NDJSON_REFACTOR_SUMMARY.md

NDJSON Refactor Summary

✅ What Was Done

1. Refactored StructuredSummarizer Service

File: app/services/structured_summarizer.py

Added/Modified:

• Updated _build_system_prompt(): Now instructs the model to output NDJSON patches instead of a single JSON object
• Added _empty_state(): Creates the initial empty state structure
• Added _apply_patch(): Applies NDJSON patches to the state (handles set, append, and done operations)
• Added summarize_structured_stream_ndjson(): New async generator method that:
  • Uses deterministic decoding (do_sample=False, temperature=0.0)
  • Parses NDJSON line-by-line with buffering
  • Applies patches to build up state incrementally
  • Yields structured events with delta, state, done, tokens_used, and latency_ms
  • Handles errors gracefully

Preserved:

• ✅ Class name: StructuredSummarizer
• ✅ Logging style
• ✅ Model loading/warmup logic
• ✅ Settings usage
• ✅ Existing summarize_structured_stream() method (unchanged)

2. Created New API Endpoint

File: app/api/v4/structured_summary.py

Added:

• /api/v4/scrape-and-summarize/stream-ndjson endpoint
• _stream_generator_ndjson() helper function
• Supports both URL and text modes
• Wraps NDJSON events in SSE format
• Includes metadata events when requested

3. Created Test Suite

Test Files Created:

1. test_v4_ndjson.py - Direct service test (requires model loaded)
2. test_v4_ndjson_mock.py - Mock test without model (validates protocol logic) ✅ PASSED
3. test_v4_ndjson_http.py - HTTP endpoint test (requires server running)

---

🎯 NDJSON Protocol Specification

Target Logical Object

{
  "title": "string",
  "main_summary": "string",
  "key_points": ["string"],
  "category": "string",
  "sentiment": "positive" | "negative" | "neutral",
  "read_time_min": number
}

Patch Operations

1. Set scalar field

{"op": "set", "field": "title", "value": "Example Title"}
{"op": "set", "field": "category", "value": "Tech"}
{"op": "set", "field": "sentiment", "value": "positive"}
{"op": "set", "field": "read_time_min", "value": 3}
{"op": "set", "field": "main_summary", "value": "Summary text..."}

2. Append to array

{"op": "append", "field": "key_points", "value": "First key point"}
{"op": "append", "field": "key_points", "value": "Second key point"}

3. Signal completion

{"op": "done"}

Event Structure

Each streamed event has this structure:

{
  "delta": {<patch>} | null,
  "state": {<current_combined_state>} | null,
  "done": boolean,
  "tokens_used": number,
  "latency_ms": number (optional, final event only),
  "error": "string" (optional, only on error)
}

---

🧪 How to Test

Option 1: Mock Test (No Model Required) ✅ WORKING

python test_v4_ndjson_mock.py

Status: ✅ Passed all validations

• Tests protocol logic
• Validates state management
• Shows expected event flow

Option 2: Direct Service Test (Requires Model)

python test_v4_ndjson.py

Requirements:

• Model must be loaded in the environment
• Transformers library installed

Option 3: HTTP Endpoint Test (Requires Running Server)

# Terminal 1: Start server
./start-server.sh

# Terminal 2: Run test
python test_v4_ndjson_http.py

---

📊 Test Results

Mock Test Results ✅

Total events: 12
Total tokens: 55

Final State:
{
  "title": "Qwen2.5-0.5B: Efficient AI for Edge Computing",
  "main_summary": "Qwen2.5-0.5B is a compact language model...",
  "key_points": [
    "Compact 0.5B parameter model designed for edge devices...",
    "Strong performance on instruction following...",
    "Supports multiple languages...",
    "Significantly lower memory and computational requirements...",
    "Ideal for applications requiring efficiency and low latency"
  ],
  "category": "Tech",
  "sentiment": "positive",
  "read_time_min": 3
}

Validations:
✅ title: present
✅ main_summary: present
✅ key_points: 5 items
✅ category: present
✅ sentiment: valid value (positive)
✅ read_time_min: present

✅ ALL VALIDATIONS PASSED - Protocol is working correctly!

---

🔄 Migration Path

Current State

• ✅ Old method still works: summarize_structured_stream()
• ✅ New method available: summarize_structured_stream_ndjson()
• ✅ Old endpoint still works: /api/v4/scrape-and-summarize/stream
• ✅ New endpoint available: /api/v4/scrape-and-summarize/stream-ndjson

When Ready to Switch

1. Update your frontend/client to use the new endpoint
2. Consume events using the new structure:

   // Parse SSE event
   const event = JSON.parse(eventData);
   
   // Use current full state
   const currentState = event.state;
   
   // Or use delta for fine-grained updates
   const patch = event.delta;
   
   // Check completion
   if (event.done) {
     console.log('Final latency:', event.latency_ms);
   }
   

3. Once migrated, you can optionally remove the old method (or keep both)

---

🎉 Benefits of NDJSON Protocol

1. Incremental State Updates: Client sees partial results as they're generated
2. Fine-Grained Control: Can update UI field-by-field
3. Deterministic: Uses greedy decoding for consistent results
4. Structured Events: Clear separation of deltas and state
5. Error Handling: Graceful error reporting with proper event structure
6. Backwards Compatible: Old endpoint continues to work

---

📝 Next Steps

1. ✅ Protocol logic verified - Mock test passed
2. ⏳ Test with actual model - Run when model is loaded
3. ⏳ Test HTTP endpoint - Run when server is up
4. ⏳ Update frontend - Integrate new endpoint in client
5. ⏳ Monitor production - Compare performance with old method

---

🐛 Troubleshooting

Model not loaded

❌ ERROR: Model not available. Please check model initialization.

Solution: Make sure transformers and torch are installed and model files are available.

Server not running

❌ Could not connect to server at http://localhost:7860

Solution: Start the server with ./start-server.sh

Invalid JSON in stream

If the model outputs invalid JSON, it will be logged as a warning and skipped:

Failed to parse NDJSON line: {...}... Error: ...

Solution: This is handled gracefully - other valid patches will still be processed.

---

📚 Files Modified/Created

Modified:

• app/services/structured_summarizer.py - Added NDJSON streaming method
• app/api/v4/structured_summary.py - Added new endpoint

Created:

• test_v4_ndjson.py - Direct service test
• test_v4_ndjson_mock.py - Mock test ✅
• test_v4_ndjson_http.py - HTTP endpoint test
• NDJSON_REFACTOR_SUMMARY.md - This file

---

Status: ✅ Refactor complete and protocol validated Ready for: Model testing and integration