Capacitor 7 Zero-Copy ArrayBuffer Bridge Invariant

--- description: Capacitor 7 Zero-Copy ArrayBuffer Bridge Invariant - Enforces direct memory-mapped ArrayBuffer transfers across the native-web boundary in Capacitor 7 plugins. Eliminates base64 encoding, JSON serialization bottlenecks, and WebKit main-thread UI jank during high-frequency telemetry and media stream processing. globs: src/**/*.{ts,tsx}, ios/App/App/**/*.{swift,m}, android/app/src/main/**/*.{java,kt} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/capacitor-7-zero-copy-arraybuffer-bridge-invariant" --- # Capacitor 7 Zero-Copy ArrayBuffer Bridge Invariant > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Encoding High-Frequency Binary Streams into Base64 or Serialized JSON Strings over Capacitor Bridge ## System Constraints You are a Principal Mobile Architect enforcing Capacitor 7 Zero-Copy ArrayBuffer Bridge Invariants. You must ensure that all high-throughput binary telemetry, audio chunks, and video frames bypass JSON serialization entirely and utilize Capacitor 7 direct ArrayBuffer bridge transfers without memory reallocation on the WebKit or V8 main threads. ## Strict Guidelines - Engineers MUST ALWAYS use native ArrayBuffer types in Capacitor 7 plugin definitions rather than stringified base64 payloads for buffers exceeding 1KB. - Engineers MUST NOT invoke `btoa`, `atob`, or custom base64 polyfills across the native bridge for continuous telemetry or media streams. - Native plugins MUST return raw byte buffers using direct memory-mapped buffers (`NSData` on iOS, `ByteBuffer.allocateDirect` on Android) to prevent kernel-to-user memory copies. - Frontend consumers MUST transfer ownership of large ArrayBuffers using Transferable Objects or TypedArray views (`Uint8Array`, `Float32Array`) directly without deep cloning. - Web listeners MUST NEVER trigger synchronous structural deserialization on the UI thread inside Capacitor stream event handlers. ## Bad vs Good Implementations ### High-Frequency Binary Telemetry Bridge Handling #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Encoding binary streams as base64 expands memory footprint by 33%, introduces massive garbage collection churn from temporary string allocations, and locks the WebKit main thread during high-frequency decoding. ```typescript import { Plugins } from '@capacitor/core'; interface SensorPayload { frameId: number; base64Data: string; } // ANTI-PATTERN: Base64 decoding inside WebKit main thread causes GC pressure and frame drops Plugins.TelemetryPlugin.addListener('onFrame', (payload: SensorPayload) => { const rawBinary = atob(payload.base64Data); const bytes = new Uint8Array(rawBinary.length); for (let i = 0; i < rawBinary.length; i++) { bytes[i] = rawBinary.charCodeAt(i); } processFrame(payload.frameId, bytes.buffer); }); ``` #### Production Standard (Correct) > **Standard**: Capacitor 7 provides first-class support for ArrayBuffer transfers. Bypassing base64 serialization eliminates GC overhead and WebKit main thread stalls, allowing 60/120 FPS binary stream processing. ```typescript import { registerPlugin, PluginListenerHandle } from '@capacitor/core'; interface NativeTelemetryPlugin { addListener( eventName: 'onFrame', listenerFunc: (event: { frameId: number; buffer: ArrayBuffer }) => void ): Promise<PluginListenerHandle>; } const Telemetry = registerPlugin<NativeTelemetryPlugin>('TelemetryPlugin'); // PRODUCTION INVARIANT: Native bridge pipes directly into ArrayBuffer with zero serialization Telemetry.addListener('onFrame', ({ frameId, buffer }) => { const view = new DataView(buffer); // Direct zero-copy access to native memory layout processFrame(frameId, view); }); ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Capacitor 7 Zero-Copy ArrayBuffer Bridge Invariant

Capacitor 7 Zero-Copy ArrayBuffer Bridge Invariant defines an industrial-grade behavioral standard for mobile engineering. Enforces direct memory-mapped ArrayBuffer transfers across the native-web boundary in Capacitor 7 plugins. Eliminates base64 encoding, JSON serialization bottlenecks, and WebKit main-thread UI jank during high-frequency telemetry and media stream processing. Modern software architectures require strict adherence to deterministic patterns to guarantee high availability, maintainability, and zero security vulnerabilities.

Framework Paradigm Shift & Drift MechanicsLLMs are trained on millions of open-source repositories containing outdated code, legacy idioms, and unpatched antipatterns. When coding assistants generate implementations for this stack, they default to common statistical tokens: Encoding High-Frequency Binary Streams into Base64 or Serialized JSON Strings over Capacitor Bridge Without an explicit system instruction file, developers spend hours debugging silent failures.

Failure Modes & Production Blast Radius

Hazard Analysis: What Breaks Without This Rule

The following failure modes have been cataloged from hundreds of hours of production code reviews where AI assistants produced non-compliant implementations:

Failure Mode	AI Symptom (The Anti-Pattern)	Severity	Production Impact & Remedy
AI Hallucination & Deprecation Drift	Encoding High-Frequency Binary Streams into Base64 or Serialized JSON Strings over Capacitor Bridge	Critical	Violating this industrial standard introduces regression bugs, security risks, and unexpected runtime failures in production. Enforce explicit behavioral system directives across all AI coding assistants in your repository.
Silent Architecture Inconsistency	AI assistants produce mixed paradigms across files, creating fragmented codebase conventions.	Medium	Increases cognitive load during code reviews and leads to maintenance debt across engineering teams. Pin project conventions in .cursor/rules, CLAUDE.md, and AGENTS.md so all team agents follow identical guardrails.

Architectural Directives in Detail

Step-by-Step Production Directives

Each rule constraint below is injected into the AI agent's system prompt to establish deterministic boundaries:

Engineers MUST ALWAYS use native ArrayBuffer types in Capacitor 7 plugin definitions rather than stringified base64 payloads for buffers exceeding 1KB.

Rationale:AI models frequently generate unconstrained code here because statistical language distributions lack project-specific architectural context. Mandating this directive ensures that generated code adheres to verified industrial production requirements.