2b:null 2c:["$","title",null,{"children":"[GameTools] AssetBundle of Unity | UnluckyNinja | Observable"}] 31:T504,

hex	00	01	04	08	0C
00	Metadata Size (old)		File Size (old)	Format Version	Data Offset (old)
10	Endianness	Reserved	Metadata Size (new)	File Size (new)
20	Data Offset (new)			Unknown

(Unity v2020.1+)

32:T51a,It's then processed as *metadata* in the following steps ([link](https://github.com/Perfare/AssetStudio/blob/master/AssetStudio/SerializedFile.cs#L68)): 1. A string sequence including the terminator byte (0x00), representing the Unity version created this file. Usually 12 bytes long, like `32 30 32 32 2E 32 2E 31 38 66 31 00` which is "2022.2.18f1". 2. An **Int32** representing [build target platform](https://github.com/Perfare/AssetStudio/blob/master/AssetStudio/BuildTarget.cs) *[metadata start]* 3. A **boolean** flag indicating if type tree is enabled 4. A **Int32** is read representing total number of types. 5. Then it processes serialized type information for every original file: 1. A **Int32** is read that represents the class ID. 2. A **boolean** flag indicating if it's stripped type. 3. A **Int16** representing its script type index. - if some conditions fulfilled, a **16-byte-long** script ID is read. 4. A **16-byte-long** old type hash is read. - Some more read if type tree is enabled. 5. So the minimal total length is 4(class ID) + 1(flag) + 2(script type index) + 16(hash) = **23 bytes**, \+ 16(if there is a script id) = **39 bytes**, + ???(if type tree enabled) = **??? bytes** 6. A Int32 is read as total objects count. 7. ... (TBD)33:T9d4,fileType = { const gzipMagic = [ 0x1f, 0x8b ]; // start at 0 const brotliMagic = [ 0x62, 0x72, 0x6F, 0x74, 0x6C, 0x69 ]; //start at 20 const zipMagic = [ 0x50, 0x4B, 0x03, 0x04 ]; // start at 0 const zipSpannedMagic = [ 0x50, 0x4B, 0x07, 0x08 ]; // start at 0 if (!fileInfo?.file) return const file = fileInfo.file // https://github.com/Perfare/AssetStudio/blob/master/AssetStudio/FileReader.cs // === check for hardcoded header string const uarray = new Uint8Array(await file.slice(0, 26).arrayBuffer()) const signature = await utils.getSignature(uarray) switch (signature) { case "UnityWeb": case "UnityRaw": case "UnityArchive": case "UnityFS": return 'BundleFile'; case "UnityWebData1.0": return 'WebFile'; } // === check for magic bytes if (utils.isEqualMagic(uarray.slice(0, 2), gzipMagic)) return 'gzip' if (utils.isEqualMagic(uarray.slice(20, 26), brotliMagic)) return 'brotli' const temp = uarray.slice(0, 4) if (utils.isEqualMagic(temp, zipMagic) || utils.isEqualMagic(temp, zipSpannedMagic)) return 'zip' // === Asset file // var m_MetadataSize = ReadUInt32(); // 0 to 4 // long m_FileSize = ReadUInt32(); // 4 to 8 // var m_Version = ReadUInt32(); // 8 to 12 // long m_DataOffset = ReadUInt32(); // 12 to 16 // var m_Endianess = ReadByte(); // 16 to 17 // var m_Reserved = ReadBytes(3); // 17 to 20 // note: asset file is big-endian if (file.size < 20) return 'resource file (or other)' const m_version = new Uint32Array(uarray.slice(8, 12).buffer)[0] let m_metadataSize, m_fileSize, m_dataOffset if (m_version >= 22) { if (file.size < 48) return 'resource file (or other)' const new_uarray = new Uint8Array(await file.slice(20, 40).arrayBuffer()) m_metadataSize = new Uint32Array(new_uarray.slice(0, 4).reverse().buffer)[0] m_fileSize = new BigUint64Array(new_uarray.slice(4, 12).reverse().buffer)[0] m_dataOffset = new BigUint64Array(new_uarray.slice(12, 20).reverse().buffer)[0] } else { m_metadataSize = new Uint32Array(uarray.slice(0, 4).reverse().buffer)[0] m_fileSize = new Uint32Array(uarray.slice(4, 8).reverse().buffer)[0] m_dataOffset = new Uint32Array(uarray.slice(8, 12).reverse().buffer)[0] } mutable metadata = { m_metadataSize, m_fileSize, m_dataOffset } if (m_fileSize != file.size) { return 'resource file (or other)'; } else if (m_dataOffset > file.size) { return 'resource file (or other)'; } return 'asset' }34:[] 2f:{"id":"676b886ffbee188b","slug":null,"title":"[GameTools] AssetBundle of Unity","thumbnail":"8499f34387d5f53aef259e4607fc505dc64941d7c17efc1f52f8daad692225c7","access_level":"public","create_time":"$D2023-08-22T21:10:51.532Z","update_time":"$D2024-10-02T09:12:44.713Z","view_time":null,"first_public_time":"$D2023-08-22T21:10:51.532Z","has_unpublished_edits":null,"fork":false,"stars":0,"starred":false,"owner":{"type":"team","id":"ebb6118c9a990a2c","login":"unluckyninja","name":"UnluckyNinja","avatar_url":"https://avatars-next.observableusercontent.com/95d8d23bafa30b0b30e2ead4a72666d02cc17899c3c958c22c65fc0fc09afe3d","tier":"starter_2024"},"version":338,"publish_version":null,"role":null,"authored":false,"authors":[{"type":"individual","id":"4df1f6fd87aa7295","login":"unluckyninja","name":"UnluckyNinja","avatar_url":"https://avatars-next.observableusercontent.com/95d8d23bafa30b0b30e2ead4a72666d02cc17899c3c958c22c65fc0fc09afe3d","tier":null}],"members":[{"type":"individual","id":"4df1f6fd87aa7295","login":"unluckyninja","name":"UnluckyNinja","avatar_url":"https://avatars-next.observableusercontent.com/95d8d23bafa30b0b30e2ead4a72666d02cc17899c3c958c22c65fc0fc09afe3d","tier":null,"role":"editor"}],"comments":[],"custom_thumbnail":false,"trashed":false,"lapsed":null,"subscribed":null,"forks":0,"collection":{"id":"6cb821d5a6280f87","slug":"games","title":"GameTools","owner":{"id":"ebb6118c9a990a2c","login":"unluckyninja","name":"UnluckyNinja"}},"type":"notebook","body":{"title":"[GameTools] AssetBundle of Unity","cells":[{"id":0,"value":"# [GameTools] AssetBundle of Unity","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":179,"value":"For an asset built by Unity, there is a 48-byte-long header chunk, written in big-endian.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":181,"value":"$31","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":240,"value":"Beyond this chunk, the file is read according to the endian specified in file header, 0 == little endian, 1 == big endian.","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":248,"value":"$32","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":11,"value":"newDropArea(fileInfo, dnd.dropHandler((r)=>mutable fileInfo = r), dnd.dragover)","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":14,"value":"mutable fileInfo = null","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":146,"value":"mutable metadata = null","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":24,"value":"$33","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":102,"value":"utils = {\n async function getSignature(buffer){\n let endpos = buffer.indexOf(0)\n return await new Blob([endpos < 0 ? buffer : buffer.slice(0, endpos)]).text()\n }\n function isEqualMagic(arraylike, magic){\n if(arraylike.length !== magic.length) return false\n return magic.every((ele, i)=>{\n return ele === arraylike[i]\n })\n }\n return {\n getSignature,\n isEqualMagic,\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":32,"value":"{\n const blob = new Blob([new Uint8Array([33,33,33,0,33])],{type:'text/plain'})\n return blob.text()\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":205,"value":"","pinned":false,"hidden":false,"mode":"html","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":22,"value":"## References\nCredits to https://github.com/Perfare/AssetStudio","pinned":false,"hidden":false,"mode":"md","author":"$undefined","summary":"$undefined","output":"","database":"$undefined"},{"id":325,"value":"{\n return {\n totalJSHeapSize: performance.memory.totalJSHeapSize,\n usedJSHeapSize: performance.memory.usedJSHeapSize,\n jsHeapSizeLimit: performance.memory.jsHeapSizeLimit,\n }\n}","pinned":false,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"},{"id":9,"value":"import { newDropArea, dnd } from 'bdb2210de11ab75a'","pinned":true,"hidden":false,"mode":"ojs","author":"$undefined","summary":"$undefined","output":"$undefined","database":"$undefined"}],"files":"$W34","stdlib":"1","titling":"auto"}} 30:"$2f:body"