fix: preserve error codes through BLS error paths

[Swigler]

Summary

Fixes triton-inference-server/server#7804

When Python models are chained via BLS, error codes (e.g. NOT_FOUND, UNSUPPORTED) were lost and always became INTERNAL. This PR preserves the original error code through all BLS error paths.

Root cause

Three structural issues caused error codes to be dropped:

1. THROW_IF_TRITON_ERROR macro — extracted the error message but discarded the error code when throwing PythonBackendException
2. ResponseBatch struct — had no error_code field, so batch-level errors were hardcoded to TRITONSERVER_ERROR_INTERNAL
3. Exception catch blocks — in ExecuteBLSRequest, SendBLSDecoupledResponse, InferResponseComplete, and several other paths, PbError was created without the error code from the caught exception

Changes

File	Change
src/pb_exception.h	Add two-arg constructor preserving error code (stored as int to avoid tritonserver.h dependency)
src/pb_utils.h	Add error_code field to ResponseBatch; update THROW_IF_TRITON_ERROR to capture error code
src/python_be.cc	Read error_code from ResponseBatch instead of hardcoding INTERNAL; propagate in ExecuteBLSRequest and SendBLSDecoupledResponse catch blocks; initialize in PrepareResponseBatch
src/request_executor.cc	Pass error code in CreateTritonErrorFromException and Infer() re-throw
src/infer_request.cc	Pass error_code from ResponseBatch to PbError in Exec(); preserve in outer catch
src/pb_stub.cc	Capture error code in ProcessRequests catch; write to ResponseBatch; pass in ProcessBLSResponseDecoupled

Test

Added examples/bls_error_code/ with two test models and a client script:

• error_source — returns an InferenceResponse with a specific TritonError code
• bls_error_caller — calls error_source via BLS and reports the received code

Tested on Triton 2.50.0 (r24.09) with an A100 GPU on RunPod:

Patched:

  Sent: NOT_FOUND       (2) -> Got: NOT_FOUND       (2)  [OK]
  Sent: INVALID_ARG     (3) -> Got: INVALID_ARG     (3)  [OK]
  Sent: UNAVAILABLE     (4) -> Got: UNAVAILABLE     (4)  [OK]
  Sent: UNSUPPORTED     (5) -> Got: UNSUPPORTED     (5)  [OK]
  Sent: CANCELLED       (7) -> Got: CANCELLED       (7)  [OK]
ALL 5 TESTS PASSED

Stock (unpatched):

  Sent: NOT_FOUND       (2) -> Got: INTERNAL        (1)  [FAIL]
  Sent: INVALID_ARG     (3) -> Got: INTERNAL        (1)  [FAIL]
  Sent: UNAVAILABLE     (4) -> Got: INTERNAL        (1)  [FAIL]
  Sent: UNSUPPORTED     (5) -> Got: INTERNAL        (1)  [FAIL]
  Sent: CANCELLED       (7) -> Got: INTERNAL        (1)  [FAIL]
ALL 5 FAILED

Test plan

• Build patched python_backend against r24.09 Triton headers
• Run integration test on live Triton 2.50.0 — all 5 error codes preserved
• Confirm stock backend loses all error codes (control test)
• Run existing CI/test suite (no existing BLS error code tests found in this repo)

🤖 Generated with Claude Code

[greptile-apps]

Greptile Summary

This PR preserves Triton error codes as exceptions and batch-level failures cross the BLS and shared-memory boundaries.

• Adds explicit error-code presence tracking to PythonBackendException.
• Carries batch error codes between the backend and Python stub for regular and decoupled BLS responses.
• Preserves INTERNAL as the fallback for exceptions without an explicit code.
• Adds an example integration test covering five non-INTERNAL error codes.

Confidence Score: 5/5

The PR appears safe to merge.

No blocking failure remains.

Important Files Changed

Filename	Overview
src/pb_exception.h	Adds explicit error-code presence tracking so message-only exceptions remain distinguishable from UNKNOWN-coded exceptions.
src/pb_utils.h	Preserves Triton error codes in the exception macro and extends the shared response-batch payload with an INTERNAL-defaulted code.
src/request_executor.cc	Propagates explicit Triton codes while retaining the INTERNAL fallback for uncoded setup and validation failures.
src/python_be.cc	Initializes, transports, and reconstructs batch-level error codes across regular and decoupled BLS paths.
src/infer_request.cc	Reconstructs Python-facing BLS errors with the transported code and safely defaults uncoded exceptions to INTERNAL.
src/pb_stub.cc	Serializes model-execution exception codes and restores them in decoupled BLS responses.

Sequence Diagram

sequenceDiagram
    participant M as Calling Python model
    participant S as Python stub
    participant B as Backend BLS executor
    participant T as Target model
    M->>S: exec()
    S->>B: BLS request via shared memory
    B->>T: Submit inference
    T-->>B: Error response with Triton code
    B-->>S: ResponseBatch with message and error_code
    S-->>M: InferenceResponse with preserved TritonError code

Loading

_{Reviews (2): Last reviewed commit: "fix: preserve INTERNAL fallback for unco..." | Re-trigger Greptile}