MIDI Type 1 -> Type 0 Converter (WordPress Plugin)

Frontend WordPress plugin that lets users upload .mid/.midi files, converts MIDI Type 1 to Type 0 asynchronously, and provides per-file or batch ZIP downloads.

Features

• Frontend upload UI via shortcode: [midi_type0_converter]
• Multi-file upload with per-job status polling
• Asynchronous conversion pipeline (queued -> processing -> done/error)
• Per-file signed download links
• Batch ZIP download link (when ZipArchive is available)
• Private storage under wp-content/uploads/mtc-private
• Rate limits for upload/status/download endpoints
• Optional ClamAV scan before storing uploads (disabled by default)

Requirements

• WordPress (plugin architecture + AJAX + cron APIs)
• PHP 8.0+ recommended (uses modern PHP features like match)
• ZipArchive extension for "Download All (ZIP)"
• Optional: clamdscan for antivirus scanning when enabled by filter

Installation

1. Copy this project folder into wp-content/plugins/.
2. Activate the plugin in WordPress admin.
3. Add shortcode [midi_type0_converter] to a page/post.
4. Open that page and upload MIDI files.

Usage

1. Select one or more .mid/.midi files.
2. Click Upload & Convert.
3. Polling starts automatically and status updates appear in the table.
4. Download files individually as they complete, or use Download All (ZIP) when available.

How It Works

• Upload endpoint: mtc_upload (wp_ajax_*)
  • Validates nonce, extension, MIDI header (MThd), size limits, and optional ClamAV scan when enabled.
  • Persists job row in DB table with initial queued status.
  • Schedules background job via wp_schedule_single_event.
• Status endpoint: mtc_status (wp_ajax_*)
  • Returns jobs for a batch_id, statuses, and signed download URLs.
  • Nudges stale queued jobs (cron spawn + fallback inline processing for very stale items).
• Conversion worker: mtc_process_job
  • Claims queued jobs atomically and runs pure-PHP conversion (includes/class-mtc-midi-converter.php).
• Download handlers:
  • ?mtc_download=1... for a single converted MIDI
  • ?mtc_zip=1... for batch ZIP
  • Links are HMAC-signed and time-limited.

Data Model

Table: {wp_prefix}mtc_jobs

• id
• batch_id
• original_name
• original_path
• converted_path
• status (queued, processing, done, error)
• error_msg
• created_at
• updated_at

Configuration (Filters)

Add filters in a must-use plugin or theme functions.php.

add_filter('mtc_max_upload_bytes', fn() => 10 * 1024 * 1024);
add_filter('mtc_max_files_per_batch', fn() => 200);
add_filter('mtc_download_ttl_seconds', fn() => DAY_IN_SECONDS);
add_filter('mtc_max_queued_ui_ms', fn() => 6000);
add_filter('mtc_poll_interval_ms', fn() => 2000);
add_filter('mtc_poll_max_backoff_ms', fn() => 15000);

add_filter('mtc_rate_limit_window_seconds', fn() => 10 * MINUTE_IN_SECONDS);
add_filter('mtc_rate_limit_max_uploads_per_window', fn() => 80);
add_filter('mtc_status_rate_limit_per_batch_window_seconds', fn() => 60);
add_filter('mtc_status_rate_limit_per_batch_per_window', fn() => 240);
add_filter('mtc_status_rate_limit_ip_window_seconds', fn() => 600);
add_filter('mtc_status_rate_limit_ip_per_window', fn() => 1000);

add_filter('mtc_queue_nudge_after_seconds', fn() => 3);
add_filter('mtc_inline_process_after_seconds', fn() => 12);

// ClamAV is disabled by default. Enable it only on hosts with a working clamdscan setup.
add_filter('mtc_clamav_enabled', fn() => true);
add_filter('mtc_clamav_fail_open', fn() => false);
add_filter('mtc_clamdscan_path', fn() => '/usr/bin/clamdscan');
add_filter('mtc_clamav_cmd_timeout_seconds', fn() => 6);
add_filter('mtc_timeout_bin', fn() => '/usr/bin/timeout');

add_filter('mtc_zip_cache_ttl', fn() => 900);
add_filter('mtc_cleanup_days', fn() => 2);

Security Notes

• Nonce-protected AJAX requests (mtc_nonce)
• Signed, expiring download URLs (HMAC with wp_salt('auth'))
• Uploaded files stored in a non-public uploads subdirectory
• Direct-access blocks for Apache/IIS (.htaccess, web.config)
• MIME/header checks plus binary MIDI magic check (MThd)
• Optional AV scanning through clamdscan when enabled

Operational Notes

• This plugin relies on WP-Cron for background processing.
• If your site has low traffic, cron events may fire late.
• Recent changes include queue nudging and inline fallback to reduce long queued waits.

Development

Project layout:

.
├── midi-type0-converter.php         # Main plugin bootstrap + AJAX/cron handlers
├── includes/
│   └── class-mtc-midi-converter.php # Pure PHP MIDI parser/merger
└── assets/
    ├── mtc.js                       # Frontend upload + polling UI
    └── mtc.css                      # Frontend styles

Syntax checks:

php -l midi-type0-converter.php
php -l includes/class-mtc-midi-converter.php

License

GPLv2 or later.