In data processing, the Mask-Control is a heading of the protocol HTTP concerning the Mémoire hiding place. Indeed the majority of the navigators Web use a reserved space on the hard drive to record a copy of the pages which are visited (often). Thus when the user asks for a page, the navigator post sometimes simply the copy which it had, to gain of time. The button to reload (reload) some navigator allows to update the page.

HTTP/1.0

This level of the protocol, it allows only one control of the rudimentary mask

Pragma: No-mask

Allows the navigator to indicate to the mask to rather recover the document near the waiter of origin than to return that to him which it preserves.

HTTP/1.1

This level of the protocol, the heading Mask-Control offers more possibility. The navigator or the waiter can give directives to a mask.

The heading Mask-Control has as a value a list of directives, separated by commas. Specification HTTP/1.1 in RFC 2616 defines several values for the heading Mask-Control. Some are used very little.

public

Answer HTTP can be put out of mask by any mask. A customer or a waiter proxy can put out of mask for example the answer. That allows the division of contents through the users who use the same waiter proxy.

For example, if a document is referred after authentification of the user by the waiter and that this authentification is intended only to make statistics and not an access control, the document can be regarded as public.

private

The message of answer is intended for a single customer and does not have is put out of mask by a divided mask. A waiter proxy should not put for example hiding place the answer of it although a customer capacity to put out of mask. That makes it possible to the customer to hold up to date a version put in memory hiding place while all the customers who use the same waiter proxy preserve the different versions put in memory hiding place.

No-mask

No mask in the integrality of access path must maintain a copy put out of hiding place of the answer. That enables you to specify that the following request for the same contents will be obligatorily returned by the waiter and not by a proxy or hides it of the navigator.

No-blind

No-transform

The directive No-transform indicates to the mask which it should not transform the body of the message that it receives.

Indeed, when the mask has behind him a line with low flow, it can be interesting to compress all the answers which it sends (Content-Encoding: gzip). The directive No-transform prohibits this kind of initiative.

max-old

This directive indicates to the mask that the customer wants a document whose freshness is to the maximum the age indicated in second.

Mask-control: max-age=600

With this directive, the mask is requested to refer a document which was produced there is at more the 10 minutes (Date heading). If not the waiter of origin is contacted to obtain a more recent version.

If the directive max-old appears in an answer, it exceeds the Expires heading.

max-stall

min-fresh

min-towards

must-revalidate

proxy-revalidate

only-yew-cached

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