webbundle_study

format/spec discussion about WebBundles
at #webbundle_study https://web-study.connpass.com/event/155002/

Transcript

1. #webbundle_study #webbundle_study 2019/12/12 Jxck
2. WebPackaging Spec • SXG (was Signing) • WebBundles (was Bundling) • Loading 2
3. draft-yasskin-wpack-bundled-exchanges-02 3
4. Web Bundles Spec 4 • Yes: How parser work • No: How encoder produce bundle
5. 5 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] All you need is CBOR encoder/decoder
6. 6 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [* any ], length: bytes .size 8 ] magic number via emoji in UTF8 webbundle file start with cbor array header(length 6) + magic so first 10 byte is below [0x86, 0x48, 0xF0, 0x9F, 0x8C, 0x90, 0xF0, 0x9F, 0x93, 0xA6] (if array length changes with adding more element to cbor array in the future. first 10 byte will change, before you reach to version number.)
7. 7 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [* any ], length: bytes .size 8 ] cbor version "1" is in this spec, chrome uses "b1" for beta.
8. 8 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [* any ], length: bytes .size 8 ] URL for this content. if parse errors, this will use as fallback url.
9. 9 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [* any ], length: bytes .size 8 ] index for section, enables direct access to section. ["index", 100, // 0- 99 "responses", 200, // 100-199 "manifest", 300, // 200-299 "signatures", 400, // 300-399 "critical", 500] // 400-499
10. 10 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] Index Section index for response section. URL => [variation, offset, length] { "http://example.com/index.html": [["ja"], 1, 100], // for Accept-Encoding: ja "http://example.com/index.html": [["en"], 101, 100], // for Accept-Encoding: en "http://example.com/style.css": [[ ], 201, 100], "http://example.com/script.js": [[ ], 301, 100], "http://example.com/favicon.ico": [[ ], 401, 100], } variation: based on Content-Language, Content-Encoding(?),
11. 11 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] Responses Section [ [ HTTP Header (Cbor Map) HTTP Body (Cbor Byte string) ], [ HTTP Header (Cbor Map) HTTP Body (Cbor Byte string) ] ... ]
12. 12 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] Manifest Section manifest = manifest-url
13. 13 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] Signature Section signatures = [ authorities: [*authority], vouched-subsets: [*{ authority: index-in-authorities, sig: bstr, signed: bstr ; Expected to hold a signed-subset item. }], ] // Reject all signatures by an RSA public key.
14. 14 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] Critical Section > The "critical" section lists sections of the bundle that the client needs to understand in order to load the bundle correctly ???
15. 15 Top Level Structure ; CBOR Array webbundle = [ magic: h'', ; UTF-8 version: bytes .size 4, primary-url: whatwg-url, section-lengths:bytes.cbor [*(section-name:tstr,length:uint)], sections: [*(index|manifest|signatures|critical|responses)], length: bytes .size 8 ] Length length of webbundle in self extracting executables (like ASAR in Electron), pointer in tail works fine. because of concatnating $ cat runtime webpackage > extracting_bin $ cat extracting_bin other_webpackage https://github.com/WICG/webpackage/issues/20
16. overview • format via cbor • has index for direct access • can contain ◦ index ◦ response ◦ signature ◦ manifest (url) ◦ etc 16
17. Serve Webbundle • Via HTTP ◦ Content-Type: application/webbundle ◦ X-Content-Type-Options: nosniff • Vai other ◦ USB ◦ AirDrop ◦ WebShare ◦ etc 17
18. how it works 18
19. 19 Q: 1 Magic String & File detection webbundle = [ magic version // 1 primary-url section-lengths sections length ] head = read_first_10_byte(path) if (head == [86 48 F0 9F 8C 90 F0 9F 93 A6]) { // this is web bundle switch (parse_cbor(path)['version']) { // version switch } } else { // this is not web bundle }
20. 20 Q: 1 Magic String & File detection webbundle = [ magic version // 2 primary-url section-lengths sections extension // new length ] head = read_first_10_byte(path) if (head == [86 48 F0 9F 8C 90 F0 9F 93 A6]) { // this is web bundle switch (parse_cbor(path)['version']) { // version switch } } else if (head == [87 48 F0 9F 8C 90 F0 9F 93 A6] // this is also new web bundle switch (parse_cbor(path)['version']) { // version switch } } else { // this is not web bundle }
21. 21 Q: 1 Magic String & File detection // current webbundle = [ magic version primary-url section-lengths sections length ] // seems better ? webbundle = [ magic body = [ version primary-url section-lengths sections ] length ] // first 10 byte always starts in any version // “83 48 F0 9F 8C 90 F0 9F 93 A6” https://github.com/WICG/webpackage/issues/528
22. 22 Q: 2 Length at end // current webbundle = [ magic version primary-url section-lengths sections length ] move length at last really works? https://github.com/WICG/webpackage/issues/20#issuecomment-564370002
23. 23 Related • Web Bundles ◦ https://wicg.github.io/webpackage/draft-yasskin-wpack-bundled-exchan ges.html
24. Jack