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Add support for host features. #91

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Add support for host features. #91

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a37d74b
Add support for host features.
PiotrSikora Sep 25, 2025
f29d033
Merge branch 'main' into host_features
PiotrSikora Feb 12, 2026
2b0589c
review: stop using `and/or`.
PiotrSikora Mar 19, 2026
58b7325
review: clarify feature ID assignment process.
PiotrSikora Mar 19, 2026
6af0359
review: add note about NOT_SUPPORTED status for hostcalls.
PiotrSikora May 21, 2026
877316b
review: "when 1" -> "when present".
PiotrSikora May 21, 2026
1042a69
review: be explicit about buffered/streaming callouts.
PiotrSikora May 21, 2026
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23 changes: 23 additions & 0 deletions abi-versions/vNEXT/HOST_FEATURES.md
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# Host features

| Identifier | Name | Values | Deprecated |
|:----------:|:-------------------------|:---------------------------------------------------------------------------------------------------|:----------:|
| 0x0001 | `HAS_CORE` | When `1`, all baseline functions considered essential are supported. | No |
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| 0x0002 | `HAS_LOGGING` | When `1`, all baseline functions for logging are supported. | No |

@leonm1 leonm1 Feb 12, 2026

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Are the SDKs expected to track which host features are supported and avoid invoking their hostcalls, or is it up to plugin authors to avoid calling such functions?

@PiotrSikora PiotrSikora Feb 17, 2026 •
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They could (to avoid crossing Wasm<>Host boundary), but for any unsupported hostcalls, they'll receive UNIMPLEMENTED status code anyway, so that's only an optimization.

The main goal is for plugins to verify support for the features they required during configuration phase, and fail to start if some are missing, instead of starting successfully and failing at runtime due to UNIMPLEMENTED errors while processing the real requests.

@PiotrSikora PiotrSikora Mar 19, 2026

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I'm going back and forth on this. Should we have a generic catch-all text about UNIMPLEMENTED status that applies to all optional hostcalls, or should we explicitly add it to each hostcall... or both?

@PiotrSikora PiotrSikora May 21, 2026

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Added text about NOT_SUPPORTED.

@mpwarres mpwarres May 21, 2026

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The generic catch-all text makes sense to me.

| 0x0003 | `HAS_HTTP_HEADERS` | When `1`, only baseline functions related to HTTP headers are supported. | No |
| 0x0004 | `HAS_HTTP_WITH_BODY` | When `1`, all baseline functions for HTTP are supported. | No |
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| 0x0005 | `HAS_HTTP_CALLS` | When `1`, all baseline functions for HTTP calls are supported. | No |
| 0x0006 | `HAS_GRPC_CALLS` | When `1`, all baseline functions for gRPC calls are supported. | No |
| 0x0007 | `HAS_GRPC_STREAMS` | When `1`, all baseline functions for gRPC streams are supported. | No |
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| 0x0008 | `HAS_TCP_FILTER` | When `1`, only baseline functions related to new TCP connections are supported. | No |
| 0x0009 | `HAS_TCP_WITH_PAYLOAD` | When `1`, all baseline functions for TCP are supported. | No |
| 0x000A | `HAS_KEY_VALUE_STORES` | When `1`, all baseline functions for key-value stores are supported. | No |
| 0x000B | `HAS_SHARED_QUEUES` | When `1`, all baseline functions for shared queues are supported. | No |
| 0x000C | `HAS_TIMERS` | When `1`, all baseline functions for timers are supported. | No |
| 0x000D | `HAS_METRICS` | When `1`, all baseline functions for metrics are supported. | No |
| 0x000E | `HAS_PROPERTIES` | When `1`, all baseline functions for properties are supported. | No |
| 0x000F | `HAS_CUSTOM_FUNCTIONS` | When `1`, all baseline functions for custom functions are supported. | No |
| 0x0F01 | `HAS_WASI_PREVIEW1_CORE` | When `1`, all baseline functions considered essential from WASI Preview1 are supported. | No |
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Identifiers below 0x2000 are reserved for standardized features and options. Random numbers above that range should be used for private extensions.
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