feat(xmtp_api_d14n): XmtpMlsBidiStreams trait + v3 Subscribe transport

[tylerhawkes]

Stack 3/4 of the XIP-83 bidi client lane: #3769 → #3770 → #3771 → #3772.

Native-only XmtpMlsBidiStreams trait in xmtp_proto::api_client — subscribe_bidi(BoxStream<SubscribeRequest>) -> Stream<Result<SubscribeResponse>> — and its V3Client implementation: prost-encode outbound frames over bidi_stream("/xmtp.mls.api.v1.MlsApi/Subscribe"), decode inbound via the existing XmtpStream. Browsers stay on XmtpMlsStreams + watchdog (gRPC-Web cannot full-duplex).

🤖 Generated with Claude Code

Note

Add XmtpMlsBidiStreams trait and V3 bidirectional Subscribe transport for native targets

• Defines a new native-only XmtpMlsBidiStreams trait in api_client.rs with a subscribe_bidi method that accepts a BoxStream<SubscribeRequest> and returns a stream of SubscribeResponse.
• Implements the trait for V3Client in a new bidi.rs module, opening a long-lived bidirectional stream at /xmtp.mls.api.v1.MlsApi/Subscribe and mapping transport errors to include the endpoint.
• Both the trait and implementation are gated behind cfg(not(target_arch = "wasm32")) and are not available in WASM builds.

📊 Macroscope summarized 0f1cead. 2 files reviewed, 0 issues evaluated, 0 issues filtered, 0 comments posted

🗂️ Filtered Issues

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[claude]

Claude finished @tylerhawkes's task —— View job

---

Code Review Complete

Review Date: 2026-06-16 21:06 UTC

Summary

The implementation is straightforward and follows established patterns. However, there are two critical issues that need to be addressed for consistency with the rest of the codebase:

---

🔴 Critical Issues

1. Missing blanket implementations for Box<T> and Arc<T> (macroscopeapp's comment is correct)

Location: crates/xmtp_proto/src/api_client.rs:192

The new XmtpMlsBidiStreams trait is missing blanket impls that exist for all other traits in this module (XmtpMlsClient, XmtpMlsStreams, XmtpIdentityClient). See api_client/impls.rs:262-329 for the pattern.

Impact: Any code that wraps the client in Box<dyn XmtpMlsBidiStreams> or Arc<dyn XmtpMlsBidiStreams> will fail to compile.

Fix needed in crates/xmtp_proto/src/api_client/impls.rs:

#[xmtp_common::async_trait]
impl<T> XmtpMlsBidiStreams for Box<T>
where
    T: XmtpMlsBidiStreams + Sync + ?Sized,
{
    type Error = <T as XmtpMlsBidiStreams>::Error;
    type SubscribeStream = <T as XmtpMlsBidiStreams>::SubscribeStream;

    async fn subscribe_bidi(
        &self,
        requests: futures::stream::BoxStream<'static, crate::mls_v1::SubscribeRequest>,
    ) -> Result<Self::SubscribeStream, Self::Error> {
        (**self).subscribe_bidi(requests).await
    }
}

#[xmtp_common::async_trait]
impl<T> XmtpMlsBidiStreams for Arc<T>
where
    T: XmtpMlsBidiStreams + ?Sized,
{
    type Error = <T as XmtpMlsBidiStreams>::Error;
    type SubscribeStream = <T as XmtpMlsBidiStreams>::SubscribeStream;

    async fn subscribe_bidi(
        &self,
        requests: futures::stream::BoxStream<'static, crate::mls_v1::SubscribeRequest>,
    ) -> Result<Self::SubscribeStream, Self::Error> {
        (**self).subscribe_bidi(requests).await
    }
}

Note: These impls also need #[cfg(not(target_arch = "wasm32"))] since the trait itself is native-only.

2. Test Coverage Missing

Location: crates/xmtp_api_d14n/src/queries/v3/bidi.rs

Codecov reports 0% coverage on the new bidi.rs file (4 lines untested: 30, 33, 36, 39). The implementation has no tests.

Recommendation: Add at least a basic integration test that:

• Opens a bidirectional stream
• Sends a SubscribeRequest
• Receives a SubscribeResponse
• Verifies error handling

---

Minor Observations

1. Performance instrumentation (insipx's comment): Consider adding #[xmtp_common::rpc_span] to subscribe_bidi at line 25 for consistency with other RPC methods in the codebase (see xmtp_api/src/mls.rs:97).

2. Error handling: The error mapping at line 39 correctly adds endpoint context via .endpoint(SUBSCRIBE_PATH.to_string()), consistent with other methods.

3. Stream construction: The prost encoding at line 30 and XmtpStream wrapping at lines 40-43 follow established patterns.

---

Non-Issues

• ✅ Native-only gating is correct (#[cfg(not(target_arch = "wasm32"))])
• ✅ Module structure follows conventions
• ✅ Type signatures are sound
• ✅ Implementation delegates correctly to underlying bidi_stream transport

---

[insipx]

could annotate with #[xmtp_common::rpc_span] when this makes it to xmtp_api to capture the perf span

libxmtp/crates/xmtp_api/src/mls.rs

Line 97 in f6823a0

#[xmtp_common::rpc_span]

[codecov]

Codecov Report

❌ Patch coverage is 0% with 4 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (tyler/xip83-2-bidi-transport@af6ab11). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
crates/xmtp_api_d14n/src/queries/v3/bidi.rs	0.00%	4 Missing ⚠️

Additional details and impacted files

@@                       Coverage Diff                       @@
##             tyler/xip83-2-bidi-transport    #3771   +/-   ##
===============================================================
  Coverage                                ?   84.41%           
===============================================================
  Files                                   ?      409           
  Lines                                   ?    59908           
  Branches                                ?        0           
===============================================================
  Hits                                    ?    50573           
  Misses                                  ?     9335           
  Partials                                ?        0           

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[macroscopeapp]

🟡 Medium src/api_client.rs:192

Adding XmtpMlsBidiStreams without blanket impls for Box<T> and Arc<T> breaks the boxed/arced client pattern used throughout xmtp_proto. Callers that erase concrete clients into Box<dyn XmtpMlsBidiStreams> or Arc<dyn XmtpMlsBidiStreams> will get a compile error when calling subscribe_bidi because the wrapper types don't implement the new trait. Consider adding the standard blanket impls: impl<T: XmtpMlsBidiStreams + ?Sized> XmtpMlsBidiStreams for Box<T> and Arc<T>.

🚀 Reply "fix it for me" or copy this AI Prompt for your agent:

In file @crates/xmtp_proto/src/api_client.rs around line 192:

Adding `XmtpMlsBidiStreams` without blanket impls for `Box<T>` and `Arc<T>` breaks the boxed/arced client pattern used throughout `xmtp_proto`. Callers that erase concrete clients into `Box<dyn XmtpMlsBidiStreams>` or `Arc<dyn XmtpMlsBidiStreams>` will get a compile error when calling `subscribe_bidi` because the wrapper types don't implement the new trait. Consider adding the standard blanket impls: `impl<T: XmtpMlsBidiStreams + ?Sized> XmtpMlsBidiStreams for Box<T>` and `Arc<T>`.