feat(transcode): return google.rpc.Status details in REST error bodies - #91
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A message whose fields all hold their defaults encodes to zero bytes. The dynamic decoder reads such a frame as no message, so the server answers Missing request message and the client loses a google.protobuf.Empty reply. These tests exercise both ends over a real tonic client and server.
- An empty gRPC frame is a message whose fields all hold their defaults (google.protobuf.Empty always is); decode it instead of reporting no message, as tonic's prost codec does - Decode from the frame buffer directly: DecodeBuf is a Buf, and its byte splits stay zero-copy - Move the codec unit test into its own file
- Error bodies keep error, code and message and gain details: the upstream's grpc-status-details-bin decoded as ProtoJSON Any entries, resolved from the product descriptors first, then from the canonical google.rpc descriptors shipped by tonic-types - Details whose type no descriptor describes keep their type URL and bytes in the structured-proxy opaque-detail extension, documented as non-ProtoJSON; google.rpc.DebugInfo is never forwarded - Unary errors, streams refused before headers and the NDJSON / SSE terminal frame of a stream that fails after it started share one renderer - A global switch plus ordered per-route glob rules, decided once per mounted route at router build - Move the config, transcode and transcode::error unit tests into their own files Refs #90
Move the in-memory google.api protos, the protox compile step, the upstream server and the proxy router builder into tests/common, so other integration tests can run the proxy against a real tonic service.
Server-streaming routes send the upstream an empty request: path parameters, query parameters and the body are ignored, and a malformed body or query opens a stream instead of answering 400. The upstream in these tests echoes the request it received.
Streaming routes sent the upstream an empty request, dropping path parameters, query parameters and the body. Both handlers now map the request through one decode_request, so a streaming call binds exactly like a unary one and a request that cannot be mapped gets a 400 before any stream is opened.
- The terminal NDJSON error line carries @type google.rpc.Status next to the error body, so a reader tells it from a data line by a marker instead of guessing from its fields; SSE keeps the stream-error event type as its framing and sends the bare body - Errors the proxy raises itself (unmappable request, unreachable upstream, unserializable response, a message that fails to serialize mid-stream) go through the same renderer as upstream errors, with code and, where enabled, empty details Refs #90
A detail of a known type whose bytes do not decode, or whose value has no valid JSON form, was passed on as opaque base64, so a broken Duration came out under the same value key a real Duration uses; a trailer that is not a google.rpc.Status silently became empty details. Both now turn the whole error into a generic INTERNAL (500 before headers, the terminal frame of a started stream), with the cause logged by the proxy only. The opaque form is reserved for types no descriptor describes. Refs #90
…PI compatible - ProxyServer::with_error_details takes an ErrorDetailsPolicy (default, disabled, route) instead of an error_details field on ProxyConfig, so struct literals of ProxyConfig keep compiling - transcode::routes and transcode::error::status_to_response keep their signatures; routes_with_error_details and status_to_response_with_details take the policy and the renderer - cargo-semver-checks against main: no major change required Refs #90
…s array
A detail whose type no descriptor describes was rendered inside details as {@type, value: base64}, which a client knowing the type could take for a message of that type, and which put a base64 string under the key well-known types use for their JSON. It now goes to opaqueDetails as {index, typeUrl, bytes}: no @type, outside details, so details stays an array of ProtoJSON Any. index is the position among the forwarded details, DebugInfo taking none, so merging both arrays restores the upstream order. The key appears only when non-empty.
Refs #90
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WalkthroughThe proxy now renders upstream ChangesTranscoded errors and request handling
Dynamic codec empty frames
Priority: ➖ Normal Estimated code review effort: 4 (Complex) | ~45 minutes Change: Feature · Severity of issue fixed: Medium Sequence Diagram(s)sequenceDiagram
participant RESTClient
participant TranscodeRoute
participant GrpcService
participant StatusRenderer
RESTClient->>TranscodeRoute: Send transcoded request
TranscodeRoute->>GrpcService: Invoke RPC
GrpcService-->>TranscodeRoute: Return gRPC status and trailer
TranscodeRoute->>StatusRenderer: Render status details
StatusRenderer-->>TranscodeRoute: Return JSON error body
TranscodeRoute-->>RESTClient: Return mapped error or terminal stream frame
Merge Risk: ⚪ Minimal · up to REST error responses now include upstream status details, while DebugInfo is filtered and malformed status details fall back to a generic internal error. Streaming responses end with a single terminal error frame. No outstanding defect has been identified at the current head, and the change appears ready to merge. Security Architecture ReviewSecurity architecture risk: 🟡 Moderate · up to REST clients may now receive upstream error data that was previously hidden, including the original bytes of detail types the proxy cannot interpret. This creates a potential disclosure risk on routes where detail rendering remains enabled; no actual secret-bearing response was established. Retained concerns
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🚥 Pre-merge checks | ✅ 4 | ❌ 1❌ Failed checks (1 warning)
✅ Passed checks (4 passed)
Full details: Out of Scope Changes checkExplanation The PR adds changes that do not implement issue
✨ Finishing Touches📝 Generate docstrings
🧪 Generate unit tests (beta)
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- Wrap well-known types with a special JSON representation under value by their type, not by the shape of their JSON: a Struct, an object Value, Empty or a nested Any was flattened next to @type, and a Struct key @type could overwrite the detail's own - Refuse a detail whose type URL does not end in a protobuf full name (trailing slash, query suffix, empty segment): such a URL could disguise a DebugInfo whose bytes then went out as an opaque detail - Refuse a trailer whose code or message disagrees with grpc-status / grpc-message, instead of attaching its details to a different error - All three fail the error safely as the generic INTERNAL; regression tests cover each case Refs #90
- Resolve detail types in one pool: the product descriptors completed with the well-known types and the canonical google.rpc files they lack. An ErrorInfo packed in a product detail no longer fails the whole error just because the product descriptors do not import google/rpc - Withhold DebugInfo packed in an Any at any depth: an Any detail wrapping one is dropped like a direct DebugInfo (and takes no index), one inside a message field, repeated field or map is cut out of the entry - Regression tests cover the nested canonical type and the singular, repeated and Any-detail DebugInfo cases Refs #90
- streaming.ndjson_envelope / ProxyServer::with_ndjson_envelope wraps every NDJSON line as {"result": message} or {"error": body}, the grpc-gateway stream shape. The default @type marker cannot be collision-free for RPCs streaming Any, Struct, Value or ListValue, whose messages can carry any key; the envelope can, but changes data lines, so it is opt-in
- error_details and streaming.ndjson_envelope are read from the config file by ProxyServer::from_yaml_str / from_file, which the binary now uses; they stay outside ProxyConfig so its struct literals keep compiling
- transcode::routes_with_options takes TranscodeOptions (error details policy plus envelope), replacing routes_with_error_details
Refs #90
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…edaction - Merge the canonical google.rpc types per type, not per file: a product that defines some of them in another file, or ships its own error_details.proto with a subset, keeps its definitions while the types it lacks still resolve (through a reduced copy that imports the product files), instead of whole canonical files dropping out and standard details turning opaque - Redact DebugInfo on the decoded message, following only fields of type google.protobuf.Any (singular, repeated, map values) and re-packing a changed Any; the JSON-level pass took a Struct key named @type for a packed DebugInfo and deleted the Struct's value - Require a / in Any.type_url, as the Any contract does - Refuse a detail whose message has a field with JSON name @type, which would replace the Any's own type URL - Note next to the well-known type list why Empty is wrapped under value - Regression tests cover each case Refs #90
ProxyServer::from_yaml_str / from_file (and so the binary) log a warning for every top-level key no setting reads, so a misspelled error_detail: shows up at startup instead of silently leaving details on. Unknown keys are still accepted, so a file that loaded before keeps loading. A test destructures ProxyConfig exhaustively so a new field cannot be left out of the known-key list. The README also lists the type URL and trailer checks that fail a status safely. Refs #90
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In @src/transcode/error.rs:
- Around line 580-584: Update scrub to recognize direct google.rpc.DebugInfo
messages by their descriptor name and redact them before recursively processing
fields; document this behavior and add regression coverage for singular,
repeated, and map values containing DebugInfo.
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A detail message with a field of type google.rpc.DebugInfo (singular, repeated or a map value) kept its stack entries and detail text, since only Any-packed DebugInfo was scrubbed. scrub now reports a DebugInfo message for removal wherever it sits; regression test debug_info_typed_fields_are_removed covers the three field shapes. Refs #90
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- A proto2 extension typed as google.rpc.DebugInfo was not among the fields scrub walked, yet ProtoJSON renders it as [full.name], so its detail text reached the client. Extensions are now scrubbed like fields (regression test debug_info_extensions_are_removed). - Clearing a proto2 required DebugInfo field left a message that violates its own schema. The enclosing message is now dropped instead: the whole detail when it is top level, the holding field when nested (regression test detail_with_required_debug_info_field_is_withheld). - README: a mapped HTTP status is promised only for a trailers-only rejection; once the upstream accepted a streaming call, any error, even before the first message, is a terminal frame, since the response starts without waiting for the first item. Refs #90
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- A proto2 detail whose payload omits a required field decodes, but has no valid ProtoJSON form, and was forwarded without the field. scrub now treats such a message, top level or nested, as a malformed status (regression test detail_missing_a_required_field_is_malformed). - A misspelled streaming key such as ndjson_envelop was ignored silently, since the two structs reading streaming: must accept each other's keys. unknown_config_keys (renamed from unknown_top_level_keys) now reports unknown streaming.* keys too, as a startup warning like the top-level ones (regression test misspelled_streaming_key_is_reported; a destructuring guard keeps the known list complete). Refs #90
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json_frames used scan, which polls the upstream before the closure can see that the terminal frame was already sent. With an upstream that stays open after the failure, the NDJSON body never closed and SSE kept sending keep-alives past its terminal error. The frames are now built with unfold, whose state (upstream included) is dropped by the terminal frame, so the next poll ends the body without touching the upstream. No allocation is added: the streams involved are Unpin, now a bound of the private helpers. Regression test terminal_frame_ends_the_body_while_the_upstream_stays_open covers both a serialization failure and an upstream error. Refs #90
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- A detail whose type no descriptor describes went to opaqueDetails as raw bytes. Those bytes cannot be inspected, so a DebugInfo nested in one of its fields reached any client that knows the schema. Such details are now withheld by default; the extension is switched on explicitly, globally or per route: error_details.opaque and a rule's opaque key in YAML, ErrorDetailsPolicy::with_opaque_details / opaque_route and StatusDetails::with_opaque_details in code. Each switch is decided by the first matching rule that sets it; a YAML rule setting neither is rejected. Routes share at most two renderers over one descriptor pool (regression test unknown_detail_type_is_withheld_by_default). - The codec accepted a response missing a proto2 required field, e.g. an empty frame for such a type, and the proxy answered 200 with it. Decoded messages are now checked like protobuf parsers do by default, failing with INTERNAL. Whether a response type has a required field at any depth is computed once per route, so proto3 responses pay one branch (regression test empty_response_missing_a_required_field_is_rejected; the no-op codec smoke test is replaced by tests of the walk). Refs #90
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Summary
REST error bodies now carry the upstream's
google.rpc.Statusdetails. The existingerror,codeandmessagefields stay;detailsis added. Nothing breaks: the REST contract is extended and the Rust API stays compatible (cargo-semver-checks againstmain: no major change required).grpc-status-details-binis decoded asgoogle.rpc.Status. Detail types resolve in one pool: the product descriptors, completed with the well-known types and the canonicalgoogle.rpctypes (fromtonic-types) they lack, merged per type so a product's own revisions win, so canonical types always render, also when packed inside a product detail. Well-known types with a special JSON representation go undervalueby their type. No trailer gives"details": [].Anydetail, or nested in a message field, repeated field, map or proto2 extension. A detail of a type no descriptor describes cannot be inspected, so it is withheld too by default.opaqueDetailsarray of{index, typeUrl, bytes}: no@type, outsidedetails, sodetailsstays an array of ProtoJSONAny.indexis the position among the forwarded details; the key appears only when non-empty. Documented as non-ProtoJSON, and as trusting the upstream not to nest a DebugInfo in such types.requiredfield or have no valid JSON form, a type URL without a/or whose last segment is not a protobuf full name, a message field whose JSON name is@type, a trailer that is not agoogle.rpc.Status, or one whose code or message disagrees withgrpc-status/grpc-messageturns the whole error into a genericINTERNAL: HTTP 500 before headers, the terminal frame after a stream started. The cause is logged only.@type: google.rpc.Status, SSE uses thestream-errorevent. The opt-in NDJSON envelope ({"result"}/{"error"}, the grpc-gateway shape) keeps the two apart even for RPCs streamingAny,Struct,ValueorListValue.error_details:(globalenabled/opaqueswitches plus ordered per-route globs, each rule setting one or both) andstreaming.ndjson_envelopeare read from the config file byProxyServer::from_yaml_str/from_file, which the binary uses and which warn about top-level andstreaming:keys no setting reads; embedders usewith_error_details/with_ndjson_envelope. Both stay outsideProxyConfig.transcode::routesandstatus_to_responsekeep their signatures;routes_with_optionsandstatus_to_response_with_detailsare the new entry points.Fixed along the way
DynamicCodecdropped all-default messages. An empty gRPC frame (e.g.google.protobuf.Empty) was read as "no message", so an upstream answeringEmptyfailed withINTERNAL: Missing response message. It now decodes to the default message, and a message missing a proto2requiredfield is rejected, as protobuf parsers do by default.Testing
Integration tests run the proxy against a real tonic upstream returning
tonic_typesdetails; unit tests cover rendering, policies, settings and stream framing. fmt, clippy, tests and doc tests pass in every CI configuration (rust_crypto, aws_lc_rs, injected_verifier, all_features), pluscargo semver-checksagainstmain.Closes #90