stacklok / toolhive / 19638645768

51%

Build Type

push

github

Committed by web-flow

Commit Message

Add output configuration support for composite tools (#2677)

# Add Output Configuration Support for Composite Tools

**Implements:** https://github.com/stacklok/stacklok-epics/issues/176

## Summary

This PR adds structured output schema support for composite tool workflows in the Virtual MCP Server. Workflows can now define explicit output schemas with type information, descriptions, default values, and template-based value construction. This enables type-safe, predictable outputs from composite tools that are properly advertised to MCP clients.

## Key Features

### 🎯 Core Functionality
- **Structured Output Schemas**: Define explicit output schemas using JSON Schema types (string, integer, number, boolean, object, array)
- **Template-Based Construction**: Use Go templates to extract and transform values from workflow step outputs and parameters
- **Type Coercion**: Automatic type conversion from string values to target types (integers, booleans, numbers)
- **Default Values**: Fallback values when template expansion or type coercion fails
- **Nested Objects**: Full support for deeply nested object structures with recursive schema definitions
- **JSON Deserialization**: Automatic deserialization of JSON strings into objects and arrays

### 🔒 Security & Validation
- **Maximum Nesting Depth**: Prevents resource exhaustion with configurable depth limit (default: 10 levels)
- **Schema Validation**: Comprehensive validation at workflow definition time
- **Type Safety**: Validates all property types and enforces required fields
- **Template Syntax Validation**: Basic validation to catch malformed templates early

### 🔄 Backward Compatibility
- **Zero Breaking Changes**: Workflows without `output` configuration continue to return the last step's output
- **Incremental Adoption**: Teams can adopt structured outputs gradually

Run Details

321 of 476 new or added lines in 5 files covered. (67.44%)

38 existing lines in 2 files now uncovered.

24802 of 50480 relevant lines covered (49.13%)

61.48 hits per line