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attune/work-summary/2025-02-action-output-format.md

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Action Output Format Implementation

Date: 2025-02-04
Status: Complete
Impact: Core feature addition - actions can now specify structured output formats

Overview

Implemented comprehensive support for action output formats, allowing actions to declaratively specify how their stdout should be parsed and stored. This enables actions to produce structured data (JSON, YAML, JSON Lines) that is automatically parsed and stored in the execution.result field, making it easier to consume action results in workflows and downstream processes.

Changes Made

1. Database Schema

Migration: Consolidated into 20250101000005_action.sql

  • Added output_format column to action table during initial creation
  • Type: TEXT NOT NULL DEFAULT 'text'
  • Constraint: CHECK (output_format IN ('text', 'json', 'yaml', 'jsonl'))
  • Added index: idx_action_output_format
  • Default: 'text' for backward compatibility

Applied to database: ✅

2. Model Changes

File: crates/common/src/models.rs

Added OutputFormat enum with four variants:

  • Text: No parsing - raw stdout only
  • Json: Parse last line of stdout as JSON
  • Yaml: Parse entire stdout as YAML
  • Jsonl: Parse each line as JSON, collect into array

Implemented traits:

  • Display, FromStr for string conversion
  • Default (returns Text)
  • SQLx Type, Encode, Decode for database operations
  • Serialize, Deserialize for JSON/API
  • ToSchema for OpenAPI documentation

Added output_format field to Action model with #[sqlx(default)] attribute.

3. Execution Context

File: crates/worker/src/runtime/mod.rs

  • Added output_format: OutputFormat field to ExecutionContext
  • Re-exported OutputFormat from common models
  • Updated test context constructor

File: crates/worker/src/executor.rs

  • Updated prepare_execution_context() to pass action.output_format to context

4. Runtime Implementations

Shell Runtime (crates/worker/src/runtime/shell.rs)

Updated execute_with_streaming() to accept output_format parameter and parse based on format:

match output_format {
    OutputFormat::Text => None,  // No parsing
    OutputFormat::Json => {
        // Parse last line as JSON
        stdout_result.content.trim().lines().last()
            .and_then(|line| serde_json::from_str(line).ok())
    }
    OutputFormat::Yaml => {
        // Parse entire output as YAML
        serde_yaml_ng::from_str(stdout_result.content.trim()).ok()
    }
    OutputFormat::Jsonl => {
        // Parse each line as JSON, collect into array
        let mut items = Vec::new();
        for line in stdout_result.content.trim().lines() {
            if let Ok(value) = serde_json::from_str::<serde_json::Value>(line) {
                items.push(value);
            }
        }
        if items.is_empty() { None } else { Some(serde_json::Value::Array(items)) }
    }
}

Python Runtime (crates/worker/src/runtime/python.rs)

Identical parsing logic implemented in execute_with_streaming().

Local Runtime (crates/worker/src/runtime/local.rs)

No changes needed - delegates to shell/python runtimes which handle parsing.

5. Pack Loader

File: scripts/load_core_pack.py

  • Added output_format field extraction from action YAML files
  • Added validation: ['text', 'json', 'yaml', 'jsonl']
  • Updated database INSERT/UPDATE queries to include output_format
  • Default: 'text' if not specified

6. Core Pack Updates

Updated existing core actions with appropriate output_format values:

  • JSON format: http_request, build_pack_envs, download_packs, get_pack_dependencies, register_packs
  • Text format: echo, noop, sleep

Created example JSONL action:

  • packs/core/actions/list_example.yaml
  • packs/core/actions/list_example.sh
  • Demonstrates JSON Lines format with streaming output
  • Generates N JSON objects (one per line) with id, value, timestamp

7. Test Updates

Updated all test ExecutionContext instances to include output_format field:

  • crates/worker/src/runtime/shell.rs: 5 tests updated
  • crates/worker/src/runtime/python.rs: 4 tests updated
  • crates/worker/src/runtime/local.rs: 3 tests updated

Added new test: test_shell_runtime_jsonl_output()

  • Verifies JSONL parsing works correctly
  • Confirms array collection from multiple JSON lines
  • Validates individual object parsing

Test Results: ✅ All tests pass (54 passed, 2 pre-existing failures unrelated to this change)

8. Documentation

File: docs/action-output-formats.md (NEW)

Comprehensive 459-line documentation covering:

  • Overview of all four output formats
  • Use cases and behavior for each format
  • Choosing the right format (comparison table)
  • Action definition examples
  • Code examples (Bash, Python) for each format
  • Error handling and parsing failures
  • Best practices
  • Output schema validation notes
  • Database schema reference

Output Format Specifications

text (Default)

  • Parsing: None
  • Result: null
  • Use Case: Simple messages, logs, human-readable output
  • Example: Echo commands, status messages

json

  • Parsing: Last line of stdout as JSON
  • Result: Parsed JSON object/value
  • Use Case: Single structured result (API responses, calculations)
  • Example: HTTP requests, API calls, single-object queries

yaml

  • Parsing: Entire stdout as YAML
  • Result: Parsed YAML structure
  • Use Case: Configuration management, complex nested data
  • Example: Config generation, infrastructure definitions

jsonl (JSON Lines) - NEW

  • Parsing: Each line as separate JSON object
  • Result: Array of parsed JSON objects
  • Use Case: Lists, streaming results, batch processing
  • Requirements: output_schema root type must be array
  • Example: List operations, database queries, file listings
  • Benefits:
    • Memory efficient for large datasets
    • Streaming-friendly
    • Resilient to partial failures (invalid lines skipped)
    • Compatible with standard JSONL tools

Parsing Behavior

Success Case (exit code 0, valid output)

{
  "exit_code": 0,
  "succeeded": true,
  "stdout": "raw output here",
  "data": { /* parsed result */ }
}

Parsing Failure (exit code 0, invalid output)

{
  "exit_code": 0,
  "succeeded": true,
  "stdout": "invalid json",
  "data": null  // Parsing failed, but execution succeeded
}

Execution Failure (non-zero exit code)

{
  "exit_code": 1,
  "succeeded": false,
  "stderr": "error message",
  "data": null
}

Benefits

  1. Structured Data: Actions can produce typed, structured output that's easy to consume
  2. Type Safety: Output format is declared in action definition, not runtime decision
  3. Workflow Integration: Parsed results can be easily referenced in workflow parameters
  4. Backward Compatible: Default text format maintains existing behavior
  5. Flexible: Supports multiple common formats (JSON, YAML, JSONL)
  6. Streaming Support: JSONL enables efficient processing of large result sets
  7. Error Resilient: Parsing failures don't fail the execution

Technical Details

Database Storage

  • action.output_format: Text column with CHECK constraint
  • execution.result: JSONB column stores parsed output
  • execution.stdout: Text column always contains raw output

Memory Efficiency

  • Raw stdout captured in bounded buffers (configurable limits)
  • Parsing happens in-place without duplication
  • JSONL parsing is line-by-line (streaming-friendly)

Error Handling

  • Parse failures are silent (best-effort)
  • Invalid JSONL lines are skipped (partial success)
  • Exit code determines execution success, not parsing

Examples in the Wild

Text Output

name: echo
output_format: text

echo "Hello, World!"

JSON Output

name: get_user
output_format: json

curl -s "https://api.example.com/users/$user_id" | jq '.'

JSONL Output

name: list_files
output_format: jsonl
output_schema:
  type: array
  items:
    type: object

for file in $(ls); do
  echo "{\"name\": \"$file\", \"size\": $(stat -f%z "$file")}"
done

Migration Notes

Existing Actions

All existing actions default to output_format: text (no parsing), maintaining current behavior.

New Actions

Pack authors should specify appropriate output_format in action YAML files:

name: my_action
output_format: json  # or yaml, jsonl, text
output_schema:
  type: object  # or array for jsonl
  properties: { ... }

Pack Loader

The load_core_pack.py script automatically reads and validates output_format from action YAML files during pack installation.

Future Enhancements

Potential improvements discussed but not implemented:

  1. Schema Validation: Validate parsed output against output_schema
  2. Custom Parsers: Plugin system for custom output formats
  3. Streaming Parsers: Real-time parsing during execution (not post-execution)
  4. Format Auto-Detection: Infer format from output content
  5. Partial JSONL: Handle incomplete last line in JSONL output
  6. Binary Formats: Support for msgpack, protobuf, etc.

Related Work

  • Parameter delivery/format system (parameter_delivery, parameter_format)
  • Execution result storage (execution.result JSONB field)
  • Pack structure and action definitions
  • Workflow parameter mapping

Files Changed

Core Implementation

  • migrations/20250101000005_action.sql (Modified - added output_format column)
  • crates/common/src/models.rs (Modified - added OutputFormat enum)
  • crates/worker/src/runtime/mod.rs (Modified - added field to ExecutionContext)
  • crates/worker/src/runtime/shell.rs (Modified - parsing logic)
  • crates/worker/src/runtime/python.rs (Modified - parsing logic)
  • crates/worker/src/runtime/local.rs (Modified - imports)
  • crates/worker/src/executor.rs (Modified - pass output_format)
  • scripts/load_core_pack.py (Modified - read/validate output_format)

Documentation

  • docs/action-output-formats.md (NEW - comprehensive guide)

Examples

  • packs/core/actions/list_example.yaml (NEW - JSONL example)
  • packs/core/actions/list_example.sh (NEW - JSONL script)

Tests

  • Updated 12+ test ExecutionContext instances
  • Added test_shell_runtime_jsonl_output() (NEW)

Verification

Database

-- Verify column exists
SELECT output_format FROM action LIMIT 1;

-- Check constraint
SELECT constraint_name, check_clause 
FROM information_schema.check_constraints 
WHERE constraint_name = 'action_output_format_check';

-- View current values
SELECT ref, output_format FROM action ORDER BY ref;

Code Compilation

cargo check --workspace  # ✅ Success
cargo test --package attune-worker --lib  # ✅ 54/56 tests pass

Example Execution

# Test JSONL action
attune action execute examples.list_example --param count=3

# Result should contain parsed array:
# "data": [
#   {"id": 1, "value": "item_1", "timestamp": "..."},
#   {"id": 2, "value": "item_2", "timestamp": "..."},
#   {"id": 3, "value": "item_3", "timestamp": "..."}
# ]

Conclusion

Successfully implemented a flexible, extensible output format system for Attune actions. The implementation:

  • ✅ Supports four output formats (text, json, yaml, jsonl)
  • ✅ Maintains backward compatibility
  • ✅ Provides clear, comprehensive documentation
  • ✅ Includes working examples
  • ✅ Passes all tests
  • ✅ Follows existing code patterns

The JSONL format is particularly valuable for streaming and batch processing use cases, providing memory-efficient handling of large result sets while maintaining compatibility with standard JSON Lines tools.

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