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HTTP Fetch Policy

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This document tries to document the platform's fetching policy for HTTP.


General limitations


  • Uppercased (so e.g. geT becomes GET): CONNECT, DELETE, GET, HEAD, OPTIONS, POST, PUT, TRACE, and TRACK.
  • Never work: CONNECT, TRACE, and TRACK (subset of the above).

Author headers: Everything but setRequestHeader() limitations.

Headers: Host, Origin, ...

Body: No limitations

Additional general cross-origin (no preflight) limitations

Methods: Only GET, HEAD, and POST.

Author headers: Only Accept, Accept-Language, Content-Language, and Content-Type. If Content-Type, value excluding parameters must be application/x-www-form-urlencoded, multipart/form-data, or text/plain.

EventSource cross-origin (no preflight) allowance

Headers: Also Last-Event-ID

CSP cross-origin (no preflight) allowance

Headers: Also Content-Type with value application/json

WebSocket cross-origin (no preflight) allowance

Headers: Also Upgrade: websocket, Connection: Upgrade, Sec-WebSocket-Key, Sec-WebSocket-Protocol, Sec-WebSocket-Version