#webbundle_study #webbundle_study 2019/12/12 Jxck

WebPackaging Spec ● SXG (was Signing) ● WebBundles (was Bundling) ● Loading 2

draft-yasskin-wpack-bundled-exchanges-02 3

Web Bundles Spec 4 ● Yes: How parser work ● No: How encoder produce bundle

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 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 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 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 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 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 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 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 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 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 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

overview ● format via cbor ● has index for direct access ● can contain ○ index ○ response ○ signature ○ manifest (url) ○ etc 16

Serve Webbundle ● Via HTTP ○ Content-Type: application/webbundle ○ X-Content-Type-Options: nosniff ● Vai other ○ USB ○ AirDrop ○ WebShare ○ etc 17

how it works 18

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 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 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 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 Related ● Web Bundles ○ https://wicg.github.io/webpackage/draft-yasskin-wpack-bundled-exchan ges.html

Jack