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Document catchall variant for protocol enums #14947

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Sep 19, 2025
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Document catchall variant for protocol enums #14947

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12 changes: 12 additions & 0 deletions develop-docs/ingestion/relay/relay-best-practices.mdx
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Expand Up @@ -16,6 +16,18 @@ Make sure changes to the event protocol and APIs are forward-compatible. Relay s
or truncate data it does not understand. It is a supported use-case to have customers running
outdated Relays but up-to-date SDKs.

For example, `enum`s in the event protocol (or any other data type received from the SDK) need to have a catchall variant
such that customer relays running an older version can still forward the data:

```rust
enum EventColor {
Red,
Green,
Blue,
/// Unknown color, for forward compatibility.
Unknown(String),
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@Dav1dde Dav1dde Sep 17, 2025

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Sometimes we use #[serde(other)] Unknown, sometimes Unknown(String) and other times our derives have something builtin #[metastructure(fallback_variant)].

Seems to be quite use-case specific and hard to phrase :/.

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@jjbayer jjbayer Sep 19, 2025

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Yes I looked at fallback_variant and it seems we only use it with Object. I guess the important part is that we have some sort of fallback such that parsing does not fail and the data is forwarded.

}
```

## Feature Gate new Functionality

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