LGTM1 On Wednesday, February 14, 2024 at 2:36:10 AM UTC+1 Nidhi Jaju wrote:
On Wed, Feb 14, 2024 at 2:48 AM James Hartig <fastest...@gmail.com> wrote: My employer ran into the window size during our pre-production validation and it was difficult to debug since it was working in cURL, the zstd CLI, and only presented itself on certain URLs. I appreciate Nidhi responding to our issue so quickly and updating Chrome to have a more helpful error message in the future. The Go package we use already updated their default <https://github.com/klauspost/compress/pull/913> to 8MB (without any awareness to Chrome's size) which should help future users of that package but there might be other packages out there that might not have a low enough default. The updated Chrome error message will help but only if you run into that error message when testing; which might not if you happen to be testing with small responses. I'm not sure where developers should be looking to be aware of the window size. Does it make sense to mention in the Chrome Status entry? If the spec is updated that might be good enough but I just wanted to discuss other avenues that might be more developer-aware. Thank you, I've included these details about the window size limits under the "Interoperability and Compatibility Risks" section in the ChromeStatus entry. On Tue, Feb 13, 2024 at 6:43 PM Yoav Weiss (@Shopify) < yoavwe...@chromium.org> wrote: On Tue, Feb 13, 2024 at 9:29 AM Nidhi Jaju <nidhij...@chromium.org> wrote: On Tue, Feb 13, 2024 at 4:18 PM Yoav Weiss (@Shopify) < yoavwe...@chromium.org> wrote: Thanks for working on this!! This is extremely exciting! On Tue, Feb 13, 2024 at 1:11 AM Nidhi Jaju <nidhij...@chromium.org> wrote: Contact emails nidhij...@chromium.org Explainer https://docs.google.com/document/d/1aDyUw4mAzRdLyZyXpVgWvO- eLpc4ERz7I_7VDIPo9Hc/edit?usp=sharing Specification https://datatracker.ietf.org/doc/html/rfc8878 Design docs https://docs.google.com/document/d/14dbzMpsYPfkefAJos124uPrlkvW7j yPJhzjujSWws2k/edit?usp=sharing Summary Zstandard, or “zstd”, is a data compression mechanism described in RFC8878. It is a fast lossless compression algorithm, targeting real-time compression scenarios at zlib-level and better compression ratios. The "zstd" token was added as an IANA-registered Content-Encoding token as per https://datatracker.ietf.org/doc/html/rfc8878#name-content-encoding. Adding support for "zstd" as a Content-Encoding will help load pages faster and use less bandwidth, and spend less time and CPU/power on compression on our servers, resulting in reduced server costs. Blink component Internals>Network <https://bugs.chromium.org/p/chromium/issues/list?q=component:Internals%3ENetwork> TAG review https://github.com/w3ctag/design-reviews/issues/930 TAG review status Pending Risks Interoperability and Compatibility Servers that have a broken implementation of zstd might exist, but the risk of this is small. Additionally, middleware and middleboxes like virus checkers that intercept HTTPS connections might not support zstd, but might fail to remove it from the Accept-Encoding header in the request. Another known risk is interoperability between clients that support zstd regarding window frame sizes. In Chrome, we limit the window frame size to 8MB to prevent excessive memory usage, but this limit does not exist in curl and when using zstd directly. We have seen very few sites that use a window size larger than 8MB which causes decoding errors, but we have added new net error codes and debugging messages to help them understand what to do in this situation. I know we discussed <https://w3c.github.io/web-performance/meetings/2023/2023-09-TPAC/index.html#h.xn2d3li0b8op> this at length at the WebPerfWG. Can you summarize developments and/or findings since that discussion on that front? Should we expect the default output of CLI tools to be compatible with what we want to ship here? Should we expect interoperability between Chromium and e.g. curl? We've been discussing it with the zstd team at Meta at https://github.com/ facebook/zstd/issues/2713. The plan is to take it to the HTTP WG at the IETF and either file an errata or publish a new document with more strict window size guidelines. The zstd CLI tool currently supports up to 8MB as a default, so the same limit. The library will use 128MB by default, however, and Curl currently supports up to 128MB windows. We expect those defaults to change to match any spec changes. In practice, we've seen very limited reports of sites running into this limit, and we've added helpful messages in Chromium to guide anyone who does run into it. Thanks! Pushing that limit into the standard and having curl (and other tools) follow that makes sense and seems important. Thinking out loud, the main risk here is for folks to be testing their content outside of Chromium (e.g. with curl) and then have that content break in Chromium. At the same time if content is tested in Chromium, it will work in another client that supports larger windows. So the (seemingly small) risk here is one we take on ourselves, rather than risk we externalize on the ecosystem. Yes, that sounds right. We'll continue to push to standardize this behavior across the ecosystem. Gecko: Positive (https://github.com/mozilla/standards-positions/issues/775) WebKit: Positive (https://github.com/WebKit/standards-positions/issues/168) Web developers: Positive (https://crbug.com/1246971) Meta (Yann and Felix) and Akamai (Nic) are positive about zstd content-encoding on the browser. Meta has collaborated with us to improve the compression ratios for Meta origins during the experiment and is seeing positive user-level results. Alibaba is also supportive of shipping zstd support as they saw massive savings on their origins in terms of server CPU cost. Other signals: Ergonomics While both Zstandard and Brotli are clear wins over gzip content-encoding, which of Zstandard or Brotli to use depends on many factors, and site authors may need to experiment to identify the optimal choice for their content. Zstandard uses more memory for decompression than gzip. However, this is also true for Brotli, and we haven't seen any problems in practice. Activation The "zstd" Content-Encoding is not as widely supported by HTTP servers as gzip. Of the top 5 web servers, Nginx has a third-party module, which should also work for OpenResty (untested). Apache, IIS, and LiteSpeed appear to have no support. Explicit server support is often only necessary for dynamic content. For static (pre-compressed) content, Zstandard can often be supported just by configuration. Only one public CDN is known to be able to compress Zstandard itself, and some CDN's may require custom configuration to pass-through Zstandard correctly. Zstd support is not particularly difficult to implement for a server that already implements multiple content encodings. The C implementation has a straightforward API and there are implementations for many other languages. There is also a lively community of Zstandard enthusiasts which should help accelerate adoption. Security CRIME <https://en.wikipedia.org/wiki/CRIME> and BREACH <https://en.wikipedia.org/wiki/BREACH> mean that the resource being compressed can be considered readable by the document deploying them. That is bad if any of them contains information that the document cannot already obtain by other means. An attacker may provide correctly formed compressed frames with unreasonable memory requirements, and dictionaries may interact unexpectedly with a decoder, leading to possible memory or other resource-exhaustion attacks. It is possible to store arbitrary user metadata in skippable frames, so they can be used as a watermark to track the path of the compressed payload. It is important to note that these concerns apply to all compression formats, not just zstd. To mitigate these risks, similar to Brotli, we'll be advertising support for "zstd" encoding only if transferred data is opaque to proxies, to ensure that resources don't contain private data that the origin cannot read otherwise. I'm not sure what that means. Can you elaborate on that? This essentially means that, like Brotli, Zstd is only available in secure contexts <https://source.chromium.org/chromium/chromium/src/+/main:net/http/http_request_headers.cc;l=284-290;drc=4787fce6c51383f5631643ac3d14cc512d656de6> i.e. over https. Limiting zstd support to secure contexts makes perfect sense. However I believe the reason we're doing that for brotli is more around compatibility concerns with old network-based proxies <https://issues.chromium.org/issues/40930163> that aren't ready for non-gzip content-encodings. I don't think secure contexts do much to protect against BREACH if attackers can control parts of the response. At the same time, I don't know that we're doing anything on that front for other compression formats, so that seems fine. Adding zstd to third_party/ in Chromium adds a large new code surface that processes untrusted data, which inevitably brings risks of new security holes. However, this is mitigated by the extensive fuzzing and security analysis done on zstd by Google and other community members. Furthermore, zstd is implemented in C, which is not a memory-safe language, and the network service is not yet sandboxed on all platforms. WebView application risks Does this intent deprecate or change behavior of existing APIs, such that it has potentially high risk for Android WebView-based applications? Apps which use a WebView to display content from Meta's servers will suddenly start using Zstandard. Since we've already extensively tested our implementation against Meta's servers in Chrome, no problems are expected. There is a killswitch. No special treatment should be needed. Debuggability No special support needed. Zstd content-encoding support is exposed to the devtools protocol, so developers are able to override it and view the headers from the inspector. A new net error has been added for decoding errors related to window frame size. Will this feature be supported on all six Blink platforms (Windows, Mac, Linux, ChromeOS, Android, and Android WebView)? Yes Is this feature fully tested by web-platform-tests <https://chromium.googlesource.com/chromium/src/+/main/docs/testing/web_platform_tests.md> ? Yes (https://wpt.fyi/results/fetch/content-encoding/zstd <https://wpt.fyi/results/fetch/content-encoding/zstd?label=experimental&label=master&aligned> ) Flag name on chrome://flags enable-zstd-content-encoding Finch feature name ZstdContentEncoding Requires code in //chrome? False Tracking bug https://bugs.chromium.org/p/chromium/issues/detail?id=1246971 Launch bug https://launch.corp.google.com/launch/4266275 Measurement https://chromestatus.com/metrics/feature/timeline/popularity/4629 Adoption plan In our experimental group, around 1% of responses use "zstd" content-encoding. Given the significant benefits of zstandard over gzip, we'd like to see it increase to 10% within 2 years. Estimated milestones Shipping on desktop 123 DevTrial on desktop 117 Shipping on Android 123 DevTrial on Android 117 Shipping on WebView 123 Anticipated spec changes Open questions about a feature may be a source of future web compat or interop issues. Please list open issues (e.g. links to known github issues in the project for the feature specification) whose resolution may introduce web compat/interop risk (e.g., changing to naming or structure of the API in a non-backward-compatible way). The current standard, RFC8878, doesn't require a limit on the window size used by HTTP servers when compressing Zstandard. An update of some form will be needed to ensure interoperability. Link to entry on the Chrome Platform Status https://chromestatus.com/feature/6186023867908096 Links to previous Intent discussions Intent to Prototype: https://groups.google.com/a/chromium.org/g/blink-dev/c/ GDsI0Hw-jYk/m/Yc5QZWD-AwAJ Intent to Experiment: https://groups.google.com/a/ chromium.org/g/blink-dev/c/I6IWfl95gRU This intent message was generated by Chrome Platform Status <https://chromestatus.com/>. -- You received this message because you are subscribed to the Google Groups "blink-dev" group. To unsubscribe from this group and stop receiving emails from it, send an email to blink-dev+unsubscr...@chromium.org. 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