.

Each bit represents a permission.

(_spPageContextInfo.webPermMasks.High).toString(2)
(_spPageContextInfo.webPermMasks.Low).toString(2)

Displays the bits

High & Low

In the good old days computer worked with 8 bits, which someone named a Byte.
With 8 bits (8 permissions) you can only count from 0 to 255

So to store a larger number of 16 bits (0- 32768) on an 8-bit CPU you need 2 Bytes.

We called these the High-Byte and the Low-Byte

SharePoint has 37 types of permissions

Present computers have evolved from CPUs that can handle 8-bits to 16-bits to 32-bits

Currently SharePoint has 37 different Security permissions.. which do not fit in those 32 bits

Like so many moons ago you need TWO 32-bit values to encode Permissions
Which some Microsoft engineer with common sense named the High and Low value

The SP.js library (available standard on most pages) has the information on which Permission is which bit number

Run this in the developer console:

for (var permLevelName in SP.PermissionKind.prototype) {
    if (SP.PermissionKind.hasOwnProperty(permLevelName)) {
        var permLevel = SP.PermissionKind.parse(permLevelName);
           console.info(permLevelName,permLevel);
        }
    }
}

Note permLevel is not the value, it is the bit-number

SP.PermissionKind.openItems is bit-number 6 and thus value 2^6

If you add up all the values you get the High order and Low order integer values for Permissions.

Note permLevel for SP.PermissionKind.manageAlerts is the 39th bit

This is in the High order integer, so the value is 2^(39-31)

webPermMasks

   _spPageContextInfo.webPermMasks.Low
   _spPageContextInfo.webPermMasks.High

Gives you 64 bits in TWO 32 bit Integers (with 37 permissions only a few are used in the High order)

indicating what Permissions the Current User has on the Current Page

All PermissionKinds (SP.PermissionsKnd.[name])

Note: This is the bit-number, not the value!

To check if someone has permissions, You have to calculate the (summed) value then binary check against the High and Low order integers.

    viewListItems: 1
    addListItems: 2
    editListItems: 3
    deleteListItems: 4
    approveItems: 5
    openItems: 6
    viewVersions: 7
    deleteVersions: 8
    cancelCheckout: 9
    managePersonalViews: 10
    manageLists: 12
    viewFormPages: 13
    anonymousSearchAccessList: 14
    open: 17
    viewPages: 18
    addAndCustomizePages: 19
    applyThemeAndBorder: 20
    applyStyleSheets: 21
    viewUsageData: 22
    createSSCSite: 23
    manageSubwebs: 24
    createGroups: 25
    managePermissions: 26
    browseDirectories: 27
    browseUserInfo: 28
    addDelPrivateWebParts: 29
    updatePersonalWebParts: 30
    manageWeb: 31
    anonymousSearchAccessWebLists: 32
    useClientIntegration: 37
    useRemoteAPIs: 38
    manageAlerts: 39
    createAlerts: 40
    editMyUserInfo: 41
    enumeratePermissions: 63

Use in script

The SP library supplies a function to check for individual levels:

  SP.PageContextInfo.get_webPermMasks().has( [bitnumber] );

  SP.PageContextInfo.get_webPermMasks().has( SP.PermissionKind.enumeratePermissions );

Using unused space (tales of the past)

Only a handfull of bits in the High Order integer are used by SharePoint.

Yet the database stores all 32 bits...

When we still built SharePoint Back End stuff we would use those unused bits for our own Permission scheme.

The free trials we let everyone install was actually the full blown product.
And when they bought the Licensed Product.. all it did was flip one bit in the database.

J1 iSPT

Answer 2

It's not "quite simple". The values high and low are used to determine permissions. The only function in SP that uses webPermsMask is called SP.PageContextInfo.get_webPermMasks(). It returns a value of high or low (High=2147483647, Low=4294967295). Then that number is used to create a SP.ContextPermissions object to determine permissions. As far as I can tell this is exclusively used for Ribbon commands (to determine if a Ribbon command should be enabled or not) Take a look at this CommandUIHandler for example:

<CommandUIHandler
    Command="Ribbon.DesignTab.Site.Logo"
    EnabledScript="javascript:
        (function (){
            var p = SP.PageContextInfo.get_webPermMasks();
            return p &amp;&amp; p.has(SP.PermissionKind.manageWeb);
        }());"
    CommandAction="javascript:
    EnsureScript('SP.js', typeof SP.PageContextInfo, function () {
        var i = document.querySelector('.ms-siteicon-img'), src = i &amp;&amp; i.src;
        SP.SOD.execute('sp.ui.dialog.js', 'SP.UI.ModalDialog.showModalDialog', {
            url: SP.Utilities.Utility.getLayoutsPageUrl('prjsetng.aspx?section=logo'), autoSize: true,
            dialogReturnValueCallback: i &amp;&amp; function (result, retval) {
                if (!result) i.src = src;
                else if (!i) location.reload();
            }
        });
});" />

My guess is this property is used to determine if a website is in read only mode or not :)

Answer 3

quite simple :P. The variable return is:

Object {High: 2147483647, Low: 4294967295}

those two values are:

int.MaxValue: 2,147,483,647

uint.MaxValue: 4,294,967,295

Dont ask me why this values are stored into an array into de SharePoint context, but that it's

Greetings :)