feat(grpc-xds): gRFC A74 model validated xDS resources and XdsConfig snapshot by YutaoMa · Pull Request #2775 · grpc/grpc-rust

YutaoMa · 2026-07-28T20:38:38Z

Motivation

Per gRFC A74, to avoid config tear across xDS layers, all watches (LDS, RDS, CDS, EDS) are moved into a single resolver behind an XdsDependencyManager that emits a single complete XdsConfig.

Solution

This PR implements the XdsConfig modeling, along with its xDS resource types(the validated types corresponding to the Envoy proto types) and validation logic. This PR is a pre-req to the XdsDependencyManager.

The shape of XdsConfig closely mirrors gRFC A74's C++ sketch, as well as other gRPC implementations such as grpc-go. A few design choices were made for Rust ergonomics, such as using an index to store selected virtual host rather than a reference to avoid self-referential borrow.

YutaoMa · 2026-07-30T18:22:18Z

Hi @ejona86 @dfawley looking for reviews on this XdsConfig PR. Thanks!

dfawley

Looks great overall, thanks! I've found a handful of things that should be fixed, but it should all be pretty small.

dfawley · 2026-07-31T17:55:35Z

+/// The atomic xDS configuration snapshot for a channel.
+#[derive(Debug, Clone)]
+#[non_exhaustive]
+pub(crate) struct XdsConfig {


I am assuming this would, itself, end up in an Arc, so that it can be shared between the name resolver and all the LB policies? If so do we need Arcs on the individual fields as well?

The individual fields Arc would still be needed to share configs across snapshots, like a CDS-only update should keep reusing the LDS/RDS Arcs.

dfawley · 2026-07-31T18:19:17Z

+                        "sum of weighted cluster weights exceeds {}",
+                        u32::MAX
+                    )));
+                }


I think there should be a validation of the total_weight field here:

Suggested change

}

}

if let Some(tw) = wc.total_weight_opt() {

let expected_total = tw.value();

if expected_total == 0 || u64::from(expected_total) != total_weight {

return Err(Error::Validation(format!(

"sum of weighted cluster weights ({total_weight}) does not match explicit total_weight ({expected_total})"

)));

}

}

per route_components.proto:

// Specifies the total weight across all clusters. The sum of all cluster weights must equal this // value, which must be greater than 0. Defaults to 100. google.protobuf.UInt32Value total_weight = 3 [(validate.rules).uint32 = {gte: 1}];

and A28:

Can be Weighted_clusters

The sum of weights must add up to the total_weight.

In the v3 proto the total_weight has been marked as deprecated: https://github.com/envoyproxy/envoy/blob/a282c557f6b18241f90bd20c2d00c985b4c3c70b/api/envoy/config/route/v3/route_components.proto#L539-L540, and the client will use the sum of all cluster weights. grpc-go also ignores this field. I assume we'd like to target v3 APIs only in gRPC Rust?

dfawley · 2026-07-31T18:27:12Z

+            && !Arc::ptr_eq(inline, &route_config)
+        {
+            return None;
+        }


Should we also validate that if route_source is RouteSource::Rds, that the rds name matches the route_config name?

Valid, adding the same name check.

dfawley · 2026-07-31T18:33:23Z

+        }
+        let any: Any = api_listener.api_listener().to_owned();
+
+        let hcm = HttpConnectionManager::parse(any.value()).map_err(|e| {


We should validate any's type_url before parsing this to ensure the message type is what we expect.

Good point, adding the type_url check.

dfawley · 2026-07-31T18:44:33Z

+}
+
+fn validate_header_matcher(hm: HeaderMatcherView<'_>) -> xds_client::Result<HeaderMatcher> {
+    let name = hm.name().to_str().unwrap_or_default().to_string();


Should we validate !name.is_empty()?

Valid, adding the check.

dfawley · 2026-07-31T18:45:54Z

+    }
+
+    fn validate(message: Self::Message) -> xds_client::Result<Self> {
+        let name = message.name().to_str().unwrap_or_default().to_string();


Should we validate !name.is_empty() here as well, matching cluster/endpoint validation?

Valid, adding the check.

dfawley · 2026-07-31T19:00:06Z

+            // DEGRADED and anything unrecognized fall back to Unknown below.
+            EnvoyHealthStatus::Unhealthy | EnvoyHealthStatus::Timeout => Self::Unhealthy,
+            EnvoyHealthStatus::Draining => Self::Draining,
+            _ => Self::Unknown,


This catch-all maps Degraded to Unknown, and then we will end up using the endpoint since we are supposed to use either HEALTHY or UNKNOWN endpoints per Envoy: https://github.com/envoyproxy/envoy/blob/8f77c4a301bd96d2c7231915e6c3d1f85ea88ae1/api/envoy/config/core/v3/health_check.proto#L36

Noted, I'll keep it aligned with other grpc impl to add in the few other variants and default to a different variant like Other(i32) instead.

dfawley · 2026-07-31T19:02:04Z

+    // of 1,000,000. runtime_key is ignored (gRPC has no runtime config).
+    let match_fraction = rm.runtime_fraction_opt().and_then(|rf| {
+        if !rf.has_default_value() {
+            return None;


If there is no default value set, this should probably error. (The field is required per the protos: https://github.com/envoyproxy/envoy/blob/b67c14052c49890a7e3afe614d50979c346c024b/api/envoy/api/v2/core/base.proto#L368-L369, so this probably won't ever happen in practice)

Makes sense, changing it to validation failure.

dfawley · 2026-07-31T20:47:45Z

+        ));
+    }
+    let any = custom.typed_config();
+    let cluster_config = AggregateClusterConfig::parse(any.value()).map_err(|e| {


This should also validate any.type_url

👍 , adding the check here as well.

YutaoMa · 2026-08-03T23:27:56Z

@dfawley all prev comments addressed, ready for another round of review. Thanks!

YutaoMa added 2 commits July 28, 2026 13:07

feat(grpc-xds): model validated xDS resources and XdsConfig snapshot

939c54a

Merge branch 'master' into yutaoma/grpc-xds-config

d2a42d0

YutaoMa marked this pull request as ready for review July 28, 2026 22:47

Merge branch 'master' into yutaoma/grpc-xds-config

b93a2b7

dfawley reviewed Jul 31, 2026

View reviewed changes

fix(grpc-xds): add additional resource validation per PR feedback

4b967bd

Merge branch 'master' into yutaoma/grpc-xds-config

ae37773

-                }
+                }
+                if let Some(tw) = wc.total_weight_opt() {
+                    let expected_total = tw.value();
+                    if expected_total == 0 || u64::from(expected_total) != total_weight {
+                        return Err(Error::Validation(format!(
+                            "sum of weighted cluster weights ({total_weight}) does not match explicit total_weight ({expected_total})"
+                        )));
+                    }
+                }

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YutaoMa commented Jul 30, 2026

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YutaoMa commented Aug 3, 2026

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YutaoMa commented Jul 28, 2026 •

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