backchannel: browser image caching

I suggest that CRVL rules on not overquoting posts due to bandwidth restrictions are well-intentioned but poorly informed.  For example, text is incredibly “cheap” and multimedia is “expensive” to transmit. Consider this ad on the first page I loaded:


The ad is 53kb.  That is 5x the bandwidth required to transmit the the Declaration of Independence.

Plus text is highly compressible compressible by the server.  For example, the ad above requires about the same bandwidth as Dickens’ A Christmas Carol when compressed during transmission (as CRVL does).

Image caching

Anyhow, this particular issue was about quoting image references in posts.  I claimed:

...repeated identical pictures do not affect data;  the browser reuses the previous image and shows it again.

and received a thoughtful response that challenged part of it.  I wrote my counter and deleted it, as I didn’t want to digress further or annoy my thoughtful respondent.   My thoughts below:

You can't know that for sure. Yes, on a laptop or desktop PC, with a standard modern browser, that is usually the case.

For sure, no.  But it is exceedingly likely.  The http 1.0 RFC included caching by Berners-Lee has been the de facto standard for over 20 years.

Even ultra-lightweight browsers like dillo implement entity caching (of which images are a type) by default.

On mobile, iOS safari, chrome, android browser, opera, and firefox implement caching by default.

But, it really depends on the forum software: it can force reloading of images thru codes and scripts.

It can, but the default is not to force reloading because it increases resource use on the server.  Cache server directives are used, for example, when one has a stable image URL for an image that changes over time.  That is not the case with user-uploaded images.

The only entity in the thread that was forbidden to cache by CRVL was the Google ads javascript.  Everything else could be (and should be) reused by the browser.

It might be set to do exactly that, especially if someone logs in to 'last unread' and the browser has not cached that image in a recent browsing session.

I don’t think this is a good example of when it would happen.  Browser caches are limited by allotted space, assuming no cache server directives have been issued.

And if the server is issuing directives to subvert caching, it’s not really the users’ responsibility to work around problems the admin has introduced.

It also depends on the cache settings of the user's browser, and I have no idea how Tap-a-Talk manages cached images.

In my experience providing technical support, very few people adjust the defaults. Most don’t know they exist.

Tapatalk handles entity caching in the app cache itself.

One thing that probably should be looked at is to disallow the uploading of large image files, or to set the forum software to automatically resize large images.

Agreed, although it seems most images on CRVL are linked rather than uploaded.  Maybe only thumbnails could be used so folks don’t have to d/l fullsize images they are not interested in.

Quotes are from this exchange.