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WASM_POLISH_IMPROVEMENTS.md

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WASM Implementation Polish Improvements

Summary

Implemented all suggested polish improvements to enhance the WASM/WASI implementation based on the review feedback.

Improvements Completed

1. ✅ Tool Result Content Format

Before: All tool outputs returned as stringified JSON in Content::Text After: Smart content detection:

  • Plain strings return as direct text
  • Objects return as pretty-printed JSON for readability
  • Preserves structure for client-side parsing
let content = if let Some(text) = result_value.as_str() {
    vec![Content::Text { text: text.to_string() }]
} else if result_value.is_object() {
    vec![Content::Text {
        text: serde_json::to_string_pretty(&result_value)
            .unwrap_or_else(|_| "{}".to_string()),
    }]
}

2. ✅ Error Code Mapping

Before: All errors mapped to INTERNAL_ERROR After: Protocol errors preserve their specific codes:

  • Protocol errors retain original error codes
  • Graceful fallback to INTERNAL_ERROR for other types
fn map_error_code(error: &Error) -> ErrorCode {
    match error {
        Error::Protocol { code, .. } => *code,
        _ => ErrorCode::INTERNAL_ERROR,
    }
}

3. ✅ Resource Pagination

Before: Simple aggregation with no cursor support After: Smart cursor handling with provider namespacing:

  • Cursor format: "provider:cursor" for multi-provider pagination
  • Sequential provider querying for proper pagination
  • Maintains cursor state across requests
// Parse cursor to determine which provider to query
let (provider_name, provider_cursor) = if let Some(cursor) = params.cursor {
    if let Some((name, cur)) = cursor.split_once(':') {
        (Some(name.to_string()), Some(cur.to_string()))
    } else {
        (None, Some(cursor))
    }
}

4. ✅ Protocol Version Negotiation

Before: Echo client version without validation After: Proper negotiation with fallback:

  • Validates client version against SUPPORTED_PROTOCOL_VERSIONS
  • Falls back to latest supported version if unknown
  • Documents behavior in response
let negotiated_version = if SUPPORTED_PROTOCOL_VERSIONS.contains(&client_version.as_str()) {
    client_version
} else {
    SUPPORTED_PROTOCOL_VERSIONS[0].to_string()
};

5. ✅ Cloudflare Example Makefile

Created: Complete build automation with targets:

  • build - Build standalone Worker
  • build-sdk - Build SDK-backed variant
  • deploy - Deploy to Cloudflare
  • test - Test deployed worker
  • clean - Clean artifacts

Key feature: Clear separation between SDK and non-SDK variants with instructions.

6. ✅ Unit Tests for WasmMcpServer

Added: Comprehensive test suite covering:

  • Initialize with supported/unsupported versions
  • List tools functionality
  • Call existing/nonexistent tools
  • Invalid parameter handling
  • Error code mapping
  • Resource pagination
  • Content format variations

Located in: src/server/wasm_server_tests.rs

Test Coverage

Test Case Status Purpose
Protocol negotiation ✅ Validates version handling
Tool discovery ✅ Ensures tools are listed correctly
Tool execution ✅ Tests successful tool calls
Error handling ✅ Validates error responses
Pagination ✅ Tests cursor-based resource listing
Content formats ✅ Validates different response types

Impact

These improvements provide:

  1. Better Alignment with TypeScript SDK: Content format and error handling now match TS SDK patterns
  2. Production Readiness: Proper error codes, pagination, and version negotiation
  3. Developer Experience: Makefile automation and comprehensive tests
  4. Maintainability: Test coverage prevents regressions

Files Modified

  • src/server/wasm_server.rs - Core improvements
  • src/server/wasm_server_tests.rs - Test suite (new)
  • src/server/mod.rs - Test module registration
  • examples/cloudflare-worker-rust/Makefile - Build automation (new)

Next Steps

While not blocking, consider:

  1. Adding integration tests with actual WASI runtimes
  2. Performance benchmarking across platforms
  3. Streaming support investigation for large responses
  4. Additional content types beyond Text (Image, Resource, etc.)

Conclusion

All suggested polish improvements have been successfully implemented, enhancing the robustness and production-readiness of the WASM/WASI implementation while maintaining the clean architecture and environment independence achieved in the main refactoring.