Ask HN:Whats the problem with SVG?

[lousy_sysadmin]

I've been playing around with Inkscape for a while now to create vector image as its one of the easiest solution for Retina-esque site. However I'm having a hard time finding image hosting that support SVG.

My question is, why is it so hard for image hosting service to support native SVG, instead of converting an image to other format. Would like to hear the limitations and challenges that comes with it.

http://imgur.userecho.com/topic/23630-svg-support/

[jahewson]

SVG implementations on browsers have historically been poor, though this is certainly improving. You'll hit many bugs and unsupported features. IE < 9 doesn't support SVG at all, and Safari < 6 only does so in XHTML. SVG fonts are sparsely supported. The alternative - rasterising SVG on the server - is a heavyweight task, I've not found any libraries which can do this quickly.

The worst problem may be SVG itself - SVG 1.2 which dates from 2004 was abandoned, and most browsers implement SVG 1.1 which is rather lacking in features. This makes it hard if you're a designer to produce SVG documents which a browser can actually render.

At a bare minimum any SVG hosting project would have to involve some sort of SVG lint, to make sure that browser-incompatible SVG elements are not present, implement workarounds for browser-specific bugs, and check that there are no <script> tags etc. The sheer size and complexity of even SVG 1.1 makes it non-trivial. One pragmatic approach to sanitize SVG may be to round-trip SVG -> PDF -> SVG via cairosvg and pdftocairo, though it may burn some CPU.

[mjn]

The alternative - rasterising SVG on the server - is a heavyweight task, I've not found any libraries which can do this quickly.

Wikipedia does it using librsvg, fwiw: https://live.gnome.org/LibRsvg

[jahewson]

Cool!

[ChuckMcM]

This is perhaps the best answer, browser support is poor. Rendering SVG to PNG prior to shipping it out works but you really want to cache it, not do that in real time.

I keep hoping that epub will generate a renaissance of interest in SVG. So far no luck.

[jarek-foksa]

SVG fonts are dead, so what? You can still embed other font formats the same way you do it in HTML/CSS.

You don't need to sanitize SVGs to host them safely - you just put them inside <img> tag and browsers will do sandboxing for you.

What features do you actually miss in SVG 1.1? Gradient meshes? 3d transforms? multiple fills? I can think of only advanced stuff that is rarely used and tricky to do with other web technologies anyway.

Also, why would you want to strip browser-incompatible SVG elements? Browsers will simply ignore such elements.

[jahewson]

Embedding other font formats in HTML != my SVG file can be rendered un-modified. If you put the raw SVG file in the browser it does not render. The SVG fonts would have to be extracted on the server side and converted to webfonts + CSS.

SVG rendered via an <img> tag has restrictions in browsers, for example Firefox will not allow the SVG to reference an external image file such as a jpg. Once again, you put the raw SVG file in the browser and it does not render...

Obviously I miss any SVG 1.2 feature which Inkscape lets me easily use. Compositing for example. User has "SVG" output from Inkscape, user puts it on an "SVG" hosting service, it does not render in the browser = unhappy user. Users don't care less about what version of SVG they are using.

Stripping browser-incompatible elements could be useful, for example, if I place my content inside an SVG 1.2 <page> then the browser will render nothing at all, where as if the server stripped out the <page> element first, I'd be able to see my content. Obviously this applies only to a single page tag. Once again, you put the raw SVG file in the browser and it does not render...

Bug-workarounds are the primary reason for wanting to manipulate the elements though, there is a Safari bug which can cause it to ignore <defs> but work if you switch out <defs> for <g>. Once again, you put the raw SVG file in the browser and it does not render...

[jarek-foksa]

Just because browsers can't render poorly authored SVG files doesn't mean that the format is not ready for prime use. Except for filters, animations and fonts, all modern browsers have good support for SVG 1.1, there are definitely fewer issues than with say CSS3 transitions or flexbox which are nonetheless misused by web develoeprs.

Inkscape is doing layer compositing by applying filters on groups. This is not SVG 1.2 feature. It was present in SVG 1.1 for years and it's still not properly implemented by all browsers and authoring tools: http://www.w3.org/TR/SVG/filters.html#feBlendElement

[jahewson]

> all modern browsers have good support for SVG 1.1

That is simply not true, as I've explained above. You can't call an SVG 1.1 file poorly authored because Safari has a bug displaying it, or Firefox doesn't support the filter you used. The fault is with the browser, not the end user.

> It was present in SVG 1.1 for years and it's still not properly implemented by all browsers

Now you're just contradicting yourself! Though "good support" was an ambiguous weasel phrase in the first place.

It's clear that you don't know much about what browsers do and don't support and what bugs exist, because your previous answer was so naively wrong. You need to not just trust statements like "supports SVG 1.1" on Wikipedia and actually apply your mind to discovering the nuanced details of what's actually out there.

[jarek-foksa]

I'm not contradicting myself, as I said: except for filters, animations and fonts, all modern browsers have good support for SVG 1.1. By "good support" I mean it's on pair or even better than HTML5 and CSS3 support.

Files that break cross-origin policy or use non-standard tags are poorly authored by my standards.

I have a lot of experience with SVG under WebKit-based browsers and so far everything renders just fine for me except for advanced features mentioned earlier.

[nwh]

I'd considered making one some time ago, but gave up when I realised that somebody had already purchased http://s.vg/.

[lmm]

XML being XML, it's hard-to-impossible to host SVG without allowing people to store arbitrary XML on your service, which sooner or later is going to be abused.

[emn13]

That's true for almost any hosting service - it's usually quite easy to encode other information in whatever wrapper is possible. Virtually all image formats (for instance) allow arbitrary metadata, and usually of arbitrary size. And if meta-data isn't allowed, a lossless format like PNG can easily be reinterpreted as a simple byte-array (e.g. 8bpp greyscale image).

Of course, why would anyone bother? It's that hard to find hosters that will host anything, so why do through the hassle to encruft your data with some somewhat unwieldy wrapper?

The fact that it's XML is in some way a "protection" here since for no particularly good reason some character codes cannot be represented by xml (not even encoded), meaning you'll need ugly workarounds to store arbitrary data.

[JD557]

Also, Its possible to use script tags to run javascript code in an svg.

If you really wanted to, you could pretty much make your own webpage run on the image hosting server.

Also, you could send a malicious script to someone hidden in a cute cat drawing, and it would look like it was the host's fault.

[threedaymonk]

I don't think this has to be a problem: it's actually rather straightforward to write some XSLT to process incoming XML and emit only whitelisted elements and attributes.

[mbq]

_Arbitrary_ SVG is a security/privacy problem -- it may inject JS or exploit quirks in rendering to manipulate site contents, import external images and fonts, or simply be a render bomb. And it is hard to filter out those problems.

[nwh]

You could just have a dedicated domain for it, then there's no risk of XSS. It's doable, but it would be rather fragile.

The render bomb point is a little trickier, as you can use some detailed filters to crash most browsers. Heck, even a single simple shape will crash any version of iOS.

[pre]

It's not hard, probably the image hosts concerned merely didn't think to include it.

You can upload svg files with the right content type to Amazon S3 without trouble, is that not good enough?

[youngtaff]

My question is why do you want to host your SVG images elsewhere?

If you just want to shop them you could convert them to bitmap or host them on GitHub

If you want to include them on your website, they're small and compress well with gzip so why have the complexity of relying on a third party services

It you have too much traffic to be able to host them yourself then you should look at something like a CDN e.g. Cloudfront, infront of S3

[timrogers]

I'm guessing you could maybe host it with Gists, using the raw link? Although the content type headers might be an issue...

[lsiebert]

It's not hard. However, I'd note that IE didn't have built in support until 2011, and the first browser with native svg support was Konqueror in 2004, whereas gif and jpeg have been around for a lot longer.

Isn't SVG just XML? I'd assume you could host it that way.

[KorvinSzanto]

It's XML based, really only uses a different schema.

[tobyink]

What schema does XML normally use?

[Zash]

XML has no default schema.

[Turing_Machine]

You might look at http://openclipart.org/ to see how they're handling it.

[wisty]

IE6. XML viruses.