[Java] Embed Rust CLI runtime 4.4: JNA binding interface and implementation by Copilot · Pull Request #2230 · github/copilot-sdk

Copilot · 2026-08-03T16:04:36Z

Implements the NativeBinding interface, JnaNativeBinding JNA-backed implementation, and OutboundCallback JNA callback — the Java bridge to the five copilot_runtime_* C ABI entry points exposed by runtime.node.

New files

OutboundCallback — JNA @FunctionalInterface Callback; invoked by the native runtime on native threads. Documents that data pointer is only valid during invocation and must be copied with Pointer.getByteArray(0, len).
NativeBinding — Internal interface abstracting the five ABI entry points. interface (not abstract class) for future FFM swappability via MR-JAR; direct instantiation, no ServiceLoader.
JnaNativeBinding — JNA implementation:
- Inner CopilotRuntimeLibrary extends Library mapping copilot_runtime_* exports
- Library-never-unloads: static volatile loadedLib/loadedPath fields; once set, never cleared in production
- Duplicate-path guard: loading a different library path throws IllegalStateException with a diagnostic message naming both paths
- Active-callback tracking: AtomicInteger activeCallbacks incremented on callback entry, decremented on exit — callers must drain to zero before connection_close/host_shutdown
- Package-private testing constructor (accepts a stub CopilotRuntimeLibrary) and resetForTesting() for unit test isolation
JnaNativeBindingTest — 24 unit tests: delegation via StubRuntimeLibrary, library load/guard, and callback invocation/tracking against the spike-3-4 libcallback_test native library.

Modified files

pom.xml — adds net.java.dev.jna:jna:${jna.version} (5.19.1, <optional>true</optional>); version is a Maven property for deliberate upgrades.
module-info.java — adds requires static com.sun.jna and opens com.github.copilot.ffi to com.sun.jna (required for JNA reflection access to callback interface methods under JPMS).

Usage sketch

// Production path (called by FfiRuntimeHost, task 4.5)
NativeBinding binding = new JnaNativeBinding(NativeRuntimeLoader.resolve());

OutboundCallback cb = (userData, data, len) -> {
    byte[] bytes = data.getByteArray(0, len); // copy before returning
    queueInputStream.enqueue(bytes);
};

int serverId = binding.hostStart(argvJson, argvJson.length, null, 0);
int connId   = binding.connectionOpen(serverId, cb, Pointer.NULL,
                   null, 0, null, 0, null, 0);

Fixes [Java] Embed Rust CLI runtime 4.4: JNA binding interface and implementation #2146

- Add JNA 5.19.1 as optional dependency to java/sdk/pom.xml with jna.version property for deliberate upgrades - Create OutboundCallback.java: JNA Callback interface for native-to-Java outbound data delivery - Create NativeBinding.java: interface abstraction for the 5 copilot_runtime_* C ABI entry points - Create JnaNativeBinding.java: JNA implementation with static singleton (library-never-unloads pattern), duplicate path guard, and active-callback AtomicInteger tracking - Create JnaNativeBindingTest.java: 24 unit tests covering delegation, loading, duplicate guard, and callback behavior using the spike-3-4 test native library - Update module-info.java: requires static com.sun.jna, opens com.github.copilot.ffi to com.sun.jna Co-authored-by: edburns <75821+edburns@users.noreply.github.com>

Copilot

Pull request overview

Adds Java’s JNA bridge to the embedded Rust runtime C ABI.

Changes:

Defines native binding and callback interfaces.
Implements guarded JNA library loading and ABI delegation.
Adds JNA configuration and unit tests.

Show a summary per file

File	Description
`java/sdk/pom.xml`	Adds optional JNA dependency.
`java/sdk/src/main/java/module-info.java`	Configures JNA module access.
`OutboundCallback.java`	Defines the native callback contract.
`NativeBinding.java`	Defines the internal runtime ABI.
`JnaNativeBinding.java`	Implements JNA loading, delegation, and callback tracking.
`JnaNativeBindingTest.java`	Tests delegation, loading, guards, and callbacks.

Review details

Suppressed comments (2)

java/sdk/src/main/java/com/github/copilot/ffi/JnaNativeBinding.java:72

This export returns the runtime's one-byte Rust/C ABI bool (rust/src/ffi.rs:43), but JNA maps Java boolean to a 32-bit C int. That ABI mismatch can decode a native false as true. Use a one-byte native return (or explicit type mapper) and convert it in connectionClose.

        boolean copilot_runtime_connection_close(int connectionId);

java/sdk/src/main/java/com/github/copilot/ffi/JnaNativeBinding.java:69

This export also returns the runtime's one-byte Rust/C ABI bool (rust/src/ffi.rs:42), whereas JNA's Java boolean mapping expects a 32-bit C int. A native false can therefore be decoded incorrectly. Use a one-byte native return (or explicit type mapper) and convert it in connectionWrite.

        boolean copilot_runtime_connection_write(int connectionId, byte[] data, int dataLen);

Files reviewed: 6/6 changed files
Comments generated: 6
Review effort level: Balanced

- Fix callback GC: store tracked callbacks per connection in a ConcurrentHashMap, removed on connectionClose (comment #3706039757) - Fix boolean ABI mismatch: Rust bool is 1 byte, JNA maps Java boolean as 32-bit int. Changed CopilotRuntimeLibrary to return byte, convert to boolean in delegation methods (comment #3706039823) - Wrap UnsatisfiedLinkError in IllegalStateException per error contract (comment #3706039855) - Replace silent return with assumeTrue for native lib tests so skips are visible in CI reports (comment #3706039896) - Rewrite activeCallbackCount test to exercise through JnaNativeBinding and assert binding.activeCallbacks (comment #3706039935) - Add ABI name documentation to CallbackTestLib, fix byte return types in test interface (comment #3706039968) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

github-actions · 2026-08-03T17:03:42Z

Cross-SDK Consistency Review ✅

All 6 changed files in this PR are scoped entirely to Java (java/sdk/). The changes introduce:

NativeBinding interface and JnaNativeBinding JNA implementation — internal Java FFI bridge to the Rust CLI runtime's C ABI
OutboundCallback — JNA-specific callback type
Maven/JPMS plumbing (pom.xml, module-info.java)

No cross-SDK consistency issues. This is Java-specific native-bridge infrastructure using JNA (Java Native Access), which is a Java ecosystem mechanism with no equivalent in the other SDKs. Each SDK integrates the native runtime through its own platform-appropriate path (Node.js via native modules, Python via ctypes/cffi, Go via cgo, .NET via P/Invoke, Rust natively). No public API surface was added or modified, so no parallel changes are needed in Node.js, Python, Go, .NET, or Rust.

Generated by SDK Consistency Review Agent for #2230 · sonnet46 17.7 AIC · ⌖ 5.39 AIC · ⊞ 6.6K · ◷

…tation (#2230) * Initial plan * feat(java): add JNA binding interface and implementation (task 4.4) - Add JNA 5.19.1 as optional dependency to java/sdk/pom.xml with jna.version property for deliberate upgrades - Create OutboundCallback.java: JNA Callback interface for native-to-Java outbound data delivery - Create NativeBinding.java: interface abstraction for the 5 copilot_runtime_* C ABI entry points - Create JnaNativeBinding.java: JNA implementation with static singleton (library-never-unloads pattern), duplicate path guard, and active-callback AtomicInteger tracking - Create JnaNativeBindingTest.java: 24 unit tests covering delegation, loading, duplicate guard, and callback behavior using the spike-3-4 test native library - Update module-info.java: requires static com.sun.jna, opens com.github.copilot.ffi to com.sun.jna Co-authored-by: edburns <75821+edburns@users.noreply.github.com> * fix: address Copilot code review findings for JNA binding - Fix callback GC: store tracked callbacks per connection in a ConcurrentHashMap, removed on connectionClose (comment #3706039757) - Fix boolean ABI mismatch: Rust bool is 1 byte, JNA maps Java boolean as 32-bit int. Changed CopilotRuntimeLibrary to return byte, convert to boolean in delegation methods (comment #3706039823) - Wrap UnsatisfiedLinkError in IllegalStateException per error contract (comment #3706039855) - Replace silent return with assumeTrue for native lib tests so skips are visible in CI reports (comment #3706039896) - Rewrite activeCallbackCount test to exercise through JnaNativeBinding and assert binding.activeCallbacks (comment #3706039935) - Add ABI name documentation to CallbackTestLib, fix byte return types in test interface (comment #3706039968) Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com> --------- Co-authored-by: copilot-swe-agent[bot] <198982749+Copilot@users.noreply.github.com> Co-authored-by: edburns <75821+edburns@users.noreply.github.com> Co-authored-by: Ed Burns <edburns@microsoft.com> Co-authored-by: Copilot <223556219+Copilot@users.noreply.github.com>

Initial plan

3af7a20

Copilot AI assigned Copilot and edburns Aug 3, 2026

Copilot started work on behalf of edburns August 3, 2026 16:05 View session

Copilot AI linked an issue Aug 3, 2026 that may be closed by this pull request

[Java] Embed Rust CLI runtime 4.4: JNA binding interface and implementation #2146

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Copilot AI changed the title ~~[WIP] Implement NativeBinding interface and JnaNativeBinding implementation~~ [Java] Embed Rust CLI runtime 4.4: JNA binding interface and implementation Aug 3, 2026

Copilot finished work on behalf of edburns August 3, 2026 16:31

Copilot AI requested a review from edburns August 3, 2026 16:31

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edburns marked this pull request as ready for review August 3, 2026 16:48

edburns requested a review from a team as a code owner August 3, 2026 16:48

Copilot AI review requested due to automatic review settings August 3, 2026 16:48

Copilot started reviewing on behalf of edburns August 3, 2026 16:49 View session

Copilot AI reviewed Aug 3, 2026

View reviewed changes

edburns merged commit 357f577 into edburns/1917-java-embed-rust-cli-runtime-dd-3039924-agentic-run-02 Aug 3, 2026
26 checks passed

edburns deleted the copilot/edburns1917-java-embed-rust-cli-runtime-dd-3039924 branch August 3, 2026 17:38

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[Java] Embed Rust CLI runtime 4.4: JNA binding interface and implementation - #2230

[Java] Embed Rust CLI runtime 4.4: JNA binding interface and implementation#2230
edburns merged 3 commits into
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Copilot AI commented Aug 3, 2026 •

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github-actions Bot commented Aug 3, 2026

Cross-SDK Consistency Review ✅

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Copilot AI commented Aug 3, 2026 •

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