dynamic_modules: add cluster filter-state read ABI#45040
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Adds two ABI callbacks so that a dynamic-module cluster's load balancer
can read filter state set by an upstream HTTP filter (or any other
producer) when picking a host. Today the cluster context only exposes
downstream headers, hash key, override-host, and SNI — filter state was
reachable from the C++ side via ``LoadBalancerContext::requestStreamInfo()
->filterState()`` but not surfaced through the ABI, forcing modules to
fall back to header round-tripping.
ABI additions:
* envoy_dynamic_module_callback_cluster_lb_context_get_filter_state_bytes
— reads a ``Router::StringAccessor``-typed filter state value. Mirrors
the existing HTTP-filter ``get_filter_state_bytes``.
* envoy_dynamic_module_callback_cluster_lb_context_get_filter_state_typed
— returns the serialized bytes of a typed filter state object via
``serializeAsString``. Mirrors the existing HTTP-filter
``get_filter_state_typed``. The serialized buffer is stashed in a
thread-local string so the returned pointer survives the current
host-selection callback.
Weak fallback definitions are added alongside the existing cluster-LB
weak stubs in ``source/extensions/dynamic_modules/abi_impl.cc`` so that
binaries that link the Rust SDK without the cluster_lib (e.g. the HTTP
filter integration test) still resolve cleanly.
The Rust SDK gains matching ``ClusterLbContext::get_filter_state_bytes``
and ``ClusterLbContext::get_filter_state_typed`` methods.
Tests:
* test_data/rust/cluster_filter_state_test.rs — single shared library
exporting an HTTP filter (``filter_state_producer``) that writes both
a bytes value and a typed value during ``on_request_headers``, plus a
cluster (``filter_state_reader``) whose load balancer reads both
values in ``choose_host`` and only returns its host when both
round-trip correctly.
* integration_test.cc registers an ``ObjectFactory`` for the typed key
and adds ``ReadsFilterStateProducedByHttpFilter``: prepends the
producer HTTP filter via ``prependFilter``, swaps cluster_0 for the
reader cluster, and asserts a 200 response — proving the
filter-state round trip from HTTP filter to cluster host selection.
Signed-off-by: Basundhara Chakrabarty <basundhara17061996@gmail.com>
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Needs main merge. |
…e-abi # Conflicts: # test/extensions/clusters/dynamic_modules/BUILD # test/extensions/clusters/dynamic_modules/cluster_test.cc
wbpcode
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May 15, 2026
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/retest |
agrawroh
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May 15, 2026
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Commit Message: Adds two ABI callbacks so that a dynamic-module cluster's load balancer can read filter state set by an upstream HTTP filter (or any other producer) when picking a host.
Additional Description:
Dynamic-module clusters get two new ABI callbacks (get_filter_state_bytes and get_filter_state_typed) so a custom load balancer can read filter state during host selection. Today the cluster LB side can only see things like SNI and route metadata — it can't reach into filter state that an upstream HTTP filter (or any other producer) attached to the request. With these callbacks, an HTTP filter can compute or look up a value, stash it on filter state, and a downstream dynamic-module cluster can use that value to pick a host.
API shape
Both callbacks mirror the existing HTTP-filter equivalents so module authors see a familiar surface:
Risk Level: Low
Testing: Integration test added
Docs Changes: N.A
Release Notes: N.A
Platform Specific Features: N.A