feat(embed)!: in-process upstream, pass-through and your own TLS on one listener - #119
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- The upstream is any gRPC tower service (`upstream::Upstream`): a remote tonic Channel or the embedder's own services, such as tonic `Routes`, called in process through their whole stack - `ProxyServer::service` builds the proxy as one tower service: gRPC and gRPC-Web requests pass through to the upstream unchanged, the rest go to the proxy's routes, unmatched ones to an optional fallback untouched by the proxy's middleware; `serve` runs it with HTTP/1.1 and HTTP/2 on one port, and the standalone binary uses it, so it passes native gRPC too - The transcoder enforces the call deadline itself for every upstream and answers DEADLINE_EXCEEDED (504) instead of the channel's CANCELLED; only the client's grpc-timeout travels upstream - An in-process upstream sees the HTTP client's address via `Request::remote_addr`, for native and transcoded calls - `upstream` is optional in the config; `ProxyServer::upstream` builds the remote channel and fails with a clear error without one - Per-request state is the upstream handle plus shared settings instead of a clone of every config string; the maintenance gate is mounted only while maintenance is on - A `prefix/**` maintenance exemption no longer exempts a sibling path that only shares the prefix (`/healthz` for `/health/**`) - The transcoder test suites run against both a remote and an in-process upstream BREAKING CHANGE: `TranscodeState` names its upstream as an associated type and hands it over with `into_upstream`; `ProxyState` is no longer public; `ProxyConfig::upstream` is an `Option`. Closes #117 Part of #118
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WalkthroughThe proxy supports remote and in-process gRPC upstreams. It routes REST, native gRPC, and gRPC-Web through a shared service. Transcoded calls use a deadline capped at five seconds. The changes add connection metadata support and configurable gRPC-Web CORS. ChangesProxy upstream and shared listener
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~60 minutes Change: Feature · Severity of issue fixed: Medium Sequence Diagram(s)sequenceDiagram
participant Client
participant ProxyService
participant Upstream
participant AxumRoutes
participant Fallback
Client->>ProxyService: Send request
alt gRPC or gRPC-Web
ProxyService->>Upstream: Forward request
Upstream-->>Client: Return response
else Other request
ProxyService->>AxumRoutes: Route request
alt No route matches
ProxyService->>Fallback: Delegate when configured
Fallback-->>Client: Return response
else Route matches
AxumRoutes-->>Client: Return response
end
end
Merge Risk: ⚪ Minimal · up to No actionable merge-blocking issue is established; the change is mergeable after normal checks. Security Architecture ReviewSecurity architecture risk: 🟠 High · up to The listener now forwards native gRPC and gRPC-Web calls without applying the proxy’s access controls. An upstream that relies on those controls could become reachable through the new path. Whether deployed upstreams enforce their own protections remains unverified. Retained concerns
Security review detailsSecurity Blast Radius
Security Findings and Attack Paths
Trust Boundaries and Controls
Resilience and Maintainability Implications
Hardening Proposals
🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Docstring CoverageExplanation Docstring coverage is 70.85% which is insufficient. The required threshold is 80.00%. Docstring coverage is scoped to functions touched by this diff. Analyzed 199 functions across 22 files. (1 skipped: 1 unsupported.)
✨ Finishing Touches 💡 1📝 Generate docstrings 💡
🧪 Generate unit tests (beta)
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Actionable comments posted: 2
- 🪄 Fix CodeRabbit comments on this PR
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Inline comments:
Review comments at @src/service.rs:
- Around line 120-141: Adapt gRPC-Web requests and responses at the serving
boundary used by ProxyServer::service, before native tonic services receive
them; ensure the adapter supports HTTP/1 and is applied to the gRPC forwarding
path in ProxyService::call rather than passing gRPC-Web payloads unchanged
through PassThrough. Add coverage for both binary and text gRPC-Web formats.
Review comments at @src/transcode/mod.rs:
- Around line 623-661: Update prepare and Call to establish one absolute
deadline before Grpc::ready(), bound readiness by that deadline, and use the
same deadline for the RPC so readiness time counts against the request budget.
Return a deadline-exceeded rejection when readiness times out, while preserving
the existing not-ready rejection for readiness errors.
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📒 Files selected for processing (22)
Cargo.tomlREADME.mdsrc/config.rssrc/config/tests.rssrc/embed.rssrc/lib.rssrc/main.rssrc/service.rssrc/service/tests.rssrc/tests.rssrc/transcode/metadata.rssrc/transcode/mod.rssrc/upstream.rssrc/upstream/tests.rstests/common/mod.rstests/edge.rstests/embedded.rstests/error_details.rstests/forwarded_headers.rstests/request_mapping.rstests/streaming_request.rstests/upstream_controls.rs
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- `ProxyService::for_connection` takes the connection an embedder's own server accepted, as tonic's `Connected` trait reports it: a TCP stream, or a rustls TLS stream with the client's certificate chain (`ConnectionInfo::tls`) - The proxy's middleware sees the client's address; a tonic upstream in process reads it with `Request::remote_addr`, and the client certificate with `Request::peer_certs`, for native and transcoded calls - `serve` uses the same path for its cleartext connections - tonic exports its TLS connection record only with a TLS backend, so it is named through the rustls stream it describes; no crypto provider is linked - README shows serving the proxy behind an embedder's own TLS acceptor; an integration test runs REST and native gRPC over one TLS port with and without a client certificate Part of #117
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changed the title
…nd protocol - Waiting for the upstream to take a transcoded call now counts against the call's deadline: an upstream under backpressure whose `poll_ready` never completes answered nothing at all, it now answers DEADLINE_EXCEEDED (504); readiness and the call share one timer - A `ProxyService` hosted by an axum server that recorded `ConnectInfo`, with no `for_connection`, passes that peer to the upstream too, so `Request::remote_addr` sees the client the middleware sees - When the upstream cannot take a gRPC-Web call, the proxy's own error answer keeps the request's protocol (`application/grpc-web+proto` or `-text+proto`) instead of a native gRPC content type a gRPC-Web client cannot read - gRPC-Web passes through for the upstream to translate; README and the `ProxyService` docs say so, with tonic-web's layer as the way to give an upstream that protocol Regression tests: a never-ready upstream against the deadline, the peer from an outer axum server for native and transcoded calls, the failure content type per protocol; plus binary and text gRPC-Web through the proxy to an upstream behind tonic-web. Part of #117
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- A non-empty `cors.origins` stopped the proxy at startup: the policy combined credentials with `*` for methods and headers, which tower-http refuses (Fetch §3.2.5). The preflight now echoes the methods and headers the browser asked for - An origin that is not a header value is a config error instead of being dropped, which quietly narrowed the policy - gRPC-Web calls passed through to the upstream carry the same CORS policy their preflight got from the proxy; without it a browser discarded the answer. `cors.grpc_web: false` leaves CORS to an upstream that sets it - `grpc-status-details-bin` is always exposed, so a gRPC-Web client reads rich error details - New settings: `cors.expose_headers` for upstream metadata a browser must read, `cors.max_age_secs` for the preflight cache - Native gRPC pass-through keeps no timer of its own; the reason is written next to it Regression tests: a listed origin on a REST route and on a gRPC-Web call, preflight and call agreeing, an unlisted origin, the new settings, and the config errors. Part of #117
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A browser's preflight for a gRPC-Web call carries no gRPC content type, so it went to the proxy's routes: behind `with_fallback` it reached the embedder's fallback with no CORS answer at all, and with `cors.grpc_web: false` the proxy answered it under its own policy while the call itself got the upstream's. A preflight announcing `x-grpc-web` is now gRPC-Web traffic: the proxy's CORS answers it when `cors.grpc_web` is on, the upstream answers it when it owns CORS. A REST preflight keeps the proxy's policy. Regression tests: a gRPC-Web preflight behind a fallback, one reaching an upstream with its own CORS, a REST preflight next to it, and the preflight classification. Part of #117
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Summary
Changes
upstream::Upstream: any gRPC tower service (a remotetonic::transport::Channel,tonic::service::Routes, or another service speaking gRPC overhttptypes).ProxyServer::service(upstream)returnsProxyService, a tower service with the upstream and a fallback slot (with_fallback, 404 by default);structured_proxy::serveruns it with cleartext HTTP/1.1 and HTTP/2 on one port. gRPC-Web passes through for the upstream to translate (tonic-web's layer) and carries the proxy's CORS policy (cors.grpc_web); its browser preflight goes where the call goes, answered by the proxy's CORS, or by the upstream when it owns CORS, never by a fallback; an error the proxy answers itself keeps the request's gRPC or gRPC-Web content type.ProxyService::for_connectiontakes the accepted connection as tonic'sConnectedtrait reports it (TCP, or rustls TLS viaConnectionInfo::tls); without it, the peer an outer axum server recorded asConnectInfois used. The middleware sees the client's address, and a tonic upstream in process readsRequest::remote_addrandRequest::peer_certsfor native and transcoded calls.ProxyServer::upstream()builds the remote channel fromupstream.default;router()keeps serving the HTTP routes in front of it.upstreamis optional in the config.grpc-timeout, covering the wait for the upstream to take the call and its response headers) and answersDEADLINE_EXCEEDED(504). Only the client'sgrpc-timeouttravels upstream.cors.originsworks (the policy echoes the preflight's methods and headers instead of*, which credentials forbid), an invalid origin is a config error,grpc-status-details-binis always exposed, andcors.expose_headers/cors.max_age_secsconfigure exposed headers and the preflight cache.prefix/**exemption coversprefixand its subtree, not a sibling path sharing the prefix.Testing
The transcoder integration suites run against both a remote and an in-process upstream, a TLS suite serves REST and native gRPC over one TLS port with and without a client certificate, binary and text gRPC-Web reach an upstream behind tonic-web, and browser calls carry the CORS policy their preflight got; tests, clippy (all features and no default features), formatting, doc tests and the doc build pass on macOS.
Closes #117
Related
BREAKING CHANGE:
TranscodeStatenames its upstream as an associated type and hands it over withinto_upstream;ProxyStateis no longer public;ProxyConfig::upstreamis anOption; an upstream timeout answers 504DEADLINE_EXCEEDEDinstead ofCANCELLED.