Optimize gojq middleware: pre-compile query for 1.8-5.25x speedup

[Copilot]

The jqschema middleware was parsing the jq query on every request, violating gojq's documented best practice of "compile once, run many."

Changes

Pre-compile query at initialization

• Move query compilation to package init() with fail-fast error handling
• Store compiled *gojq.Code in package-level variable for reuse
• Replace Parse() + Run() pattern with Compile() + RunWithContext()

Before:

func applyJqSchema(jsonData interface{}) (string, error) {
    query, err := gojq.Parse(jqSchemaFilter)  // Parse on every call
    if err != nil {
        return "", err
    }
    iter := query.Run(jsonData)
    // ...
}

After:

var jqSchemaCode *gojq.Code

func init() {
    query, _ := gojq.Parse(jqSchemaFilter)
    jqSchemaCode, _ = gojq.Compile(query)  // Compile once at startup
}

func applyJqSchema(ctx context.Context, jsonData interface{}) (string, error) {
    iter := jqSchemaCode.RunWithContext(ctx, jsonData)  // Reuse compiled code
    // ...
}

Add context support

• Thread context.Context from HTTP handler to query execution
• Enable timeout/cancellation via RunWithContext()

Enhance error handling

• Type-check for *gojq.HaltError to distinguish clean halts from failures
• Include exit codes in error messages

Benchmark suite

• Validate 1.8-5.25x speedup across payload sizes (small: 5.25x, medium: 3.47x, large: 1.80x)
• Document 55-83% reduction in memory allocations

Performance Impact

Payload	Before (ns/op)	After (ns/op)	Speedup
Small	37,523	7,148	5.25x
Medium	42,209	12,161	3.47x
Large	60,304	33,546	1.80x

Original prompt

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This section details on the original issue you should resolve

<issue_title>[go-fan] Go Module Review: gojq</issue_title>
<issue_description># 🐹 Go Fan Report: gojq

Module Overview

gojq is a pure Go implementation of jq, the powerful JSON query and transformation language. It provides both a command-line tool and a Go library for parsing and executing jq queries, enabling JSON schema inference and transformation without external dependencies.

Current Version: v0.12.18 (latest, released Dec 1, 2025)
License: MIT
Stars: 3,666+
Maintenance: Active (last push 12 days ago)

Current Usage in gh-aw-mcpg

The project uses gojq in the jqschema middleware (internal/middleware/jqschema.go) to transform JSON responses into type schemas.

• Files: 3 files (jqschema.go, jqschema_test.go, jqschema_integration_test.go)
• Import Count: 1 import
• Key APIs Used:
  • gojq.Parse(query) - Parse jq query strings
  • query.Run(input) - Execute queries against JSON data
  • Iterator pattern with iter.Next()

Current Pattern:

query, err := gojq.Parse(jqSchemaFilter)
iter := query.Run(jsonData)
v, ok := iter.Next()

This parses the same jq query on every request which is a significant performance bottleneck.

Research Findings

Recent Updates

v0.12.18 (Dec 1, 2025) - Latest release includes:

• Performance improvements for long-running queries
• Thread-safety fix: Stop numeric normalization for concurrent execution
• Memory allocation optimizations
• Array index limit increased to 536M
• New functions: trimstr/1, toboolean/0
• Improved gojq.NewIter as generic function

Best Practices from Maintainers

The gojq documentation strongly recommends a compile-once pattern for repeated queries:

"You can use gojq.Compile and code.Run to reuse the compiled code against multiple inputs to avoid compilation of the same query."

Key recommendations:

1. Compile once, run many - Pre-compile queries at startup
2. Use context - RunWithContext for timeout/cancellation
3. Type-specific errors - Check for gojq.HaltError, ParseError
4. Thread safety - v0.12.18 fixes ensure safe concurrent access to compiled code

Improvement Opportunities

🏃 Quick Wins

1. Compile Query Once (CRITICAL - High Impact, Low Effort)

Current Problem: Query is parsed on every request
Impact: 3-10x performance improvement
Effort: 10 minutes
Risk: Very low

Implementation:

var (
    jqSchemaCode *gojq.Code
    jqSchemaCompileErr error
)

func init() {
    query, err := gojq.Parse(jqSchemaFilter)
    if err != nil {
        jqSchemaCompileErr = fmt.Errorf("failed to parse jq schema filter: %w", err)
        return
    }
    jqSchemaCode, jqSchemaCompileErr = gojq.Compile(query)
}

func applyJqSchema(jsonData interface{}) (string, error) {
    if jqSchemaCompileErr != nil {
        return "", jqSchemaCompileErr
    }
    iter := jqSchemaCode.Run(jsonData)  // Reuse compiled code
    // ... rest
}

2. Add Context Support (Medium Impact, Low Effort)

Current Problem: No timeout/cancellation support
Impact: Better resource management, prevents runaway queries
Effort: 5 minutes
Risk: Very low

Implementation:

func applyJqSchema(ctx context.Context, jsonData interface{}) (string, error) {
    if jqSchemaCompileErr != nil {
        return "", jqSchemaCompileErr
    }
    iter := jqSchemaCode.RunWithContext(ctx, jsonData)
    // ... rest
}

3. Improve Error Handling (Low Impact, Low Effort)

Current Problem: Generic error checking
Impact: Better debugging experience
Effort: 15 minutes
Risk: Very low

Implementation:

if err, ok := v.(error); ok {
    if haltErr, ok := err.(*gojq.HaltError); ok && haltErr.Value() == nil {
        break  // Clean halt - no error
    }
    return "", fmt.Errorf("jq schema filter error: %w", err)
}

✨ Feature Opportunities

1. Custom Functions for Schema Inference

   • Use gojq.WithFunction to add custom schema functions
   • Enable more sophisticated schema analysis
   • Reduce query complexity

2. Performance Monitoring

   • Add metrics tracking query execution time
   • Alert on slow queries (>100ms)
   • Monitor memory usage patterns

3. Query Validation at Startup

   • Compile all jq queries during initialization
   • Fail fast if queries are invalid
   • Better error messages at startup vs runtime

4. Multiple Query Support

   • Pre-compile multiple schema strategies
   • Select query based on response type/size
   • Optimize for common patterns

📐 Best Practice Alignment

Aspect	Current	Recommended	Benefit
Query Compilation	Parse on every request	Compile once at startup	3-10x performance
Context Support	None	Use `RunWithContext...

• Fixes [go-fan] Go Module Review: gojq #350

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