matrix-spec-proposals/content/rooms/v4.md

title	type	weight
Room Version 4	docs	40

This room version builds on version 3 using a different encoding for event IDs.

Client considerations

This room version changes the format form event IDs sent to clients. Clients should already be treating event IDs as opaque identifiers, and should not be concerned with the format of them. Clients should still encode the event ID when including it in a request path.

Clients should expect to see event IDs changed from the format of $randomstring:example.org to something like $Rqnc-F-dvnEYJTyHq_iKxU2bZ1CI92-kuZq3a5lr5Zg (note the lack of domain).

Though unchanged in this room version, clients which implement the redaction algorithm locally should refer to the redactions section below for a full overview.

Server implementation components

{{% boxes/warning %}} The information contained in this section is strictly for server implementors. Applications which use the Client-Server API are generally unaffected by the intricacies contained here. The section above regarding client considerations is the resource that Client-Server API use cases should reference. {{% /boxes/warning %}}

Room version 4 uses the same algorithms defined in room version 3, however using URL-safe base64 to generate the event ID.

Event IDs

{{% boxes/rationale %}} Room version 3 generated event IDs that were difficult for client implementations which were not encoding the event ID to function in those rooms. It additionally raised concern due to the / character being interpreted differently by some reverse proxy software, and generally made administration harder. {{% /boxes/rationale %}}

{{% rver-fragment name="v4-event-ids" withVersioning="true" %}}

Unchanged from v3

The following sections have not been modified since v3, but are included for completeness.

State resolution

{{% rver-fragment name="v2-state-res" %}}

Authorization rules

{{% rver-fragment name="v3-auth-rules" %}}

Handling redactions

{{% rver-fragment name="v3-handling-redactions" %}}

Canonical JSON

{{% rver-fragment name="v1-canonical-json" %}}

Redactions

{{% rver-fragment name="v1-redactions" %}}

Event format

The event format is the same as room version 3, however the event IDs in the following example are updated to reflect the changes in this room version.

{{% rver-fragment name="v4-event-format" %}}