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feat(router): decide stream-vs-buffer per request; deprecate --stream-request-bodies-over - #2286
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WalkthroughThe request-body threshold is replaced with a configurable retry-buffer cap. Routing now selects buffering or streaming per request based on router policy, body requirements, retry settings, content length, WASM hooks, and worker behavior. ChangesRequest body routing
Estimated code review effort: 4 (Complex) | ~45 minutes Merge Risk: ⚪ Minimal · up to The PR changes request-body handling to choose buffering or streaming per request and removes the old size-based flag; no actionable merge-blocking risk remains after normal checks and review. Sequence Diagram(s)sequenceDiagram
participant Client
participant Middleware
participant Router
participant WorkerRegistry
participant Metrics
Client->>Middleware: send request body
Middleware->>Router: evaluate body policy and WASM hooks
Router->>WorkerRegistry: inspect worker retry behavior
Router->>Router: choose buffering or streaming
Router->>Metrics: record path and reason
Router-->>Client: forward request
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Clean PR. The per-request body-path decision matrix in request_body_path() is well-structured with clear first-match semantics. Deprecation mapping via effective_max_buffered_request_bytes() is sound — resolves at Router construction time. The registration-race guard after worker selection correctly covers mutating workers that join between the fleet check and dispatch. Metric accounting has exactly one record_request_body_path per code path with accurate labels. Test coverage is comprehensive: every branch of the decision matrix has a unit test, and integration tests verify end-to-end behavior including the deprecated-flag mapping, retries-disabled streaming, and default-config crossover at 1MiB.
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| Some(selected) => selected, | ||
| None => return next.run(req).await, | ||
| None => { | ||
| Metrics::record_request_body_path(BODY_PATH_BUFFERED, "model_selection"); |
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🟡 Nit: "model_selection" is a bare string literal here (and on line 1891), while every other reason string used in Metrics::record_request_body_path is a const (REASON_POLICY_NEEDS_TEXT, REASON_WORKER_MUTATES_BODY, etc.). A typo in either copy would silently create a new metric label. Consider extracting a constant alongside the others:
const REASON_MODEL_SELECTION: &str = "model_selection";The same literal also appears as MustBuffer("model_selection") in RouterManager::request_body_policy() — a shared constant would keep all three sites in sync.
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Fixed in 6a67e10 — one shared REASON_MODEL_SELECTION const used at all three sites, and the whole reason vocabulary now lives in one module (routers/common/body_policy.rs); repo-wide grep confirms zero bare reason/path literals outside it.
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Inline comments:
In `@model_gateway/src/routers/http/router.rs`:
- Around line 1715-1721: Update the streamed request handling around
request_body_path and select_worker_for_model so model-aware worker selection is
preserved: buffer the body whenever selection requires the request model, or use
a trusted pre-body model selector instead of UNKNOWN_MODEL_ID. Add a regression
test covering two workers serving different models and verify the request
reaches the matching worker.
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bindings/python/src/lib.rsbindings/python/src/smg/router_args.pybindings/python/tests/test_arg_parser.pymodel_gateway/benches/wasm_middleware_latency.rsmodel_gateway/src/config/builder.rsmodel_gateway/src/config/types.rsmodel_gateway/src/config/validation.rsmodel_gateway/src/main.rsmodel_gateway/src/routers/anthropic/router.rsmodel_gateway/src/routers/gemini/router.rsmodel_gateway/src/routers/grpc/router.rsmodel_gateway/src/routers/http/pd_router.rsmodel_gateway/src/routers/http/router.rsmodel_gateway/src/routers/mod.rsmodel_gateway/src/routers/openai/router.rsmodel_gateway/src/routers/router_manager.rsmodel_gateway/src/server.rsmodel_gateway/tests/api/request_formats_test.rsmodel_gateway/tests/routing/stream_request_body_test.rs
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- model_gateway/src/config/validation.rs
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Actionable comments posted: 1
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Inline comments:
In `@model_gateway/src/routers/router_manager.rs`:
- Around line 1017-1046: Extend
body_policy_delegates_to_a_lone_router_and_buffers_multi_router with a stub
router whose request_body_policy returns BodyPolicy::ForwardCapable, then assert
that a manager containing only that router returns ForwardCapable. Keep the
existing MustBuffer assertions for stub and multi-router behavior unchanged.
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model_gateway/src/routers/mod.rsmodel_gateway/src/routers/router_manager.rs
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RouterTrait gains a BodyPolicy capability whose default is MustBuffer
keyed by the family's router_type — buffering is always correct, so
transforming families (PD, gRPC, external providers) take it for free
and only the forward-capable HTTP regular router overrides it (the
RouterManager delegates a lone router's policy and turns multi-router
dispatch into a buffer reason). The capability, its reason vocabulary
and the per-request decision matrix live in routers/common/body_policy.
The forward-capable router chooses the body path per request, before
the body arrives: requests it must parse (text-routing policy without
a hint waiver, a registry serving more than one model — content-blind
selection could land on the wrong model's worker — a body-mutating
worker, WASM request hooks, missing Content-Length) buffer as before;
eligible requests buffer only up to --max-buffered-request-bytes
(default 1MiB) to stay retryable, and otherwise stream to the worker
verbatim, forfeiting router-level retries. The never-released
--stream-request-bodies-over flag is removed. Every decision on an
eligible route is observable via
smg_router_request_body_path_total{path,reason}.
Signed-off-by: Simo Lin <25425177+slin1237@users.noreply.github.com>
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Review round addressed in 6a67e10, plus a structural change from maintainer review: the whole capability now lives in routers/common/body_policy.rs - the BodyPolicy enum, every reason constant, and the decision matrix as a pure function over explicit per-request inputs (unit-testable without constructing a router). http/router.rs keeps only a thin adapter that gathers its state and calls it. The matrix gained one hard-buffer reason from this round: model_ambiguous - a multi-model registry buffers so selection can read the model from the body; single-model registries (the production video lane) stream as before. Full suite re-run green: 26 binaries zero failures, wheel + arg-parser pytest, golang check. |
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Description
Problem
--stream-request-bodies-overmade an operator pre-decide, fleet-wide and by size, whether request bodies buffer (store, parse, re-serialize, send) or stream through verbatim. That one guessed number silently coupled three unrelated questions: does anything downstream need the bytes, who validates, and how much memory one request may pin. The default (disabled) buffered everything: on the video shadow lane that was ~340GB of slow client uploads pinned per router until the flag was discovered. Operators tuning routing knobs should not inherit a memory model as a side effect - and "we only fixed router.rs" should not be possible either: whether a router family can forward bodies verbatim is a property of the family, and it should be declared, not implied by a downcast.Solution
Two layers, no operator input:
Body policy is part of the router contract.
RouterTraitgains a non-defaultedrequest_body_policy() -> BodyPolicy: eitherForwardCapable(the regular HTTP router) orMustBuffer(reason)-per_leg_construction(PD),protocol_transformation(gRPC),pipeline_transform(Anthropic/Gemini/OpenAI),model_selection(multi-router dispatch). The compiler forces every family, present and future, to declare; there is no silent default. Every request incrementssmg_router_request_body_path_total{path, reason}exactly once, so the buffered/streamed mix per lane is on a dashboard with reasons attached.ForwardCapable routers decide per request, before the body arrives, from facts the router already has:
--max-buffered-request-bytes(default 1MiB, 0 = never) to keep router retries; past the bound, stream and forfeit retries for that request, observably.--stream-request-bodies-overis REMOVED, not deprecated - it never shipped in a tagged release.Breaking change
Changes
BodyPolicyin the router trait's home with a DEFAULTEDrequest_body_policy(): buffering is the safe default, with the counter reason derived from the existingrouter_type()identity - zero code per family. Exactly two overrides: the regular HTTP router (ForwardCapable) andRouterManager(lone-router delegation;model_selectionwhen dispatching across several). The middleware consults the capability, never a downcastRouter::request_body_pathper-request decision matrix (one compact doc comment); middleware renamedstream_eligible_request_bodies, no longer size-gated--max-buffered-request-bytesthrough both config paths, builder, serde default, Python bindings; old flag removed from every surface (CLI, config, validation, bindings, tests)smg_router_request_body_path_total{path, reason}counter, tiny label setTest Plan
cargo test -p smg: 26 binaries, zero failures (lib 1822); Python wheel rebuilt via maturin, arg-parser pytest 56 passed; smg-golang clean; clippy--all-targets -- -D warningsclean; fmt silentChecklist
cargo +nightly fmtpassescargo clippy --all-targets --all-features -- -D warningspasses