20 lines
827 B
Markdown
20 lines
827 B
Markdown
---
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toc_hide: true
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---
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The event ID is the [reference
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hash](/server-server-api#calculating-the-reference-hash-for-an-event) of
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the event encoded using a variation of [Unpadded
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Base64](/appendices#unpadded-base64) which replaces the 62nd and
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63rd characters with `-` and `_` instead of using `+` and `/`. This
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matches [RFC4648's definition of URL-safe
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base64](https://tools.ietf.org/html/rfc4648#section-5). Event IDs are
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still prefixed with `$` and may result in looking like
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`$Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg`.
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Just like in room version 3, event IDs should not be sent over
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federation to servers when the room uses this room version. On the
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receiving end of an event, the server should compute the relevant event
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ID for itself. Room version 3 also changes the format of `auth_events`
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and `prev_events` in a PDU.
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