Capacitor 7 Native Bridge Serialization Quarantine and Thread Isolation

--- description: Capacitor 7 Native Bridge Serialization Quarantine and Thread Isolation - High-frequency bi-directional bridge traffic between the WebView and native runtime in Capacitor 7 can monopolize the UI thread and trigger Out-Of-Memory (OOM) faults via unmetered JSON serialization. This rule enforces an off-main-thread serialization quarantine via dedicated Web Workers on the web layer and explicit background dispatch queues/coroutines with bounded chunk buffers on native platforms. globs: src/**/*.{ts,tsx}, android/app/src/main/java/**/*.java, android/app/src/main/kotlin/**/*.kt, ios/App/App/**/*.swift alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/capacitor-7-native-bridge-serialization-quarantine" --- # Capacitor 7 Native Bridge Serialization Quarantine and Thread Isolation > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Synchronous Main-Thread JSON Bridge Flooding with Unbounded Large Payloads ## System Constraints You are a Principal Mobile Architect enforcing Capacitor 7 Bi-Directional Native Bridge Serialization Quarantine. You must strictly mandate that all high-frequency (>30Hz) or large-payload (>64KB) bridge communications are isolated from the main/UI thread on both the WebView and native layers. You must prohibit direct JSON.stringify/parse calls on the DOM main thread for bridge traffic, mandate off-thread worker processing or binary transfer via ArrayBuffers/File handles, and reject any native plugin implementation that executes heavy deserialization directly inside the main UI dispatch queue. ## Strict Guidelines - Engineers MUST ALWAYS process bridge payloads exceeding 64KB or running at higher frequencies than 30Hz inside a Web Worker before sending them to Capacitor plugins. - Engineers MUST NOT dispatch plugin callbacks containing large payloads directly onto the Android UI Thread or iOS Main Dispatch Queue. - Native Android plugins MUST consume payloads on Dispatchers.Default or an isolated ExecutorService, and iOS plugins MUST execute deserialization on an isolated DispatchQueue with QoS .utility or .userInitiated. - Services MUST chunk high-throughput sensor or streaming data into pre-allocated TypedArray buffers, avoiding raw JSON string serialization across the bridge. - Components NEVER attach high-frequency event listeners directly to Capacitor plugin interfaces without applying client-side backpressure (e.g., throttling, batching, or windowing). ## Bad vs Good Implementations ### High-Frequency Native Bridge Dispatch with Worker Quarantine #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Executing JSON.stringify on multi-megabyte payloads directly on the browser main thread causes severe frame drops (UI starvation). Furthermore, passing huge JSON strings over the native bridge forces synchronous string marshaling on the UI thread. ```typescript import { registerPlugin } from '@capacitor/core'; interface StreamPlugin { pushBatch(options: { data: string }): Promise<void>; } const NativeStream = registerPlugin<StreamPlugin>('StreamPlugin'); // ANTI-PATTERN: Serializing 5MB payload on UI thread and blocking the WebView event loop export async function sendTelemetryData(largeDataset: Record<string, unknown>[]): Promise<void> { const serialized = JSON.stringify(largeDataset); await NativeStream.pushBatch({ data: serialized }); } ``` #### Production Standard (Correct) > **Standard**: The CPU-intensive serialization is quarantined to an isolated Web Worker. Instead of flooding the bridge string-marshalling pipe, data is persisted to a scratchpad file or handled as chunked memory, passing only a pointer descriptor across the native bridge. ```typescript import { registerPlugin } from '@capacitor/core'; interface StreamPlugin { pushBatchChunked(options: { chunkPath: string; byteCount: number }): Promise<{ success: boolean }>; } const NativeStream = registerPlugin<StreamPlugin>('StreamPlugin'); // PRODUCTION FIX: Quarantine serialization to Web Worker and stream via file reference/chunking export async function sendTelemetryData(largeDataset: Record<string, unknown>[]): Promise<void> { const worker = new Worker(new URL('./serialization.worker.ts', import.meta.url), { type: 'module' }); const chunkFileRef = await new Promise<string>((resolve, reject) => { worker.onmessage = (event: MessageEvent<{ filePath: string }>) => resolve(event.data.filePath); worker.onerror = (err) => reject(err); worker.postMessage({ payload: largeDataset }); }); try { await NativeStream.pushBatchChunked({ chunkPath: chunkFileRef, byteCount: largeDataset.length }); } finally { worker.terminate(); } } ``` ### Native iOS Plugin Off-Thread Bridge Handling (Swift) #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: The plugin method runs on the default bridge thread context without offloading JSON deserialization. Doing heavy parsing in ingestBatch directly blocks Capacitor's internal message processing loop, stalling the WebView. ```swift import Foundation import Capacitor @objc(SensorStreamPlugin) public class SensorStreamPlugin: CAPPlugin, CAPBridgedPlugin { public let identifier = "SensorStreamPlugin" public let jsName = "SensorStream" public let pluginMethods: [CAPPluginMethod] = [ CAPPluginMethod(name: "ingestBatch", returnType: CAPPluginReturnPromise) ] // ANTI-PATTERN: Deserializing large raw JSON directly on the UI dispatch thread @objc func ingestBatch(_ call: CAPPluginCall) { guard let rawPayload = call.getString("data") else { call.reject("Missing data") return } let data = Data(rawPayload.utf8) let json = try! JSONSerialization.jsonObject(with: data, options: []) // Mutating models or doing intensive parsing on the caller thread call.resolve(["status": "processed", "items": (json as? [Any])?.count ?? 0]) } } ``` #### Production Standard (Correct) > **Standard**: The computationally expensive JSON deserialization is quarantined to a dedicated utility DispatchQueue, preventing the Capacitor bridge loop and the Main UI Thread from dropping frames. ```swift import Foundation import Capacitor @objc(SensorStreamPlugin) public class SensorStreamPlugin: CAPPlugin, CAPBridgedPlugin { public let identifier = "SensorStreamPlugin" public let jsName = "SensorStream" public let pluginMethods: [CAPPluginMethod] = [ CAPPluginMethod(name: "ingestBatch", returnType: CAPPluginReturnPromise) ] // Dedicated QoS quarantine queue with concurrency bounding private let processingQueue = DispatchQueue(label: "io.capacitor.bridge.quarantine", qos: .utility) @objc func ingestBatch(_ call: CAPPluginCall) { guard let rawPayload = call.getString("data") else { call.reject("Missing data payload") return } // PRODUCTION FIX: Offload deserialization and processing off the main/bridge queue processingQueue.async { [weak self] in guard let self = self else { return } do { let data = Data(rawPayload.utf8) guard let json = try JSONSerialization.jsonObject(with: data, options: .fragmentsAllowed) as? [String: Any] else { call.reject("Invalid payload structure") return } let processedCount = json.keys.count call.resolve(["status": "processed", "keys": processedCount]) } catch { call.reject("Deserialization failed: \(error.localizedDescription)") } } } } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Capacitor 7 Native Bridge Serialization Quarantine and Thread Isolation

Capacitor 7 Native Bridge Serialization Quarantine and Thread Isolation defines an industrial-grade behavioral standard for mobile engineering. High-frequency bi-directional bridge traffic between the WebView and native runtime in Capacitor 7 can monopolize the UI thread and trigger Out-Of-Memory (OOM) faults via unmetered JSON serialization. This rule enforces an off-main-thread serialization quarantine via dedicated Web Workers on the web layer and explicit background dispatch queues/coroutines with bounded chunk buffers on native platforms. 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: Synchronous Main-Thread JSON Bridge Flooding with Unbounded Large Payloads 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	Synchronous Main-Thread JSON Bridge Flooding with Unbounded Large Payloads	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 process bridge payloads exceeding 64KB or running at higher frequencies than 30Hz inside a Web Worker before sending them to Capacitor plugins.

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.