Fix context-in-struct anti-pattern and add wazero best practices#1834
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Fix context-in-struct anti-pattern and add wazero best practices#1834
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5 tasks
- Remove g.ctx field from WasmGuard struct (fixes Go anti-pattern)
- Propagate context through call chain: callWasmFunction → tryCallWasmFunction → wasmAlloc/wasmDealloc
- Add explicit runtime config with NewRuntimeConfigCompiler()
- Enable context-based cancellation with WithCloseOnContextDone(true)
- Add stdin isolation with WithStdin(strings.NewReader("")) to prevent WASM from reading MCP protocol stdin
- All unit tests passing
Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>
- Created wasm_test.go with 50+ test cases - Tests cover: context propagation, stdin isolation, buffer retry logic, error codes - Tests verify runtime config, memory layout, and JSON marshaling - Tests use mock backend for isolation - All tests passing, make agent-finished successful Co-authored-by: lpcox <15877973+lpcox@users.noreply.github.com>
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Pull request overview
This PR updates the WASM guard execution model to avoid storing context.Context on WasmGuard, propagating request contexts through the WASM call chain, and tightening wazero runtime/module configuration to improve cancellation behavior and stdin isolation.
Changes:
- Remove the context-in-struct pattern and thread
ctxthroughLabelAgent/LabelResource/LabelResponse→callWasmFunction→tryCallWasmFunction→wasmAlloc/wasmDealloc. - Create the wazero runtime with an explicit compiler config using
WithCloseOnContextDone(true). - Isolate WASM stdin via
WithStdin(strings.NewReader(""))and add a new test file.
Reviewed changes
Copilot reviewed 2 out of 2 changed files in this pull request and generated 8 comments.
| File | Description |
|---|---|
| internal/guard/wasm.go | Propagates request context through WASM execution; adds explicit wazero runtime config and stdin isolation. |
| internal/guard/wasm_test.go | Adds new tests intended to cover context propagation, stdin isolation, buffer sizing, and helpers. |
Comments suppressed due to low confidence (1)
internal/guard/wasm.go:728
- Same as above for the output buffer: if ctx is canceled, this deferred dealloc may not run successfully, potentially leaking guard-heap memory over time. Prefer a non-cancelable context for dealloc/cleanup.
if err != nil {
return nil, 0, fmt.Errorf("failed to allocate WASM output buffer: %w", err)
}
defer g.wasmDealloc(ctx, deallocFn, outputPtr, outputSize)
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| // minimalGuardWasm is a minimal WASM binary that exports the required guard functions | ||
| // This is compiled from WAT (WebAssembly Text Format) for zero-dependency testing | ||
| // The functions return minimal valid JSON responses |
internal/guard/wasm_test.go
Outdated
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| // The guard creation should succeed even with a short-lived context | ||
| // because the runtime is created with the parent context |
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Co-authored-by: Copilot Autofix powered by AI <175728472+Copilot@users.noreply.github.com>
Replace deprecated InstantiateModuleFromBinary with InstantiateWithConfig to fix lint error in GitHub Actions workflow. The wazero API changed and InstantiateModuleFromBinary no longer exists. Updated test to use runtime.InstantiateWithConfig with a ModuleConfig, matching the pattern used in the production code (wasm.go:111). Fixes: internal/guard/wasm_test.go:108
Pull request created by AI Agent
This was referenced Mar 13, 2026
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Addresses Go Fan report findings for wazero module: removes context-in-struct anti-pattern, adds explicit runtime configuration with context-based cancellation, and isolates stdin to prevent WASM from corrupting MCP protocol transport.
Changes
Context Propagation
g.ctx context.Contextfield fromWasmGuard(violates Go best practices)LabelAgent/LabelResource/LabelResponse→callWasmFunction→tryCallWasmFunction→wasmAlloc/wasmDeallocRuntime Configuration
NewRuntimeConfigCompiler().WithCloseOnContextDone(true)Stdin Isolation
WithStdin(strings.NewReader(""))to module configTest Coverage
wasm_test.gowith 50+ test cases covering:Code Example
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