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/14dbzMpsYPfkefAJos124uPrlkvW7jyPJhzjujSWws2k/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. 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. 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. To view this discussion on the web visit https://groups.google.com/a/chromium.org/d/msgid/blink-dev/CAMZNYAN7VRca4VfRqP7pi%2BnqwDuor4ZVjF9yDNH1mZcXteQURw%40mail.gmail.com.
