WS9: Restore the receiver prefetch option on the Rust AMQP transport

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@j7nw4r ya está trabajando en esto.

Desde el 2/8/2026.

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Descripción

Event Hubs

Summary

The Rust AMQP transport ignores the receiver prefetch option. PartitionClientOptions::Prefetch and ProcessorOptions::Prefetch are public options. Their documented default is 300, and a negative value disables the prefetch. The Event Hubs client copies these options into MessageReceiverOptions::MaxLinkCredit. The uAMQP transport sends that value to the wire. The Rust transport does not read it. Each receiver link therefore attaches with the Rust crate default of 100 credits.

The Rust transport is the default transport today (sdk/core/azure-core-amqp/CMakeLists.txt:36). A default build therefore has a public option that does nothing.

The AMQP transport decision in #7253 gates this item. The severity tags below apply if that decision selects the Rust transport. If the decision selects the uAMQP transport, this item closes with no code change. The severity tags follow the key in #7252. All code anchors refer to commit f1039fe23.

Motivation

AMQP link flow control is receiver driven. The receiver grants the link credit. The sender must stop when the credit becomes zero. The prefetch option sets that credit. It controls how many events the service sends before the client grants more credit.

The Event Hubs client sets the credit in both transport branches. src/partition_client.cpp:130-133 and :162-167 each contain the comment "Set the link credit to the prefetch count". Each branch assigns receiverOptions.MaxLinkCredit = options.Prefetch. The documented default is 300 (inc/azure/messaging/eventhubs/partition_client.hpp:50, inc/azure/messaging/eventhubs/processor.hpp:61).

The uAMQP receiver sends the value to the wire. src/impl/uamqp/amqp/message_receiver.cpp:121-123 tests m_options.MaxLinkCredit != 0. It then calls m_link->SetMaxLinkCredit.

The Rust receiver discards the value. MessageReceiverImpl::Open sets the name, the receiver settle mode, the target, and the properties. It then calls amqpmessagereceiver_attach (src/impl/rust_amqp/amqp/message_receiver.cpp:131-178). It never sets the credit. The MaxLinkCredit field stays commented out at src/impl/rust_amqp/amqp/message_receiver.cpp:129.

The Rust crate default reaches the wire instead. rust_amqp/azure_core_amqp/src/fe2o3/receiver.rs:59 calls options.credit_mode.clone().unwrap_or_default(). rust_amqp/azure_core_amqp/src/receiver.rs:32-34 sets that default to ReceiverCreditMode::Auto(100).

The three documented behaviors therefore become one fixed value of 100 credits on a default build:

Documented behavior The uAMQP transport The Rust transport
Prefetch has a default of 300 300 credits 100 credits
Prefetch has a value of N N credits 100 credits
A Prefetch value below 0 disables the prefetch the uAMQP default applies 100 credits

Both sides of the language boundary have the necessary capability. Only the call between them is missing. The FFI exports amqpmessagereceiveroptions_set_credit_mode (rust_amqp/rust_wrapper/src/amqp/message_receiver.rs:382). That function accepts a RustReceiverCreditMode { manual: bool, credit_mode: u32 } (:375-379). It then sets ReceiverCreditMode::Manual or ReceiverCreditMode::Auto(n). No C++ code calls this function.

The impact is silent. A caller who increases Prefetch to adjust the receive throughput sees no change. A caller who sets Prefetch below zero to disable the prefetch still receives events. The library reports no error to either caller. No test finds the difference.

One related item needs an examination, but not a fix in this issue. The FFI also exports amqpmessagereceiveroptions_set_auto_accept. No C++ code calls that function either.

Proposal

  • Set the credit mode in MessageReceiverImpl::Open on the Rust transport (src/impl/rust_amqp/amqp/message_receiver.cpp:131-178). The FFI entry point exists already. [GA blocker]
  • Delete the commented MaxLinkCredit field at src/impl/rust_amqp/amqp/message_receiver.cpp:129. [GA blocker]
  • Decide how MessageReceiverOptions::MaxLinkCredit shows a disabled prefetch, and record the decision in this issue. The C++ option is a uint32_t with a default of 0. src/partition_client.cpp:130 assigns it only when Prefetch is 0 or more. A disabled prefetch is therefore the same as an option that the caller did not set. The Rust side shows the disabled condition as ReceiverCreditMode::Manual. [GA blocker]
  • Examine the Rust receiver shim for more options that Open discards. Start with the auto accept option. [GA blocker]
  • Add an offline test that makes sure the receiver attaches with the requested credit. This test is cheap, and it finds this defect. [GA blocker]
  • Make the two transport branches at src/partition_client.cpp:128-133,162-167 agree after the fix. #7253 can also remove one of the two branches. [GA quality bar]
  • Add a live test that shows a different Prefetch value changes the receive behavior. [GA quality bar]

Validation

  • A receiver with the default options attaches with 300 credits on the transport that #7253 selects.
  • A receiver with a custom Prefetch value attaches with that value.
  • A receiver with a Prefetch value below zero operates as the recorded decision states.
  • The offline credit test passes. This test fails today on the Rust transport, and it must pass after the fix.
  • The path from the Event Hubs client to the wire discards no other MessageReceiverOptions field.
Lenguaje dominante
C++
Estrellas
206
Forks
178
Merge medio
2 d 15 h
PR fusionados (30 d)
33

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