Blob and File serialization steps drop the type attribute (all engines keep it; WPT asserts it)
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评估
- 难度
- 3/5
- 预计耗时
- 1-2 天
- 新手友好度
- 74/100
- Issue 类型
- 缺陷
- 描述清晰度
- 描述清楚
- 活跃度
- 活跃
- 技术栈
- html, javascript
- 领域
- web-dev
调研方向
Read the Blob and File serialization and deserialization sections in the File API specification, then inspect WPT's compare_Blob in html/webappapis/structured-clone/structured-clone-battery-of-tests.js. Update the four algorithms to preserve type and verify the structured-clone, postMessage, and IndexedDB cases pass.
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描述
The serialization and deserialization steps for Blob and File don't carry the type attribute, but every engine keeps it and WPT asserts it.
What the spec says
Blob's serialization steps set serialized.[[SnapshotState]] and serialized.[[ByteSequence]], and the deserialization steps restore only those two. File's steps add [[Name]] and [[LastModified]]. None of the four algorithms mentions type, so read literally:
structuredClone(new Blob(["x"], { type: "text/plain" })).type // "" by the spec text
structuredClone(new File(["x"], "a.txt", { type: "text/plain" })).type // "" by the spec text
The same holds for postMessage, history.pushState, and IndexedDB's StructuredSerializeForStorage.
What engines do
All three keep the type ("text/plain" above):
- Blink:
V8ScriptValueSerializer::WriteDOMObjectwrites the blob's uuid, type and size (kBlobTag), and File's type with its other fields. - WebKit:
SerializedScriptValue.cpp:CloneSerializerwritesblob->type()after the URL (BlobTag) andfile.type()(FileTag), andreadFilepasses the type toFile::deserialize. - Gecko:
StructuredCloneHolder.cpp:WriteBlobkeeps a reference to theBlobImpl(which holds the content type), andReadBlobwraps the same impl, so the type carries over.
Tests
WPT's compare_Blob (html/webappapis/structured-clone/structured-clone-battery-of-tests.js) asserts actual.type === input.type for every cloned Blob and File, across the structured-clone, postMessage and IndexedDB variants.
Proposal
- Blob serialization steps: add "Set
serialized.[[Type]]to the value ofvalue'stypeattribute." - Blob deserialization steps: add "Initialize the value of
value'stypeattribute toserialized.[[Type]]." - File serialization and deserialization steps: the same two steps.
Possibly related: #98 (whether a clone copies or references the data), which doesn't cover type.
Found while implementing structured serialization for Blob and File in Crane, a web platform engine, which keeps the type as the engines do.
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