CFN Utilities Skill

Description

Reusable bash utility functions for the CFN Loop system. Provides standardized logging, error handling, retry logic, and atomic file operations with zero external dependencies.

Purpose

Structured Logging: JSON-formatted logs compatible with TypeScript logging system
Error Handling: Consistent error management across bash scripts
Retry Logic: Exponential backoff for transient failures
File Operations: Atomic writes and file locking primitives

Dependencies

POSIX-compliant bash (4.0+)
Coreutils (standard Linux/macOS utilities)
No external dependencies required

Usage

Direct Function Invocation

# Source all utilities
source ./.claude/skills/cfn-utilities/execute.sh

# Use individual functions
log_info "Task started" '{"task_id":"abc123"}'
retry_with_backoff 3 2 curl https://api.example.com
atomic_write "/path/to/file.txt" "content here"

Via Execute Script

# Execute specific function
./.claude/skills/cfn-utilities/execute.sh log_json "info" "Message" '{"key":"value"}'

# Source and call
source ./.claude/skills/cfn-utilities/execute.sh
log_error "Operation failed" '{"error_code":"E001"}'

Available Functions

Logging (lib/logging.sh)

log_json(level, message, context)

log_json "info" "Task started" '{"task_id":"abc123","agent":"backend-dev"}'
# Output: {"timestamp":"2025-11-15T20:00:00Z","level":"info","message":"Task started","context":{"task_id":"abc123","agent":"backend-dev"}}

log_info(message, context)

log_info "Processing file" '{"file":"data.txt"}'

log_warn(message, context)

log_warn "Deprecated function used" '{"function":"old_func"}'

log_error(message, context)

log_error "Failed to connect" '{"host":"api.example.com","code":500}'

log_debug(message, context)

export LOG_LEVEL=debug
log_debug "Variable state" '{"var":"value"}'

Error Handling (lib/errors.sh)

error_exit(message, exit_code, context)

error_exit "Database connection failed" 1 '{"db":"postgres"}'

error_handle(message, context)

if ! validate_input "$data"; then
    error_handle "Invalid input" '{"input":"'$data'"}'
    return 1
fi

is_error_code(expected_code)

curl https://api.example.com
if is_error_code 7; then
    echo "Connection failed"
fi

Retry Logic (lib/retry.sh)

retry_with_backoff(max_attempts, base_delay_sec, command, args...)

# Retry curl with exponential backoff (2s, 4s, 8s)
retry_with_backoff 3 2 curl -f https://api.example.com/data

# Retry custom command
retry_with_backoff 5 1 cfn-spawn agent "backend-developer" --task "task"

File Operations (lib/file-ops.sh)

atomic_write(filepath, content)

atomic_write "/tmp/data.json" '{"status":"complete"}'

acquire_lock(lockfile, timeout_sec)

if acquire_lock "/tmp/resource.lock" 30; then
    # Critical section
    release_lock "/tmp/resource.lock"
fi

release_lock(lockfile)

release_lock "/tmp/resource.lock"

with_lock(lockfile, timeout_sec, command, args...)

with_lock "/tmp/database.lock" 60 ./scripts/migrate-db.sh

Integration Points

TypeScript Compatibility

Logging Format:

JSON output compatible with src/utils/logging.ts
Correlation ID format matches TypeScript UUID generation
Timestamp format: ISO 8601 (UTC)

Error Codes:

Error codes align with src/utils/errors.ts
Exit codes: 0=success, 1=general error, 2=usage error, 130=timeout

File Locking:

Lock files use .lock extension (same as src/utils/file-operations.ts)
Timeout behavior matches TypeScript implementation

CFN System Integration

Used By:

.claude/hooks/cfn-invoke-pre-edit.sh - atomic backup creation
.claude/skills/cfn-coordination/ - structured logging
.claude/skills/cfn-loop-orchestration/orchestrate.sh - retry logic
All CFN agents - standardized error handling

Correlation IDs:

# Generate correlation ID (compatible with TypeScript)
CORRELATION_ID=$(uuidgen 2>/dev/null || echo "$(date +%s)-$$-$RANDOM")
log_info "Request started" '{"correlation_id":"'$CORRELATION_ID'"}'

Testing

# Run all tests
./.claude/skills/cfn-utilities/test.sh

# Expected output:
# PASS: log_json outputs valid JSON
# PASS: retry_with_backoff succeeds after failures
# PASS: atomic_write creates file atomically
# PASS: with_lock prevents concurrent execution
# All tests passed (15/15)

Implementation Patterns

Safe Script Template

#!/usr/bin/env bash
set -euo pipefail

SCRIPT_DIR="$(cd "$(dirname "${BASH_SOURCE[0]}")" && pwd)"
source "$SCRIPT_DIR/.claude/skills/cfn-utilities/execute.sh"

main() {
    log_info "Script started" '{"script":"'$(basename "$0")'"}'

    retry_with_backoff 3 2 risky_operation || {
        error_exit "Operation failed after retries" 1
    }

    atomic_write "/tmp/result.txt" "Success"
    log_info "Script completed" '{"status":"success"}'
}

main "$@"

Critical Section Pattern

#!/usr/bin/env bash
source ./.claude/skills/cfn-utilities/execute.sh

# Ensure only one instance modifies shared resource
with_lock "/tmp/shared-resource.lock" 30 bash -c '
    log_info "Updating shared resource"
    echo "new data" >> /tmp/shared-resource.txt
    log_info "Update complete"
'

Best Practices

Always use structured logging - Include context objects for debugging
Set strict mode - Use set -euo pipefail in all scripts
Use atomic operations - Prevent partial writes with atomic_write()
Implement retries - Handle transient failures gracefully
Lock shared resources - Prevent race conditions with file locks

Version History

1.0.0 (2025-11-15): Initial release with logging, errors, retry, and file ops