Capacitor 7 Type-Safe Native RPC and Zero-Copy Buffer Marshalling

--- description: Capacitor 7 Type-Safe Native RPC and Zero-Copy Buffer Marshalling - Enforces compile-time and runtime type safety on all Capacitor 7 native bridge invocations while eliminating binary-to-base64 serialization overhead. Prevents IPC injection vulnerabilities, JavaScriptCore heap exhaustion, and UI thread blocking across the WebKit/Blink-to-native boundary. globs: src/plugins/**/*.{ts,tsx}, src/services/**/*.{ts,tsx}, ios/App/App/**/*.{swift,m}, android/app/src/main/java/**/*.{java,kt} alwaysApply: true verified_by: "agentrules.org" license: "CC-BY-4.0" source: "https://agentrules.org/rules/capacitor-7-native-bridge-rpc-buffer-marshalling" --- # Capacitor 7 Type-Safe Native RPC and Zero-Copy Buffer Marshalling > **Severity**: CRITICAL | **Category**: mobile > **Anti-Pattern Warning**: Untyped Base64 Marshalling and Unvalidated IPC Payloads across Native Execution Boundaries ## System Constraints You are a Principal Mobile Architect enforcing Capacitor 7 Native Bridge Type-Safe RPC & Memory Buffer Marshalling. Mandate strict runtime schema validation, prohibit base64 string encoding for binary payloads over the bridge, and require zero-overhead typed array/buffer marshalling. ## Strict Guidelines - Engineers MUST ALWAYS define strict Zod or TypeBox schemas for all bridge request payloads and response envelopes prior to invoking native plugins. - Engineers MUST NOT marshal binary payloads (images, audio, cryptographic keys, sensor batches) as base64 strings across Capacitor plugin methods. - Code MUST transfer binary buffers using TypedArray (Uint8Array/ArrayBuffer) or direct file descriptors/content URIs supported by Capacitor 7's binary bridge. - Services MUST sanitize and freeze all IPC inputs on the JavaScript side before dispatch to prevent Prototype Pollution and IPC command injection. - Components NEVER execute raw `registerPlugin` calls inline; all native bridge calls must be wrapped behind an encapsulated, strongly-typed domain adapter service. - Native plugins MUST enforce symmetric contract validation on Android (Kotlin reflection/data classes) and iOS (Swift Decodable/Codable structs) before memory allocation. ## Bad vs Good Implementations ### Naive Base64 Serialization vs Type-Safe Binary Buffer Marshalling #### Bad Antipattern (AI Common Hallucination) > **Why it fails**: Iterating over an ArrayBuffer to construct a base64 string blocks the JS event loop, expands memory by ~33%, causes severe JavaScriptCore heap thrashing, and exposes the native bridge to unvalidated string injection. ```typescript import { Plugins } from '@capacitor/core'; // ANTI-PATTERN: Untyped plugin invocation with base64 string serialization // Causes 33% memory expansion, GC pressure in WebKit, and IPC payload injection risk export async function uploadEncryptedBlob(data: ArrayBuffer): Promise<any> { const bytes = new Uint8Array(data); let binary = ''; for (let i = 0; i < bytes.byteLength; i++) { binary += String.fromCharCode(bytes[i]); } const base64Data = btoa(binary); // No schema validation, untyped invocation, memory ballooning return (Plugins as any).SecureStoragePlugin.writeEncryptedChunk({ id: 'chunk-123', payload: base64Data, meta: JSON.stringify({ timestamp: Date.now() }) }); } ``` #### Production Standard (Correct) > **Standard**: Uses Capacitor 7's direct TypedArray marshalling to avoid base64 expansion, validates payload schema on both boundaries using Zod, and strictly types the bridge contract with compile-time verification. ```typescript import { registerPlugin } from '@capacitor/core'; import { z } from 'zod'; // 1. Define immutable runtime schema for IPC boundaries export const WriteChunkPayloadSchema = z.object({ chunkId: z.string().uuid(), checksumSha256: z.string().regex(/^[a-f0-9]{64}$/i), buffer: z.instanceof(Uint8Array) }); export const WriteChunkResponseSchema = z.object({ bytesWritten: z.number().int().nonnegative(), persisted: z.boolean() }); export type WriteChunkPayload = z.infer<typeof WriteChunkPayloadSchema>; export type WriteChunkResponse = z.infer<typeof WriteChunkResponseSchema>; // 2. Strongly typed plugin interface leveraging Capacitor 7 binary buffer transfer export interface SecureStoragePluginContract { writeEncryptedChunk(options: WriteChunkPayload): Promise<WriteChunkResponse>; } const NativeSecureStorage = registerPlugin<SecureStoragePluginContract>('SecureStoragePlugin'); // 3. Robust domain service wrapping the bridge with bidirectional validation export async function uploadEncryptedBlob( chunkId: string, checksumSha256: string, data: Uint8Array ): Promise<WriteChunkResponse> { const validatedPayload = WriteChunkPayloadSchema.parse({ chunkId, checksumSha256, buffer: data }); const rawResult = await NativeSecureStorage.writeEncryptedChunk(validatedPayload); return WriteChunkResponseSchema.parse(rawResult); } ```

Architectural Specification & Invariant Rationale

Architectural Invariant Design: Capacitor 7 Type-Safe Native RPC and Zero-Copy Buffer Marshalling

Capacitor 7 Type-Safe Native RPC and Zero-Copy Buffer Marshalling defines an industrial-grade behavioral standard for mobile engineering. Enforces compile-time and runtime type safety on all Capacitor 7 native bridge invocations while eliminating binary-to-base64 serialization overhead. Prevents IPC injection vulnerabilities, JavaScriptCore heap exhaustion, and UI thread blocking across the WebKit/Blink-to-native boundary. 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: Untyped Base64 Marshalling and Unvalidated IPC Payloads across Native Execution Boundaries 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	Untyped Base64 Marshalling and Unvalidated IPC Payloads across Native Execution Boundaries	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 define strict Zod or TypeBox schemas for all bridge request payloads and response envelopes prior to invoking native 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.